Tektronix 7L13 Instruction manual
TEKTRONIX 7L13 SPECTRUM ANALYZER INSTRUCTION Tektronix, Inc. P.O . Box 500 Beaverton, Oregon 070-1673-00 97005 MANUAL Serial Number First Printing APR 1974 WARRANTY All TEKTRONIX instruments are warranted against defective materials and workmanship for one year. Any questions with respect to the warranty, should betaken up with yourTEKTRONIX Field Engineeror representative . All requests for repairs and replacement parts should be directed to the TEKTRONIX Field Office or representative in your area. This will assure you the fastest possible service . Please include the instrument Type Number or Part Number and Serial Number with all requests for parts or service . Specifications and price change privileges reserved . Copyright c 1974 by Tektronix, Inc ., Beaverton, Oregon . Printed in the United States of America . All rights reserved . Contents of this publication may not be reproduced in any form without permission of Tektronix, Inc . U .S.A . and foreign TEKTRONIX products covered by U .S. and foreign patents and/or patents pending . TEKTRONIX is a registered trademark of Tektronix, I SECTION 1 TABLE OF CONTENTS GENERAL INFORMATION & SPECIFICATIONS Electrical Characteristics Environmental Characteristics Accessories SECTION 2 1-2 1-4 OPERATING INSTRUCTIONS Introduction Function of the Front Panel Controls . Operational Check Using the Analyzer Signal Application Resolution, Sensitivity, and Frequency Span Gain Desensitization Near 0 Hz Using the Video Filter Selecting Sweep Rate Triggering the Display Manual Scan of the Spectrum How to Use an External Sweep Source External Trigger Operation Using the CAL OUT Signal Reference for Accurate Frequency and Amplitude Measurements Using the Analyzer Below 100 kHz SECTION 3 Page 2-1 2-5 2-9 2-10 2-11 2-12 2-13 2-14 PERFORMANCE CHECK Operational Performance and Instrument Familiarization Equipment Required Preliminary Preparation Check the 10 dB/Div and LIN Mode Calibration Check the Frequency Readout Accuracy Check the Range of the REF VAR Control, the Range and Accuracy of the Gain Selector, and the Gain Accuracy of the 10 dB Pushbutton Check the Operation of the Video Filters Check Sensitivity Check Spurious Signals from Internal Sources (Residual Responses) Check Resolution Bandwidth and Shape Factor Check Incidental Wing Check Sweep Circuit Operation with the TIME/DIV in the MANUAL, and OFF Positions Performance Checks Requiring Test Equipment Equipment Required Check the Calibrator Frequency Check Calibrator Output Level Check RF Attenuator Accuracy Check Display Flatness Check Intermodulation Distortion Check Pulse Stretcher Operation Check Triggering Operation and Sensitivity Check The External Horizontal Input Voltage Requirement Check the Video Output Level Check Frequency Span Accuracy and Linearity Check Time/Div Accuracy 3-1 3-2 3-3 3-5 3-6 3-7 3-9 3-10 3-11 3-12 3-13 3-14 3-15 3-16 TABLE OF CONTENTS (cont) SECTION 4 CALIBRATION Equipment Required Short Form Procedure and Record Time Base Section Adjust Sweep Length, Offset, and Triggering Function IF Alignment Adjust the LIN Mode Baseline Offset Adjust the Gain Compensation and Calibrate the Reference Level 1st LO Phase Lock Loop Error Amplifier Offset Adjustment Frequency Span and 1st LO Calibration Adjust the Frequency Span of the 1st LO and the 16-19 MHz Oscillators Calibrate the Center Frequency and Frequency Readout Phase Lock Calibration Adjustments Adjust Memory Gain Adjust Error Amplifier Gain Resolution Adjust the Bandpass of the 105 MHz IF Amplifier and 300 kHz Filter Adjust the Resolution Gain Leveling Compensation Adjust the Post Resolution Amplifier Gain Minimize Intermodulation Products Page 4-1 4-3 4-6 4-8 4-10 4-11 4-12 4-14 4-16 50 MHz Calibrator Adjust the Calibrator Output SECTION 5 CIRCUIT DESCRIPTION Block Diagram Description Detailed Circuit Description RF or Microwave Circuits Phase Lock and Frequency Stablization YIG Driver, Voltage Memory and Phase Lock Logic Frequency Tuning Control and Readout Tuning Control YIG Driver Frequency Span Marker Generator 105 MHz IF Amplifier, 3rd Mixer and Oscillator 10 MHz IF Pre-resolution Amplifier and Resolution Filter Circuits YIG Oscillator Power Supply 30 Hz Filter 50 MHz Calibrator Function IF Amplifier Video Filter, Pulse stretcher, Baseline Clipper & Vertical Output Frequency Readout Uncal Circuit Sweep Triggering Sweep Generator and Horizontal Amplifiers 5-1 5-2 5-3 5-4 5-5 5-6 5-7 5-8 5-9 5-11 5-12 TABLE OF CONTENTS (cont) SECTION 6 MAINTENANCE INSTRUCTIONS Page Preventive Maintenance Cleaning Lubrication Visual Inspection Transistor and Integrated Circuit Checks Performance Checks and Recalibration 6-1 Troubleshooting Troubleshooting Aids Diagrams Circuit Board Illustrations Wiring Color Code Multiple Terminal (Harmonic) Connector Holders Resistor Code Capacitor Marking Diode Color Code Transistor and Integrated Circuit Electrode Configuration Diode Checks IC Checks General Troubleshooting Techinque Corrective Maintenance Obtaining Replacement Parts Repair and Exchange Program Soldering Technique Replacing Square Pins for Multi-pin Connectors Replacing Assemblies Front Panel Controls and Selectors Circuit Board Assemblies DVM Logic and Readout Circuit Board Replacing the Sweep Circuit Board Replacing the IF Function Circuit Board Replacing the Resolution Circuit Board Replacing Circuit Boards in the Honeycomb Assembly Replacing Microwave Assemblies Replacing the 2.095 GHz Filter Assembly A10, or the Multiplier-Bandpass Filter A401 Replacing the Multipler 2.18 GHz Bandpass Filter and 16-19 MHz Mixer Circuit Board Assembly 6-2 SECTION 7 OPTIONS AND MODIFICATIONS SECTION 8 ELECTRICAL PARTS LIST SECTION 9 DIAGRAMS AND CIRCUIT BOARD ILLUSTRATIONS SECTION 10 MECHANICAL PARTS LIST CHANGE INFORMATION 6-3 6-5 6-6 6-8 6-10 6-11 6-13 Fig. 1-1 . 71-13 Spectrum Analyzer. Section 1-71-13 GENERAL INFORMATION AND SPECIFICATIONS INTRODUCTION Abbreviations used in the text and diagrams are based on ANSI Y 1 .1, 1972 Standards . This manual is divided into ten major sections that provide the following information : Section 1 - General Information and Specifications : Contains the instrument description and specifications . Section 2 - Operation Instructions : Information relative to installing and operating the instrument. Section 3 - Performance Check: Provides procedures to check the operational performance of the instrument plus additional performance check procedures that require test equipment to verify that instrument performance is in accordance to specifications . Section 4 - Calibration Procedure : Describes test equipment setup and adjustment procedures required to calibrate the instrument . Section 5 - Circuit Description : Provides basic and general circuit analysis that may be useful when servicing or operating the instrument . Section 6 - Maintenance Instructions : Describes routine and corrective maintenance procedures with detailed instructions for replacing assemblies, subassemblies, and individual components. Troubleshooting procedures, plus general information that may aid in servicing the instrument, are also provided . An exploded drawing is part of Section 10 . Section 7 - Options : Describes options available for the instrument. Section 8 - Electrical Parts List : Provides information necessary to order replaceable parts and assemblies. Section 9 - Diagrams: Provides functional block diagram and detailed circuit schematics. Located adjacent to the diagram (usually on the back of the preceding diagram) are pictoral layout drawings that show sub- assembly and component locations . IC logic diagrams, waveforms and voltage data, for troubleshooting orcircuit analysis, are also provided adjacent to or on the diagram . Section 10 - Mechanical Parts List, Exploded Drawings and Accessories : Provides information necessary to order replaceable parts. The Parts List is cross-referenced to the Electrical Parts List . Exploded drawing shows sequence of assembly and identifies assemblies. Changes and Corrections : Provides updating information for the manual in the form of inserts. These inserts are incorporated into the manual text and diagrams when the manual is reprinted . DESCRIPTION The 71-13 Spectrum Analyzer is a high-performance communication spectrum analyzer that plugs into and operates with the 7000-Series mainframe oscilloscopes . It is a swept front end analyzer that displays absolute amplitude information of signals within the frequency span of 0 Hz to 1 .8 GHz. Time domain characteristics, within a 3 MHz bandpass, can also be displayed . Important features of the 71-13 are : 1) Greater than 70 dB dynamic range. 2) Sensitivity down to -128 dBm . 3) Resolution capability from 3 MHz to 30 Hz. 4) Incidental Wing less than 10 Hz . 5) Fully calibrated display modes of either 10 dB/Div, 2 dB/Div, or Linear ; and a calibrated reference level in dBm . 6) Calibrated sweep spans from 100 MHz/Div to 200 Hz/Div . 7) Digital frequency readout . 8) Full range of video filtering for noise averaging . 9) Baseline clipping to subdue the bright baseline of displays when photographing . 10) Pulse stretching, to enhance pulsed spectra when using wide frequency spans and resolution bandwidths . 11) Access for a tracking generator . 12) Frequency and amplitude reference calibrator. If the 7000-Series mainframe features crt readout, the signal parameters and other pertinent information, such as resolution bandwidth, video filtering, and frequency span, are displayed on the crt readout to simplify the operation of the instrument. Records can then be made of pertinent data by photographing the display . Specification-7L13 The analyzer requires three plug-in widths in the 7000Series mainframe. ELECTRICAL CHARACTERISTICS The following characteristics and features of the 7L13 Spectrum Analyzer are applicable after a warmup period of 30 minutes or more . CENTER FREQUENCY Range: 1 kHz to 1 .8 GHz. Resolution of the Center Frequency Indicator: Within 1 MHz. STABILITY (after a 2 hour warmup period) Within 2 kHz per hour at a fixed temperature, when phase locked ; within 50 kHz when not phase locked . INCIDENTAL FM (see Fig. 3-5) 10 Hz (peak-to-peak) or less when phase locked, and 10 kHz (peak-to-peak) or less for 5 seconds when out of phase locked mode . VIDEO FILTERING Three selections of video filtering; 10 Hz, 300 Hz and 30 kHz are provided for signal or noise averaging . DISPLAY Accuracy : f(5 MHz + 20% of the Freq Span/Div) . The center frequency is indicated by LED readout on the 7L13 and crt readout when the 7000-Series mainframe has this feature. FREQUENCY SPAN Calibrated spans from 200 Hz/Div to 100 MHz/Div in a 1-2-5 sequence, plus O Hz and MAX SPAN positions. In the 0 Hz position, the analyzer is a fixed tuned receiver for time domain analysis . In the MAX SPAN position the frequency span is approximately 1 .8 GHz. Accuracy : Within 5%of the indicated frequency separation . Linearity over the center 8 divisions is within 5% . RESOLUTION Six resolution bandwidth selections from 30 Hz to 3 MHz, in decade steps, are provided . Resolution bandwidth may be coupled or uncoupled from the frequency span selector . Bandwidth accuracy : Resolution bandwidth, at the 6 dB down point, is within 20% of the resolution selected . Shape factor (60:6 dB ratio) : 12 :1 or better for 30 Hz resolution and 4:1 or better with resolution of 300 Hz or more except 3 MHz. Maximum bandwidth 60 dB down with 3 MHz resolution, is 13 MHz. LOG 10 dB/DIV : Provides a calibrated 70 dB dynamic range with an accuracy that is within 0.1 dB/1 dB to a maximum of 1 .5 dB over the full dynamic range. LOG 2 dB/DIV : Provides a calibrated 14 dB dynamic range with an accuracy that is within t0 .4 dB/2 dB to a maximum of 1 .0 dB over the 14 dB dynamic range. LIN: Provides a linear display from approximately 0 .7 /jV (100 dBm) full scale, to 7 .07 volts (+30 dBm) . Amplitude linearity is within 10% over the graticule height . REFERENCE LEVEL Reference level operation is in calibrated 10 dB steps from -110 dBm to +30 dBm, within t2 dB . (Accuracy includes the attenuator and gain switching effects when the two are not offsetting each other.) Reference level operation below 100 kHz becomes limited to a rangefrom +30 dBm to-50 dBm as the center frequency approaches 1 kHz. Reference level deviation, between display modes, is less than 2 dB from 2 dB/DIV to 10 dB/DIV and less than 0.5 divisions from 2 dB/DIV to LIN. This deviation is a function of the oscilloscope vertical linearity. An LINCAL indicator signifies when the display is not calibrated . DISPLAY FLATNESS Signal level change over the six resolution bandwidth selections is less than 0.5 dB . +1 dB, -2 dB with respect to the level at 50 MHz, over any selected frequency span . '^ Specification-7L13 CALIBRATOR 50 MHz ±0 .01% with an absolute amplitude level of -30 dBm ±0 .3 dB, at 25°C . 50 MHz harmonics are generated to provide a comb of markers for frequency span calibration . CW SENSITIVITY (Signal + noise = 2x noise, In LIN display mode) The following characteristics are applicable from 100 kHz to 1 .8 GHz: Below 100 kHz the sensitivity degrades approximately 0.3 dB/kHz ; for example, the sensitivity at 50 kHz with 30 Hz resolution is, -113 dBm or better; at 1 kHz, -98 dBm or better . RESOLUTION BANDWIDTH 30 300 3 30 .3 3 Hz Hz kHz kHz MHz MHz SIGNAL LEVEL -128 -120 -110 -100 -90 -80 dBm dBm dBm dBm dBm dBm positions provide an additional 40 dB of gain only in the 2 dB/DIV and LIN modes. The 10 dB pushbutton provides the additional 10 dB of gain, when the resolution bandwith is 30 Hz and the REFERENCE LEVEL is -100 dBm in the 2 dB/DIV or LIN mode . The REF VARiable control provides continuous gain adjustment between each calibrated REFERENCE LEVEL setting. RFATTENUATOR Provides 60 dB of attenuation in calibrated 10 dB steps. Accuracy is ±0 .2 dB or 1 % of the dB reading, whichever is greater . MAXIMUM INPUT POWER LEVEL -30 dBm with the RF Attenuator at 0 dB, for linear operation, +30 dBm with the RF Attenuator at 60 dB . (+30 dBm is also the power rating of the RF Attenuator .) NOTE SPURIOUS SIGNALS FROM INTERNAL SOURCES (Residual Response) Equal to or less than -100 dBm, referred to the 1st mixer input. INTERMODULATION DISTORTION (Fig . 3-6) 100 kHz - 1 .8 GHz: Third order intermodulation products are down 70 dB or more from two -30 dBm signals within any frequency span, second order products are down 70 dB or more from two -40 dBm signals within any frequency span . 100 kHz - 1 kHz: Intermodulation products (3rd and 2nd) are down 50 dB or more for the same input level as above. GAIN The gain range is 80 dB total . An eight position selector changes the IF gain 70 dB in 10 dB (±1 .0 dB) steps and a 10 dB pushbutton adds an additional 10 dB of gain when the REFERENCE LEVEL is -100 dBm and 30 Hz resolution bandwidth is used, in the 2 dB/DIV or LIN mode . Four positions (blue sector) of the selector provide 30 dB of change in all display modes. The remaining four The maximum input power level to the RFA ttenuator is 1 watt average and 200 watts peak. +13 dBm will destroy the 1st mixer. SWEEP MODES AND RATE Selection of an external sweep source, manual sweep, or calibrated sweep rates from 10 s/Div to 1 ps/Div in a 12-5 sequence are provided . Sweep rate accuracy is within 5% of that selected . TRIGGERING Three triggering sources can be selected . INTernal selects the vertical or video component from either vertical plug-in compartment, EXTernal selects the signal applied to the EXT IN HORIZ/TRIG connector and LINE selects a sample of the mainframe line voltage . INTernal signal is ac coupled with an approximate frequency range from 15 Hz to 1 MHz. The external and line signals are do coupled . Input impedance for the external input is about 30 kid for the trigger mode and 9 kQ for external horizontal sweep mode . Trigger sensitivities are: 1) <0 .5 division of internal signal (peak-to-peak) and <0 .5 volt of signal (peak-topeak) of external signal for NORM mode . 2) <0 .5 division of internal signal peak-to-peak and <0 .5 volt of external signal for SGL SWP mode . Specification-71-13 In the NORM mode the sweep will automatically recur at the end of holdoff time if a trigger signal is absent, to provide a baseline on the crt. The SGL SWP and "start" buttons function together to provide a single sweep each time the "start" button is pushed . VIDEO OUTPUT CONNECTOR Provides 50 mV t5% of video signal per display division, aboutthe crt vertical center. Source impedance is approximately 1 kit. A maximum of 50 mV offset may be introduced by the error from the mainframe vertical centering interface . ACCESSORIES AND OPTIONS STANDARD ACCESSORIES 1 . Spectrum Analyzer Graticule: Clear plastic implosion shield with LOG, LIN, REF and f (frequency) direction markings. Tektronix Part No. 337-1439-01 for 7403N oscilloscope and 337-1159-02 for other 7000-Series oscilloscopes. 2. Filter Light Amber 378-0684-01 3. 50 i2 Coaxial Cable, with BNC connectors, 6 foot 012-0113-00 4. BNC Male to N Female Adapter 103-0058-00 5. Manual 070-1673-00 HORIZONTAL/TRIGGER INPUT EXTERNAL CONNECTOR Requires 0 V to 10 V t1 V, to sweep the full frequency span . OPTIONAL ACCESSORIES 1 . DC Block (for applying signals riding on a DC potential) . Maximum potential is 50VDC Requires 0.5 volt peak-to-peak to trigger the sweep circuits . Maximum safe input; 50 volts (dc + peak ac) . 2 . 75 0 to 50 i2 minimum loss attenuator with DC block ENVIRONMENTAL CHARACTERISTICS This instrument will meet the electrical characteristics over the environmental limits of the 7000-Series mainframe. Complete details on test procedures, including failure criteria, etc., can be obtained from Tektronix, Inc. Contract your local Tektronix Field Office or representative . 015-0221-00 011-0112-00 OPTIONS TO 7000-SERIES OSCILLOSCOPES 1 . CRT with P7 phosphor and time domain graticule . The external graticule for spectrum analysis (part of standard accessories) should be used. 2. CRT with P7 phosphor and an internal spectrum analyzer graticule (designated P7SA). This is recommended when the oscilloscope mainframe is to be used exclusively with spectrum analyzer systems . Section 2-71-13 OPERATING INSTRUCTIONS INTRODUCTION This section describes : 1) Function of the front panel controls, selectors, indicators and connectors . 2) Installation of the 71-13 into a 7000-Series oscilloscope . 3) General operation information, such as : Adjustments required to mate the 71-13 to a 7000-Series oscilloscope . Signal application to the RF INput. How to use the calibrator for accurate frequency and power level measurements, etc . 4) Some typical applications .' The first steps of the General Operating information calibrate and check the analyzer Frequency, Span/Div, and the display modes . These steps serve as part of an acceptance check and describe how to obtain a display on the oscilloscope crt . Performing this Operational Checkout procedure will acquaint you with the functions of the controls and selectors and the overall operation of the 71-13. A safety latch must be released before the 71-13 can be pulled from the oscilloscope compartment. The unit will pull out part way, when the front panel release is pulled, then the spring safety latch mustbe pushed up to free the unit so it can be pulled the rest of the way out. This safety latch is located underneath the right rail near the front corner (see Fig . 2-113) . FUNCTION OF THE FRONT PANEL CONTROLS AND ADJUSTMENTS The following is a general description of the 71-13 controls, indicators and connectors. This description will familiarize you with theirfunction and Figs . 2-1Aand 2-1 B illustrate their location . A MARKER indicator lights when the FREQ SPAN/DIV is at the MAX SPAN position and a notch on the baseline of the display indicates the center portion of the span that will be displayed when the FREQ SPAN/DIV is reduced. The center frequency or marker frequency is indicated by an LED digital readout dial . CAL : Calibrates the frequency readout so it represents the center of the span . NOTE When operating with Freq Spans of 50 kHz/Div or less, the AUTO PHASE LOCKED switch must be OFF if you want the center frequency and LED readout to change when tuning . FREQ SPAN/DIV : This switch selects the frequency span of the display. The calibrated range of the selector is 100 MHz/DIV to 200 Hz/DIV in a 1, 2, 5 sequence . A MAX SPAN position provides approximately 1 .8 GHz of spectrum and a 0 Hz position converts the analyzer to a fixed tuned receiver for time domain displays . Time analysis of the signal characteristics, within the bandwidth capabilities selected with the RESOLUTION control, can then be performed. The FREQ SPAN/DIV knob is large enough to provide ease in switching; however, excess torque applied when the selector is at either of its extreme positions may cause the aluminum bushing inside the knob to slip. When this occurs, the selectors may double detent or switch with a grinding noise. Refer to Knob Removal and Installation instructions in the Maintenance section of the manual for realignment. FREQUENCY CONTROLS TUNING : The center frequency is tuned by a two-speed control with a ratio of approximately 1 :2.8 in the position and 45 :1 in the slow orfine position . In addition, the tuning range is decreased to 1 MHz (±9500 kHz) when the FREQ SPAN/DIV is 50 kHz or less. I A treatise on spectrum analyzer measurements and applications Is contained In Tektronix Measurements Concepts Booklet; "Spectrum Analyzer Measurement Theory and Practice :", Part No. 082-1334-00 . RESOLUTION : This control selects the resolution bandwidth for the analyzer . The calibrated range (within 20%) is 30 Hz to 3 MHz in decade steps . The RESOLUTION is normally coupled to the FREQ SPAN/DIV control so the display amplitude remains constant as the FREQ SPAN is changed ; however, a concentric sleeve labeled PULL TO UNLOCK will uncouple the two selectors when it is pulled out and allow independent settings of each control . Operating Instructions-7L13 Fig . 2- 1 A . Front panel controls and selectors. Operating Instructions-7L13 Fig. 2-28 . Front panel controls and selectors. 2-3 Operating Instructions-71 .13 DISPLAY CONTROLS AND SELECTORS LOG 10 dB/DIV : Selects a calibrated display with a dynamic range of 70 dB (to the 7th graticule line, from the reference) at 10 dB/DIV . The bottom graticule division is not calibrated . reference level. The dynamic range of the display is now -114 dBm (-100 dBm + 14 dB display window to the 7th graticule line) . An additional 10 dB of gain, fora calibrated -124 dBm, can be switched in with the 10 dB GAIN pushbutton, when the RESOLUTION is 30 Hz . LOG 2 dB/DIV : When this pushbutton is depressed, the dynamic range of the display is a calibrated 14 dB at 2 dB/DIV . VIDEO FILTERS : Three filters (30 kHz, 300 Hz, and 10 Hz) can be switched in to restrict the video bandwidth and reduce high frequency components for display noise averaging . Two pushbuttons select 30 kHz or 300 Hz when depressed, and 10 Hz when both are depressed. LIN : Selects a linear display. The LIN graticule calibration permits relative signal level measurements as follows: Adjust the level of one signal to the 1 .0 line, with the gain or RF Attenuation . Read the level of the other signals as a percentage of this reference. BASELINE CLIPPER: This controls the vertical amplitude of that portion (baseline plus signal) of the display that the intensity is subdued. REFERENCE LEVEL (RF Attenuator and IF Gain) : These are concentric controls that are connected in an electro-mechanical differential arrangement. They select input attenuation to the input mixer, and the IF gain . They indicate, via readout windows; REFERENCE LEVEL in dBm, of the full scale display, MAXimum signal input level (in dBm) for linear operation, and the input RF attenuation (from 0 to 60 dB) . The RF attenuation is in series with the input signal path to the input mixer, therefore its settings affect the maximum input signal level to the 71-13 . With 0 dB attenuation, maximim input signal level for linear operation, is -30 dBm . Changing the RF Attenuator to 60 dB increases the maximum input signal level to +30 dBm . The IF gain selector has a range of 70 dB in 10 dB steps. The combination of RF Attenuator and IF gain settings establishes the REFERENCE LEVEL ; therefore, both controls function as REFERENCE LEVEL selectors. The maximum sensitivity of the display will not exceed -130 dBm . Since the dynamic window is 70 dB in the 10 dB/DIV display mode, the REFERENCE LEVEL readout is valid to -60 dBm. With the RF Attenuator at 0 dB and the IF gain fully ccw, the REFERENCE LEVEL is -30 dBm . Increasing the IF gain 30 dB, changes the REFERENCE LEVEL to -60 dBm, which is the limit for a calibrated reference level in the 10 dB/DIV mode . The blue tint, that borders the 10 dB/DIV switch and four positions of the gain selector, correlates REFERENCE LEVEL readout to the gain settings applicable in the 10 dB/DIV mode. Readings, with the gain selector outside the blue tint sector are erroneous because the gain is electrically locked out; the crt readout will display the < symbol to signify that the reading is incorrect. In the 2 dB/DIV mode, the full 70 dB range of the gain selector is usable . Switching the gain fully cw with the RF Attenuator at 0 dB, produces an accurate -100 dBm 2-4 CONTRAST : Adjusts the brightness ratio between the clipped (subdued) baseline and the unclipped display. The display intensity is set by the mainframe Intensity control . PULSE STRETCHER: Switching this on, stretches the falltime of pulsed signals to enhance the visibility of pulsed RF signals that may be within wide frequency spans and resolution bandwidths . LOG and AMP CAL: The LOG adjustment calibrates the logarithmic accuracy of the display. The AMP adjusts the REFERENCE LEVEL to the top graticule line . AUTO PHASE LOCKED : This switch is used to disable the phase lock for some applications, such as tuning the analyzer more than 1 MHz when the analyzer is used as a tuned receiver (0 span) . VERTICAL POSITION : Positions the crt beam vertically. HORIZ POSITION : Positions the crt beam horizontally . OUTPUT AND INPUT CONNECTORS VIDEO OUT: Provides ±50 mV of video per displayed division of signal . The amplitude and polarity of this signal is relative to the graticule vertical centerline . Source impedance is about 1 kf2. This signal can be used to drive an external device such as a recorder . TRACK GEN: A source of control signals for a Tracking Generator. Pin 5 of the connector is the source of a +10 V to -10 V sweep ramp, with +10 V representing the left edge of the display and -10 V the right side of the display. Operating Instructions-71 .13 RF IN : A 50 f2 input connector for applying the input signal to the 71-13. REFERENCE LEVEL readout refers to the signal level at this connector . Any signals riding on some do potential must be applied through a do block. Refer to the General Operating Procedure with regard to signal applications . 1st and 2nd LO OUT: These connectors provide access to the output of the respective local oscillators . They must be terminated into 50 O. Keep the termination plugs on the output jacks unless these ports are connected to an external device such as a tracking generator. CAL OUT: Provides an accurate -30 dBm, 50 MHz signal source . This signal provides an absolute reference on the display to calibrate the REFERENCE LEVEL and check dBm readings . Harmonics of the 50 MHz fundamental provide a comb of markers across the frequency span for accurate frequency and span measurements . SWEEP CONTROLS TRIGGERING SOURCE : Three sweep triggering sources can be selected plus a free run mode : INTernal selects the vertical orvideo component from eithervertical plug-in compartment. The signal is ac coupled with an approximate frequency range from 15 Hz to 1 MHz; EXTernal selects the signal that is applied to the EXT IN HORIZ/TRIG connector; and LINE selects a sample of the mainframe line voltage . External and line signals are do coupled to the triggering circuits . Maximum signal input to the external input connector should not exceed 50 volt (dc + ac peak) for triggering . Input impedance for the external input is about 30 kf2. The FREE RUN mode will not sync the sweep to any triggering signal . MODE : Two modes are available, NORM and SGL SWP. In the NORM mode the sweep will automatically recur at the end of holdoff time, if a trigger signal is absent . This feature provides a baseline on the display. In this mode triggering occurs at the slope and level selected by the SLOPE/LEVEL controls unless the triggering signal is below the required amplitude or beyond the frequency limits of the circuit. Minimum signal amplitudefor internal triggering is 0.5 division of signal (peak-to-peak) and 0.5 volt of signal for external triggering . In the SGL SWP mode, the sweep is triggered by pushing the adjoining button . This button lights during sweep time and serves as an indicator to determine camera shutter time when photographing slow scan-time displays . Minimum signal amplitude for triggering is 0.5 division of signal and 0.5 volt of external signal . TIME/DIV and MANUAL SCAN : Three sweep modes, plus an off state, are provided : A calibrated TIME/DIV in a 1, 2, 5 sequence from 10 s/DIV to 1 Ns/DIV, a manual sweep control, and an external sweep . The TIME/DIV control selects the sweep rates and the modes. In the OFF position, the crt beam is horizontally centered and the analyzer becomes a fixed tuned receiver at the frequency indicated by the readout. The EXT position connects any signal applied to the EXT/HORIZ TRIG connector to the horizontal deflection circuits of the 71-13. External sweep voltage (0 V to 10 V) signal can be used to slave the 71.13 to an external device such as a recorder . The MANUAL position connects the sweep circuits of the 71-13 to the MANUAL SCAN control, so the crt beam deflection can be manually controlled . SWEEP CAL : The adjustment calibrates the amplitude of the sweep voltage to the FREQ SPAN circuits and compensates for differences in deflection sensitivities between oscilloscopes. OPERATIONAL CHECK that 1 . Preliminary Operational Procedure Mainframe Calibrates the 71-13 to the Osciliscope When the 71_13 plug-in unit is installed in a 7000-Series mainframe, the spectrum analyzer should be calibrated to ensure correlation between plug-in and the mainframe deflection sensitivities. We recommend that the front panel calibration procedure be performed anytime the instrument is first turned on, to ensure optimum accuracy . a. Plug the 71-13 Spectrum Analyzer into the 7000Series mainframe. Ensure that the 71-13 is securely latched in the compartment. This is a safeguard to ensure that the instrument does not slide out, if the mainframe is tipped forward. NOTE A safety latch is used to reduce the possibility of the instrument slipping out of the mainframe. b. Connect the oscilloscope mainframe to a suitable power source and switch the power on . Allow about 30 minutes for instrument stablization . 2- 5 Operating Instructions-71 .13 c. Set the front panel controls as illustrated in Fig . 2-2 and connect the CAL OUT signal through a short coaxial cable to the RF INput . 3. Calibrate the Sweep Span d . Adjust the oscilloscope Intensity, Focus and Astigmatism controls for optimum display definition with normal intensity. b. Position the 0 Hz response, or LO feedthrough, on the zero (left) graticule line with the HORIZ POSITION control . e. Depress the 2 dB/DIV display mode button . Position the baseline of the display to the bottom graticule line with the VERTICAL POSITION control and center the display with the HORIZ POSITION control. c. With the CAL OUT signal applied to the RF INput, decrease the FREQ SPAN/DIV to 50 MHz and tune the 5th marker (250 MHz) to the center graticule line (see Fig . 23) . f. Depress the 10 dB/DIV (LOG) display button . Display should now resemble that shown in Fig . 2-2. d . Calibrate the frequency span to 50 MHz/DIV by adjusting the SWP CAL for 1 marker/division. It may be necessary to keep the 250 MHz marker centered with the frequency TUNING control as the sweep is calibrated . Final display should resemble that illustrated in Fig. 2-3. NOTE When the oscilloscope has a crt with P7 phosphor, a viewing hood will help shield ambient light and enhance the display information. 2. Calibrate the Frequency Readout Due to hysteresis in the tuning system, the calibration and accuracy of the readout must be performed and checked by approaching each check point from the same direction (low to high) . a. Apply the calibrator signal to the RF INput, switch the FREQ SPAN/DIV to MAX SPAN, and tune the CENTER FREQUENCY to 0000. b. Decrease the FREQ SPAN/DIV setting to 10 MHz and increase the CENTER FREQUENCY until the 50 MHz calibrator signal is tuned to thecenterl ine of the graticule. NOTE a. Switch the FREQ SPAN/DIV to MAX SPAN position . 4. Check and Adjust LOG-AMPL Calibration The LOG CAL adjustment calibrates the gain of the analyzer vertical output so the 2 dB/DIV and 10 dB/DIV modes may be accurately set . The AMPL CAL adjustment sets the reference level to thetop graticule line . There is no interaction between these two, adjustments . a. Set the 71-13 selectors and controls as directed in step 2 and tune the fundamental 50 MHz calibrator signal to the center of the graticule . b. Uncouple the RESOLUTION selector from the FREQ SPAN/DIV by pulling out the PULL TO UNLOCK sleeve, then switch the FREQ SPAN/DIV to 5 MHz. The RESOLUTION should remain at 3 MHz. As the FREQ SPAN is decreased, it may be necessary to re-adjust the tuning control to keep the signal centered on screen . c. Switch the Display Mode to 2 dB/DIV and position the baseline of the display on the bottom gratiucle line with the VERTICAL POSITION . It is important to tune the signal from low to high . If the tuning direction is reversed, repeat the procedure by returning the FREQ SPAN/DIV to MAX SPAN and the CENTER FREQUENCY to 0000 to establish the same reference point on the hysteresis loop . d. Adjust the AMPL CAL and the LOG CAL (if necessary) to bring the 50 MHz signal within the graticule window . Adjust the AMPL CAL to establish a signal reference amplitude of 8 divisions (Fig . 2-4 shows a full screen display) . c . When the 50 MHz signal is centered on screen, adjust the frequency CAL for a CENTER FREQUENCY readout of 50 MHz. e. Switch in 10 dB of attenuation with the RF Attenuator . Amplitude change should equal 5 divisions at 2 dB/DIV . 2- 6 '~ - Operating Instructions-71-13 CENTER FREQUENCY RESOLUTION Top line is dBm level indicated by REFERENCE LEVEL window and Readout . Display Mode : 10 dB/DIV Frequency : 250 MHz UNCAL Light OUT RF Attenuator : 0 dB Sleeve pushed in so FREQ SPAN/DIV and RESOLUTION are coupled together . FREQ SPAN/DIV : 50 MHz PULSE STRETCHER Out Termination caps on Output Ports CAL OUT : Connect to RF Input Fig . 2-2 . Front panel selector positions and signal connections for initial operational check and front panel calibration . Operating Instructions-71-13 Set the 250 MHz (5th) marker at the centerline with the HORIZ POSITION control . 0 Hz response I-Jodam 0I"M IM, J 1 MHz, pz g . Switch out the 10 dB of RF Attenuation . Now adjust the AMPL CAL to return the signal level to the reference line . (Ensure that the baseline of the display is still on the bottom graticule line .) h . Repeat these steps until the 2 dB/DIV display is calibrated (see Fig . 2-4), then return the RF Attenuator to 0 dB (REFERENCE LEVEL -30 dBm) . Ensure that the -30 dBm signal is 8 divisions in amplitude . 11 11 1I1 " ,s'~ 1 ,ll, NOTE ll~" An alternate method of calibrating the display is to switch between the 10 d8/DIVand2 d8/DIVdisplay modes while adjusting the LOG CAL so the display amplitudes are equal, then adjust the AMPL CAL so the display amplitude, in 2 d8/DIV mode, equals -30 dBm reference. Check the final calibration in the 2 d8/DIV mode . Fig . 2-3. Calibrating the sweep span . 2) Adjust AMP CAL to position -30 dBm signal to the REFERENCE LEVEL (top graticule line) . -J(~dDm 40 050 _J __ __ T , ~MHZI Ai:S k, 1) Adjust LOG CAL for 10 dB amplitude change with 10 dB change in RF Attenuator . 5. Check the 10 dB/DIV and LIN Mode Display Operation -so Baseline of the display must be positioned on the bottom graticule line . Fig . 2-4 . Calibrating the LOG and REFERENCE LEVEL . (Double exposure to illustrate the relationship of the two displays .) f. If the change is more than 5 divisions (e .g ., amplitude decreases from 8 to 2 .5 div), adjust LOG CAL to further increase the amplitude change (i .e ., decrease the signal amplitude) . Conversely, if the change is less than 5 divisions (e .g ., amplitude changes from 8 to. 3.5 div), adjust the LOG CAL to further decrease the amplitude change (i .e ., increase the signal amplitude) . Correct for approximately 1/2 the total indicated error. This adjustment may seem opposite to what is expected ; however, the LOG CAL adjustment also shifts the reference level . This, therefore will require a correction to the amplitude change . 2- 8 i. Switch the display modes from 2 dB/DIV to 10 dB/DIV, then from 2 dB/DIV to LIN. Signal amplitude reference level should not change more than 2 dB from 2 dB/DIV to 10 dB/DIV, or 0 .5 division from 2 dB/DIV to LIN mode . a . After completing the LOG CAL and AMPL CAL adjustments, described in step 4, depress the 10 dB/DIV button . Ensure that the RF Attenuator is at 0 dB and the Gain selector is fully ccw so the REFERENCE LEVEL reads -30 dBm . b. Switch the FREQ SPAN/DIV to 1 MHz and the RESOLUTION to .3 MHz. Tune the 50 MHz marker to the graticule center . c . Increase the RF Attenuator setting in 10 dB steps and note that the signal amplitude decreases 1 divison each step . d . Switch the RF Attenuator back to 10 dB, and depress the LIN display mode button . e . Ensure that the baseline of the display is at the bottom graticule line, and the 50 MHz signal is centered, then adjust the VARIABLE Gain control for a signal amplitude of 6.3 divisions. f. Switch the RF Attenuator to 20 dB to add 10 dB of attenuation, and note that the signal amplitude decreases Operating Instructions-71-13 USING THE ANALYZER to approximately 2 divisions fora ratio change of 3.16 (this is equivalent to 10 dB in LIN mode) . 1. Signal Application g . Return the RF Attenuator to 0 dB, the VARIABLE Gain control to CAL. The signal amplitude should return to full screen and the REFERENCE LEVEL should indicate -30 dBm. The RF INput impedance to the 71-13 is 50 O. At high frequencies, impedance mismatches between the RF INput and the signal source can cause reflections in the transmission line and degrade instrument performance. Flatness, sensitivity, spurious response, etc., are all affected . To reduce mismatch, use good quality 50 f2 coaxial cable to connect the signal source to the RF INput and keep the cable as short as possible . Cable losses become excessive above frequencies of 1 GHz . 6. Adjust Contrast and Check Baseline Clipper Operation NOTE Avoid applying high level signals (above -30 dBm) to the 1st mixer of the 71-13. High level signals overload the mixer and may produce spurious signals . A conversion chart shown in Fig . 2-5 will aid in determining inputsignal level, in dBm,pV, and uW, from a voltage or power source . The contrast ratio between the clipped portion of the display baseline and the rest of the display is affected by the sweep rate, frequency span, resolution, and ambient light. a. With the BASELINE CLIPPER control set midrange, adjust the CONTRAST control for the desired ratio between the clipped or subdued portion and the rest of the display. Usually the contrast is adjusted so the clipped baseline portion is just visible. The input maximum power level to the RFAttenuator is 1 watt average or 200 watts peak. When the RF input signals are riding on a do potential, use the do block (Part No . 015-0221-00), to prevent the do from reaching the 1st mixer. When the signal source is 75 n and you are using the 75 to 50 0 minimum loss attenuator, a do block is not required because one is incorporated in the attenuator . b. Adjust the BASELINE CLIPPER control so the baseline is subdued. If there is excessive noise it may be desirable to clip noise level as well . NORMAL OPERATING RANGE ~100pv 1Av 10'av OdBm -130d13m -120dBm -110d13m -100dBm -90dBm 11W NOTE : 11W 0.001pw 0.01pw 0.1PW 1 .0pw 100uv 1mv ~10mv -80dBm -70dBm -60dBm -50dBm -40dBm -30dBm 10pw 100PW 1 .0nW 10nW 1OOnW 1 .OgW 100mv -20dBm -10dBm 10JAW 100kW OdB Volts RMS . . . multiply by 2.8 for peak-to-peak . 0 dBm 1 milliwatt Fig. 2-5. Volts-dBm-Watts conversion chart for 50 t2 Impedance. 2-9 Operating Instructions-71-13 Spurious response, caused by signal overload into the 1st mixer, can be minimized if the signal amplitude is kept within the graticule limits . A recommended procedure is to adjust the Gain selector for some baseline noise on the display, then increase the RF Attenuator setting until the strongest signals are within the graticule limits . If this does not bring these signals within limits, add external attenuators . The 71-13 can be used with a 75 f2 signal source by using a 75 f2 to 50 f2 minimum loss attenuator . This attenuator is available as an optional accessory (refer to the optional accessories list in the catalog or Accessory page in the manual for ordering information) . Sensitivity and power levels are often rated in dBm (dB with reference to 1 mW regardless of impedance) . Sensitivity and power levels for 75 fl systems are usually rated in dBmV (dB with reference to 1 mV across 75 f2) . Fig . 2-6 is a circuit diagram of a suitable matching pad for this purpose. The conversion from dBmV to dBm, and dBm (75 0) to dBm (50 0) through the matching attenuators, is shown in Fig . 2-7 and described as follows:  (dBmV, into 75 f2) - (dBm, at 50 f2 end) =54.46 dB ordBmV=54.5 dB+dBm . Forexample :-30 [email protected] () = 54 .5 dB + (-30 dBm) or + 24 .5 dBmV at the 75 f2 input . [31 [21 dBm dBMV (75 s2) (5092) INE NOME [11 dBmV (75 s2) +87 M +67 +47 EMIMMOMME No MEMNON, MEEMERNME EMEMOMMIN i MPAAVMMMIM M 0 -107 -100 -80 -60 -40 dBm (50 92) -104 .7 -20 Fig. 2-7. Graph to Illustrate relationship between dBm, dBmV, and dBMV . [21 dBm @ 75 f1 = dBm @ 50 f1 + 5.72 dB . For example : -30 dBm @ 50 f2 + 5.72 dB = 24 dBm @ 75 0 . bandwidth, sweep speed, frequency span, and incidental FM . The frequency span and sweep time are adjusted for minimum bandwidth to a cw signal . Theoretically, resolution and resolution bandwidth become synonymous at very long sweep times.  For some applications you may wish to know the relationship between dBm and dBNV . For 50 f2 systems dB,uV = (dBm) + 107 dB . Resolution bandwidth is measured and specified for the 71-13 as the bandwidth (separation) at the 6 dB down point on the signal . As the analyzer sweep rate is increased, the signal amplitude will decrease and bandwidth will increase, signifying that both sensitivity and resolution have been degraded . The best resolution with no video filter, for a given frequency span and sweep time is expressed as : -Frequency Span (in kHz) Ro _ Sweep Time (in ms) Fig. 2-6. Circuit of a 75-0 to 50-f) matching pad (ac coupled) . 2. Resolution, Sensitivity, and Frequency Span Resolution is the ability of a spectrum analyzer to discretely display adjacent signals within a frequency span . This resolution ability is a function of analyzer 2- 1 0 Bandwidth determines both noise level and the resolution capability of the analyzer . As the bandwidth decreases, the signal-to-noise level and, therefore, sensitivity increases. Maximum sensitivity, therefore, is obtained at the higher resolution settings . The frequency span is symmetrical about the center frequency. The frequency span to be used, depends on the application . Wide frequency spans are used to monitor a O Operating Instructions-71-13 frequenc y spectru m for spurious signals, check harmonic distortion, etc. Narrow frequency spans are used to identify a particular signal ; check its characteristics such as modulation, bandwidth, etc. Again, the UNCAL indicator will light if thesweepspeed is too fast for the video filtering, RESOLUTION and FREQ SPAN/DIV selected . When wide frequency spans are displayed, sweep rate is usually increased to eliminate flicker; this requires the use of wide resolution bandwidths . When narrowfrequency spans are used, high resolution capability is usually desired and slow sweep speeds are required . The FREQ SPAN/DIV and RESOLUTION selectors for the 71-13 are normally coupled together to optimimize resolution for the frequency span selected ; however, either can be independently set by pulling out the "PULL TO UNLOCK" sleeve around the FREQ SPAN/DIV selector. An UNCAL indicator will light when the sweep time is too fast for an amplitude calibrated display. Sweep speed should be reduced to maintain a calibrated reference level if the UNCAL indicator lights . 11rMM21MOME (A) I """ IM distortion obscured by noise. (1 MHz + 94 MHz) For pulsed applications, the resolution bandwidth of the analyzer should be on the order of 1/10 the side lobe frequency width, or the reciprocal of the pulse width, in order to ensure adequate resolution . The RESOLUTION selector is usually set, after the sweep rate has been adjusted, for optimum main lobe detail . 3. Gain Desensitization Near 0 Hz If the Gain selector is set for a REFERENCE LEVEL that is -50 dBm or more (e .g ., -60 dBm) with the RF Attenuator at 0 dB, a decrease insensitivity will be noticed below 1 MHz. This effect is caused by the 0 Hz response overdriving the list IF amplifier. If you are operating between 0 Hz and 2 MHz, do not set the Gain selector in this region . 4. Using the Video Filter The video filter is used for effective averaging of distributed signals, such as noise, and high frequency components on the display (see Fig . 2-8) . When signals are closely spaced, the filter may be useful in reducing modulation between the two signals so they can be more easily analyzed . The filters can also be used to average the envelope of pulsed RF spectra that has a relatively high PRF (pulse repetition frequency) ; however, because the filter is basically an integrating circuit, low PRF signals produce poor results. The use of the video filter may require a reduction in sweep speed in order to maintain a calibrated display . (B) Display with VIDEO FILTER added to average the noise level. Fig. 2-8. Integrating the display with the VIDEO FILTER . 5 . Selecting Sweep Rate Because the FREQ SPAN changes the resolution and sensitivity, the sweep rate must be decreased as the frequency span and resolution bandwidth are decreased, or when the UNCAL indicator lights . When the FREQ SPAN is reduced to 0, the analyzer functions as a fixed tuned receiver . The analyzer now displays time domain characteristics of the signal, within the bandwidth capabilities of the analyzer . Sweep Time/Div can now be used to examine or analyze such characteristics as modulation pattern, pulsed repetition rates, etc. 2- 1 1 Operating Instructions-71,13 NOTE The RESOLUTION bandwidth should be maximum for time domain analysis. 6. Triggering the Display The sweep trigger source is usually switched to the FREE RUN mode for normal spectrum displays ; however, it may be desirable or necessary to trigger the display when the event is time related to some source, or when the frequency span has been reduced to zero and a time domain analysis is performed . 7. Manual Scan of the Spectrum This position is used to examine a particular point or portion of the display, such as one of the null points of a frequency modulation spectrum . a. Calibrate the sweep span with the TIME/DIV selector in one of the scan positions as previously described, then switch to the MANUAL position . b. Use the MANUAL SCAN control to scan the selected frequency spectrum . The sweep can be triggered from the vertical or video signal from either vertical plug-in compartment, from the power line voltage, or from an external source. Trigger slope for any mode can be + or -; the triggering level is adjustable over the full range of a displayed signal when using INTernal trigger source, over a 10 V range of an external signal when using EXTernal source, and over the peak-to-peak range of the line signal when using LINE . 8. Using an External Sweep Source A signal source is required to sweep the analyzer externally. A voltage ramp from 0 V to 10 V f1 V will sweep the analyzer through its full span . 0 V corresponds to 0 Hz and 10 V to the high frequency end of the selected span. Input impedance is approximately 12 kC2 for an external sweep signal. In the NORM triggering mode, the display is triggered when the triggering signal source is within specifications . If the triggering signal is absent or outside of specifications, the sweep recurs automatically to provide a display baseline . Before switching to external operation, calibrate the sweep span using the internal sweep and the 50 MHz calibrator signal as described under Operational Check . Switch the TIME/DIV selector to its EXT position and apply the external voltage to the EXT IN HORIZ/TRIG jack. Adjust the upper end of the voltage (10 V) until the analyzer sweep span is calibrated . The amplitude of triggering signal that is required to trigger the sweep depends on the sweep mode selected . The internal signal is ac coupled ; the line and external signals are do coupled . Trigger sensitivities are: 1) <0 .5 division of signal (peak-to-peak) and <0.5 volt (peak-to-peak) of external signal for NORM mode . 2) <0 .5 division of signal (peak-to-peak) and <0.5 volt (peak-topeak) of external signal for SGL SWP mode. Maximum safe trigger input signal level to the EXT INput is 50 volts (dc + peak ac) . In the FREE RUN state, the sweep will not synchronize with any input trigger signal . When the SGL SWP button is depressed, the sweep will run after the adjoining button is depressed . During the sweep cycle, the activating button lights to indicate that the sweep is running. This feature is useful when photographing displays at slow sweep rates . The activating button does not arm the trigger circuit like some time base units . When triggering on pulsed spectra, it may be necessary to fine tune the sweep start away from a null point to trigger the display. 2-1 2 NOTE The frequency deviation across the selected span is a linear function (within 20%)of the inputvoltage, so +5 V do should tune the analyzer to the center of the selected frequency span. 9. External Trigger Operation This procedure is applicable when an external trigger source, such as a pulse generator or modulator, is used to trigger the display so it can be synchronized to an event (e.g ., measuring PRF of a radar signal) . a. Apply the trigger signal (>0.5 V peak) to the EXT IN HORIZ/TRIG jack of the 71-13 . Switch the TRIGGERING SOURCE to EXT and the TIME/DIV selectorto thedesired sweep rate. b . Adjust the triggering SLOPE and LEVEL for the desired triggering point. c. If time domain information is desired, reduce the FREQ SPAN/DIV to 0 and set the RESOLUTION to 3 MHz. Operating Instructions-71 .13 --, The analyzer is now triggered by the external source so the display sweep rate can be contolled externally . 10 . Using the CAL OUT Signal Reference for Accurate Frequency and Amplitude Measurements The accuracy of frequency measurements may be improved by using harmonics of the crystal controlled Calibrator . The Calibrator accuracy is within 0.01% . Frequency measurements within 2 MHz are possible by using either of the two methods described below. Measuring the Frequency Span between a Calibrator Marker and the Signal to Obtain an Absolute Frequency Measurement a. Tune the signal to the center graticule line, approaching this point from the low frequency side of the display. Couple the FREQ SPAN/DIV and RESOLUTION selectors together and open up the display to obtain an accurate setting, by reducing the FREQ SPAN/DIV to 5 MHz and increasing RESOLUTION to .3 MHz. Adjust SWP CAL, if necessary, to calibrate the display for 10 divisions between the 50 MHz calibration markers. (Remember to approach the center point from the low frequency side .) b. Connect the CAL OUT signal and the signal source through a BNC "T" connector to the RF INput so both signal and markers are displayed . c . Measure the frequency span between the signal and the nearest 50 MHz marker . (Frequency span is 5 MHz/Div .) d . Add or subtract the frequency span to the respective marker to obtain thesignal frequency. Since the maximum frequency span between the signal and marker is 25 MHz f5%, marker accuracy is 0 .01% and human observation error is approximately 1/2 a minor division or0.5 MHz. The accuracy using this method is within 2 MHz. Measuring the Frequency after the Frequency Readout Correction Factor Has Been Established a . As described for the frequency span method, tune the signal to the graticule centerline, opening the display to 5 MHz/Div to obtain an accurate setting. Tune the signal to the center from the low frequency side . b. Note the frequency readout (e .g ., 1002 MHz) . c. Apply the CAL OUT signal to the RF INput and tune the nearest 50 MHz marker to the graticule centerline . d . Set the frequency readout, with the CAL adjustment to read the exact frequency (e .g ., 1000 MHz) . e . Retune to the unknown signal, approaching it from the low side and note the frequency readout. Measuring Absolute Signal Levels Since the top of the graticule is a calibrated REFERENCE LEVEL and the graticule is calibrated in dB/DIV, as described in the Preliminary Front Panel Calibration procedure, at the beginning of this section, it is easy to measure the absolute level of most signals. a. Calibrate the graticule as previously described in step 4 of the Operational Check procedure. Ensure that the REF VARiable (gain) control is in its CAL detent . b . Connect the signal source to the RF INput, as described under Signal Application . Switch to the 10 dB/DIV or 2 dB/DIV display mode . NOTE For maximum accuracy, use the same cable that was used to calibrate the REFERENCE LEVEL and use the 2 dB/DIV display mode . c. Select a REFERENCE LEVEL with the RF Attenuator and gain selector to bring the signal, to be measured, within the screen or graticule window . NOTE If you are operating in the 10 dB/DIV mode, thegain selector must be within the blue sector. d . The absolute signal level equals the number of dB graticule divisions from the reference level (top of the screen) to the signal reference (usually the signal peak) plus the REFERENCE LEVEL readout in dBm. For example: A signal level 4.5 divisions below the top with a REFERENCE LEVEL readout of-60 dBm, in the2 dB/DIV display mode, is -60 dBm + (-9 dB) or -69 dBm . This refers to the signal level at the RF INput connector. Add the insertion loss of anyexternal attenuators and cables (if they are used) between the signal source and the RF INput. NOTE The maximum input level to the RF INput, for linear operation, is -30 dBm with 0 dB RF attenuation ; or +30 dBm with 60 dB of RF attenuation . Accurate measurement of signals above this level can only be performed if an external attenuator is used . 2-13 Operating Instructions-71-13 Accurate Signal Level Difference Measurements in dB a. Using the 2 dB/DIV display mode, position the top of the lowest amplitude signal to a reference line within the graticule area with the REF VARiable or VERTICAL POSITION controls . If display noise is excessive, use the VIDEO FILTER and reduce the sweep speed to maintain signal amplitude, or decrease the RESOLUTION bandwidth . b . Use the RF Attenuator selector to reduce the amplitude of the larger signal until it iswithin thegraticule area, and note the increased attenuator reading. Figure 2-9 shows the performance of the 71-13 below 10 kHz. The center frequency is 2.5 kHz, with zero hertz marker visible at the extreme left graticule. Two signals were applied simultaneously to the input, one at 2.5 kHz and one at 3 kHz . Ivs I -30 i. -30 -50 c . Measure the signal level from the reference line established for the smallersignal (graticule is calibrated in 2 dB/DIV), then add the change in RF Attenuator reading to obtain the difference level (in dB) between the two signals. Measuring Relative Signal Amplitude in LIN Display Mode The vertical scale on the spectrum analyzer graticule is calibrated in dB for LOG display and in increments of 0.2 for the LIN display. Relative signal levels can be made by adjusting the amplitude of one signal with the gain and attenuator controls to 1 .0 division, then directly reading from the graticule, the amplitude of the other signals as a percentage of this reference. Using the Analyzer Below 100 kHz The sensitivity of the analyzer degrades about 0.3 dB/kHz below 100 kHz; for example, the sensitivity is about -113 dBm at 50 kHz with 30 Hz resolution . Reference level operation becomes limited to-50 dBm as the center frequency approaches 1 kHz, because of the LO energy that exists in the 1st IF pass-band . Fig. 2-9 . Illustrating the dynamic range and performance at a center frequency of 2.5 kHz . APPLICATIONS Applications for the spectrum analyzers, such as the 71-13, include: measuring intermodulation products, cross modulation, radiation interference, modulation percentage, modulation index, absolute and relativesignal levels, etc. A treatise on measurement and signal evaluation is provided in the Tektronix Measurement Concept booklet, "Spectrum Analyzer Measurement Theory" ; Part No . 0621334-00, and Spectrum Analysis and CATV Systems brochure A2515 . If you desire assistance for a specific application or current information on additional applications, contact your local Tektronix Field Office or representative . Section 3-71 .13 PERFORMANCE CHECK Introduction This section consists of two parts ; an operational checkout procedure for instrument familiarization and incoming inspection, and a performance check that verifies that the instrument meets specification characteristics. The first part requires the minimum of test equipment; the second part requires test equipment that will serve as a standard to verify instrument specifications . Performing this procedure will indicate if and what circuits in the instrument need calibration . We recommend performing the checks as part of your routine maintenance program. OPERATIONAL PERFORMANCE AND INSTRUMENT FAMILIARIZATION This portion of the section contains a sequence of procedures that will check the operational performance of the 71-13 . It provides an adequate incoming performance inspection and a good familiarization of the instrument operation . Because the 71-13 calibrator is a very accurate signal source and the RF attenuator an accurate step attenuator, they are used as the reference for this part of the check. If you wish, their accuracy can be checked by referring to the second part of this section . Equipment Required The following fixtures and equipment are required for this part of the performance check. These are available through your local Tektronix Field Office or representative . The 1st and 2nd LO OUT ports must be terminated into 50 f2 at all times. For optimum performance, keep the termination caps in place when these ports are not used . 2. Check the 10 dB/DIV and LIN Mode Calibration a. Switch the RF Attenuator to 0 dB and turn the Gain selector fully ccw, so the REFERENCE LEVEL readout is -30 dBm. Ensure that the REF VARiable control is in its CAL detent . Set the FREQ SPAN/DIV to 10 MHz and the RESOLUTION bandwidth to 0.3 MHz. b. Apply the Calibrator signal to the RF INput and tune the fundamental 50 MHz signal to center screen . c . Reduce the FREQ SPAN/DIV setting to 5 kHz and the RESOLUTION bandwidth to 3 kHz, keeping the signal centered on screen with the TUNING control. d. Position the top of the signal to the top graticule line with the VERTICAL POSITION control to establish a reference level . e. Increase the RF Attenuator settings in 10 dB increments, noting that the signal amplitude decreases 1 ±0 .1 division between steps . NOTE 1 . 80 dB of attenuation, in 20 dB increments : Four (4) 10X (20 dB) attenuators, Tektronix Part No . 011-0059-01 . It may be easier to observe the change if the VIDEO FILTER is switched in . If used, decrease the sweep speed until the UNCAL indicator light goes out. 2. BNC to pin-jack adapter cable. Used to apply signals to the EXT IN connectors . Tektronix Part No . 1751178-00. f. Since the RF Attenuator range is 60 dB, the last 10 dB step of the 70 dB dynamic range may be checked as follows: 1 . Preliminary Preparation Perform the Preliminary Front Panel Setup Procedure described in the Operating Instructions and calibrate the 71-13 sweep to the oscilloscope deflection sensitivity . Adjust the contrast ratio between the clipped (subdued) baseline and the remaining display. (1) Return the RF Attenuator to 30 dB and add a 20 dB attenuator between the RF INput and CAL OUT signal . Adjust the signal amplitude to some reference line on the graticule with the REF VARiable control. (2) Increase the RF Attenuator setting 20 dB and note that the signal is still visible above the noise level . Performance Check-71_13 The total deviation over the 70 dB dynamic range of the display must not exceed 1 .5 dB or 0 .75 minor divisions . g . Remove the 20 dB attenuator and again apply the CAL OUT signal directly to the RF INput. Switch off the VIDEO FILTER and set the RFAttenuatorto 10 dB . Set the FREQ SPAN/DIV to 1 MHz and the RESOLUTION to .3 MHz . h . Change the display mode to LIN . Position the baseline of the display on the bottom graticule line then adjust the 50 MHz signal amplitude with the REF VARiable control so it is 6.3 divisions . i . Increase the RF Attenuation 10 dB by switching to 20 dB, and note that the signal amplitude decreases to 2.0 t0.6 division for an amplitude change ratio of 3.16:1, t10%. j . Return the REF VARiable control it its CAL detent and the RF Attenuator to 0 dB. 3 . Check the Frequency Readout Accuracy NOTE Due to hysteresis in the tuning system (1st LO), the accuracy of the frequency readout should be checked by approaching each check point from the same direction (low to high). The FREQ SPAN/DIV is first switched to MAX SPAN and the center frequency tuned to 0000 before tuning to the desired check point. If for any reason the direction of tuning is reversed, this procedure must be repeated to establish the same point of reference on the hysteresis loop, a. Switch the display mode to 10 dB/DIV, the FREQ SPAN/DIV to MAX SPAN and tune the CENTER FREQUENCY to 0000 . With the Calibrator signal applied to the RF INput, decrease the FREQ SPAN/DIV to 1 MHz and increase the CENTER FREQUENCY readout towards 50 MHz until the 50 MHz signal is centered on screen . (The signals will move from right to left as the frequency is increased .) b . Adjust the front panel CAL for a CENTER FREQUENCY readout of 50 MHz. c . Tune the CENTER FREQUENCY from low to high, checking the accuracy of the readout in 50 MHz increments . Readout accuracy, when the signal is centered on the screen, should be within f(5 MHz + 20% of the FREQ SPAN/DIV) orwithin f5 MHz with a frequency span of 1 MHz/DIV . 3-2 4. Check the Range of the REF VAR control, the Range of the Gain Selector and Gain Accuracy of the 10 dB GAIN pushbutton . (Accuracy within f1 dB/10 dB step . Variable range -10 dB.) a . Switch the display mode to 10 dB/DIV, FREQ SPAN/DIV to 0.5 MHz and the RESOLUTION bandwidth to 30 kHz . Apply the CAL OUT signal to the RF INput and tune the 50 MHz signal to the center of the screen then decrease the FREQ SPAN/DIV to 50 kHz keeping the signal centered with the TUNING control . b. Switch the 30 kHz VIDEO FILTER in, turn the Gain selector ccw and switch the RF Attenuator to 50 dB to establish +20 dBm REFERENCE LEVEL. c . Position the top of the signal at the 4th graticule line (center screen) with the VERTICAL POSITION control . d. Check the REF VAR control range by turning it fully cw from its CAL detent . Gain increase should equal approximately 10 dB or the signal amplitude should increase 1 division . Return the REF VAR control to its CAL detent. e. Position the top of the 50 MHz signal at the 6th graticule line from the reference level (top of graticule), with the VERTICAL POSITION control . f . Check the Gain selector accuracy of the three 10 dB steps for the 10 dB/DIV display mode (blue sector) . Accuracy between steps must equal 10 dB f1 dB . g. Decrease the RF Attenuator to 40 dB so the REFERENCE LEVEL is -20 dBm . Change the display mode to 2 dB/DIV and position the top of the signal at the 5th graticule line from the reference, with the VERTICAL POSITION control . h. Increase the Gain selector setting 10 dB (one step) . Check that the signal amplitude increases 10 dB f1 .0 dB or 5 div t0.5 div. i . Increase the RF Attenuator setting to 50 dB, and if necessary, reposition the top of the signal to the 5th graticule line from the reference . Check the accuracy of the next 10 dB step of the Gain selector . j . Increase the RF Attenuator setting to 60 dB and check the accuracy of the next 10 dB step of the Gain selector. Performance Check-71-13 k. Return the RF Attenuator to 50 dB . Insert a 50 Q, 20 dB (10X) attenuator between the CAL OUT signal and the RF INput. -HddDm I . Position the top of the 50 MHz signal at the 6th graticule line from the reference with the VERTICAL POSITION control and check the accuracy of the final 10 dB step of the Gain selector . The signal level into the 1st mixer is now approximately -100 dBm. " ' ~)KHZI RE5 ., ie -zo -30 a m . Insert four (4) 20 dB attenuators, for a total of 80 dB, in series with the Calibrator signal and switch the RF Attenuator to 0 dB so the REFERENCE LEVEL is -100 dBm. NOTE 1 -4s `ro (A) Display without filter . flEt n . Reduce the FREQ SPAN/DIV to 0.2 kHz and the RESOLUTION bandwidth to 30 Hz, keeping the 50 MHz signal on screen with the TUNING control . Reduce the sweep speed if necessary, until the UNCAL indicator light goes out. o. Position the top of the signal to a reference line with the VERTICAL POSITION control (6th from the top is usually the most convenient) . p . Check for an additional 10 dB of gain when the 10 dB GAIN pushbutton is depressed . q . Return the REFERENCE LEVEL to -30 dBm, remove the 80 dB of attenuation and reconnect the calibrator signal to the RF INput. 5. Check the Operation of the VIDEO FILTERS The VIDEO FILTERS reduce or average the noise level on the display. See Fig . 3-1 . Tune to one of the Calibrator signals and check the operation of the filters with RESOLUTION settings of 3 MHz and 3 kHz . 6. Check Sensitivity (-128 dBrn to -80 dBm, depending on the resolution bandwidth) NOTE Sensitivity is measured in the LIN mode, and is based on a signal amplitude that equals two times the noise level. dam 1.350 MH t J0 ° KHZ PEKI_, G -su _ I -ao 8 e -so (B) Same display with video filter . Note decrease in noise level. Fig. 3-1. Video Filter operation. a. Apply the CAL OUT signal to the RF INput and switch the display mode to LIN . Uncouple the FREQ SPAN/DIV selector from the RESOLUTION selector and set the span for 2 MHz/DIV with a RESOLUTION of 3 MHz. Switch the RF Attenuatorto 0 dB and turn the Gain selector fully ccw so the REFERNCE LEVEL readout equals -30 dBm. b . Tune to the 50 MHz fundamental signal and position the baseline of the display on the bottom graticule line . Verify that the signal amplitude is 8 divisions or -30 dBm signal level . c . Increase the RF Attenuator setting to 50 dB so the signal level into the 1st mixer of the 71-13 is now -80 dBm (-30 dBm calibrator signal reduced 50 dB by the RF Attenuator) . 3-3 Performance Check-7L13 d. Measure the instrument sensitivity (at 50 MHz) with a resolution bandwidth of 3 MHz as follows: (1) Adjust the Gain selector and REF VARiable control settings for a noise level of 1 divison, in the LIN display mode . Switch the 300 Hz VIDEO FILTER in, to average the noise level . Decrease the sweep speed if the UNCAL indicator lights . (2) Compare the signal amplitude to the noise level . Signal amplitude must equal or exceed 2X the noise level (see Fig . 3-2A) . e. Disconnect the CAL OUT signal to the RF INput, return the REF VAR to its CAL detent and switch the RF Attenuator to 0 dB . Set the Gain selector, if necessary, so the REFERNCE LEVEL reads -60 dBm, then switch the display mode to 10 dB/DIV . f. Note or check the average noise level over the 20 MHz span . Noise level should be down 20 dB or more from the 60 dBm REFERENCE LEVEL (2nd graticule line from the top) . Since sensitivity is a measure of signal-to-noise __ amplitude [(S + N], the noise floor is indicative of the sensitivity value. This was verified in step d; therefore, the average noise level should appear within or below the specified sensitivity level (see Fig . 3-2B) . Noise level set by Gain controls to 1 .0 division . (A) Check sensitivity at 50 MHz, with 3 MHz resolution . Signal input level -30 dBm, RF attenuation 50 dB for an input level, to the 1st mixer, of -80 dBm . REFERENCE LEVEL 7_e_T_.__"". I.. . __T . .I _ I Sensitivity level is 90 dBm . Note : I Noise level moves up the screen as the Gain is increased, because the _ top of the screen is the reference level . NOTE Because the gain and noise floor of the display are referenced to the top line of the graticule, the noise floor may shift with Gain selector changes. g . Switch the display to LIN mode, turn the Gain selector fully ccw and the REF VAR control to is CAL detent . Position the base of the display on the bottom graticule line then switch the display mode to 10 dB/DIV . h . Switch the RF Attenuator to 0 dB and increase the Gain selector setting for a REFERENCE LEVEL readout of -60 dBm (Gain selector must be in the blue sector) . i. Reduce the FREQ SPAN/DIV to 1 MHz and the RESOLUTION bandwidth to .3 MHz. Note the average noise level below -60 dBm . Sensitivity for a resolution bandwidth of 0.3 MHz must equal or exceed -90 dBm (noise floor should be 30 dB below the reference level, or below the 3rd graticule line from the top) . 3-4 (B) Average noise level, below the reference sensitivity . level is the Fig . 3-2 . Measuring sensitivity . j . Decrease the FREQ SPAN/DIV to 10 kHz and the RESOLUTION bandwidth to 30 kHz. The noise floor must be below the 4th graticule line or -100 dBm (-60 dBm + 40 dB) . k. Decrease the RESOLUTION bandwidth to 3 kHz and again note the noise level . Noise floor must be below the 5th graticule line from the reference, or -110 dBm. It may be desirable to switch in 10 Hz of video filtering by depressing both VIDEO FILTER pushbuttons. Reducethe sweep speed if the UNCAL indicator lights . I . Decrease the RESOLUTION bandwidth to 300 Hz and again note the noise level. The average noise level must be below the 6th graticule line for a sensitivity that equals or exceeds -120 dBm . Performance Check-71-13 m. Decrease the RESOLUTION bandwidth to 30 Hz and the FREQ SPAN/DIV to 0.5 kHz. Note that the noise floor is 6.8 or more divisions below the reference level fora sensitivity of -128 dBm or better . NOTE (2) Decrease the sweep speed if the UNCAL indicator lights . Note the spurious response amplitude and verify that it does not exceed specifications . f. Return the FREQ SPAN/DIV and RESOLUTION selectors to their original settings (step. d) . If the Gain selector is setso the REFERENCE LEVEL is -50 dBm or more (e .g ., -60 dBm) with the RF Attenuator at 0 dB, a decrease in sensitivity will be noticed below 1 MHz. This effect or desensitization, is caused by the 0 Hz response overdriving the 1st IF amplifier. If you are operating in this frequency range do not set the Gain selector this high . 8. Check Resolution Bandwidths and Shape Factor. (Bandwidth 3 MHz to 30 Hz within 20% in decade steps; shape factor 4:1 to 300 Hz except 3 MHz resolution . Maximum bandwidth 60 dB down, with 3 MHz resolution is 13 MHz. Shape factor for 30 Hz is 12 :1) 7. Check for Spurious Signals from Internal Sources (Residual Responses) . (,< -100 dBm, referred to the RF INput) a. Apply the Calibrator signal to the RF INput and set the RF Attenuator to 0 dB . Turn the Gain selector fully ccw for a REFERENCE LEVEL of -30 dBm . a. Remove any signal connected to the RF INput so it is free of signals from any external source . Switch the RF Attenuator to 30 dB to further isolate the 1st mixer from the input. b. Tune the 50 MHz marker to the center of the screen, set the FREQ SPAN/DIV to 1 MHz, and the RESOULITON bandwidth to 3 MHz . b. Switch out the VIDEO FILTER, turn the Gain selector fully ccw and ensure that the REF VARiable control is in its CAL detent . The REFERENCE LEVEL will now read 0 dBm . The signal level at the 1st mixer of the 71-13 however represents -30 dBm, because the RF Attenuator subtracts an additional 30 dB . c. Set the FREQ SPAN/DIV to 1 MHz and the RESOLUTION bandwidth to 30 kHz . Switch the TIME/DIV to 50 ms or less so the UNCAL indicator is not lighted . d. Switch to the 2 dB/DIV display mode, verify that the trace is on the bottom graticule line, then switch the display mode to 10 dB/DIV . The dynamic range of the graticule is now a calibrated 10 dB/DIV, with the top line representing -30 dBm into the 1st mixer as described in step b. e. Tune slowly across the frequency band (0 to 1 .8 GHz) checking for spurious signals. The amplitude of any spurious signal must not exceed -100 dBm (signals above the 7th graticule line from the top) . NOTE : Subtract 2 dB for noise which will be riding on top of the signal . If the spur is marginal (within 3 dB of specifications) and you desire to check its amplitude more accurately, proceed as follows: (1) Decrease the FREQ SPAN/DIV to 50 kHz or less and the RESOLUTION bandwidth to 3 kHz. (This will decrease the noise with respect to the signal amplitude.) Keep the signal centered on screen with the TUNING control as the FREQ SPAN is decreased . O c. Switch the display mode to 2 dB/DIV and adjust the REF VARiable control if necessary, for a full screen display. NOTE Ensure that the sweep rate is set so the UNCAL light is out and the baseline of the display is on the bottom graticule line . d . Check the bandwidth of the signal at the 6 dB down level (see Fig. 3-3A). Bandwidth must equal 3 MHz ±600 kHz . e. Switch the display mode to 10 dB/DIV and the 300 Hz VIDEO FILTER in . Switch the FREQ SPAN/DIV to 2 MHz and check the shaper factor (see Fig. 3-38) . f. Return the display mode to 2 dB/DIV, decrease the FREQ SPAN/DIV to .1 MHz and the RESOLUTION bandwidth to .3 MHz. Keep the signal centered on screen with the TUNING control as the FREQ SPAN is decreased. g . Check the bandwidth at the 6 dB down level . Bandwidth must equal 300 kHz ±60 kHz. h. Switch the FREQ SPAN/DIV to .2 MHz, display mode to 10 dB/DIV, and check the shape factor as described in step e. 3- 5 Performance Check-7L13 i. Reduce the FREQ SPAN/DIV to 10 kHz, the RESOLUTION bandwidth to 30 kHz, and the display mode to 2 dB/DIV . REF ,, OB1 ~Jddotool MH J JMHZ Its' _Eo j. Check the bandwidth . Bandwidth must equal 30 kHz ±6 kHz. -20 7 ~ 6 dB do Lo -30 Bandwidth r2 .6 MHz k. Reduce the FREQ SPAN/DIV to .2 kHz and the RESOLUTION bandwidth to 300 Hz . Center the display with the TUNING control if necessary. -40 r~r~r~r~rr~~rr~~rr (A) I. Check the bandwidth of the response at the -6 dB level . Bandwidth must equal 300 Hz ±60 Hz . Display mode LIN. Bandwidth measured at 6 dB down level. Resolution 3 MHz. Frequency Span 1 MHz/DIV. 'I Edsm -6 dB e, HZ CO) 50 m . Switch the display mode to 10 dB/DIV, depress the 30 kHz VIDEO FILTER pushbutton to increase the filtering to 10 Hz . Reduce the sweep speed to 2 s/Div to maintain a calibrated display. Measure the response shape factor . ;MHz Shape factc r I 12 .6 = 4.E 2 .6 z n . Reduce the RESOLUTION to 30 Hz and change the display mode to 2 dB/DIV . Check the bandwidth at the -6 dB (half screen) level . Bandwidth must equal 30 Hz ±6 Hz . _40 6 T man -60 dB (B) Display mode 10 dB/DIV . Shape factor is ratio of bandwidth at -60 dB to -6 dB levels . 4 2 ,_ i .o e t - -JC deM, REF Hz 30 Hz } . n Shape Facto r 360 3 0 = 12 :' _ .E MMM 6 (C) Shape factor of 12 :1 with 30 Hz resolution . Fig. 3-3. Three displays to illustrate how to measure bandwidth and shape factor. 3-6 o . Switch the display mode to 10 dB/DIV and measure the shape factor . Shape factor for 30 Hz resolution must equal 12 :1 or better (see Fig. 3-3C) . 9. Check Incidental Wing . (<10 Hz for any internal sweep rate, when phase locked ; <20 kHz without phase lock) . NOTE A storage mainframe is FM'ing . desirable when measuring a. With the Calibrator signal applied to the RF INput, switch the RF Attenuator to 0 dB and the Gain fully ccw. Switch the FREQ SPAN/DIV to0 .1 MHz, RESOLUTION to 30 kHz, display mode to LIN, VIDEO FILTERS off, sweep rate to 20 ms/Div, and the AUTO PHASE LOCKED mode OFF. b. Tune the CENTER FREQUENCY to one of the 50 MHz markers, then adjust the Gain selector or REF VAR control for a fully screen display. Decrease the FREQ SPAN/DIV to 10 kHz and the RESOLUTION bandwidth to 3 kHz. c. Check the FM'ing of the displayed marker . FM'ing must not exceed 20 kHz (2 .0 div) . Fig . 3-4 illustrates one method of measuring FM'ing . Performance Check-71_13 -J df~m , ;-O05io ` MH JO #4Z bES HEr -ID I I - Power line frequencY ands down more 40 dB from th e . .1 reference level J Fig . 3-4 . Measuring incidental Wing . d. Switch the AUTO PHASE LOCKED mode on and tune the signal to center screen . Decrease the FREQ SPAN/DIV to .2 kHz and the RESOLUTION to 30 Hz . Decrease the sweep rate to 1 s/Div or until the UNCAL light goes out and add both VIDEO FILTERS so filter bandwidth is 10 Hz . Switch the oscilloscope mainframe to store mode with auto erase, if available. e. Switch the display mode to 10 dB/DIV . Check the Wing for each sweep. 10 Hz is only a trace width at 200 Hz/DIV ; however, Wing can be checked by noting that the line frequency sidebands are down at least 40 dB from the reference level . See Fig . 3-5. 10 . Check Sweep Circuit Operation with the TIME/DIV Selector in the MANUAL and OFF Positions a. Switch the TIME/DIV to the MANUAL position and rotate the MANUAL SCAN control through its range . Note that the crt beam scans the full 10 divison graticule width. b. Switch the selector to the OFF position and note that the crt beam is now centered on the screen . c. Return the TIME/DIV selector to 50 ms position for normal operation . This completes the verification of the major characteristics of the 71-13 . The remaining characteristics have indicated by reliability tests that they can be accepted without further checks ; however, the procedure to verify these characteristics is contained in the second part of this section . These checks require elaborate test equipment. If you wish to verify the remaining characteristics, continue to the next part of this section . w Fig. 3-5. Illustration to show how Wing is measured with a resolution bandwidth of 30 Hz . PERFORMANCE CHECKS THAT REQUIRE TEST EQUIPMENT Introduction The following procedures check the accuracy of the 71-13 calibrator and RF Attenuator, the display flatness, intermodulation distortion, video output amplitude, sweep triggering operation, sweep Time/Div accuracy, and external sweep operation . It does not include any internal adjustment or checks . If the instrument fails to meet a specified performance requirement, the adjustment procedure for the related circuits will be found under a similar title in the Calibration Procedure, Section 4. History Information The instrument and manual are continually evaluated and updated . Circuits as well as procedures are modified . Procedures and information, applicable to earlier instruments, are included as deviations within these steps or as subparts of the steps . These are indicated in the procedure . Equipment Required and Recommended The following test equipment and fixtures are recommended to perform this portion of the performance check . Test equipment specifications arethe minimum for accurate checks . Substitute equipment must meet or exceed these specifications . Special calibration fixtures are used where necessary to facilitate the procedure. These are available from Tektronix, Inc., and may be ordered through your local Tektronix Field Office or representative . 3-7 Performance Check-7L13 When equipment is required to check or verify close tolerance specifications, a compromise is made . Any compromise is indicated by a footnote to the equipment list, along with a statement that the high tolerance specification is not checked because of the compromise . TABLE 3-1 EQUIPMENT LIST NOTE This equipment is also required to recalibrate the instrument . EQUIPMENT OR TEST FIXTURE CHARACTERISTICS REQUIRED TYPE OR MODEL RECOMMENDED 7000-Series Storage or Variable Persistence Oscilloscope with Readout Frequency bandwidth: 50 MHz Tektronix 7313, 7613 mainframe Test Oscilloscope Vertical sensitivity : 50 mV/Div to 5 V/Div Any Tektronix 7000-Series Oscilloscope with plug-in units for a real time display Bandwidth : 50 MHz Time Mark Generator Marker outputs : 1 s to 1 /is Accuracy : 0.001% Pulse Generator Pulse period : 40 ps Pulse duration : 0.2 ps Tektronix 2901 with Harmonic Modulator, Part No . 067-0640-00 (Used to check TIME/DIV and FRED SPAN/DIV accuracies) Tektronix 2101 Pulse Generator (Used to check PULSE STRETCHER) Pulse amplutude: 0.5 V P-P Digital Counter To 50 MHz Tektronix 7D14 Digital Counter with a readout 7000Series Oscilloscope and Vertical Amplifier Unit . (Used to check 50 MHz accuracy of the Calibrator) Signal Generators Frequency range: 10 Hz to 1 .8 GHz. Used to check intermodulation, triggering, and flatness characteristics Output amplitude: 0 V to 5 V (10 Hz to 10 MHz) ; -110 dBm to 0 dBm (10 MHz to 1 .8 GHz) . Output variable and calibrated in dBm from 10 MHz to 1 .8 GHz. Accuracy f1 .0 dB . LF 1 Hz to 1 MHz, output amplutide at least 10 V peak . Output impedance 50 f2 to 600 f2 General Radio Model 1310A or Hewlett Packard Model 202C HF 22 kHz to 10 MHz Hewlett Packard Model 8651A Performance Check-71-13 TABLE 3-1 (cont) TYPE OR MODEL RECOMMENDED CHARACTERISTICS REQUIRED EQUIPMENT OR TEST FIXTURE VHF 10 MHz to 480 MHz Hewlett Packard Model 608D or 608E UHF 450 MHz to 1230 MHz and 800 MHz to 4500 MHz Hewlett Packard Model 612A and HP Model 8614A or 8614B Measure -30 dBm within ±0 .1 dB . Filter must have rolloff >40 dB at 100 MHz. General Microwave Model 454A ; or Hewlett Packard Model 432A -30 dBm, 50 MHz Signal Source Power source may be calibrated by Power Meter. Hewlett Packard Model 608D or 608E or Vector Voltmeter' Frequency: 50 MHz Hewlett Packard Model 8405A RG-58C/U Tektronix Part No . 012-0076-00 Power Meter with 50 MHz Low Pass Filter; or Two 18 inch 50 Q low loss coaxial cables BNC-to-BNC connectors Two 10 :1 50 S2 Attenuators Tektronix Part No. 011-0031-00 BNC "T" connector Tektronix Part No . 103-0030-00 Pin-jack to BNC Adapter cable; 20 inch Signal application to the EXT IN pin jacks or connect an external device to the VIDEO OUT jack Tektronix Part No . 175-1178-00 'Three methods are described to check output power level of the Calibrator . Refer to this step in the procedure to determine which test equipment you desire. 1 . Check the Calibrator Frequency a . Frequency check: (Accuracy 50 MHz ±0 .01%) The frequency of the calibrator may be checked by an accurate frequency counter, such as Tektronix 7D14 Digital Counter Plug-In Unit with a readout 7000-Series oscillosocope and a 50 MHz vertical plug-in unit . The Vertical Amplifier (e .g ., 7A15) is used to amplify the -30 dBm 50 MHz signal to approximately 30 mV peak-topeak to trigger the 7D14 . No procedure for this check is provided because the CAL OUT signal frequency can be measured by connecting through an amplifier unit to the input of the counter . 2. Check ±0 .3 dB) Calibrator Output Level (-30 dBrn Three procedures are given : Vector Voltmeter method, Power Meter method, and the use of an accurate-30 dBm source . The output of the calibrator contains harmonics; therefore, direct measurement is not possible . a. Vector Voltmeter Method (Hewlett Packard Model 8405A Vector Voltmeter) (1) Terminate the "A" probe with a BNC 50 0 feedthrough termination and connect the probe, through the termination, to the CAL OUT connector on the 71-13. 3-9 Performance Check-711.13 (2) Switch the Vector Voltmeter frequency to 50 MHz . (5) If necessary, adjust the output of the calibrator as described in the Vector Voltmeter method, for -30 dBm . (3) Check for an RMS reading between 6.85 mV to 7.3 mV (-30 dBm is 7.07 mV-RMS, into 50 C2) . If output is out of specification refer to Calibrator Output adjustment in the Calibration Procedure . 3. Check RF Attenuator Accuracy (Within f0.2 dB +1% of the dB readout whichever is greater .) b. Accurate Power Meter (within 0 .1 dB) and a 50 MHz Low Pass Filter with 40 dB or more rolloff at 100 MHz (General Microwave Power Meter Model 454A, or Hewlett Packard Model 432A Power Meter) . NOTE The insertion loss, of the filter, must be accounted for to an accuracy of 0.1 dB (1) Connect the power meter through the filter to the CAL OUT connector . (2) Measure the output level. c. Using a -30 dBm Signal Source to check the Output by Signal Substitution Method . NOTE The power meters suggested for the second method can be used to verify the signal source output level. (1) Set the FREQ SPAN/DIV to 0.5 MHz and the RESOLUTION bandwidth to .3 MHz . Switch the RF Attenuator to 10 dB and the Gain selector fully ccw . Push the 2 dB/DIV LOG display button . (2) Apply 50 MHz, from the calibrated - dBm source, to the RF INput of the 71_13 and tune the signal to the graticule center . Adjust the REF VAR control to position the top of the signal to some reference line (2nd or 3rd from the top) . (3) Disconnect the -30 dBm reference signal, then apply the 71_13 CAL OUT signal to the RF INput connector . (4) Check-The displacement of the 71_13 calibrator 50 MHz signal level, from the reference signal level must not exceed 110 .3 dB (0.75 minor divisions with a 2 dB/DIV display mode) . 3- 1 0 NOTE The RF Attenuator accuracy is checked at the factory to ensure that it is within specifications. This check will detect any component failure within the attenuator but it will not check the tolerance characteristics . If the exact attenuation error of the selector is required, a reference attenuator, calibrated by the user or manufacturer to more rigid specifications than the 71_13 attenuator, must be used. a. Set the front panel controls and selectors as follows : RF Attenuator Gain Display Mode FREQ SPAN/DIV RESOLUTION Center Frequency 0 dB ccw LOG 2 dB/DIV 1 MHz .3 MHz 200 MHz b. Apply a -60 dBm, 200 MHz signal from the VHF signal generator to the RF INput. Adjust the Gain selector and REF VAR control fora signal amplitude of 4 divisions . c . Check the RF Attenuator selector accuracy by increasing the RF Attenuator setting in 10 dB increments, and decreasing the Variable Attenuator setting (on the VHF generator) 10 dB . The display amplitude should remain at 4 divison f0.2 dB or 1% of the RF Attenuator setting, whichever is greater . 4. Check Display Flatness (Maximum amplitude variation over the 100 kHz to 1 .8 GHz frequency span is +1 dB, -2 dB, with respect to the reference level established at 50 MHz .) a. Set the front panel controls and selectors as follows : CENTER FREQUENCY Display Mode RF Attenuator Gain FREQ SPAN/DIV RESOLUTION 50 MHz 2 dB/DIV 10 dB Fully ccw MAX SPAN 3 MHz Performance Check-71-13 b. Apply a -30 dBm, 50 MHz signal from the VHF signal generator to the RF INput of the 71-13. Adjust the REF VAR control for an amplitude of 6 divisions. c . Check the flatness response, by tuning the signal generator across its frequency range, maintaining a constant output level, and noting signal amplitude variations . Amplitude variations about the reference 6 division level should not exceed +1 dB, -2 dB . d. Change to a UHF signal generator, then a SHF signal generator as required, to check flatness over the remaining frequency span of the 71_13. freq fl f2 (A) Third (3rd) order intermodulation products. NOTE Cable losses become significant at frequencies above 1 .0 GHz. Use RG-8C cable with BNC to N adapter, or use very short cable lengths (< 1 foot) between the signal generator and the 71-13 RF INput connector. Impedance levels between the source and RF INput are also important; refer to General Operating Information; "Signal Application". 5. Check Intermodulatlon Distortion (Third order distortion, 100 kHz-1 .8 GHz, is down 70 dB or more from two -30 dBm signals within any frequency span . Second order distortion is down 70 dB or more from two -40 dBm signals . Intermodulation products, 1 kHz to 100 kHz, (3rd and 2nd) are down 50 dB or more for the same input level. Fig . 3-6 illustrates third and second order intermodulation products .) a. Set the FREQUENCY SPAN to 1 MHz/Div and RESOLUTION bandwidth to 30 kHz. Set the RF Attenuator to 0 dB and the Gain selector fully ccw . The REFERENCE LEVEL should read out -30 dBm. Switch the 300 Hz VIDEO FILTER on and the display mode to 10 dB/DIV . Decrease the sweep speed until the UNCAL indicator light goes out. b. Apply two signals that are separated approximately 2 MHz, from the output of two 50Q signal sources, through 10X attenuators (for isolation), then through a BNC "T" connector, to the RF INput of the 71_13 . Fig. 3-7 illustrates this setup. freq--P-f1 f2 (t3) Second 12nd) order intermodulation products (cross modulation) Fig . 3-6 . Intermodulatlon products (distortion) . the level of the two signals, or below the 7th graticule line from the top. NOTE Typically these intermodulation products are difficult to see. An alternate procedure, which will average noise level, is to switch the 300 VIDEO FILTER on and use a very slow sweep, looking for any sidebands. If your oscilloscope has storage or variable persistence, use the storage mode . e. Tune the CENTER FREQUENCY towards 10 MHz until the 0 Hz response is on screen . f. Tune one signal generator frequency to approximately 500 kHz and adjust its output for a signal level of -40 dBm or 1 division below the top of the graticule (-30 dBm reference) . NOTE c. Adjust the output of both generators for -30 dBm signal amplitude (full screen) . Both generators must be connected as described in step b. d . Check the amount of third order intermodulation distortion, by noting the amplitude of the IM products . The amplitude of these IM products must be down 70 dB from g. Tune the CENTER FREQUENCY of the 71-13 to the frequency of the second signal generator and adjust the generator output for a signal level of -40 dBm . 3- 1 1 Performance Check-71_13 7000 Series Oscilloscope with 71-73 Spectrum Analyzer 10X attenuators for isolation and BNC "T" connector Fig . 3-7 . Equipment setup and connections necessary to measure Intermodulation distortion . NOTE Refer to step b and have the frequency above 10 MHz . h. Switch the Gain selector one step cw to shift the -40 dBm signal to the REFERENCE LEVEL. Decrease the FREQ SPAN/DIV to .2 MHz and the RESOLUTION bandwidth to 3 kHz. Change the sweep rate to establish a calibrated display (UNCAL indicator out) . The noise amplitude should now equal about 1 division . The dynamic range below the reference is now 70 dB . i . Check-Second order intermodulation distortion must not exceed 1 division, or 70 dB below the two reference signals (see Fig. 3-7B). j . Check-Intermodulation products from 1 kHz to 100 kHz, using the above procedures . IM products must not exceed 50 dB below the reference signals . 6. Check PULSE STRETCHER Operation (Pulse Stretcher should increase pulse falltime to at least 2 .5 ps per vertical division .) 3- 1 2 Since the pulse stretcher responds only to pulsed spectra, a pulse generator is used to make this check. Use extreme care to ensure that the pulse amplitude, into the RF INput of the 71_13, does not exceed 100 mV (100 mV is approximately-3 dBm) . a. Switch the display mode to LIN and the VIDEO FILTER off. Set the TIME/DIV to 10 ms, the FREQ SPAN/DIV to 2 MHz, and the RESOLUTION bandwidth to 300 kHz . Switch the RF Attenuator to 0 dB and the Gain selector for a REFERENCE LEVEL readout of -30 dBm . b . Tune the CENTER FREQUENCY to center the 0 Hz response . c. After ensuring that the pulse generator output is below 1 V, apply its output through a 20 dB (10X) 50 Q attenuator, to the RF INput of the 71_13 . d . Set the generator pulse duration to .2 /is and its period to 40 ps . O Performance Check-71_13 e . Adjust the oscilloscope Intensity and the 71-13 BASELINE CLIPPER controls until the pulsed spectrum, about the 0 Hz response, can be observed (see Fig . 3-8) . It may be necessary to adjust the output of the pulse generator to approximately 0.1 V ; however, do not exceed 1 V peak . d3m' v at' 0 - 'I+MHz 300KHZ1 f6 tc f. Depress the PULSE STRETCHER pushbutton . Note that the intensity of the pulsed spectra increases . Return the pushbutton to its off position . g . Switch AUTO PHASE LOCKED mode OFF, and tune the 0 Hz response to the left edge of the screen . Decrease the FREQ SPAN/DIV to 0 and switch the TIME/DIV to the 10 us position . Switch the Trigger SOURCE to INT and the Trigger MODE to NORM, then adjust the Trigger LEVEL control for a triggered display of two or more pulses . 0 -so (A) Display without PULSE STRETCHING . NOTE To increase the display amplitude, tune the CENTER FREQUENCY towards 10 MHz and increase the pulse generator output until the signal amplitude equals 4 divisons . h . Depress the PULSE STRETCHER button and note that the pulse falltime increases to approximately 10 us (2 .5 us/DIV) . i . Return the TIME/DIV selector to the 0.1 s position, the FREQ SPAN/DIV to 10 MHz, and release the PULSE STRETCHER pushbutton . Disconnect the pulse generator signal to the RF Input connector. 7. Check Triggering Operation and Sensitivity a. Apply a 100 MHz signal from the VHF signal generator to the RF Input of the 71-13 and tune the CENTER FREQUENCY to the signal . b. Apply a 10 kHz signal from the sine wave signal generator; through a "T" connector, BNC to BNC cable, and BNC to pin-jack cable, to both the EXT IN HORIZ/TRIG jacks on the 71-13 and the External Modulation Input of the VHF signal generator (see Fig. 3-9) . c . Modulate the VHF signal with a O.5 V peak-to-peak, 10 kHz signal . NOTE If the output of the sine wave generator is not calibrated, monitor its output with a test oscilloscope . (B) Same display with PULSE STRETCHING . Fig. 3-8. Displays of a pulsed spectra that illustrate the effect of the PULSE STRETCHER. d . With the CENTER FREQUENCY of the 71-13 tuned to the 100 MHz signal from the VHF signal generator, uncouple the FREQ SPAN/DIV and reduce the span to 0, leaving the RESOLUTION at 3 MHz . Switch the display mode to LIN. e. Adjust the VHF signal generator output for a display amplitude of 1 divison . Switch the Triggering to INT (SOURCE) and NORM (MODE) . Set the TIME/DIV to .1 ms . f. Adjust the TRIGGERING LEVEL for a triggered display, then reduce the VHF signal generator output to decrease the display amplitude to 0.5 division and ensure that the 71-13 will still trigger on the 1 kHz modulation . 3-13 Performance Check-71-13 7000 Series Oscilloscope with 71-13 Spectrum Analyzer Fig. 3-9. Equipment setup to check triggering operation. g. Check triggering operation through the frequency range of 15 Hz to 1 MHz, maintaining 0.5 division of display. h. Switch the TRIGGERING (SOURCE) to EXT . Set the sine wave generator output level for 0.5 V peak-topeak at 10 kHz. i . Check triggering through the frequency range of 15 Hz to 1 MHz as described in step g . Ensure that the input level remains at 0.5 V peak-to-peak . j. Switch the TRIGGERING (SOURCE) to FREE RUN and note that the display will not trigger. k . Switch the TRIGGERING (SOURCE) to LINE and check that the display triggers at line frequency. I. Switch the TRIGGERING (MODE) to SGL SWP and the TIME/DIV to 1 s. Check for a single sweep each time the sweep button is pushed . NOTE The pushbutton should light during sweep time . 3- 1 4 m . Return the TRIGGERING (SOURCE) to FREE RUN and the (MODE) to NORM . 8. Check the External Horizontal Input Voltage Requirement . (0 V to 10 V ±1 V should sweep the analyzer the full span .) a. Switch the oscilloscope (mainframe) Vert Mode switch off the vertical signal (right for 3-hole mainframes) and the 71-13 TIME/DIV to EXT. b. With no signal applied to the EXT IN HORIZ/TRIG input jacks, position the crt beam to the left graticule edge to establish 0 V, 0 Hz reference . c. Apply a variable voltage source, such as a variable power supply, to the EXT IN HORIZ/TRIG pin-jacks and adjust the voltage source so the beam is deflected the full span . Check that the voltage source equals +10 V ±1 V. NOTE : The sine wave generator can be used to check external sweep operation as follows : 1) After the beam has been positioned to the 0 V, 0 Hz reference, apply a 10 V peak (positive swing will go to +10 V), 10 Hz sine wave to the EXT IN connectors . Performance Check-71-13 2) The crt beam should sweep to the graticule centerline when the input voltage is 10 V peak f1 V. 10 . Check Frequency Span Accuracy and Linearity. (Freq Span accuracy within 5%, linearity accuracy within 5% over the center 8 divisions.) d . Disconnect the pin-jacks to the EXT IN connectors ; return the TIME/DIV selector to 50 ms and the oscilloscope Vert Mode to Left . a. Apply the marker and trigger output from the time mark generator through the Harmonic Modulator to the RF Input of the 71-13. Set the 71-13 selectors and controls as follows: 9. Check the Video Output Level. (50 mV t5% per displayed division about the crt center.) FREQUENCY Display Mode RF Attenuator REFERENCE LEVEL PHASE LOCKED Mode FREQ SPAN DIV RESOLUTION (Uncoupled) a. Apply the VIDEO OUT signal to the Input of a vertical amplifier unit in the test oscilloscope . Use the pinjack to BNC cable adapter. Set the Volts/Div selector of the amplifier to 50 mV . b. Apply the CAL OUT signal to the RF Input of the 71-13, set the FREQ SPAN/DIV to 2 MHz, and tune the CENTER FREQUENCY to center one of the 50 MHz markers in the display. 800 MHz 10 dB/DIV O dB -30 dBm ON 100 MHz 3 MHz b . Check frequency span accuracy and linearity as per Table 3-2 . c. Adjust the RF Attenuator and the Gain of the 71-13 for a signal amplitude of 4 divisons, then position the display about the vertical center of the crt with the VERTICAL POSITION control. Adjust the REF VARiable control for precisely 4 divisons of signal amplitude. NOTE A t some settings a better display may be obtained by using the VIDEO FILTER or by tuning the FREQUENCY to a different setting. When the VIDEO FILTER is used, the sweep speed must be decreased to obtain optimum marker amplitude. d. Check the video output amplitude on the test oscilloscope . Amplitude should equal 200 mV ±10 mV . TABLE 3-2 FREQ SPAN/DIV RESOLUTION 100 MHz 50 MHz 20 MHz 10 MHz 5 MHz 2 MHz 1 MHz .5 MHz .2 MHz .1 MHz 50 kHz 20 kHz 10 kHz 5 kHz 2 kHz 1 kHz .5 kHz 200 Hz 3 MHz 3 MHz 300 kHz 300 kHz 300 kHz 300 kHz 30 kHz 30 kHz 30 kHz 30 kHz 3 kHz 3 kHz 300 Hz 300 Hz 300 Hz 300 Hz 300 Hz 30 Hz Marker 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns Time Mark Generator Trigger Markers/Div 0 0 0 .1 us .1 ps .1 Ps 1 us 1 PS 10 ps lops 10 /is 10 ps .1 ms .1 ms .1 ms 1 ms 1 ms 1 ms 1 per div 1 per 2 div 1 per 5 div 1 per div 1 per 2 div 1 per 5 div 1 per div 1 per 2 div 2 per div 1 per div 1 per 2 div 1 per 5 div 1 per div 1 per 2 div 1 per 5 div 1 per div 1 per 2 div 1 per 5 div Tolerance (over center 8 div) 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 3- 1 5 Performance Check-71-13 11 . Check the Time/Div Accuracy . within 2% of the sweep rate selected .) (Accuracy a . Switch the RF Attenuator to 0 dB and the Gain selector fully ccw for a REFERENCE LEVEL of -30 dB . b. Apply a 100 MHz, -40 dBm signal from the VHF signal generator to the RF INput of the 71-13 and tune the CENTER FREQUENCY to the signal . Apply .1 ms time markers from the Marker Output of the time mark generator to the External Modulation input of the VHF signal generator (see Fig . 3-10) so the signal generator output can be modulated by time markers. c . With the CENTER FREQUENCY tuned to the 100 MHz signal from the VHF signal generator, uncouple the FREQ SPAN/DIV selector and reduce the span to 0, leaving the RESOLUTION at 3 MHz. Switch the display mode to 2 dB/DIV . d. Switch the TRIGGERING to INT (SOURCE) and NORM (MODE) and the TIME/DIV to .1 ms . Adjust the VHF signal generator output for a display amplitude of approximately 2 divisions (see Fig . 3-11) . EE_ Edam rs 0 ov*MH _U_ I i MHz a~ '° i -50 low Fig. 3-11 . Display showing time markers for checking TIME/DIV accuracy . e . Adjust the TRIGGERING LEVEL for a triggered display, then check the accuracy of the TIME/DIV selections by applying appropriate markers from the time mark generator and noting the displacement error between the graticule marks and the time markers. The error must not exceed ±2% (0 .2 div) over the center 8 divisions of a 10 division display . 7000 Series Oscilloscope with 71-13 Spectrum Analyzer ccacT-'~_-` Marker Ou Fig. 3-10 . Test equipment setup to check TIME/DIV accuracy. Performance Check-71-13 NOTE Use the HORIZ POSITION control to position a marker on the 1st graticule line, then note the error between each marker and its respective graticule line . f. Disconnect the signal to the RF INput and return the 71-13 to normal spectrum operation. This completes the performance check for the 71-13. It will now perform within the specifications described in Section 1 . Section 4-71-13 CALIBRATION PROCEDURE This section provides procedural information for internal checks and adjustment . Performing the complete procedure will recalibrate the instrument to its specifications . After calibration, the instrument performance can be verified by performing the Performance Check . Limits, tolerances, and waveform illustrations in this procedure are guides or aids to calibrate the instrument; they are not intended as instrument specifications . Waveform illustrations are typical. Complete or Partial Calibration The instrument should be cleaned and inspected as outlined in the Maintenance section, before performing a complete calibration . Perform the checks and adjustments in sequence for a complete calibration, then verify the performance by the Performance Check . Many circuits within this instrument, are very stable, and some require extensive facilities with expensive test equipment to calibrate. It may therefore be desirable, to perform only a partial calibration . Turn to the desired step, prepare the instrument for adjustment by referring to the nearest setup and control instructions, proceeding the step, then adjust or calibrate as directed . History Information The manual and instrument are constantly evaluated and updated . These modifications may require changes in the calibration procedure . History information that is applicable to earlier instruments is included either as a deviation within a step or as a subpart to a step. Interaction Differential Comparator (optional) : Common mode signal range ±10 V, comparator accuracy 0 .1% . Tektronix 7A13 plug-in unit. Adapter : BNC female to subminiature (SEALECTRO) female . Tektronix Part No. 175-1162-00, SEALECTRO Part No . 51-077-6801 . Adapter: SEALECTRO male to male. Tektronix Part No . 103-0098-00, SEALECTRO Part No. 51-072-0000 . Shorting Strap or Jumper: Jumper lead approximately 4 inches long with miniature alligator clips. 00. Plug-in Extenders (three) : Tektronix Part No. 067-0616- SHORT Equipment for calibration includes the equipment listed for the Performance Check plus the following additional equipment: DC voltmeter : Checked to within 1% at 15 V, 5 V and 20 V, for example; Triplett Model 630-PL. AND The following abridged procedure provides a calibration record and an index to help locate adjustment steps . 71_13 Serial No . Calibration Date Calibrator TIME BASE SECTION 1. Adjustments that interact with other circuits are noted and reference is made to the affected circuit which may require re-adjustment . Equipment Required FORM PROCEDURE RECORD Adjust Sweep Length, Offset, and Triggering Timing, Page 4-3 FUNCTION IF 2. Adjust LIN Mode Baseline Offset Page 4-6 3. Adjust Gain Compensation and Calibrate the Reference Level Page 4-6 1ST LO PHASE LOCK 4. Error Amplifier Offset Adjustment Page 4-8 .13 Calibration Procedure-71 Preliminary Procedure FREQ SPAN AND 1ST LO CALIBRATION 5. 6. Adjust the Frequency Span of the 1st LO and 16-19 MHz Oscillator Calibrate the Center Frequency and Frequency Readout PHASE 7. 8. LOCK CALIBRATION JUSTMENTS Page 4-8 Page 4-10 AD- Adjust the Memory Gain Adjust the Error Amplifier Gain Page 4-11 Adjust the Bandpass of the 105 MHz IF Amplifier and 300 kHz Filter Page 4-12 10 . Adjust the Resolution Gain Leveling Compensation Page 4-14 11 . Adjust the Post Resolution Amplifier Gain Page 4-16 12 . Minimize Intermodulation Products Page 4-16 1 . Check the front panel controls and selectors for smooth operation and proper indexing . 2 . Remove the 71-13 from the mainframe and reconnect it to the mainframe interface through the flexible plug-in extenders. (Connect the 71-13 into the two vertical and left horizontal compartments of four hole mainframes .) NOTE 50 MHz CALIBRATOR 13 . Adjust the Calibrator Output Level Instrument calibration should be performed at a temperature equal to the ambient operating temperature that is normally within +20° C to +30° C after a warmup period (with power on) of atleast 30 minutes to allow the instrument to stabilize. Page 4-11 RESOLUTION 9. NOTE Page 4-16 The guide pin on the extender cable plug to the RF section of the 71.13 must be removed before it will plug into the interface connector. The guide pin is removed by pulling it out with a pair of pliers. 3. Turn the power ON and allowthe instrument circuits to stabilize before making any adjustments (approximately 20 minutes) . Calibration Procedure-71-13 TIME BASE SECTION 1 . Adjust Sweep Length, Offset, and Triggering Set the front panel controls and selectors as follows : 71-13 TIME/DIV Triggering SOURCE Triggering MODE FREQ SPAN/DIV RESOLUTION Display Mode .5 ms FREE RUN NORM MAX Coupled to the FREQ SPAN 2 dB/DIV Test Oscilloscope Time/Div Volts/div (Calibrated) Input Coupling .1 ms 5V do f. Decrease the FREQ SPAN/DIV to .1 MHz, keeping the marker centered with the CENTER FREQUENCY control . g . Increase the FREQ SPAN/DIV to 100 MHz and adjust the Swp Offset with R1255 to bring the signal to the center of the screen . This will eliminate signal shift as the dispersion is changed . h . Repeat steps f and g until the signal remains on screen as the frequency span is decreased from 100 MHz/Div to approximately 200 kHz. NOTE The hysteresis in the tune control system may shift the center frequency slightly when the frequency span is switched back through its positions . TRACK GEN b . Connect the test oscilloscope probe to pin 3 of the TRACK GEN connector (Fig . 4-1A) . r-~ c. Adjust the Swp Gain with R1250 (Fig . 4-2) on the sweep board, fora 20 volt (±10 V) sweep ramp (Fig . 4-1 B) . Adjust R1255 (Fig . 4-2) to center the ramp about 0 volts. NOTE This sweep ramp should be an accurate 20 volt (±10 V) ramp . If a differential comparator plug-in (A) unit (e .g ., 7A13) is available, use the comparator to measure the amplitude and offset of the sweep ramp . The offset level should be adjusted to 0 volt with R1255 (Swp Offset) . d . Adjust the sweep length of the 71-13 to 10 divisions, with the front panel SWP CAL, then center the trace within the graticule area . Apply the CAL OUT signal to the RF INput and switch the display mode to 10 dB/DIV . e . Change the FREG SPAN/DIV to 10 MHz and tune the center frequency to one of the calibrator markers. (B) Location of pin 3 on the TRACK GEN connector . NEENE SaMEN NNa MEN"EE "K IMEEMENE Adjust R1250 for an accurate 20-volt ramp . Fig . 4-1 . Calibrating the sweep ramp . Calibration Procedure-7t_13 Fig. 4-2. Location of adjustments on the Sweep board. i . Switch the display mode to 2 dB/DIV . Turn the BASELINE CLIPPER fully ccw. Pull transistor Q1210 (Fig 4-3) and use a screwdriver with a small blade to short between the base and collector terminals. This pulls the collector terminal to ground potential and disables the sweep so a reference near center screen is provided . j . Position the crt beam at the center line of the graticule with Integrator Offset Adjust R1215 (Fig . 4-2) . Replace transistor 01210. k. Remove the flexible extender plug from the right vertical compartment of the 71-13 mainframe oscilloscope and install a vertical amplifier unit (e .g ., 7A16, 7A18) . I. Switch the mainframe trigger Source to Vert Mode and apply the 40 mV Calibrator signal to the amplifier input. Set the Volts/Div to .1 V . m . Switch the 71-13 TRIGGERING SOURCE to INT and adjust the LEVEL control for a triggered display. 4-4 Use . ; screwdriver short between the base and collector terminals Fig. 4-3. Base to collector terminals for 01210. n . Check that the display triggers on either the+ orslope. If the index mark on the LEVEL control is off center, loosen the set screws and reposition the control. Calibration Procedure-71-13 r~ o. Change the TRIGGERING MODE to SGL SWP and the TIME/DIV to .5 s. s. Adjust the Time/Div Cal R1190 (Fig . 4-2) for 1 marker/division . p. Check that the sweep runs each time the sweep button is pushed and that the button lights while the sweep is running. t. Check the timing accuracy for each TIME/DIV selection. Timing accuracy must be within 5% . NOTE The remaining triggering modes of operation can be checked if desired by referring to the Performance Check section of the manual. q. Return the TRIGGERING MODE to NORM, the TIME/DIV to 1 ms and remove the signal from the Calibrator to the vertical amplifier plug-in unit . Apply 1 ms markers from a time mark generator (e.g ., 2901) through a 50 0 feedthrough termination, to the Input of the vertical amplifier unit . Set the VoltslDiv to .5 V. r. Adjust the 71-13 TRIGGERING LEVEL control for a triggered display. u . Change the TIME/DIV to 50 /is and apply 50 ps markers from the time mark generator. v. Adjust Miller marker/division. Offset R1200 (Fig . 4-2) for 1 w . Repeat 1 ms/DIV and 50 ps/DIV adjustments to compensate for interaction . x. Disconnect the signal from the time mark generator, remove the vertical plug-in unit and reconnect the extender from the 71-13 interface to the right vertical interface connector. CParloic FUNCTION IF ALIGNMENT Preliminary Pull the harmonica (multipin) connector P560, on the Function IF circuit board (Fig . 4-4) . Set the following controls to the positions indicated . 71-13 RF Attenuator Gain Selector REF VAR Display Mode TIME/DIV Triggering MODE SOURCE FREQ SPAN/DIV RESOLUTION 0 dB Fully ccw CAL LIN 20 ms NORM FREE RUN 50 MHz 3 MHz Oscilloscope Vertical Mode Horizontal Mode Right A (if applicable) 2. Adjust the Lin Mode Baseline Offset a . Position the trace to the lower area of the graticule with the VERTICAL POSition control . b. Adjust the Lin Baseline Offset R803 (Fig . 4-4) clockwise, from a fully ccw position to a point where the trace stops moving down . (Do not adjust past this point) . c . Switch between LIN and LOG display modes, checking the baseline shift. Repeat the Offset adjustment if the baseline shifts . 3. Adjust the Gain Compensation and Calibrate the Reference Level a. Switch the display mode to 2 dB/DIV and position the baseline of the display on the bottom graticule line if necessary . b . Apply a 10 MHz signal at -10 dBm, from a calibrated signal source, through appropriate adapters (BNC female to SEALECTRO female, SEALECTRO male to male adapter, and SEALECTRO female to harmonica connector) to P560 . (Fig . 4-4) . Part numbers for these adapters are provided under Equipment Required List . If an accurate 10 dB, 50 Q step attenuator is available, connect it in series with the signal source . Fig . 4-4 . Calibration adjustments and test points on the Function IF board . 4-6 Calibration Procedure-71.13 c. Adjust the 2 dBm/Div Ref Level R801 (Fig . 4-4) so the trace is at the 5th graticule line down from the top. d . Increase the signal input level 10 dB . Adjust the front panel LOG CAL for a 5 division increase in signal amplitude, (trace is at the top graticule line) . e. Return the signal level to -10 dBm. Repeat steps c and d to null the interaction between the adjustments. NOTE Because of some mainframe drift, it is advisable to periodically remove the signal and check that the display baseline returns to the bottom graticule line. '~ k. Increase the signal level to 0 dBm, then adjust the 10 dB Ref Linearity R542 (Fig . 4-4) so the trace is at the graticule line . I. Decrease signal level in 10 dB steps, checking the display calibration for the 10 dB/DIV mode . Trace should shift down 1 f0 .1 division per each 10 dB step, to a maximum of 1 .5 dB overthe 70 dB dynamic range. Repeat steps h through k until this accuracy is obtained . m . Set the signal input level to-20 dB m and switch the display mode to2 dB/DIV . If necessary, adjust the trace to the bottom graticule line with the VERTICAL POSITION control . n. Increase the Gain selector setting 50 dB so the REFERENCE LEVEL readout is -80 dBm . f. Switch the display mode to LIN and the signal input level to 0 dBm. o. Adjust the 40 dB Gain R603 (Fig . 4-4) so the trace is at the reference level or top of the graticule . g . Adjust Lin Ref Level R733 (Fig . 4-4) so the trace is at the top graticule line . p. Decrease the signal level to -40 dBm. If necessary, position the trace on the bottom graticule line with the VERTICAL POSITION control. h . Switch the display mode to 10 dB/DIV . Decrease the signal input level to -70 dBm . i . Adjust the 10 dB/DIV Ref Level R802, (Fig . 4-4) so the trace is 7 divisions down from the top graticule line . j . Increase the signal input level so it is -10 dBm. Adjust the trace so it is 1 division from the top graticule line with 10 dB/DIV R703 (Fig . 4-4) . q . Increase the Gain selector setting 20 db for a REFERENCE LEVEL readout of -100 dBm . r. Adjust the 60 dB Gain R663, (Fig . 4-4) so the trace is at the reference level . s . Remove the signal from the input to the Function IF amplifier and replace the connector P560 . Calibration Procedure-71.13 Fig . 4-5 . Grounding strap connected to pin 2 of U2200 . Fig . 4-6 . Location of P69 and R51 on Hybrid Assembly A50. 1st LO PHASE LOCK LOOP a. Set the front panel selectors as follows: 4 . Error Amplifier Offset Adjustment a . Switch the 71_13 into phase locked mode by setting the FREQ SPAN/DIV to 50 kHz and switch the AUTO PHASE LOCKED switch on . Ground pin 2 of U2200 on the tune control circuit board, with a jumper strap (Fig . 4-5) . Remove P69 (Fig . 4-6) from the hybrid assembly A50 . b . Set the test oscilloscope Time/Div to 10 ms and the vertical amplifier deflection sensitivity to 1 V/div . Connect the test oscilloscope probe to J69 and observe the beat signal from the error amplifier . c . Adjust R51, (Fig . 4-6) so the do reference level of the error signal is 0 volt . d . Check for a beat note amplitude that equals or exceeds 4 volts peak-to-peak through the frequency range of the 71-13 . e . Reconnect P69 and remove the grounding strap to pin 2 of U2200 . FREQUENCY SPAN AND CALIBRATION 1st LO 5. Adjust the Frequency Span of the 1st LO and 1619 MHz Oscillators NOTE If the gain and offset adjustments run out of range during this procedure, check the accuracy of the 20 volt ramp as set in step 1 . 4-8 FREQ SPAN/DIV 100 MHz RESOLUTION (Uncoupled) 3 MHz TIME/DIV CENTER FREQUENCY Display Mode REFERENCE LEVEL VIDEO FILTER SWP CAL 10 ms 500 MHz 10 dB/DIV Minimum sensitivity, then increase for full screen display . 30 kHz 10 division trace b . Apply the marker and Trigger output of the time mark generator through the Harmonic Modulator (0670640-00) to the RF INput of the 71-13 . Switch on the 10 ns markers . This provides 100 MHz markers . If this equipment is not available the 50 MHz Calibrator signal can be used . c . Adjust the YIG oscillator driver gain with R2510 (Fig . 4-7) to calibrate the 100 MHz/div frequency span at 1 marker/division (see Fig . 4-8) . NOTE Adjusting the driver gain also adjusts the display offset. The gain should be adjusted for the correct marker interval and the offset should be adjusted last. It may be helpful to hold one marker at screen center while adjusting the gain so the markers fall on graticule lines each side of center . d . Switch the FREQ SPAN/DIV to MAX and increase the RF Attenuator setting to 60 dB to attenuate the time markers . Adjust the offset to the YIG oscillator main coil with R2505 (Fig . 4-7) so the 0 Hz marker is at the left edge or start of the display . Calibration Procedure-7L13 Fig. 4-7. Location of the YIG Driver and Voltage Memory adjustments . e . Decrease the RF Attenuator setting to 0 dB, FREQ SPAN/DIV to 1 MHz, and the RESOLUTION bandwidth to 30 kHz. Apply 10 ns markers and 1 us trigger signals from the time mark generator. g . Decrease the FREQ SPAN/DIV to 50 kHz, RESOLUTION bandwidth to 3 kHz, and the TIME/DIV to 20 ms . Apply 10,us trigger signals and 10 ns markers to the Input . f. Adjust the FM coil driver gain with R2530, (Fig . 4-7) to calibrate the 1 MHz/div frequency span . h . Adjust the 16-19 MHz sweep gain with R1960, (Fig . 4-9) for 1 marker/2 divisons . -3od ~Emm ='IMENEEMEM SENNE Fig. 4-8. 100 MHz markers on a 100 MHz/DIV frequency span . Fig. 4-9. Location of R1069, Sweep Driver adjustment for the 1619 MHz oscillator. 4- 9 Calibration Procedure-71-13 i . Return the FREQ SPAN/DIV to MAX, RESOLUTION to 3 MHz, and the TIME/DIV to 10 ms . j . Check the frequency span accuracy as per the procedure in the Performance Check Section . 6. Calibrate the Center Frequency and Frequency Readout Couple the FREQ SPAN/DIV and RESOLUTION selectors together and switch the FREQ SPAN/DIV to 100 MHz. Tune the CENTER FREQUENCY for an LED readout of 0888 . b. Adjust the DVM reference current with R2065 (Fig . 4-10) so the mainframe readout matches the 71-13 readout. (This adjustment is not necessary if the 71-13 is operated in a non-readout mainframe.) c. Apply 10 ns markers from the time mark generator. Couple the FREQ SPAN/DIV to the RESOLUTION selector and switch the FREQ SPAN/DIV to 100 MHz. Tune the CENTER FREQUENCY to center the 900 MHz marker on screen as the FREQ SPAN/DIV is decreased to 1 MHz. (The 900 MHz marker is the 9th marker to the right of the 0 Hz marker .) d . Adjust the DVM offset with R2135 (Fig . 4-10) so the LED readout is 900 MHz. e . Return the FREQ SPAN/DIV to 100 MHz and tune the CENTER FREQUENCY to the 100 MHz marker . Reduce the FREQ SPAN/DIV to 1 MHz, so the 100 MHz signal can be accurately tuned to center screen . f. Adjust the DVM gain with R2110, (Fig . 4-10) so the LED readout is 0100 . g . Repeat the offset and gain adjustments respectively, to compensate for any interaction . Fig . 4-10 . Frequency Readout circuit adjustments . h . Check the readout tracking accuracy from 0100 to 1800 MHz in 100 MHz increments, approach each check point from the low side . Accuracy must equal ±(5 MHz + 10% of the Freq Span/Div) . i. Switch the FREQ SPAN/DIV to MAX. j. Check that the center frequency marker position corresponds to the CENTER FREQUENCY through the tuning range . PLACHODJS Calibration Procedure-7L13 7 . Adjust the Memory Gain a . Couple the FREQ SPAN/DIV and RESOLUTION selectors together, then switch the FREQ SPAN/DIV and RESOLUTION to 10 MHz/300 kHz . Turn the error amplifier loop gain R1755 (Fig . 4-11 B) fully cw . Connect a shorting strap across S2608 (Fig . 4-11 A) . Apply the CAL OUT signal to RF INput and tune the CENTER FREQUENCY to one of the calibrator markers . b . Switch the front panel AUTO PHASE LOCKED switch off, decrease the FREQ SPAN/DIV and RESOLUTION to 50 kHz/30 kHz, keeping the signal within the display area with the CENTER FREQUENCY tuning . ShoW~oy suat. ~cro~~ ti2(~~£ : c. Tune the CENTER FREQUENCY so the signal is approximately two divisions to the right of center . d . Switch the AUTO PHASE LOCKED switch on and off while adjusting R2605 (Fig . 4-12) so the signal locks near the same position it was at with phase lock off . If it appears that R2605 does not have enough range, proceed with step e . 81755 e. Switch the phase lock off and tune the signal two divisions to the left of center . (B) f. Switch the phase lock on and off and check that the signal locks remain near the same point. Phase lock error amplifier gain and adjustment . Fig . 4-11 . Location of the Phase Lock calibration adjustments. g . Remove the shorting strap across S2608. Switch the AUTO PHASE LOCKED switch on and center the signal on screen . 8. Adjust the Error Amplifier Gain a . With the signal centered, decrease the FREQ SPAN/DIV and RESOLUTION to 200 Hz/30 Hz . Switch the display mode to 10 dB/DIV and decrease the sweep rate so the display remains calibrated . Switch the mainframe to Store mode so the full span can be observed . b. Adjust 81755 (Fig . 4-11 B) to obtain the best signal to noise ratio and still maintain phase lock . If phase lock is lost, turn 81755 cw and repeat the above procedure. '- c. Switch FREQ SPANQDIV to 5 kHz, RESOLUTION to 3 kHz. Check that the noise level, 25 kHz from center, is down at least 70 dB from the signal reference level . Fig . 4-12 . Location of Memory Adjust 82605 . 4- 1 1 CParloic RESOLUTION 9. Adjust the Bandpass of the 105 MHz IF Amplifier and 300 kHz Filter a. Set the following front panel selectors to the positions indicated . FREQUENCY FREQ SPAN/DIV RESOLUTION 400 MHz 1 MHz 30 kHz (Uncoupled from the FREQ SPAN/DIV selector) 2 dB/DIV On 10 ms OFF Display Mode Phase Lock TIME/DIV VIDEO FILTER Helical resonator : Adjust 1st two on left for bandpass shape and the right adjustment for center freq . b. Apply either a 400 MHz signal from a signal generator, or the 50 MHz CAL OUT signal from the 71_13 calibrator to the RF INput. Adjust the generator output or the gain from the 71-13, until the 400 MHz signal is displayed on screen . Center the signal on screen with the tuning control. c. Change the RESOLUTION to 3 MHz and establish a signal amplitude of approximately 7 divisions with the signal generator output control or the 71-13 REF VARiable control. d. Adjust the response of the 105 MHz IF amplifier, and the wide filter bandpass, with C82, the 3 MHz helical resonator. (Fig . 4-13) and C456, in the filter circuit. (Fig . 4-14) so the response is similar to that illustrated in Fig . 4-16 . (B) Center section extended so 105 MHz, 3 MHz bandwidth helical resonators can be adjusted . Fig . 4-13 . 105 MHz IF and 3 MHz bandwidth adjustments . NOTE Keep the signal centered as the tuning adjustments are made . Switch back to 30 kHz or 3 kHz RESOLUTION periodically, to ensure that the signal is tuned to the graticule center. This locates the center of the 10 MHz IF. There is no recommended sequence of adjustments, however, the following is applicable for most instruments: 1) Adjust C82 so the response moves slightly to the left of center or the low frequency side of the display. 2) Adjust the input and center resonators to shape the display and the output resonator to keep the response centered . 3) Adjust C456 (Fig . 4-14) for maximum bandwidth and amplitude. Fig . 4-14 . Wide-Band Filter adjust C456 . Calibration Procedure-7L13 Bandpass, at the -6 dB down point, should equal 3 MHz ±10% ; however, the bandwidth specification is within 20% of the resolution bandwidth selected . The response flatness can vary as much as 2 dB . Fig . 4-15 illustrates this variation with dashed lines . The shape should resemble that of the illustration . t, NEEMOOM Jumper P304 r for relay K357e (remove) able W356 on P303 (Remove and plug J307 on,;.-, ()" ' Flatness can vary as much as 2 dB 00011M = EME111 ONE ENEIMEMM MEMCAMisal MENNEREE MMMMOMEMM ur Fig. 4-15 . Typical response characteristics for the 105 MHz IF through the Wide Filter. e. Set the FREQ SPAN/DIV to .1 MHz and the RESOLUTION to 30 kHz. Carefully center the signal with the tuning controls . NOTE It is important to calibrate in the phase lock mode. Remove the shield cover over the post-resolution amplifier. Remove P304 (jumper for relay K357, see Fig. 4-16A) . Remove P301 and P303, of cables W307 and W356 . Connect P301 of cable W307 to J303 . Ensure that the signal lead, of P303, is connected to pin 1 of J303 . f. Change the RESOLUTION to 3 MHz. Adjust the narrow filter circuits with C472 and C475 (Fig . 4-16A), for a flat-topped response that is similar to that illustrated in Fig . 4-16B. Keep the response centered as these adjustments are made . Do not change the front panel tuning control setting or the frequency of the signal generator . Bandpass at the 6 dB down point, should range between 500 kHz to 600 kHz. 5 0 kHz to 600 kHz MONEENEW RENE NONE I (B) Typical flat top response when narrow filter is adjusted correctly . Fig. 4-16. Connections, adjustments, and typical response when adjusting the Narrow Post-Amplifier Filter. g . Reconnect, the plugs for cables W307 and W356, to their respective pins and replace the jumper plug for relay K357 . h. Switch the RESOLUTION to 30 kHz, FREQ SPAN/DIV to 100 kHz. Ensure that the signal is still centered on screen . If necessary, tune the signal to center then switch the RESOLUTION to 300 kHz. Calibration Procedure-7L13 i. Adjust the 300 kHz filter, with C322 through C348 (Fig . 4-17A), for a response that is similar to that shown in Fig . 4-1713 . NOTE If the response is similar to the illustration of Fig. 4-17, try tweaking each capacitor a slight amount . If the response is not centered or is assymetrical, adjust the capacitors to center and peak the amplitude of the response, then adjust each filteruntil the response is symmetrical and300 kHz±10% wide . (The input and output resonators usually affect the centering and bandwidth of the display and the center resonators the display slope.) _---_-_s_- t ~ 9 E d . Compensate the gain for each RESOLUTION setting, with the amplitude adjustments listed in Table 4-1 and illustrated in Fig. 4-18, so the signal amplitude remains constant through all resolution settings . , NOTE Decrease the sweep speed to maximize the signal amplitude for the 300 Hz RESOLUTION setting . r TABLE 4-1 f F 3 9 1 (A) 300 kHz filter shaper adjustments C322, C326, C328, C342, C345, C348 . JIM 11 + 11,1 -6 dB down 300 kHz + 30 kHz "I I "M i (B) 300 kHz filter response . Fig . 4-17 . 300 kHz Filter adjustments and typical response characteristics . 4- 1 4 Leveling a. With the signal phase locked, reduce the FREQ SPAN/DIV to 10 kHz and switch the RESOLUTION to 30 kHz . Center the signal on screen with the tuning control and set the signal amplitude to approximately 7 divisions with the REF VARiable control . . i s Gain c . Switch the RESOLUTION between 30 kHz at 10 kHz/Div span and 3 kHz at 1 kHz/Div span . Select the RESOLUTION setting with the lowest signal amplitude and adjust the signal level to 7 divisions with the REF VARiable control . I i i . Resolution b . Preset R367 and R377 for maximum amplitude at 3 kHz and 30 kHz resolution . I t t 10 . Adjust the Compensation . RESOLUTION 3 MHz .3 MHz 30 kHz 3 kHz 300 Hz 30 Hz FREQUENCY SPAN/DIV ADJUST 1 MHz .1 MHz 10 kHz 1 kHz .5 kHz 200 Hz R307 (3 MHz Ampl) R2705 (300 kHz Ampl) R367 (30 kHz Ampl) R377 (3 kHz Ampl) R387 (300 Hz Ampl) 82730 (30 Hz Ampl) e . Change the FREQ SPAN/DIV to 1 MHz, RESOLUTION to 3 MHz, RF Attenuator to 0 dB, and turn the Gain selector fully ccw. Position the baseline of the display on the bottom graticule line, then adjust the REF VARiable control for a signal level of 7 divisions. If you run out of range on the REF VARiable control, tune to a lower frequency signal . f. Switch the RF Attenuator to 10 dB and increase the Gain setting 10 dB (one position cw from the reference setting) . g . Adjust the 10 dB gain R267 (Fig . 4-18) so the signal amplitude equals the 7 division reference amplitude established in step e . h . Increase the RF Attenuator setting to 20 dB and the Gain setting an additional 10 dB . Switch in the 300 Hz VIDEO FILTER . i . Adjust the 20 dB Gain R297, (Fig . 4-18) sothesignal amplitude is again 7 divisions. Calibration Procedure-7L13 Pr-11111,m -or :ihrW-11111, i .l ;- dB GAIN 82730 >J Hz AMPL (B) Gain compensation adjustments on the YIG driver, 30 Hz filter circuit boar Fig . 4-18 . Resolution gain compensating adjustments. 4- 1 5 Calibration Procedure-71 .13 j. Switch the RF Attenuator to 30 dB and increase the Gain setting 10 dB. Check that the signal amplitude equals 7 divisions f0 .5 divisions . Since there is no adjustment for 30 dB gain, it may be necessary to compromise between the 10 dB gain adjustment and the 20 dB gain adjustment . k. Apply the CAL OUT signal through a 10 d8 step attenuator (such as Hewlett Packard Model 355D) to the RF INput ; orapply a 50 MHz signal from a signal generator with a calibrated variable attenuator, such as Hewlett Packard Model 608D, to the 71-13 RF INput . I . Tune the signal to center screen . Decrease the FREQ SPAN/DIV and RESOLUTION bandwidth to 200 Hz/30 Hz while keeping the signal centered on screen with the tuning control . m. Switch the 300 Hz VIDEO FILTER on and the display mode to 2 dB/DIV . Increase the signal input attenuation, with the step attenuator or the variable attenuation, while increasing the 71-13 gain until the REFERENCE LEVEL is-100 dBm and the signal attenuation is 80 dB. The signal level is now -110 dBm . n. Adjust the signal amplitude to some reference point on the graticule, with the REF VARiable control . Increase the signal attenuation 10 dB and switch the 10 dB GAIN button on. o. Adjust the signal amplitude to the reference established in step n, with R2735 (Fig. 4-18) . p. Disconnect and remove the test equipment cables. Switch the 10 dB GAIN off and return the REFERENCE LEVEL to -30 dBm . Switch out the VIDEO FILTER . 11 . Adjust the Post Resolution Amplifier Gain This adjustment sets the gain of the post resolution amplifier so an input of -17 dBm will provide full screen deflection . a . Switch the FREQ SPAN/DIV to .1 MHz (100 kHz) and the RESOLUTION to .3 MHz (300 kHz) . Set the TIME/DIV to 10 ms . Switch the REF VARiable to CAL. Switch the display mode to 2 dB/DIV and position the trace at the bottom graticule line . b. Apply a 10 MHz signal at -17 dBm, from the signal generator, through a BNCto subminiature (SEALECTRO) adapter, to J2700 (Fig . 4-18b) . 4-1 6 c. Adjust the post resolution amplifier gain with R425 (Fig. 4-18a) for a display reference level of 8 divisions . d . Remove the cable from the signal generator to J2700 and replace P2700 . 12. Minimize Intermodulation Products a. Set the following front panel controls as indicated : FREQ SPAN/DIV RESOLUTION Display Mode RF Attenuator Gain REFERENCE LEVEL .5 MHz 30 kHz 10 dB/DIV 0d13 Fully ccw -30 dBm b. Apply two signals, separated by 1 MHz, from two 50 Q signal generators, through 10X attenuators (for isolation) then through a BNC "T" connector to the RF INput . (Fig . 4-19) . c. Tune the 71-13 CENTER FREQUENCY midway between the two signals and adjust the output of the generators so the amplitude of both signals is at least full screen, or until sidebands can be observed on the display . d . Adjust IM Adj C95 (Fig. 4-20) to minimize the amplitude of the sidebands . e. Remove the signal generator hookup to the RF INput . 50 MHz CALIBRATOR 13. Adjust t0 .3 dB) the Calibrator Output (-30 dBrn Since the output of the 71-13 Calibrator contains harmonics, direct power measurement is not possible. The following are suggested methods and procedures : Vector Voltmeter Method (Hewlett Packard Model 8405A Vector Voltmeter) 1) Terminate the "A" probe, with a BNC 50 A feedthrough termination and connect the probe through the termination, to the CAL OUT connector on the 71-13. Calibration Procedure-71-13 7000 Series Oscilloscope with 71-13 Spectrum Analyzer 10X attenuators for isolation and BNC "T" connector Fig. 4-19 . Equipment setup to measure IM distortion. 2) Switch the Vector Voltmeter frequency to 50 MHz. 3) Check that the RMS reading is between 6.85 mV and 7.3 mV (-30 dBm is 7.07 mV RMS, into 50 i2) . 4) The calibrator output level can be adjusted by, removing the left vertical plug-in unit and the oscilloscope left side panel to gain access to the 71-13 calibrator . Adjust R956 (Fig . 4-21) for an output level of -30 dBm (7 .07 mV RMS) . C95 Adjust for minimum 3rd order intermodulation products Fig. 4-20. Location of C95 in 3rd Mixer Assembly . Fig. 4-21 . Location of R956, Calibrator Output Level adjustment . 4- 1 7 Calibration Procedure-71.13 Using a Power Meter (within 0.1 dB) and 50 MHz Low Pass Filter, with 40 dB or more rolloff at 100 MHz through 2.0 GHz; (General Microwave Power Meter Model 454A, or Hewlett Packard Model 432A Power Meter) NOTE The insertion loss of the filter and cables, must be accounted for to an accuracy of 0.1 dB . 1) Connect the power meter through the filter to the CAL OUT connector and measure the output level . 1) Set the FREQ SPAN/DIV to .5 MHz and the RESOLUTION to .3 MHz . Switch the RF attenuator to 10 dB and the Gain selector fully ccw. Push in the 2 dB/DIV, LOG display button . 2) Apply a calibrated -30 dBm 50 MHz signal to the RF INput of the 71-13 and tune the frequency to center the signal in the graticule window . Adjust the VARIABLE Gain control to position the top of the signal to a reference line (2nd or 3rd from the top) . 2) If necessary, adjust the 71-13 calibrator output as described in the Vector Voltmeter method (step 4) . 3) Disconnect the -30 dBm reference signal, then apply the71 .13 CAL OUT signal to the RF I Nput connector. Accurate -30 dBm Signal Source (Signal substitution method) 4) Adjust R956 so the output of the 71-13 Calibrator is -30 dBm . NOTE The power meters that were recommended for the preceding method, can be used to verify the signal source output level. This completes the calibration of the 71.13. The Performance Check will verify that the instrument meets specifications . Section 5-71.13 CIRCUIT DESCRIPTION This section describes the functions of the major circuits in the 71-13 and their relationship in the overall operation of the instrument . The description is general and intended as an aid for the technician and operator to help service or operate the instrument at maximum efficiency . A general description of circuit concepts, common to spectrum analyzers, is provided in Tektronix Concept Booklet, "Spectrum Analyzer Circuit," Part No . 062-1055-00. The section begins with a functional block diagram description, followed with more detailed analysis of the major circuits . Positive logic is used for digital circuits . The diagrams contain typical waveform and voltage data that should be helpful to understand circuit functions and aid in troubleshooting the instrument . BLOCK DIAGRAM The 71-13 is a swept front end spectrum analyzer that covers the frequency range from 1 kHz to 1 .8 GHz and provides a frequency span of 1 .8 GHz. A detailed block diagram in the Diagrams section, illustrates signal paths and function of the major circuits . Refer to this diagram while reading the description . The input signal path to the 1 st mixer consists of a 0 to 60 dB step attenuator, a 1 .8 GHz low-pass filter, and a 3 dB isolation pad . The stop band for the filter begins at 2.095 GHz. The filter attenuates frequencies of 2 .095 GHz (1st IF) and higher, that may exist between the 1st mixer and the RF INput. This reduces susceptibility to image responses, IF direct feed-through from the RF INput, and keeps the 1st LO output from reaching the RF INput connector. The 1st mixer is a double-balanced type mixer, with its input and output isolated by a 3 dB pad and a traveling wave directional filter, respectively . The 3 dB pad reduces VSWR interaction and improves the response flatness . The traveling wave directional filter reduces intermodulation distortion and provides a termination for image responses from the 1st mixer. The frequency of the 1st LO is swept, when the frequency span is 100 kHz/Div or more, through some portion or all of the frequency range from 2.095 GHz to 3.895 GHz. The center frequency of the oscillator can also be tuned through the selected frequency span . When the frequency span is 50 kHz/Div or less, the 1st LO frequency is fixed and the 2nd LO is swept through the selected span . The output of the 1st mixer (1st IF) is centered at 2 .095 GHz. A bandpass filter 10 MHz wide (with a center frequency of 1 .095 GHz) attenuates the upper sideband, and a 2.2 GHz low-pass filter ensures the outband integrity of the bandpass filter . The 1st IF is converted to 105 MHz (2nd IF) in the 2nd mixer by mixing the 2nd LO frequency of 2 .2 GHz with the 1st IF of 2.095 GHz. The 2nd IF signal is amplified by a Pre-Resolution amplifier, then reduced in bandwidth to 3 MHz by a threecavity helical resonator filter . The 105 MHz IF is converted down to 10 MHz in the 3rd mixer by the 3rd LO frequency off 95 MHz mixing with the 2nd IF of 105 MHz. Amplification and bandwidth of the 10 MHz 3rd IF, are controlled in the resolution and function IF amplifier stages . Amplification is controlled by switching in amplifier stages . Bandwidth is controlled, in decade steps from .3 MHz to 30 Hz, by switching bandpass filters into the signal path . IF gain can be selected in 10 dB steps from 0 to 70 dB . Gain stages are in the Pre-Resolution amplifier and the Function IF amplifier, with an additional 10 dB of gain in the 30 Hz filter . The additional 10 dB of gain may be added only when the resolution bandwidth is 30 Hz and the display mode is 2 dB/DIV or LIN . Variable gain between the 10 dB steps, is provided by a variable gain stage in the Post-Resolution amplifier. The Function IF amplifier contains circuits for logarithmic, linear, and vertical deflection factor . The log displays are 2 dB/Div and 10 dB/Div . The amplifier also compensates for the gain variation when the resolution bandwidth and display modes are changed, so the reference level remains constant through all combinations of resolution and display modes . The detected signal from the Function IF amplifier is amplified and summed with voltage levels for vertical positioning, then applied through push-pull amplifiers to the oscilloscope mainframe interface. Three auxiliary circuits can be switched into the video signal path . These circuits provide; video filtering (30 kHz, 300 Hz, and 10 Hz), pulsed video signal processing or pulse stretching, and baseline suppression. The sweep circuits provide the frequency base or time base for the display. In the frequency domain, the output from the sweep generator is applied through the horizontal amplifier to the mainframe interface, for the horizontal deflection, and through the frequency span attenuator to the 1 st or 2nd local oscillator, for frequency sweeping . The frequency span of the display is therefore a function of how much the 1st LO or the 2nd LO is swept . Circuit Description-7L13 The sweep ramp from the sweep generator, is attenuated in calibrated increments by the FREQ SPAN/DIV attenuator, then applied through switch contacts to either the 1st LO (YIG) driver circuits or the voltage controlled 16-19 MHz oscillator in the 2nd LO phase lock loop . A current ramp through the main tuning coil, sweeps thelstLOforfrequency spans from 100 MHz/Divthrough 5 MHz/Div, the current ramp is then applied to the FM coil of the YIG oscillator for spans of 2 MHz/Div through 0.1 MHz/Div. When the frequency span is decreased to 50 kHz/Div or less, the 1st LO may be phase locked and the sweep ramp is applied through switch contacts to a voltage controlled 16-19 MHz oscillator in the 2nd LO phase lock loop . The 2nd LO phase lock loop is a servo system which transmits changes of the 16-19 MHz oscillator frequency to the 2nd LO . The marker (or ditch) that is displayed when the FREQ SPAN/DIV selector is in MAX position, is produced by the marker generator. The marker position is relative to the setting of the TUNE control so it indicates to the operator the portion of the span that will be display center, when the frequency span is reduced. The marker, is summed with the video at the amplifier that drives the vertical output stage. This completes the signal path flow and the function of the frequency span circuits . DETAILED CIRCUIT DESCRIPTION The following is more detailed than the block diagram description and should assist in servicing and operating the instrument . RF or Microwave Circuits O2 The RF section consists of sealed microwave assemblies that contain hybrid circuits on ceramic substrates, or circuit boards mounted in a metal substrate . The cover of the assembly is then sealed with a conductive sealant. This seal should not be broken, nor repair attempted . Components in the RF microwave assemblies are identified with a circuit number when they are referred to in the calibration procedure (e .g ., C15, C16, and C17 in A10) . The circuitry within the block is simplified to illustrate the function of the hybrid assembly . As previously described in the block diagram description, input signals to the unit can be attenuated in 10 dB increments up to 60 dB, by AT1 . These signals then pass through a 1 .8 GHz low-pass filter (FL2) with a stop band that begins at 2.095 GHz. Signals in the frequency band from 0 to 1 .8 GHz, then pass through a 3 dB isolation pad to the 1st mixer. 5-2 The 1st mixer, a double balanced type, converts the incoming broad spectrum of signals to a 2.095 GHz IF, by mixing these incoming signal frequencies with the output of the 1st LO (Al 2) . The 1st LO may be swept and tuned within the 2.095 GHz to 3.895 GHz band . The output of the 1st mixer (A11) is isolated by a traveling wave directional coupler that couples the 2.095 GHz IF signal to a 2.2 GHz LP filter, 2.095 GHz band pass filter, and into the 2nd mixer in assembly A11 . As previously described this isolation improves the performance of the 1st mixer and reduces spurious signals. The 2nd mixer in assembly A11, mixes the output of the 2.2 GHz 2nd LO (in A20) to convert 2.095 GHz down to 105 MHz IF . The bandpass and center frequency of the 2 .095 GHz IF is adjusted by the capacitors C15, C16, and C17 (in A10) and the coupling of the 2nd mixer, in assembly A11 . These adjustments are performed to obtain a bandpass of 10 MHz that is centered at 2.095 GHz with optimum skirt shape. The mixer is oriented in the chamber to one of two balance points to provide the best rejection of spurious products generated by the 1st LO and 2nd LO . Band reject filters, consisting of 1/4 wavelength stubs that are separated 1/4 wavelength, are distributed along the output transmission lines of the 2nd mixer to the 105 MHz IF . These suppress 2.3 GHz and 4.6 GHz . The active component for the 2nd LO (in A20) is transistor Q20. Its collector load is a stripline resonator. The center frequen^,y of this oscillator and the frequency span are controlled by an error voltage from the 2nd LO frequency servo system . The oscillator output is coupled through a directional coupler to the 2nd mixer and through a low pass filter to another directional coupler which is part of the 2nd LO frequency servo system . The phase lock loop for the 2nd LO (in A20) contains a 99 .2045 MHz oscillator which is multiplied by a factor of 22 . This frequency of 2.1825 GHz is then passed through a bandpass filter (A40) and mixed in A41 with the output of the 2nd LO to produce an IF between 16 to 19 MHz. Bandpass characteristics and center frequency response of A40 are adjusted by the same procedure that is used to adjust the bandpass characteristics of assemblies A10 and Al 1 . The 16-19 MHz IF output from assembly A41, is also passed through a 2.3 GHz and 4 .3 GHz filter that is identical to the filter in assembly A20. Circuit Description- 7L13 The 1st LO (in A12) is a YIG (yittruim-iron-garnet) tuned oscillator . YIG is a material that changes its resonant frequency when it is subjected to a changing magnetic field . The intensity of this field is controlled by current through the tuning coil . When the oscillator is swept, a current ramp from the YIG driver amplifier stage is applied to this tuning coil . The amplitude of this current depends on the setting of the FREQ SPAN/DIV selector . With FREQ SPAN/DIV settings of 100 kHz/Div or less, the normal state of the 1st LO is to operate in a phase locked mode at a frequency which depends on the setting of the TUNING control and some multiple of a 2.21 MHz reference oscillator. switch is in the OFF position . The 2nd LO is always phase locked by a translation phase lock system which is described below. Stabilization The 1st LO phase lock loop contains a reference oscillator, a pulse generator and sampler, a phase detector, an error amplifier, and a compensating amplifier that drives thefrequency determining element of the oscillator . A narrow rectangular pulse from the sampler driver, at one-half the reference oscillator period, and the output of the 1st LO are applied to a diode detector . The detector output charges to the voltage of the pulse plus the amplitude (at the instant) of the coupled oscillator signal . The summation of these signals is proportional to the phase difference between the 1st LO and the reference oscillator. This voltage is amplified by the error amplifier and drives the compensating amplifier. The output of the compensating amplifier maintains a constant phase difference between the 1st LO and some multiple of the reference oscillator . While a phase difference may exist, there is no frequency error. When locked, the long term frequency stability of the locked oscillator is that of some multiple of the reference oscillator . Frequency stabilization is increased and incidental FM'ing reduced to 10 Hz or less, by a phase lock system that automatically locks the 1st LO at frequency spans of 50 kHz/Div or less unless the front panel PHASE LOCK To achieve the required stability, the 2nd LO is controlled by a translation phase lock oscillator system . The phase lock loop consists of the circuitry shown in Fig. 5-1 . The 2nd LO output is applied through a direc- The front panel 1st LO and 2nd LO OUT jacks (J30 and J36) provide access to the two oscillator outputs. These outputs are used by tracking generators . The two ports must be terminated at all times to prevent reflections back into the system . Termination plugs P30 and P36 provide this termination when the ports are not used . Phase Lock and Frequency SUM OF : OFFSET, TUNE CONTROL, AND MEMORY VOLTAGE SWP IN (50 kHz/DIV TO 0.2 kHz/DIV) Frequency of 2nd LO - 2182 .5 MHz + Frequency of 16-19 MHz VCO . Fig. 5-1 . Functional block diagram of 2nd LO phase lock circuit or frequency servo system . 5-3 Circuit Description-71 .13 tional coupler to the phase lock loop mixer A41 . It mixes with the 22nd multiple of a 99 .2045 reference oscillator in A1400A4, and generates an IF signal between 16 to 19 MHz. The 16 to 19 MHz IF signal is amplified and applied to a phase detector (A1400A3) where it is compared with the signal from a 16 to 19 MHz oscillator (A1400A2) . The phase difference is detected, amplified by the error amplifier (A1400A5), and applied as a control voltage to the 2nd LO . When the 1st LO switches from a swept oscillator to phase locked mode, it may shift in frequency. This shift in frequency is coupled through to the VCO for the 2nd LO frequency servo system and pulls the frequency of the 2nd LO in a direction to offset the frequency shift of the 1st LO . The center frequency on the display therefore remains stable . This offset information is provided by the memory offset digital circuit. The memory looks at the offset voltage of the 1st LO before and after phase lock is set, then generates an offset voltage to apply through a summing amplifier to the 2nd LO frequency servo system . The 16 to 19 MHz oscillator consists of an emitter coupled logic (ECL) IC with a high Q resonant circuit, that is tuned by a hyperabrupt tuning diode CR1564 . The frequency of this voltage controlled oscillator (VCO) is affected by the voltage it receives from the TUNE control memory circuit, offset voltage, and at spans 50 kHz/Div or less, the sweep voltage. The control voltages are applied to both ends of the diode. The summed combination of offset, tune control, and memory voltage is applied through pin F to one side of the tuned circuit and the sweep voltage is applied through pin G, a 30 :1 divider (R1560, R1562) to the anode of CR1564 . The sweep voltage comes through the 5 volt regulator circuit board, where its amplitude is adjusted by the Swp Gain adjustment R1960 . Additional filtering with C1960, C1962, is switched in at the slower sweep rates to reduce the amount of residual line related noise that may be riding on the sweep line . The summing amplifier for the tune control, memory, and offset voltage, is U1735. The memory voltage is applied through pin AC and the tune control voltage through pin AN, to the input of the amplifier. The offset voltage that establishes the center frequency of tuning, is supplied by VR1720 and a selectable resistor R1725. Select resistor R1735 sets the gain of U1735 and the response of the 16 to 19 MHz oscillator to the tune and memory voltage. The output of the phase detector (A1400A3) is amplified by the error amplifier U1715, Q1715, on A1400A5. The amplifier output drives the collector of the 2.2 GHz oscillator to control its frequency. 5- 4 The sampling generator and driver (A1400A6) are part of the 1st LO phase lock loop . The output from a 2.1944 MHz crystal controlled oscillator is applied through Q1820 and Q1825 to a divide-by-two counter U1825. The 1 .0972 MHz output, from the counter, triggers avalanche diode CR1832 to generate strobe pulses for the sampling gate in A50 . The error voltage from the phase detector is applied through J1900 and pin S to the input of U1755, which is the active component for a double-bounded conditionally stable search amplifier. The double bounding of this amplifier is achieved with diodes CR1748 and CR1749 (low leakage, temperature stable diodes) which limit the search amplitude ; and CR1742, CR1744, CR1745, and CR1746 which limit the holding range of the loop within the stable gain response range of the phase detector . The 5 volt regulator board contains ; a 5 volt regulated supply, phase lock enable relay K1955, sweep gain adjustment for the 16-19 MHz oscillator, and additional filtering for the sweep voltage line when the resolution is 30 Hz . The phase lock enable relay K1955 switches the 1 st LO FM coil from the sweep voltage source to the output of compensating amplifier U1755 (in the phase lock circuit) when phase lock is set. Relay K1965 is energized when the resolution bandwidth is reduced to 30 Hz and adds additional filtering to the sweep line . Gain adjustment R1960 calibrates the 5 kHz/Div and less, frequency spans . YIG Driver, Voltage Memory, and Phase Lock Logic 4O The YIG driver consists of a main coil driver and an FM coil driver . The main coil driver contains an operational amplifier U2510, and a Darlington transistor Q2520. The FM coil driver contains amplifier U2530, driving transistors Q2540 and Q2545. Operation of these drivers is described under Frequency Tuning and Readout that follows this title . The sequence of events required to phase lock the 1st local oscillator are performed by the phase lock logic circuit. When phase lock mode is set, the sequence of events is as follows: 1) The 2nd LO tune control is engaged and the 1st LO tune control is disengaged . At the same time the sampling generator for the 1st LO phase lock loop is enable . 2( At the end of a delay period, the phase lock enable relay is energized and the search cycle of the loop begins . 3) At the end of another delay period, the memory is activated and it looks at the shift the 1st LO made to reach a lock point. 4) The memory stores this data, which is later applied to the 2nd LO and summed with other controlling voltages to shift the 2nd LO frequency an equivalent amount so it compensates for the shift of the 1 st LO frequency when it locked . Circuit Description-71 .13 Pin 1 of P2550 (input to U2560E) is grounded through the FREQ SPAN/DIV selector when the frequency span is 50 kHz/Div or less . The output of a set-reset flip-flop (U2565A, U2565C) is low when the PHASE LOCK switch S125 is ON . The two high inputs at U2565B produce a lowto-enable signal out, which is inverted by U2560A and applied through pin 4 of P2550 to switch the tuning logic from the 1st LO tuning potentiometertothe2nd LO tuning potentiometer R20. This high is also applied through U2575A, 02570, and 02575 to enable the sampling generator for the 1st LO phase lock loop . The low-to-enable signal out of the NAND gate U2565B, also triggers a mono-stable multivibrator, U2570. At the end of some delay period, the output of U2570 goes high . This is compared by NAND gate U2565D, to the high at the output of U2560A . The delayed low, out of U2565D, is applied through buffer amplifier U2575D and energizes phase lock enable relay K1955, on the 5 V regulator board . The delayed low signal is also inverted by U2560B and applied through buffer amplifier U2575B, as a high for the TRACK GEN connector J70, and through a second buffer, U2575C, to another delay circuit in the voltage memory . At this time, the phase lock loop is closed and starts its search mode . Before one cycle is complete, the 1st LO should acquire lock . To provide the time necessaryforthe loop to lock, a second delay is inserted in the sequence path by a one shot mono-stable multivibrator U2620 and NAND gate U2625B . At the end of this delay, the outputof U2625B goes high which is inverted by U2625A and energizes L2608 to close S2608. The closing of S2608 contacts allows the capacitor C2610 to charge to the input error voltage at pin 2 of P2600 . This error voltage is indicative of the direction and amount the 1st LO traveled to reach a lock point. The contacts of S2608 open and the output of 02610 and 02615 goes to the voltage that was stored across C2610. Memory now sends this compensation voltage to the 2nd LO and the center frequency on the display remains stationary . Frequency Tuning Control and Readout Three modes of operation are used to tune the center frequency: 1) Tune control voltage is summed with the sweep voltage at the driver input for the main coil of the YIG oscillator, over frequency spans of 100 MHz/div through 5 MHz/div. 2) The sweep voltage is removed from the main coil driver and applied to the FM coil driver for frequency spans of 2 MHz/div to 0.1 MHz/div . The tune control voltage is still applied to the main coil driver . 3) The sweep and tune control voltages are removed from the YIG oscillator driver circuits and applied to the 2nd LO driver, for frequency spans of 50 kHz/div or less . The 1st LO is phase locked, providing the front panel PHASE LOCK switch is on . Tuning Control OS The input to P2230-3 (U2200F, U2200D, U2200E) is high when the phase lock is set (PHASE LOCK switch S125 on and FREQ SPAN/DIV selector 50 kHz or less). This condition energizes MP22, which engages the drive clutch to the tuning potentiometer R20 for the 2nd LO . MP20 engages when the input to P2230-3 is low, which is its state for frequency spans of .1 MHz/div (100 kHz/div) and higher . This drives the tuning potentiometer R22 for the 1st LO . The voltage source for the tuning potentiometers is the outputs of operational amplifiers U2210, 02215, and U2220, 02225. Zener diode VR2212 sets the inverting input of U2210 at 9.0 volts, which establishes approximately -9 .2 volts at the emitter of 02215 and +9 .2 volts at the emitter of 02225 . The output of U2225 is proportional to the position of the tuning potentiometer . This voltage is summed with the sweep voltage at the input to the search marker generator, then applied through cam 33 (100 MHz/Div or less) to the YIG driver . The center arm potential of the tuning potentiometer R20, is applied to the summing point at U1735, which drives the frequency determing circuits for the 2nd LO oscillator . YIG Driver 4O The do level, out of the center frequency tuning potentiometer R22, is summed with the sweep voltage at the inverting input to U2510. U2510 is an operational amplifier with a Darlington transistor 02520 as the negative supply source . Increasing the voltage input to the amplifier increases the current demand from the negative supply . This forward biases 02520 and increases the current output so the current through the YIG main coil increases until the voltage output of R22 balances the input voltage change to U2510. As the current increases through the YIG main coil, the frequency of the oscillator increases. When the FREQ SPAN/DIV is reduced to 2 MHz or less, the sweep voltage is removed from the input to U2510 and applied to the FM coil driver (U2530, 02545 and 02540) . Current through the main coil is now dependent on thedc level from the tune potentiometer R22, which sets the center frequency of the YIG oscillator . K2526 is energized to shunt the main coil with a filter network consisting of R2525, C2524 and C2526. 5-5 Circuit Description-71 .13 The FM coil driver is similar to the main coil driver, with the addition of Q2540 supplying positive current to the FM coil . is reduced to 3 MHz. The 3rd mixer converts the 105 MHz IF to 10 MHz IF, by mixing 105 MHz with the output of a crystal controlled 95 MHz oscillator . R2505 adjusts an offset voltage into the summing point of U2510 so the center frequency of the YIG oscillator can be calibrated . R2510 and R2530 set the gain of the operational amplifiers so the frequency span of the YIG oscillator is calibrated for spans of 100 kHz/div and higher . Aperature coupling is used between each section of the helical resonator. The 3rd mixer is a blanced mixer. 1.85, and C95 are tuned to the sum of the two input frequencies (about 95 MHz) . This reflects the upper sideband back into the mixer and reduces IM signals. C87, R87, L89, and R241 provide a constant impedance matching circuit to the input of the 10 MHz IF amplifier. Frequency Span O 10 MHz IF Pre-resolution Amplifier and Resolution 1>0 The sweep ramp from either the sweep generator (U1170), the external sweep source, of the manual control circuit, is applied through R1254 to the inverting input of operational amplifier U1250A . This is a voltage ramp from 0 to about 9 volts, which is summed with a do offset voltage set by R1255 . The output sweep amplitude of U1250A, is set by R1250 (Swp Gain) so the ramp is a calibrated 20 volts centered about 0 V. This voltage ramp drives both the search marker generator (U2580A and U2580B) and the frequency span attenuator circuit. Three circuit blocks comprise the resolution circuit; the 10 MHz preamplifier, five selectable resolution filters, and a post-resolution amplifier. As the resolution bandwidth is selected, gain compensation is provided to maintain a constant signal level input to the Function IF amplifier. The Function IF amplifier is then adjusted so a constant signal reference level is maintained on the display for changes of resolution or display modes. U1250B is the active component of an operational amplifier whose gain is a function of the input-to-feedback resistance ratio. This ratio is selected by the FREQ SPAN/DIV selector S108B. The output voltage ramp of U1250B is applied to the YIG oscillator main tuning coil driver U2510, for frequency spans of 5 MHz/Div or more and to the FM coil for spans of 0.1 MHz/Div and 2 MHz/Div. When the FREQ SPAN/DIV is 50 kHz or less, this sweep is applied to the phase lock loop forthe 2nd LO . The signal path through the Resolution Preamplifier depends on the position of relay K28 . This relay is energized in all positions of the Gain selector except the first two (0 dB and 10 dB). When energized, the signal path is through Q280 and 0290, which has a gain of 20 dB . Gain of the operational amplifier, containing Q250 and Q260, is increased by 10 dB when the base of 0270 is grounded through the gain selector . This occurs every odd 10 dB step of the selector . Marker Generator O Switching the FREQ SPAN/DIV selectorto MAX SPAN, closes cam 34 and opens cams 33 and 32 . This routes the tune control do voltage and sweep voltage output from U1250A to the input of amplifier U2580A . The YIG oscillator is now swept its full frequency span and a marker is generated that is commensurate to the do potential out of the list LO tune control (R22) . The output of U2580A causes diodes CR2590 and CR2592 to switch as the sweep ramp crosses through the do level setting of the tune control circuit, developing a negative ditch or marker at the output of U2580B . This marker is applied to the vertical output circuit to provide the center frequency marker on the display. 105 MHz Oscillator IF Amplifier, 3rd Mixer and Signals within the 10 MHz bandwidth of the 105 MHz IF, are amplified by Q85. The output load for Q85, is a three sectional helical resonator that is tuned so the bandwidth 5-6 Filter Circuits With the gain selector fully ccw (0 db), the 10 MHz input signal to T240 is amplified by the IF amplifier Q240 and the operational amplifier that contains Q250 and 0260 . The front panel AMPL (CAL) adjustment R80, sets the gain of Q240 so a -30 dBm 50 MHz signal, at the RF INput provides full-screen signal amplitude. Switching the Gain selector one position cw, grounds the base of Q270, turning the transistor on, and bypasses some of the feedback current of the operational amplifier Q250 . The closed loop gian of the stage is therefore increased 10 dB . Gain is accurately calibrated by the 10 dB gain adjustment R267 . Increasing the Gain selector position an additional 10 dB, opens the base of 0270 and energizes relay K281 . The output of T264 is now switched through Op Amp Q280-Q290, for 20 dB of additional gain . Increasing the Gain position to30 dB grounds the base of 0270, increasing the gain of the preamplifier an Circuit Description-71 .13 .s additional 10 dB for a total gain increase through the preamplifier of 30 dB . As previously described, the relay K281 remains energized through the remaining four positions of the Gain selector (total range of the selector is 70 dB, the additional gain variation is provided by the Function IF) . The resolution section contains four crystal filters (for 30 Hz to 30 kHz resolution) and a 300 kHz coupledresonator filter . The 300 kHz filter consists of six resonant sections and an amplifier. Signal path through or around the filters, is directed and controlled by relays K300, K353, K354, K355, K356, and K357 . (The 30 Hz filter is located on YIG Driver Voltage Memory and 30 Hz filter board, Diagram 8) . These relays are energized as the RESOLUTION cam switch S108A is switched to positions that connect the relay armature to the -15 V power source . Amplitude adjustments for each filter section establish a signal output level as the resolution is changed, so the signal reference level on screen remains constantthrough the RESOLUTION range . It is important when aligning the filters, that their center frequency is centered on the others . This is done by switching in one of the crystal filters periodically to re-establish the center of the bandpass for the 300 kHz and 3 MHz filters. The resolution output amplifier provides approximately 15 dB of gain . The gain compensates for loss in sensitivity through the microwave circuits . The response across the 1 .8 GHz span remains relatively flat (within +1 dB, -2 dB) . The 10 MHz IF signal is routed (by K357) through either a wide filter (3 MHz) or a narrow filter, for additional shaping and noise reduction. Bandpass of the narrow filter is between 500 kHz and 600 kHz. K357 is de-energized when the RESOLUTION is switched from 3 MHz to 0.3 MHz . YIG Oscillator Power Supply O8 This supply furnishes a regulated +20 volt and -5 volt to the YIG oscillator . The +20 volt supply uses +50 volt supply from the mainframe. R2550 and R2554 set the reference to the non-inverting input of U2555 . U2555 drives the output transistor 02555. 02565 is a current limiter for the supply . Reference level for the -5 volt supply is set by R2583 and R2584 at the non-inverting input to U2585. U2585 drives the output transistor 02580. 30 Hz Filter 18 This filter contains an amplifier, crystal filter, and a 10 dB gain boost circuit. The 10 MHz IF is routed through the filter when K354 is de-energized, and K2710 is energized . 02710 and 02715 are emitter coupled amplifiers . Gain of the amplifier is set by adjusting the amount of feedback from the output of T2714 to the base of 02715 . This adjustment is R2730. An additional 10 dB of gain is provided when the 30 Hz filter is in the signal path and S27 (10 dB Gain) is closed . This turns 02735 on and decreases the negative feedback for the amplifier. Gain is calibrated by adjusting R2735 . 50 MHz Calibrator O8 The calibrator is a crystal controlled oscillator configured with the crystal in the feedback loop of a multivibrator . Output of the oscillator is calibrated to a -30 dBm with adjustment R956 . Output impedance is 500. Function IF Amplifier O9 The Function IF consists of six cascode amplifier cells or blocks connected in cascade. Each cell operates as a linear or logarithmic amplifier depending on the display mode selected to provide the gain characteristics required for the three display modes of the 71-13. The gain of each cell is a function of the emitter resistance of the input transistor. In the Log mode, diodes in the emittercircuitof the amplifier reduce the gain at a logarithmic rate from 10 kB to 0 dB as the signal level increases. When the operator depresses the 10 dB/DIV display button, +15 V is applied through S130A, pin 1 of P135 and pin 2 of P520 to the anodes of the log diodes ; CR511CR512, CR514-CR515, CR517-CR518, CR521-CR522, CR524-CR525, and CR531-CR532. These diodes are forward biased (with no signal input) and the amplifier cell operates at full gain . As the signal input level increases, the emitter voltage approaches the bias of the diodes to turn the diodes off . The amplifiergain therefore decreases to 0dB . The gain decreases to 0 dB progressively as the signal level increases, starting with Q720-0710 and progesses towards the front end . In the 2 dB/DIV mode, +15 V is applied to diodes CR527-CR528 and CR534-CR535 in the emitters of Q680 and Q720 and +15 V is removed from the anode of the 10 dB log diodes so they are now back biased . 5- 7 Circuit Description-71 .13 CR534-CR535, in the emitter of Q720, and CR527CR528 in the emitter of Q680, provide approximately 4 dB of log gain per amplifier cell . This provides two break points, at about 4 dBend 8 dB of the gain curve over the dynamic window . These two break points change the curve slope sufficiently to shape the curve for 2 dB/DIV . R737 and R697 set the slope of the curve after the break point. The 10 dB and 2 dB/Div Ref Level adjustments R802 and R801, position the linear portion of the log gain curve (see Fig . 5-2) within the 8 division graticule window . The 2 dB/DIV and LIN mode displays require at least 70 dB of gain through the analyzer's IF ; therefore, additional stages are switched in to increase the Function IF gain . S130A is disengaged when the 2 dB/DIV or LIN mode buttons are pressed . The base of transistors Q570 and Q600 now have a return path to ground, through S83 and pin 4 of P84, in the40 dB or 50 dB positions of the gain selector . Grounding the base of the transistors, turn them on and boost the gain through these amplifier cells an additional 10 dB per cell . Transistors 0630 and Q660 are turned on when S83 is switched to the 60 or 70 dB positions. Gain of the Function IF amplifier, in the LIN and 2 dB modes, is calibrated at the 40 dB and 60 dB steps by adjusting R603 and R664 . 0730 is turned on when the LIN mode is selected and R733 (LIN Ref Lvl) sets the reference level of the display to the top line of the graticule. The output signal of Q700 is coupled to a linear detector . The linear detector consists of Q740 driving the common emitter amplifier Q750-Q760 with feedback through C766, the detector diodes CR772-CR771, resistors R775-R776, and C776 to the input of the amplifier. During the positive and negative excursion of the IF signal, feedback current is supplied through CR772 and CR771 . This produces a circulating current through the diodes proportional to the average signal input level. The negative video output signal is developed across R772R819 and R771 . The video is then applied through a filter network to the vertical output stages . Linear Baseline Offset adjustment R803, compensates for baseline shift when the display mode is switched from LOG to LIN. Video Filter, Pulse Stretcher, Baseline Clipper and Vertical Output Video signals from the detector, are amplified by operational amplifier U820B . Its feedback resistance, R826, is shunted by baseline clamping diodes and fast or slow video filter circuits that are switched in by U830 and U840 . Clamping diodes CR825 and CR826 maintain thevideo baseline reference by clamping the amplifier input and output signal levels . CR825 clamps the input of the amplifier from shifting positive and CR826 clamps the output at P820-2 so this point cannot shift negative . The three sections of U840 are connected so they operate as OR gates to connect C840 in the feedback loop for U820B . Pulling pin 2 or 3 of P830 low, or closing the front panel 30 kHz switch S90C, turns one section of U840 on, to connect C840 in the feedback loop . Pin 2 of P830 is pulled low when the front panel RESOLUTION selector is switched to the 30 kHz position and pin 3 of P830 is pulled low when the RESOLUTION is switched to 3 kHz or 300 Hz position . The three sections of U830 and one section of U840 are connected to operate as an AND-OR gate . When 300 Hz (S90A) switch is closed, one section of U830 is turned on to connect C830 in the feedback loop . Closing both S90A and S90C (300 Hz and 30 kHz) turns two sections of U830 and one section of U840 on . This connects C830, C832, and C840 in the feedback loop . The following logic describes the three filter combinations : 30 kHz = (30 kHz RESOLUTION) OR (3 KHz to 300 Hz RESOLUTION) OR (C90C closed) . 300 Hz = (S90A closed) . Fig. 5-2. Log converter curve. 5-8 10 Hz = (S90A) AND (S90C closed) . O Circuit Description-71-13 The output of U820B is isolated from summing amplifier U820C by Op Amp U820D . U820C sums the video signal with the do level set by the vertical position control plus the search marker, when present. The output of U820C drives the positive output for the oscilloscope interface, the inverting amplifier U820A (which drives the negative output to the oscilloscope interface) and the Baseline Clipper circuit. state is high, 02320 is switched on and positive current through the interface pin A17 (High) reduces or clips the crt beam intensity. The amount of current through 02320 or 02330 is a function of the Baseline Clipper logic circuit. The common emitter current switch Q887-0890, switches transistor 0898 off when 0887 is on . Composite video from U820C will cause the circuit to switch at some level set by the BASELINE CLIPPER control R96. When Q890 switches on, Q898 is switched on increasing the current through 02320 to increase the crt beam intensity. Closing the PULSE STRETCHER switch S90B, turns 0880 on . Current through an emitter follower output transistor, of amplifier U820D, provides a fast charge path for C880 on the positive excursion of pulsed video signals and a long discharge time-constant to stretch the decay time . The BASELINE CLIPPER control range isabout50%of the display amplitude. The CONTRAST control sets the quiescent current through CR898 which establishes the contrast between the clipped and unclipped portions of the display. The Baseline Clipper circuit consists of a common emitter current switch (0887-0890) and a logic circuit (0895-0898) that modulates the Z Axis switching circuit. The Z Axis switching circuit consists of a current switch (02320-02330) that is controlled by an exclusive OR gate (02335 and CR2336). The output of the current switch drives the Z axis common (pin B17) and the AuxZ axis (pin A17) . Frequency Readout The frequency readout system looks at the frequency tune control voltage and outputs both a standard readout signal for the mainframe and a LED readout for the frequency indicator on the 71-13. The system consists of a digital voltmeter, driversfor multiplexing the LED readout, and an A to D converter to drive the mainframe readout circuits . Fig. 5-3 is a basic functional block diagram . 02335 with CR2336, operate as an exclusive OR, to gate the state of either interface pin B7 (channel switch) or A16 (mode info) to the base transistor 02330. When this INTEGRATOR IS FROM TUNE POTENTIOMETER U2145 U2030A +10 V CLOCK 0-20,000 COUNTER MEN IR IS IR CX CX C_X CF CFIS IR LATCH LATCHES STROBED -V -10 V REF \ 1 R -1 S Ic 1 R -1 S -- CF Fig. 5-3. Functional block da - 9 - ONE DRIVERS MEN LED's of the Frequency Readout circuit. 5-9 Circuit Description-71 .13 The DVM is a precision oscillator . An integrator is ramped up and down by switching its input currents . These input currents are switched by commands from a digital counter and an analog comparator . During one transition, the count is loaded into latches . This number is then displayed during the next transition . The integrator generates an output ram with a timing sequence proportional to the do level set by the tuning potentiometer for the 1st LO . The comparator generates a step signal output when the ramp signal crosses a reference voltage which triggers the multivibrator. The counter counts towards 20,000 during the run-up time of the ramp . When the output of the comparatorsteps positive, it triggers the flip-flop which loads the count into the latch and also shifts its number into decoders and drivers for the LED readout. The new state of the flip-flop also switches the reference current off and the output voltage of the integrator ramps down towards 0 volts. Referring to the schematic diagram 12 ;the voltage output of the amplifier U2110 is proportional to the input voltages at pins 2 and 3. The voltage at pin 3 is from the tuning potentiometer, and ranges from about -9 volt to +9 volt . An offset voltage can be summed in with this tuning voltage, for calibration, by adjustment R2135. Reference current for the integrator U2140, is supplied by a buffered operational amplifier U2120 and 02120. An input reference voltage of 11 .7 volts to U2120 is set by Zener diode VR2115 . This sets the current output of 02120 to a value that is independent of the signal voltages . The current from this source is steered either to the input of the integrator or to the power supply by diodes CR2130, CR2132, and CR2134 . The voltage state of pin F is set by the multivibrator U2030A, U2030B in the digital section of the DVM. When the state is low, CR2132 and CR2134 are off and reference current is steered through CR2130 to the input of the integrator . When the state is high, the diodes areturned on to steer the reference current through R2147 to the power supply . As indicated in Fig. 5-3, the reference current is larger , than the signal current so the output of the integrator is a positive-going ramp when it is summed with the signal current. When the reference current is switched off, the output of the integrator is a negative-going ramp . The reference voltage source for the comparator 02115, is the output of operational amplifier U2130. The 11 .7 volt Zener diode VR2115 sets this output at a very 5-10 stable 11 .7 volts. This source provides the reference for the offset current through R2135 and the reference forthe negative input of the comparator 02145. As the positive-going ramp from U2110 crosses the reference voltage, the output of the comparator steps high . This triggers the multivibrator U2030A, U2030B and the voltage at pin F goes high to turn diodes CR2132 and CR2134 on . The output of the integrator swings past the reference voltage a slight amount before it starts negative . When it again crosses the reference potential, the output of the comparator switches low. 02015, in the digital section of the DVM, is a 0 to 20,000 counter and latch . When it counts to 20,000 or 0, pin 18 goes high . This high is fed back through two inverters U2000B and U2000C to reset the flip-flop. The resultant low on pin F turns diodes CR2132 and CR2134 off. The reference current is again summed with the signal current and the cycle repeats . The slope of the positive-going ramp determines the time required for the voltage to reach the reference that determines the count of the counter. The clock input to the counter U2015 is generated by oscillator 02005-02010. The output of the oscillator is applied through emitter follower 02015, to pin 1 of 02015. The digit output on pins 4, 5, 6, and 10 is in binary format . The count in the latch of U2015 is transferred, when the latch is strobed, to a BCD-to-7 segment decoder (02020) and through inverter drivers (2000A, U2000D, U2000E, and U2000F) to a digital-to-analog converter U2065. The converter sums the digital current input and provides column sense data (at pin 19) for the readout circuits of the mainframe . The digits are displayed sequentially . The seven digit code for the LED's is applied from decoder 02070; however, only one digit lights at a time . The command to light eachh digit is sent out on pins 8, 7, 17, and 22 of 02015, to LED DS2075 . The clock pulse that strobes the display command from one digit to the next is applied to pin 11 of U2015 from NAND gate U2030D . When a time slot goes low, the clock continues to strobe the counter from one digit to the next (1, 10, 100, 1000) until the corresponding digit display command is gated through AND-NOR gate U2040. At this time the clock signal through the NAND gate U2030D is blocked and the column sense signal current is sent from pin 19 of the D to A converter 02065, to the mainframe readout. One unit of current differential exists between the LED readout and the mainframe . Resistors R2020, R2026, R2133, and R2137 are connected between the respective time slot line and the sense line to add an additional unit of current for the mainframe readout circuit. Circuit Description- 7L13 Uncal Circuit Reference level calibration of the display depends on the combination of frequency span, resolution bandwidth, sweep rate, and video filter bandwidth . It was determined from the amplitude loss factor equation' ; a = 1+0.195 2 _ +~e tB2 that the display is calibrated when the combination of the above parameters cause the equations ; Freq Span 0.5 (min B, V) (B) (t) to equal or exceed 1, where min B, V = minimum bandwidth of either the resolution or video filter B = Resolution bandwidth t = Sweep time The multiplication and division of quantities in this equation can be done by summing the logarithm of the various parameters. The equation becomes : log (freq span) - log (0.5) - log (min B, V) - log (t) > 1 By normalizing these parmeters so each term is equals or is greater than zero, the equation becomes : . - log 200x 10 6 ( Freq Span) + log 6 log (10 I ( max 106 or B 106 V + ),] - log ( 1 ) - 1 .097 > 0 B ) 5 x 10-a The logarithmic summation of these parameters is performed by an analog circuit and compared against ground or zero. The resultant indicates if the display is uncalibrated or calibrated . Fig . 5-4 illustrates the basic uncal circuit . I Morris Engelson, "Spectrum Analyzer Measurements (Theory and Practice)" . Tektronix Concept Booklet No 062-1334-00 . R1284 NOTE : log [max (B,V)l - max (log B or log V) If It is positive, and is disconnected from OV current source, the voltage will go positive . If It is negative, the voltage will drop or go negative. For this reason a ground referenced voltage comparator can be used. The UNCAL indicator lights when It is positive. Fig. 5-4. Basic functional diagram of the Uncal circuit. 5-11 Circuit Description-71 .13 Sweep Triggering, Sweep Generator and Horizontal Amplifiers The sweep ramp is generated by U1170 when it is gated on by a positive gate signal from U1180. U1180 can be triggered, or it will automatically recycle after an RC time interval (set at pin 12) to provide a constant baseline . Triggering for the sweep generator circuit is supplied from one of three sources which are selected by S101 . The selected trigger signal is applied to the input of an operational amplifier U1010B . The output of U1010B is summed with the do level set by the LEVEL control R100 . When the triggering signal amplitude exceeds this do level, CR1038 is switched on to generate a positive trigger signal for the trigger input to U1180 . The following occurs as each source is selected : 1) EXT connects the EXT IN HORIZ/TRIG connector to the input of operational amplifier U1010B . 2) INT selects the output of a differential amplifier U1010A, which receives its trigger signal from the mainframe interface. 3) LINE selects a sample of the line voltage from the mainframe interface and applies it to the input of U1010B . FREE RUN (a triggering mode) grounds the input of U1010B, which sets the output of U1010C to approximately 0 volt and the input to pin 4 of U1180 low (approximately -0 .7 volt) . The gate generator free runs when pin 4 is low. The positive gate out of U1180 provides the signal for the sweep generator U1170. The negative gate is amplified and inverted by 01230 to provide the unblanking gate for the crt. Pin 15 goes high at the end of the sweep gate and gates a holdoff pulsethrough U1 160A, U1 160B and 01160 to the mainframe interface. Current for the SWP indicator light DS1152, is supplied by transistor 01150. During gate time, in the SGL SWP mode, the lamp drive from U1180 goes low. This gates a low out of U1 160B to turn transistor 01150 on . In the SGL SWP mode, pin 6 of U1180 is grounded so the gate generator will not run until it has been reset by pushing the Start button and gating a signal through the NAND gate U1160C to trigger 01120. This pulls pin 7 of U1180 high and resets the gate generator so it recycles . U1170 generates a sweep ramp of 10 volts, with a duration that depends on the timing current into the summing point at pin 9. The timing current for the capacitors C1173, C1174, and C1175 is supplied through timing resistors R1220, R1221, R1222, and R1224 by operational amplifier U1120A . Timing combinations are switched into the circuit by the TIME/DIV selector S104 . The do level at the input to U1 120A is adjusted by R1200 to compensate for offset of the IC U1170 . The jumper across P1200 permits a step compensation when U1170 is replaced and the offset is outside the range of R1200. Pin 6 of P1160 is an input from a Tracking Generator. When this input is high, 01215 and 01216 are turned on . 01216 shunts the integrating current for U1170 from U1 120A to ground . 01215 sets the sweep output line to a do level that represents center sweep. R1215 adjusts or calibrates this offset do level of the sweep integrator in U1170 so the crt beam is centered during the input signal period from the tracking generator. The sweep output of U1170 is connected through cam 29 of S104, to the output amplifier U1 050A . Ul 050A drives U1 040D and both amplifiers supply approximately 0.5 volt of push-pull drive to the mainframe deflection circuit. Gain of U1050A is set by SWP CAL adjustment R107 . U1050C provides a sweep to the mainframe for sweep logic, which provides the + Sawtooth Output at the front panel of the 7000-Series oscilloscope .
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