Agilent Technologies TV Converter Box E7403A User manual

Agilent Technologies TV Converter Box E7403A User manual
Signal Analysis Measurement Guide
Agilent Technologies
EMC Series Analyzers
This guide documents firmware revision A.08.xx
This manual provides documentation for the following instruments:
E7401A (9 kHz- 1.5 GHz)
E7402A (9 kHz - 3.0 GHz)
E7403A (9 kHz - 6.7 GHz)
E7404A (9 kHz - 13.2 GHz)
E7405A (9 kHz - 26.5 GHz)
Manufacturing Part Number: E7401-90049
Supersedes: E7401-90025
Printed in USA
December 2001
© Copyright 2001 Agilent Technologies
Notice
The information contained in this document is subject to change
without notice.
Agilent Technologies makes no warranty of any kind with regard to this
material, including but not limited to, the implied warranties of
merchantability and fitness for a particular purpose. Agilent
Technologies shall not be liable for errors contained herein or for
incidental or consequential damages in connection with the furnishing,
performance, or use of this material.
Safety Information
The following safety symbols are used throughout this manual.
Familiarize yourself with the symbols and their meaning before
operating this instrument.
WARNING
Warning denotes a hazard. It calls attention to a procedure
which, if not correctly performed or adhered to, could result in
injury or loss of life. Do not proceed beyond a warning note
until the indicated conditions are fully understood and met.
CAUTION
Caution denotes a hazard. It calls attention to a procedure that, if not
correctly performed or adhered to, could result in damage to or
destruction of the instrument. Do not proceed beyond a caution sign
until the indicated conditions are fully understood and met.
NOTE
Note calls out special information for the user’s attention. It provides
operational information or additional instructions of which the user
should be aware.
The instruction documentation symbol. The product is
marked with this symbol when it is necessary for the
user to refer to the instructions in the documentation.
This symbol is used to mark the on position of the
power line switch.
This symbol is used to mark the standby position of the
power line switch.
This symbol indicates that the input power required is
AC.
2
WARNING
This is a Safety Class 1 Product (provided with a protective
earth ground incorporated in the power cord). The mains plug
shall be inserted only in a socket outlet provided with a
protected earth contact. Any interruption of the protective
conductor inside or outside of the product is likely to make the
product dangerous. Intentional interruption is prohibited.
WARNING
No operator serviceable parts inside. Refer servicing to
qualified personnel. To prevent electrical shock do not remove
covers.
WARNING
If this product is not used as specified, the protection provided
by the equipment could be impaired. This product must be used
in a normal condition (in which all means for protection are
intact) only.
CAUTION
Always use the three-prong AC power cord supplied with this product.
Failure to ensure adequate grounding may cause product damage.
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This Agilent Technologies instrument product is warranted against
defects in material and workmanship for a period of three years from
date of shipment. During the warranty period, Agilent Technologies
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defective.
For warranty service or repair, this product must be returned to a
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shall pay all shipping charges, duties, and taxes for products returned
to Agilent Technologies from another country.
Agilent Technologies warrants that its software and firmware
designated by Agilent Technologies for use with an instrument will
execute its programming instructions when properly installed on that
instrument. Agilent Technologies does not warrant that the operation of
the instrument, or software, or firmware will be uninterrupted or
error-free.
3
LIMITATION OF WARRANTY
The foregoing warranty shall not apply to defects resulting from
improper or inadequate maintenance by Buyer, Buyer-supplied
software or interfacing, unauthorized modification or misuse, operation
outside of the environmental specifications for the product, or improper
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NO OTHER WARRANTY IS EXPRESSED OR IMPLIED. AGILENT
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Where to Find the Latest Information
Documentation is updated periodically. For the latest information about
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application information, please visit the following Internet URL:
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Microsoft is a U.S. registered trademark of Microsoft Corporation.
4
Contents
1. Making Basic Measurements
What is in This Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Comparing Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Signal Comparison Example 1: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Signal Comparison Example 2: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Resolving Signals of Equal Amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Resolving Signals Example: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Resolving Small Signals Hidden by Large Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Resolving Signals Example: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Making Better Frequency Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Better Frequency Measurement Example: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Decreasing the Frequency Span Around the Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Decreasing the Frequency Span Example: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Tracking Drifting Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Tracking Signal Drift Example 1: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Tracking Signal Drift Example 2: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Measuring Low Level Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Measuring Low Level Signals Example 1: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Measuring Low Level Signals Example 2: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Measuring Low Level Signals Example 3: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Measuring Low Level Signals Example 4: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Identifying Distortion Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Distortion from the Analyzer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Identifying Analyzer Generated Distortion Example: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Third-Order Intermodulation Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Identifying TOI Distortion Example: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Measuring Signal-to-Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Signal-to-Noise Measurement Example: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Making Noise Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Noise Measurement Example 1: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Noise Measurement Example 2: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Noise Measurement Example 3: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Demodulating AM Signals (Using the Analyzer As a Fixed Tuned Receiver) . . . . . . . . . . . . . . . . . 59
Demodulating an AM Signal Example 1: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Demodulating FM Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Demodulating a FM Signal Example: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
2. Making Complex Measurements
What’s in This Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Required Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Making Stimulus Response Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
What Are Stimulus Response Measurements? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using An Analyzer With A Tracking Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stepping Through a Transmission Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
70
70
71
71
71
71
5
Contents
Tracking Generator Unleveled Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Measuring Device Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Measuring Stop Band Attenuation Using Log Sweep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Making a Reflection Calibration Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84
Example: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Reflection Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Measuring the Return Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86
Demodulating and Listening to an AM Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88
Demodulating and Listening to an AM Signal
Example 1: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Demodulating and Listening to an AM Signal
Example 2: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
6
1
Making Basic Measurements
7
Making Basic Measurements
What is in This Chapter
What is in This Chapter
This chapter demonstrates basic analyzer measurements with
examples of typical measurements; each measurement focuses on
different functions. The measurement procedures covered in this
chapter are listed below.
• “Comparing Signals” on page 10.
• “Resolving Signals of Equal Amplitude” on page 14.
• “Resolving Small Signals Hidden by Large Signals” on page 18.
• “Making Better Frequency Measurements” on page 22.
• “Decreasing the Frequency Span Around the Signal” on page 24.
• “Tracking Drifting Signals” on page 27.
• “Measuring Low Level Signals” on page 34.
• “Identifying Distortion Products” on page 42.
• “Measuring Signal-to-Noise” on page 49.
• “Making Noise Measurements” on page 51.
• “Demodulating AM Signals (Using the Analyzer As a Fixed Tuned
Receiver)” on page 59.
• “Demodulating FM Signals” on page 65.
To find descriptions of specific analyzer functions, refer to the Agilent
Technologies EMC Analyzers User’s Guide.
8
Chapter 1
Making Basic Measurements
What is in This Chapter
Test Equipment
Test Equipment
Specifications
Recommended Model
0.25 MHz to 4.0 GHz
Ext Ref Input
E4433B or E443XB
series
Signal Sources
Signal Generator (2)
Adapters
Type-N (m) to BNC (f) (3)
1250-0780
Termination, 50 Ω
Type-N (m)
908A
Cables
(3) BNC, 122-cm (48-in)
10503A
Miscellaneous
Directional Bridge
86205A
Bandpass Filter
Center Frequency:
200 MHz
Bandwidth: 10 MHz
Lowpass Filter (2)
Cutoff Frequency:
300 MHz
RF Antenna
Chapter 1
0955-0455
08920-61060
9
Making Basic Measurements
Comparing Signals
Comparing Signals
Using the analyzer, you can easily compare frequency and amplitude
differences between signals, such as radio or television signal spectra.
The analyzer delta marker function lets you compare two signals when
both appear on the screen at one time or when only one appears on the
screen.
Signal Comparison Example 1:
Measure the differences between two signals on the same display
screen.
1. Perform a factory preset by pressing Preset, Factory Preset (if
present).
2. Connect the 10 MHz REF OUT from the rear panel to the
front-panel INPUT.
3. Set the center frequency to 30 MHz by pressing FREQUENCY,
Center Freq, 30, MHz.
4. Set the span to 50 MHz by pressing SPAN, Span, 50, MHz.
5. Set the resolution bandwidth to spectrum analyzer coupling by
pressing BW/Avg, Res BW (SA).
6. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
7. Set the reference level to 10 dBm by pressing AMPLITUDE, Ref Level,
10, dBm.
The 10 MHz reference signal appears on the display.
8. Press Peak Search to place a marker at the highest peak on the
display. (The Next Pk Right and Next Pk Left softkeys are available to
move the marker from peak to peak.) The marker should be on the
10 MHz reference signal. See Figure 1-1.
10
Chapter 1
Making Basic Measurements
Comparing Signals
Figure 1-1
Placing a Marker on the 10 MHz Signal
9. Press Marker, Delta, to activate a second marker at the position of the
first marker.
10. Move the second marker to another signal peak using the
front-panel knob, or by pressing Peak Search and then either
Next Pk Right or Next Pk Left. Next peak right is shown in Figure 1-2.
The amplitude and frequency difference between the markers is
displayed in the active function block and in the upper right corner
of the screen. See Figure 1-2.
11. The resolution of the marker readings can be increased by turning
on the frequency count function. For more information refer to
“Making Better Frequency Measurements” on page 22.
12. Press Marker, Off to turn the markers off.
Chapter 1
11
Making Basic Measurements
Comparing Signals
Figure 1-2
Using the Marker Delta Function
Signal Comparison Example 2:
Measure the frequency and amplitude difference between two signals
that do not appear on the screen at one time. (This technique is useful
for harmonic distortion tests when narrow span and narrow bandwidth
are necessary to measure the low level harmonics.)
1. Perform a factory preset by pressing Preset, Factory Preset (if
present).
2. Connect the 10 MHz REF OUT from the rear panel to the
front-panel INPUT.
3. Set the center frequency to 10 MHz by pressing FREQUENCY,
Center Freq, 10, MHz.
4. Set the span to 5 MHz by pressing SPAN, 5, MHz.
5. Set the resolution bandwidth to spectrum analyzer coupling by
pressing BW/Avg, Res BW (SA).
6. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
7. Set the reference level to 10 dBm by pressing AMPLITUDE, Ref Level,
10, dBm.
The 10 MHz reference signal appears on the display.
8. Press Peak Search to place a marker on the peak.
9. Press Marker→, Mkr→CF Step to set the center frequency step size
equal to the frequency of the fundamental signal.
12
Chapter 1
Making Basic Measurements
Comparing Signals
10. Press Marker, Delta to anchor the position of the first marker and
activate a second marker.
11. Press FREQUENCY, Center Freq, and the (↑) key to increase the center
frequency by 10 MHz. The first marker moves to the left edge of the
screen, at the amplitude of the first signal peak. See Figure 1-3.
12. Press Peak Search to place the second marker on the highest signal
with the new center frequency setting. See Figure 1-3.
The annotation in the upper right corner of the screen indicates the
amplitude and frequency difference between the two markers.
13. To turn the markers off, press Marker, Off.
Figure 1-3
Frequency and Amplitude Difference Between Signals
Chapter 1
13
Making Basic Measurements
Resolving Signals of Equal Amplitude
Resolving Signals of Equal Amplitude
Two equal-amplitude input signals that are close in frequency can
appear as a single signal trace on the analyzer display. Responding to a
single-frequency signal, a swept-tuned analyzer traces out the shape of
the selected internal IF (intermediate frequency) filter. As you change
the filter bandwidth, you change the width of the displayed response. If
a wide filter is used and two equal-amplitude input signals are close
enough in frequency, then the two signals will appear as one signal. If a
narrow enough filter is used, the two input signals can be discriminated
and will appear as separate peaks. Thus, signal resolution is
determined by the IF filters inside the analyzer.
The bandwidth of the IF filter tells us how close together equal
amplitude signals can be and still be distinguished from each other. The
resolution bandwidth function selects an IF filter setting for a
measurement. Typically, resolution bandwidth is defined as the 3 dB
bandwidth of the filter. However, resolution bandwidth may also be
defined as the 6 dB or impulse bandwidth of the filter.
Generally, to resolve two signals of equal amplitude, the resolution
bandwidth must be less than or equal to the frequency separation of the
two signals. If the bandwidth is equal to the separation and the video
bandwidth is less than the resolution bandwidth, a dip of
approximately 3 dB is seen between the peaks of the two equal signals,
and it is clear that more than one signal is present. See Figure 1-7.
In order to keep the analyzer measurement calibrated, sweep time is
automatically set to a value that is inversely proportional to the square
of the resolution bandwidth (1/BW2 for resolution bandwidths ≥ 1 kHz).
So, if the resolution bandwidth is reduced by a factor of 10, the sweep
time is increased by a factor of 100 when sweep time and bandwidth
settings are coupled. Sweep time is also a function of the type of
detection selected (peak detection is faster than sample or average
detection). For the shortest measurement times, use the widest
resolution bandwidth that still permits discrimination of all desired
signals. Sweeptime is also a function of which Detector is in use, Peak
detector sweeps more quickly than Sample or Average detector. The
analyzer allows you to select from 10 Hz (or 1 Hz with Option 1D5) to
3 MHz resolution bandwidths in a 1, 3, 10 sequence and select a 5 MHz
resolution bandwidth. In addition you can select the three CISPR
bandwidths (200 Hz, 9 kHz, and 120 kHz) for maximum measurement
flexibility.
14
Chapter 1
Making Basic Measurements
Resolving Signals of Equal Amplitude
Resolving Signals Example:
Resolve two signals of equal amplitude with a frequency separation of
100 kHz.
1. Connect two sources to the analyzer input as shown in Figure 1-4.
Figure 1-4
Setup for Obtaining Two Signals
2. Set one source to 300 MHz. Set the frequency of the other source to
300.1 MHz. The amplitude of both signals should be approximately
−20 dBm at the output of the bridge.
3. Set the analyzer as follows:
a. Press Preset, Factory Preset (if present).
b. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
c. Set the center frequency to 300 MHz by pressing FREQUENCY,
Center Freq, 300, MHz.
d. Set the span to 2 MHz by pressing SPAN, Span, 2, MHz.
e. Set the resolution bandwidth to 300 kHz by pressing BW/Avg,
Res BW , 300, kHz.
A single signal peak is visible. See Figure 1-5
NOTE
If the signal peak is not present on the display, do the following:
1. Increase the span to 20 MHz by pressing SPAN, Span, 20, MHz.
The signal should be visible.
2. Press Peak Search, FREQUENCY, Signal Track (On)
3. Press SPAN, 2, MHz to bring the signal to center screen.
4. Press FREQUENCY, Signal Track (Off)
Chapter 1
15
Making Basic Measurements
Resolving Signals of Equal Amplitude
Figure 1-5 Unresolved Signals of Equal Amplitude
4. Since the resolution bandwidth must be less than or equal to the
frequency separation of the two signals, a resolution bandwidth of
100 kHz must be used. Change the resolution bandwidth to 100 kHz
by pressing BW/Avg, Res BW, 100, kHz. The peak of the signal has
become flattened indicating that two signals may be present as
shown in Figure 1-6. Use the knob or step keys to further reduce the
resolution bandwidth and better resolve the signals.
Figure 1-6
Resolving Signals of Equal Amplitude Before Reducing the
Video Bandwidth
16
Chapter 1
Making Basic Measurements
Resolving Signals of Equal Amplitude
5. Decrease the video bandwidth to 10 kHz, by pressing Video BW, 10,
kHz. Two signals are now visible as shown in Figure 1-7. Use the
front-panel knob or step keys to further reduce the resolution
bandwidth and better resolve the signals.
Figure 1-7
Resolving Signals of Equal Amplitude After Reducing the Video
Bandwidth
As the resolution bandwidth is decreased, resolution of the individual
signals is improved and the sweep time is increased. For fastest
measurement times, use the widest possible resolution bandwidth.
Under factory preset conditions, the resolution bandwidth is “coupled”
(or linked) to the center frequency.
Since the resolution bandwidth has been changed from the coupled
value, a # mark appears next to Res BW in the lower-left corner of the
screen, indicating that the resolution bandwidth is uncoupled. (For
more information on coupling, refer to the Auto Couple key description
in the Agilent Technologies EMC Analyzers User’s Guide.)
NOTE
To resolve two signals of equal amplitude with a frequency separation of
200 kHz, the resolution bandwidth must be less than the signal
separation, and resolution of 100 kHz must be used. The next larger
filter, 300 kHz, would exceed the 200 kHz separation and would not
resolve the signals.
Chapter 1
17
Making Basic Measurements
Resolving Small Signals Hidden by Large Signals
Resolving Small Signals Hidden by Large
Signals
When dealing with the resolution of signals that are close together and
not equal in amplitude, you must consider the shape of the IF filter of
the analyzer, as well as its 3 dB bandwidth. (See “Resolving Signals of
Equal Amplitude” on page 14 for more information.) The shape of a
filter is defined by the selectivity, which is the ratio of the 60 dB
bandwidth to the 3 dB bandwidth. (Generally, the IF filters in this
analyzer have shape factors of 15:1 or less for resolution bandwidths
≥ 1 kHz and 5:1 or less for resolution bandwidths ≤ 300 Hz). If a small
signal is too close to a larger signal, the smaller signal can be hidden by
the skirt of the larger signal. To view the smaller signal, you must select
a resolution bandwidth such that the separation between the two
signals (a) is greater than half the filter width of the larger signal (k)
measured at the amplitude level of the smaller signal. See Figure 1-8.
Figure 1-8
Resolution Bandwidth Requirements for Resolving Small
Signals
18
Chapter 1
Making Basic Measurements
Resolving Small Signals Hidden by Large Signals
Resolving Signals Example:
Resolve two input signals with a frequency separation of 155 kHz and
an amplitude separation of 60 dB.
1. Connect two sources to the analyzer input as shown in Figure 1-9.
Figure 1-9
Setup for Obtaining Two Signals
2. Set one source to 300 MHz at −10 dBm.
3. Set the second source to 300.155 MHz, so that the signal is 155 kHz
higher than the first signal. Set the amplitude of the signal to
−70 dBm (60 dB below the first signal).
4. Set the analyzer as follows:
a. Press Preset, Factory Preset (if present).
b. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
c. Set the center frequency to 300 MHz by pressing FREQUENCY,
Center Freq, 300, MHz.
d. Set the span to 2 MHz by pressing SPAN, Span, 2, MHz.
NOTE
If the signal peak is not present on the display, do the following:
1. Increase the span to 20 MHz by pressing SPAN, Span, 20, MHz.
The signal should now be visible.
2. Press Peak Search, FREQUENCY, Signal Track (On)
3. Press SPAN, 2, MHz to bring the signal to center screen.
4. Press FREQUENCY, Signal Track (Off)
e. Set the resolution bandwidth to spectrum analyzer coupling by
pressing BW/Avg, Resolution BW (SA).
Chapter 1
19
Making Basic Measurements
Resolving Small Signals Hidden by Large Signals
5. Set the 300 MHz signal to the reference level by pressing Mkr → and
then Mkr → Ref Lvl.
If a 10 kHz filter with a typical shape factor of 15:1 is used, the filter
will have a bandwidth of 150 kHz at the 60 dB point. The
half-bandwidth (75 kHz) is narrower than the frequency separation,
so the input signals will be resolved. See Figure 1-10.
Figure 1-10
Signal Resolution with a 10 kHz Resolution Bandwidth
6. Place a marker on the smaller signal by pressing Marker, Delta,
Peak Search, Next Pk Right. Refer to Figure 1-11.
Figure 1-11
Signal Resolution with a 10 kHz Resolution Bandwidth
20
Chapter 1
Making Basic Measurements
Resolving Small Signals Hidden by Large Signals
7. Set the resolution bandwidth to 30 kHz by pressing BW/Avg, Res BW,
30, kHz.
When a 30 kHz filter is used, the 60 dB bandwidth could be as wide
as 450 kHz. Since the half-bandwidth (225 kHz) is wider than the
frequency separation, the signals most likely will not be resolved.
See Figure 1-12. (In this example, we used the 60 dB bandwidth
value. To determine resolution capability for intermediate values of
amplitude level differences, assume the filter skirts between the
3 dB and 60 dB points are approximately straight.)
Figure 1-12
Signal Resolution with a 30 kHz Resolution Bandwidth
Chapter 1
21
Making Basic Measurements
Making Better Frequency Measurements
Making Better Frequency Measurements
A built-in frequency counter increases the resolution and accuracy of
the frequency readout. When using this function, if the ratio of the
resolution bandwidth to the span is too small (less than 0.002), the
Marker Count: Widen Res BW message appears on the display. It
indicates that the resolution bandwidth is too narrow.
Better Frequency Measurement Example:
Increase the resolution and accuracy of the frequency readout on the
signal of interest.
1. Perform a factory preset by pressing Preset, Factory Preset (if
present).
2. Turn on the internal 50 MHz amplitude reference signal of the
analyzer as follows:
• For the E7401A, use the internal 50 MHz amplitude reference
signal of the analyzer as the signal being measured. Press
Input/Output, Amptd Ref (On).
• For all other models connect a cable between the front-panel
AMPTD REF OUT to the analyzer INPUT, then press
Input/Output, Amptd Ref Out (On).
3. Set the center frequency to 50 MHz by pressing FREQUENCY,
Center Freq, 50, MHz.
4. Set the span to 80 MHz by pressing SPAN, Span, 80, MHz.
5. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
6. Set the resolution bandwidth to spectrum analyzer coupling pressing
BW/Avg, Resolution BW (SA).
7. Press Freq Count. (Note that Marker Count has On underlined turning
the frequency counter on.) The frequency and amplitude of the
marker and the word Marker will appear in the active function area
(this is not the counted result). The counted result appears in the
upper-right corner of the display.
8. Move the marker, with the front-panel knob, half-way down the skirt
of the signal response. Notice that the readout in the active
frequency function changes while the counted frequency result
(upper-right corner of display) does not. See Figure 1-13. To get an
accurate count, you do not need to place the marker at the exact
peak of the signal response.
22
Chapter 1
Making Basic Measurements
Making Better Frequency Measurements
NOTE
Marker count properly functions only on CW signals or discrete spectral
components. The marker must be >26 dB above the noise.
9. Increase the counter resolution by pressing Resolution and then
entering the desired resolution using the step keys or the numbers
keypad. For example, press 10, Hz. The marker counter readout is in
the upper-right corner of the screen. The resolution can be set from
1 Hz to 100 kHz.
10. The marker counter remains on until turned off. Turn off the marker
counter by pressing Freq Count, then Marker Count (Off). Marker, Off
also turns the marker counter off.
Figure 1-13
Using Marker Counter
Chapter 1
23
Making Basic Measurements
Decreasing the Frequency Span Around the Signal
Decreasing the Frequency Span Around the
Signal
Using the analyzer signal track function, you can quickly decrease the
span while keeping the signal at center frequency. This is a fast way to
take a closer look at the area around the signal to identify signals that
would otherwise not be resolved.
Decreasing the Frequency Span Example:
Examine a signal in a 200 kHz span.
1. Perform a factory preset by pressing Preset, Factory Preset (if
present).
2. Turn on the internal 50 MHz amplitude reference signal of the
analyzer as follows:
• For the E7401A, use the internal 50 MHz amplitude reference
signal of the analyzer as the signal being measured. Press
Input/Output, Amptd Ref (On).
• For all other models connect a cable between the front-panel
AMPTD REF OUT to the analyzer INPUT, then press
Input/Output, Amptd Ref Out (On).
3. Set the start frequency to 20 MHz by pressing FREQUENCY,
Start Freq, 20, MHz.
4. Set the stop frequency to 1 GHz by pressing FREQUENCY, Stop Freq,
1, GHz.
5. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
6. Set the resolution bandwidth to spectrum analyzer coupling pressing
BW/Avg, Resolution BW (SA).
7. Press Peak Search to place a marker at the peak. See Figure 1-14.
24
Chapter 1
Making Basic Measurements
Decreasing the Frequency Span Around the Signal
Figure 1-14
Detected Signal
8. Turn on the frequency tracking function by press FREQUENCY and
Signal Track and the signal will move to the center of the screen, if it
is not already positioned there. See figure Figure 1-15. (Note that
the marker must be on the signal before turning signal track on.)
Because the signal track function automatically maintains the
signal at the center of the screen, you can reduce the span quickly for
a closer look. If the signal drifts off of the screen as you decrease the
span, use a wider frequency span. (You can also use Span Zoom, in
the SPAN menu, as a quick way to perform the Peak Search,
FREQUENCY, Signal Track, SPAN key sequence.)
Figure 1-15
Signal with Signal Tracking On
Chapter 1
25
Making Basic Measurements
Decreasing the Frequency Span Around the Signal
9. Reduce span and resolution bandwidth to zoom in on the marked
signal by pressing SPAN, Span, 200, kHz.
If the span change is large enough, span will decrease in steps as
automatic zoom is completed. See Figure 1-16. You can also use the
front-panel knob or step keys to decrease the span and resolution
bandwidth values.
10. Press FREQUENCY, Signal Track (so that Off is underlined) to turn off
the signal track function.
Figure 1-16
After Zooming In on the Signal
26
Chapter 1
Making Basic Measurements
Tracking Drifting Signals
Tracking Drifting Signals
The signal track function is useful for tracking drifting signals that
drift relatively slowly. To place a marker on the signal you wish to
track, use Peak Search. Pressing FREQUENCY, Signal Track (On) will
bring that signal to the center frequency of the graticule and adjust the
center frequency every sweep to bring the selected signal back to the
center. A quick way to perform the Peak Search, FREQUENCY,
Signal Track, SPAN key sequence is to use the Span Zoom key in the
SPAN menu.
Note that the primary function of the signal track function is to track
unstable signals, not to track a signal as the center frequency of the
analyzer is changed. If you choose to use the signal track function when
changing center frequency, check to ensure that the signal found by the
tracking function is the correct signal.
Tracking Signal Drift Example 1:
Use the signal track function to keep a drifting signal at the center of
the display and monitor its change.
This example requires a signal generator. The frequency of the signal
generator will be changed while you view the signal on the display of
the analyzer.
1. Connect a signal generator to the analyzer input.
2. Set the signal generator frequency to 300 MHz with an amplitude of
−20 dBm.
3. Set the analyzer as follows:
a. Press Preset, Factory Preset (if present).
b. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
c. Set the resolution bandwidth to the spectrum analyzer coupling
by pressing BW/Avg, Resolution BW (SA). See Figure 1-17.
d. Set the center frequency to 300 MHz by pressing FREQUENCY,
Center Freq, 300, MHz.
Chapter 1
27
Making Basic Measurements
Tracking Drifting Signals
Figure 1-17
Signal With Default Span
4. Press Peak Search.
5. Set the span to 10 MHz by pressing SPAN, Span, 10, MHz.
See Figure 1-18.
Figure 1-18
Signal With 10 MHz Span
6. Press SPAN, Span Zoom, 500, kHz.
Notice that the signal has been held in the center of the display.
See Figure 1-19.
28
Chapter 1
Making Basic Measurements
Tracking Drifting Signals
Figure 1-19
Signal With 500 kHz Span
7. Tune the frequency of the signal generator in 10 kHz increments.
Notice that the center frequency of the analyzer also changes in
10 kHz increments, centering the signal with each increment.
See Figure 1-20. Note that the center frequency has changed.
Figure 1-20
Using Span Zoom to Track a Drifting Signal
Chapter 1
29
Making Basic Measurements
Tracking Drifting Signals
8. The signal frequency drift can be read from the screen if both the
signal track and marker delta functions are active. Set the analyzer
and signal generator as follows:
a. Press Marker, Delta.
b. Tune the frequency of the signal generator. The marker readout
indicates the change in frequency and amplitude as the signal
drifts. See Figure 1-21.
Figure 1-21
Using Signal Tracking to Track a Drifting Signal
Tracking Signal Drift Example 2:
The analyzer can measure the short- and long-term stability of a
source. The maximum amplitude level and the frequency drift of an
input signal trace can be displayed and held by using the
maximum-hold function. You can also use the maximum hold function if
you want to determine how much of the frequency spectrum a signal
occupies.
1. Connect a signal generator to the analyzer input.
2. Set the signal generator frequency to 300 MHz with an amplitude of
−20 dBm.
3. Set the analyzer as follows:
a. Press Preset, Factory Preset (if present).
b. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
c. Set the resolution bandwidth to spectrum analyzer coupling by
pressing BW/Avg, Resolution BW (SA).
30
Chapter 1
Making Basic Measurements
Tracking Drifting Signals
d. Set the center frequency to 300 MHz by pressing FREQUENCY,
Center Freq, 300, MHz. See Figure 1-22.
Figure 1-22
Signal With Default Span
4. Press Peak Search.
5. Set the span to 10 MHz by pressing SPAN, Span, 10, MHz.
See Figure 1-23.
Figure 1-23
Signal With 10 MHz Span
Chapter 1
31
Making Basic Measurements
Tracking Drifting Signals
6. Press SPAN, Span Zoom, 500, kHz.
Notice that the signal has been held in the center of the display.
See Figure 1-24.
Figure 1-24
Signal With 500 KHz Span
7. Turn off the signal track function by pressing FREQUENCY,
Signal Track (Off).
8. To measure the excursion of the signal, press Trace/View, Max Hold.
As the signal varies, maximum hold maintains the maximum
responses of the input signal.
Annotation on the left side of the screen indicates the trace mode.
For example, M1 S2 S3 indicates trace 1 is in maximum-hold mode,
trace 2 and trace 3 are in store-blank mode.
9. Press Trace/View, Trace, to select trace 2. (Trace 2 is selected when 2
is underlined.)
10. Press Clear Write to place trace 2 in clear-write mode, which displays
the current measurement results as it sweeps. Trace 1 remains in
maximum hold mode, showing the frequency shift of the signal.
11. Slowly change the frequency of the signal generator ± 50 kHz in
1 kHz increments. Your analyzer display should look similar to
Figure 1-25.
32
Chapter 1
Making Basic Measurements
Tracking Drifting Signals
Figure 1-25
Viewing a Drifting Signal With Max Hold and Clear Write
Chapter 1
33
Making Basic Measurements
Measuring Low Level Signals
Measuring Low Level Signals
The ability of the analyzer to measure low level signals is limited by the
noise generated inside the analyzer. A signal may be masked by the
noise floor so that it is not visible. This sensitivity to low level signals is
affected by the measurement setup.
The analyzer input attenuator and bandwidth settings affect the
sensitivity by changing the signal-to-noise ratio. The attenuator affects
the level of a signal passing through the instrument, whereas the
bandwidth affects the level of internal noise without affecting the
signal. In the first two examples in this section, the attenuator and
bandwidth settings are adjusted to view low level signals.
If, after adjusting the attenuation and resolution bandwidth, a signal is
still near the noise, visibility can be improved by using the video
bandwidth and video averaging functions, as demonstrated in the third
and fourth examples.
Measuring Low Level Signals Example 1:
If a signal is very close to the noise floor, reducing input attenuation
brings the signal out of the noise. Reducing the attenuation to 0 dB
maximizes signal power in the analyzer.
CAUTION
The total power of all input signals at the analyzer input must not
exceed the maximum power level for the analyzer.
1. Connect a signal generator to the analyzer input.
2. Set the signal generator frequency to 300 MHz with an amplitude of
−80 dBm.
3. On the analyze, perform a factory preset by pressing Preset,
Factory Preset (if present).
4. Set the center frequency of the analyzer to 300 MHz by pressing
FREQUENCY, Center Freq, 300, MHz.
5. Set the span to 5 MHz by pressing SPAN, Span, 5, MHz.
6. Set the resolution bandwidth to spectrum analyzer coupling by
pressing BW/Avg, Res BW (SA).
7. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
8. Set the reference level to −40 dBm by pressing AMPLITUDE, Ref Level,
–40, dBm.
9. Place the signal at center frequency by pressing Peak Search,
Marker→, Mkr→CF.
34
Chapter 1
Making Basic Measurements
Measuring Low Level Signals
10. Reduce the span to 1 MHz. Press SPAN, Span, and then use the
step-down key (↓) until the span is set to 1 MHz. See Figure 1-26.
Figure 1-26
Low-Level Signal
11. Press AMPLITUDE, Attenuation. Press the step-up key (↑) to select
20 dB attenuation. Increasing the attenuation moves the noise floor
closer to the signal.
A # mark appears next to the Atten annotation at the top of the
display, indicating the attenuation is no longer coupled to other
analyzer settings.
Figure 1-27
Using 20 dB Attenuation
Chapter 1
35
Making Basic Measurements
Measuring Low Level Signals
12. To see the signal more clearly, enter 0 dB. Zero decibels of
attenuation makes the signal more visible. See Figure 1-28.
Figure 1-28
CAUTION
Using 0 dB Attenuation
Before connecting other signals to the analyzer input, increase the RF
attenuation to protect the analyzer input: press Attenuation so that Auto
is underlined or press Auto Couple.
Measuring Low Level Signals Example 2:
The resolution bandwidth can be decreased to view low level signals.
1. Connect a signal generator to the analyzer input.
2. Set the signal generator frequency to 300 MHz with an amplitude of
−80 dBm.
3. On the analyzer, perform a factory preset by pressing Preset,
Factory Preset (if present).
4. Set the center frequency of the analyzer to 300 MHz by pressing
FREQUENCY, Center Freq, 300, MHz.
5. Set the span to 5 MHz by pressing SPAN, Span, 5, MHz.
6. Set the resolution bandwidth to spectrum analyzer coupling by
pressing BW/Avg, Res BW (SA).
7. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
8. Set the reference level to −40 dBm by pressing AMPLITUDE, Ref Level,
–40, dBm.
36
Chapter 1
Making Basic Measurements
Measuring Low Level Signals
9. Place the signal at center frequency by pressing Peak Search,
Marker→, Mkr→CF.
10. Press BW/Avg, Res BW , and then ↓. The low level signal appears
more clearly because the noise level is reduced. As shown in
Figure 1-29.
A # mark appears next to the Res BW annotation at the lower left
corner of the screen, indicating that the resolution bandwidth is
uncoupled. As the resolution bandwidth is reduced, the sweep time
is increased to maintain calibrated data.
Figure 1-29
Decreasing Resolution Bandwidth
Measuring Low Level Signals Example 3:
Narrowing the video filter can be useful for noise measurements and
observation of low level signals close to the noise floor. The video filter
is a post-detection low-pass filter that smooths the displayed trace.
When signal responses near the noise level of the analyzer are visually
masked by the noise, the video filter can be narrowed to smooth this
noise and improve the visibility of the signal. (Reducing video
bandwidths requires slower sweep times to keep the analyzer
calibrated.)
Using the video bandwidth function, measure the amplitude of a low
level signal.
1. Connect a signal generator to the analyzer input.
2. Set the signal generator frequency to 300 MHz with an amplitude of
−80 dBm.
Chapter 1
37
Making Basic Measurements
Measuring Low Level Signals
3. On the analyzer, perform a factory preset by pressing Preset,
Factory Preset (if present).
4. Set the center frequency of the analyzer to 300 MHz by pressing
FREQUENCY, Center Freq, 300, MHz.
5. Set the span to 5 MHz by pressing SPAN, Span, 5, MHz.
6. Set the resolution bandwidth to spectrum analyzer coupling by
pressing BW/Avg, Res BW (SA).
7. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
8. Set the reference level to −40 dBm by pressing AMPLITUDE, Ref Level,
–40, dBm.
9. Place the signal at center frequency by pressing Peak Search,
Marker→, Mkr→CF. See Figure 1-30.
Figure 1-30
30 kHz Video Bandwidth
10. Narrow the video bandwidth by pressing BW/Avg, Video BW, and the
step-down key (↓). This clarifies the signal by smoothing the noise,
which allows better measurement of the signal amplitude.
A # mark appears next to the VBW annotation at the bottom of the
screen, indicating that the video bandwidth is not coupled to the
resolution bandwidth. See Figure 1-31. As the video bandwidth is
reduced, the sweep time is increased to maintain calibrated data.
Instrument preset conditions couple the video bandwidth to the
resolution bandwidth. If the bandwidths are uncoupled when video
bandwidth is the active function, pressing Video BW (so that Auto is
underlined) recouples the bandwidths.
38
Chapter 1
Making Basic Measurements
Measuring Low Level Signals
NOTE
Figure 1-31
The video bandwidth must be set wider than the resolution bandwidth
when measuring impulse noise levels.
Decreasing Video Bandwidth
Measuring Low Level Signals Example 4:
If a signal level is very close to the noise floor, video averaging is
another way to make the signal more visible.
NOTE
The time required to construct a full trace that is averaged to the
desired degree is approximately the same when using either the video
bandwidth or the video averaging technique. The video bandwidth
technique completes the averaging as a slow sweep is taken, whereas
the video averaging technique takes many sweeps to complete the
average. Characteristics of the signal being measured, such as drift and
duty cycle, determine which technique is appropriate.
Video averaging is a digital process in which each trace point is
averaged with the previous trace-point average. Selecting Average Type,
Video Avg and Average (On) changes the detection mode from peak to
sample. The result is a sudden drop in the displayed noise level. The
sample mode displays the instantaneous value of the signal at the end
of the time or frequency interval represented by each display point,
rather than the value of the peak during the interval. Sample mode is
not used to measure signal amplitudes accurately because it may not
find the true peak of the signal.
Video averaging clarifies low-level signals in wide bandwidths by
averaging the signal and the noise. As the analyzer takes sweeps, you
can watch video averaging smooth the trace.
Chapter 1
39
Making Basic Measurements
Measuring Low Level Signals
1. Connect a signal generator to the analyzer input.
2. Set the signal generator frequency to 300 MHz with an amplitude of
−80 dBm.
3. On the analyzer, perform a factory preset by pressing Preset,
Factory Preset (if present).
4. Set the center frequency of the analyzer to 300 MHz by pressing
FREQUENCY, Center Freq, 300, MHz.
5. Set the span to 5 MHz by pressing SPAN, Span, 5, MHz.
6. Set the resolution bandwidth to spectrum analyzer coupling by
pressing BW/Avg, Res BW (SA).
7. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
8. Set the reference level to −40 dBm by pressing AMPLITUDE, Ref Level,
–40, dBm.
9. Place the signal at center frequency by pressing Peak Search,
Marker→, Mkr→CF. See Figure 1-32.
Figure 1-32
Without Video Averaging
10. Pressing BW/Avg, Average Type, (Video Avg), Average (On), initiates
the video averaging routine. As the averaging routine smooths the
trace, low level signals be come more visible. Average 100 appears
in the active function block. The number represents the number of
samples (or sweeps) taken to complete the averaging routine. Once
the set number of sweeps has been completed, the analyzer
continues to provide a running average based on this set number.
40
Chapter 1
Making Basic Measurements
Measuring Low Level Signals
11. To set the number of samples, use the numeric keypad. For example,
press Average (On), 25, Enter. As shown in Figure 1-33.
During averaging, the current sample number appears at the left
side of the graticule. The number of samples equals the number of
sweeps in the averaging routine. Changes in active function settings,
such as the center frequency or reference level, will restart the
sampling. The sampling will also restart if video averaging is turned
off and then on again. To see the sample number increment, turn
video averaging off and on again by pressing Average (Off),
Average (On).
Figure 1-33
Using the Video Averaging Function
Chapter 1
41
Making Basic Measurements
Identifying Distortion Products
Identifying Distortion Products
Distortion from the Analyzer
High level input signals may cause analyzer distortion products that
could mask the real distortion measured on the input signal. Using
trace 2 and the RF attenuator, you can determine which signals, if any,
are internally generated distortion products.
Identifying Analyzer Generated Distortion Example:
Using a signal from a signal generator, determine whether the
harmonic distortion products are generated by the analyzer.
1. Connect a signal generator to the analyzer INPUT.
2. Set the signal generator frequency to 200 MHz and the amplitude to
0 dBm.
3. On the analyzer, perform a factory preset by pressing Preset,
Factory Preset (if present).
4. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
5. Set the resolution bandwidth to spectrum analyzer coupling by
pressing BW/Avg, Res BW (SA).
6. Set the center frequency of the analyzer to 400 MHz by pressing
FREQUENCY, Center Freq, 400, MHz.
7. Set the span to 500 MHz by pressing SPAN, Span, 500, MHz.
The signal produces harmonic distortion products in the analyzer
input mixer as shown in Figure 1-34.
42
Chapter 1
Making Basic Measurements
Identifying Distortion Products
Figure 1-34
Harmonic Distortion
8. Change the center frequency to the value of one of the observed
harmonics by pressing Peak Search, Next Peak, Marker→, Mkr→CF.
9. Change the span to 50 MHz: press SPAN , Span, 50, MHz.
10. Ensure that the signal is still at the center frequency, if necessary
press Peak Search, Marker→, Mkr→CF.
11. Change the attenuation to 0 dB: press AMPLITUDE, Attenuation, 0,
dBm . Your display should be similar to Figure 1-35.
Figure 1-35
Harmonic Distortion with 0 dB Attenuation
Chapter 1
43
Making Basic Measurements
Identifying Distortion Products
12. To determine whether the harmonic distortion products are
generated by the analyzer, first save the screen data in trace 2 as
follows:
a. Press Trace/View, Trace (2), then Clear Write.
b. Allow the trace to update (two sweeps) and press Trace/View, View,
Marker, Delta. The analyzer display shows the stored data in trace
2 and the measured data in trace 1.
13. Next, increase the RF attenuation by 10 dB: press AMPLITUDE,
Attenuation, and the step-up key (↑) twice. See Figure 1-36.
Notice the ∆Mkr1 amplitude reading. This is the difference in the
distortion product amplitude readings between 0 dB and 10 dB input
attenuation settings. If the ∆Mkr1 amplitude absolute value is
approximately ≥1 dB for an input attenuator change, the distortion
is being generated, at least in part, by the analyzer. In this case more
input attenuation is necessary.
Figure 1-36
RF Attenuation of 10 dB
14. Press Peak Search, Marker, Delta
Change the attenuation to 15 dB by pressing Attenuation, 15, dB.
If the ∆Mkr1 amplitude absolute value is approximately ≥1 dB as
seen in Figure 1-36, then more input attenuation is required; some
of the measured distortion is internally generated. If there is no
change in the signal level, the distortion is not generated internally.
For example, the signal that is causing the distortion shown in
Figure 1-37 is not high enough in amplitude to cause internal
distortion in the analyzer so any distortion that is displayed is
present on the input signal.
44
Chapter 1
Making Basic Measurements
Identifying Distortion Products
Figure 1-37
No Harmonic Distortion
Third-Order Intermodulation Distortion
Two-tone, third-order intermodulation distortion is a common test in
communication systems. When two signals are present in a non-linear
system, they can interact and create third-order intermodulation
distortion products that are located close to the original signals. These
distortion products are generated by system components such as
amplifiers and mixers.
Identifying TOI Distortion Example:
Test a device for third-order intermodulation. This example uses two
sources, one set to 300 MHz and the other to approximately 301 MHz.
(Other source frequencies may be substituted, but try to maintain a
frequency separation of approximately 1 MHz.)
1. Connect the equipment as shown in Figure 1-38. This combination of
signal generators, low pass filters, and directional coupler (used as a
combiner) results in a two-tone source with very low
intermodulation distortion. Although the distortion from this setup
may be better than the specified performance of the analyzer, it is
useful for determining the TOI performance of the source/analyzer
combination. After the performance of the source/analyzer
combination has been verified, the device-under-test (DUT) (for
example, an amplifier) would be inserted between the directional
coupler output and the analyzer input and another measurement
would be made.
Chapter 1
45
Making Basic Measurements
Identifying Distortion Products
Figure 1-38
NOTE
Third-Order Intermodulation Equipment Setup
The combiner should have a high degree of isolation between the two
input ports so the sources do not intermodulate.
2. Set one source (signal generator) to 300 MHz and the other source to
301 MHz, for a frequency separation of 1 MHz. Set the sources equal
in amplitude as measured by the analyzer (in this example, they are
set to −5 dBm).
3. On the analyzer, perform a factory preset by pressing Preset,
Factory Preset (if present).
4. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
5. Set the resolution bandwidth to spectrum analyzer coupling by
pressing BW/Avg, Res BW (SA).
6. Set the span to 5 MHz by pressing SPAN, Span, 5, MHz. This is wide
enough to include the distortion products on the screen.
7. Tune both test signals onto the screen by setting the center
frequency 300.5 MHz, press FREQUENCY, Center Freq, 300.5, MHz.
If necessary, use the front-panel knob to center the two test signals
on the display.
8. To be sure the distortion products are resolved, reduce the resolution
bandwidth until the distortion products are visible by pressing
BW/Avg, Res BW, and then use the step-down key (↓) to reduce the
resolution bandwidth until the distortion products are visible.
9. For best dynamic range, set the maximum mixer input level to
−30 dBm and move the signal to the reference level: press
AMPLITUDE, More, Max Mixer Lvl, –30, dBm .
46
Chapter 1
Making Basic Measurements
Identifying Distortion Products
The analyzer automatically sets the attenuation so that a signal at
the reference level will be a maximum of −30 dBm at the input
mixer.
10. Press BW/Avg, Res BW, and then use the step-down key (↓) to reduce
the resolution bandwidth until the distortion products are visible.
11. To measure a distortion product, press Peak Search to place a marker
on a source signal.
12. Set the marked signal to the reference level by pressing Mkr → and
then Mkr → Ref Lvl.
13. To activate the second marker, press Marker, Delta, Peak Search.
Using the Next Peak key to place the second marker on the peak of
the distortion product that is beside the test signal. The difference
between the markers is displayed in the active function area. See
Figure 1-39.
Figure 1-39
Measuring the Distortion Product
14. To measure the other distortion product, press Marker, Normal,
Peak Search, Next Peak. This places a marker on the next highest
peak, the other source signal.
15. To measure the difference between this test signal and the second
distortion product, press Delta, Peak Search. Using the Next Peak key
to place the second marker on the peak of the second distortion
product. See Figure 1-40.
Chapter 1
47
Making Basic Measurements
Identifying Distortion Products
Figure 1-40
Measuring the Distortion Product
48
Chapter 1
Making Basic Measurements
Measuring Signal-to-Noise
Measuring Signal-to-Noise
The signal-to-noise measurement procedure below may be adapted to
measure any signal in a system if the signal (carrier) is a discrete tone.
If the signal in your system is modulated, it will be necessary to modify
the procedure to correctly measure the modulated signal level
In this example the 50 MHz amplitude reference signal is used as the
fundamental source. The amplitude reference signal is assumed to be
the signal of interest and the internal noise of the analyzer is measured
as the system noise. To do this, you will need to set the input attenuator
such that both the signal and the noise are well within the calibrated
region of the display.
Signal-to-Noise Measurement Example:
Perform the steps below to measure the signal-to-noise.
1. Perform a factory preset by pressing Preset, Factory Preset (if
present).
2. Turn on the internal 50 MHz amplitude reference signal of the
analyzer as follows:
• For the E7401A, use the internal 50 MHz amplitude reference
signal of the analyzer as the signal being measured. Press
Input/Output, Amptd Ref (On).
• For all other models connect a cable between the front-panel
AMPTD REF OUT to the analyzer INPUT, then press
Input/Output, Amptd Ref Out (On).
3. Set the center frequency to 50 MHz by pressing FREQUENCY,
Center Freq, 50, MHz.
4. Set the span to 1 MHz by pressing SPAN, Span, 1, MHz.
5. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
6. Set the resolution bandwidth to spectrum analyzer coupling by
pressing BW/Avg, Res BW (SA).
7. Set the reference level to –10 dBm by pressing AMPLITUDE, Ref Level,
–10, dBm.
8. Set the attenuation to 40 dB by pressing AMPLITUDE, Attenuation, 40,
dB.
9. Press Peak Search to place a marker on the peak of the signal.
10. Press Marker, Delta, 200, kHz to put the delta marker in the noise at
the specified offset, in this case 200 kHz.
Chapter 1
49
Making Basic Measurements
Measuring Signal-to-Noise
11. Press More, Function, Marker Noise to view the results of the signal to
noise measurement. See Figure 1-41.
Figure 1-41
Measuring the Signal-to-Noise
Read the signal-to-noise in dB/Hz, that is with the noise value
determined for a 1 Hz noise bandwidth. If you wish the noise value for a
different bandwidth, decrease the ratio by 10 × log ( BW ) . For example, if
the analyzer reading is −70 dB/Hz but you have a channel bandwidth of
30 kHz:
S/N = – 70 dB/Hz + 10 × log ( 30 kHz ) = –25.23 dB ⁄ ( 30 kHz )
Note that the display detection mode is now average. If the delta
marker is within half a division of the response to a discrete signal, the
amplitude reference signal in this case, there is a potential for error in
the noise measurement. See “Making Noise Measurements” on page 51.
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Chapter 1
Making Basic Measurements
Making Noise Measurements
Making Noise Measurements
There are a variety of ways to measure noise power. The first decision
you must make is whether you want to measure noise power at a
specific frequency or the total power over a specified frequency range,
for example over a channel bandwidth.
Noise Measurement Example 1:
Using the marker function, Marker Noise, is a simple method to make a
measurement at a single frequency. In this example, attention must be
made to the potential errors due to discrete signal (spectral
components). This measurement will be made near the 50 MHz
amplitude reference signal to illustrate the use of Marker Noise.
1. Perform a factory preset by pressing Preset, Factory Preset (if
present).
2. Turn on the internal 50 MHz amplitude reference signal of the
analyzer as follows:
• For the E7401A, use the internal 50 MHz amplitude reference
signal of the analyzer as the signal being measured. Press
Input/Output, Amptd Ref (On).
• For all other models connect a cable between the front-panel
AMPTD REF OUT to the analyzer INPUT, then press
Input/Output, Amptd Ref Out (On).
3. Set the center frequency to 49.98 MHz by pressing FREQUENCY,
Center Freq, 49.98, MHz.
4. Set the span to 100 kHz by pressing SPAN , Span, 100, kHz.
5. Set the resolution bandwidth to 1 kHz by pressing BW/Avg,
Res BW (Man), 1, kHz.
6. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
7. Set the attenuation to 60 dB by pressing AMPLITUDE, Attenuation
(Man), 60, dB. See Figure 1-42.
NOTE
When making noise measurements and AMPLITUDE, Scale Type (Log) is
selected (10 dB/division), position the trace between 3 and 6 graticule
lines above the bottom by adjusting the reference level (AMPLITUDE,
Ref Level). Measurement inaccuracies may occur if displayed trace is
positioned outside this range.
Chapter 1
51
Making Basic Measurements
Making Noise Measurements
Figure 1-42
Setting the Attenuation
8. Activate the noise marker by pressing Marker, More, Function,
Marker Noise.
Note that the display detection automatically changed to “Avg”
which can be manually set by pressing Det/Demod,
Average (Video/RMS). The marker is floating between the maximum
and the minimum of the noise. For firmware revisions earlier than
A.08.00, the detection type when using Marker Noise changed to
sample. If you wish to use sample detection, press Det/Demod,
Detector, Sample and verify that “Average Type” is set to “Video
average” by pressing BW/Avg, Average Type, Video Avg. This is not
recommended as it is slower and does not increase accuracy.
The marker readout is in dBm(Hz) or dBm per unit bandwidth. See
Figure 1-43. For noise power in a different bandwidth, add
10 × log ( BW ) . For example, for noise power in a 1 kHz bandwidth, add
10 × log ( 1000 ) or 30 dB to the noise marker value.
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Chapter 1
Making Basic Measurements
Making Noise Measurements
Figure 1-43
Activating the Noise Marker
9. The noise marker value is based on the mean of 5% of the total
number of sweep points centered at the marker. The points averaged
span one-half of a division. To see the effect, move the marker to the
50 MHz signal by pressing Marker, 50, MHz (or use the front-panel
knob to place marker at 50 MHz). See Figure 1-44.
Figure 1-44
Noise Marker at 50 MHz
10. The marker does not go to the peak of the signal because not all
averaged points are at the peak of the signal. Widen the resolution
bandwidth by pressing BW/Avg, Res BW, 10, kHz (or up arrow) to see
what happens. The marker is now much closer to the peak of the
signal. See Figure 1-45.
Chapter 1
53
Making Basic Measurements
Making Noise Measurements
NOTE
Figure 1-45
Notice the video bandwidth changed to 100 kHz. The ratio between the
video bandwidth (VBW) and the resolution bandwidth (RBW) must be ≥
10/1 to maintain the accuracy of the measurement.
Increased Resolution Bandwidth
11. Return the resolution bandwidth to 1 kHz. Press BW/Avg, 1, kHz.
12. Measure the noise very close to the signal by pressing Marker,
50.0000, MHz (or use the front-panel knob to place the marker). See
Figure 1-46.
Note that the marker reads a value that is too high because some of
the averaged trace points are on the skirt of the signal response.
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Chapter 1
Making Basic Measurements
Making Noise Measurements
Figure 1-46
Noise Marker in Signal Skirt
13. Set the analyzer to zero span at the marker frequency by pressing
Mkr →, Mkr → CF, SPAN, Zero Span, Marker. Note that the marker
amplitude value is now correct since all points averaged are at the
same frequency and not influenced by the shape of the bandwidth
filter. See Figure 1-47.
Figure 1-47
Noise Marker with Zero Span
Chapter 1
55
Making Basic Measurements
Making Noise Measurements
Noise Measurement Example 2:
The Normal marker can also be used to make a single frequency
measurement as described in the previous example, again using video
filtering or averaging to obtain a reasonably stable measurement.
While video averaging automatically selects the sample display
detection mode, video filtering does not. With sufficient filtering that
results in a smooth trace, there is no difference between the sample and
peak modes because the filtering takes place before the signal is
digitized.
Be sure to account for the fact that the averaged noise is displayed
approximately 2 dB too low for a noise bandwidth equal to the
resolution bandwidth. Therefore, you must add 2 dB to the marker
reading. For example, if the marker indicates –100 dBm, the actual
noise level is –98 dBm.
Noise Measurement Example 3:
You may use adjustable markers to set the frequency span over which
power is measured. The markers allow you to easily and conveniently
select any arbitrary portion of the displayed signal for measurement.
However, while the analyzer does select the average (video/rms) display
detection mode, you must set all of the other parameters.
1. Reset the analyzer by pressing Preset, Factory Preset (if present).
2. Tune the analyzer to the frequency of 50 MHz. In this example we
are using the amplitude reference signal. Press FREQUENCY, 50,
MHz.
3. Set the span to 100 kHz by pressing SPAN, 100, kHz.
4. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
5. Set the resolution bandwidth to 1 kHz by pressing BW/Avg,
Resolution BW , 1, kHz.
6. Set the reference level to −20 dBm by pressing AMPLITUDE, Ref Level,
–20, dBm.
7. Set the input attenuator to 40 dB by pressing Attenuation, 40, dB .
8. Set the marker span to 40 kHz by pressing Marker, Span Pair (Span),
40, kHz.
The resolution bandwidth should be about 1 to 3% of the
measurement (marker) span, 40 kHz in this example. The 1 kHz
resolution bandwidth that the analyzer has chosen is fine. The video
bandwidth should be ten times wider.
9. Set the video bandwidth to 10 kHz by pressing BW/Avg,
Video BW (Man), 10, kHz.
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Making Noise Measurements
10. Measure the power between markers by pressing Marker, More,
Function, Band Power. The analyzer displays the total power between
the markers. See Figure 1-48.
11. Add a discrete tone to see the effects of the reading. Turn on the
internal 50 MHz amplitude reference signal of the analyzer (if you
have not already done so) as follows:
• For the E7401A, use the internal 50 MHz amplitude reference
signal of the analyzer as the signal being measured. Press
Input/Output, Amptd Ref (On).
• For all other models connect a cable between the front-panel
AMPTD REF OUT to the analyzer INPUT, then press
Input/Output, Amptd Ref Out (On).
Figure 1-48
Viewing Power Between Markers
12. Move the measured span by pressing Marker, Span Pair (Center).
Then use the knob to exclude the tone and note reading. You could
have also used Band Pair or Delta Pair to set the measurement start
and stop points independently. See Figure 1-49.
Chapter 1
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Making Basic Measurements
Making Noise Measurements
Figure 1-49
Measuring the Power in the Span
58
Chapter 1
Making Basic Measurements
Demodulating AM Signals (Using the Analyzer As a Fixed Tuned Receiver)
Demodulating AM Signals (Using the Analyzer
As a Fixed Tuned Receiver)
The zero span mode can be used to recover amplitude modulation on a
carrier signal. The analyzer operates as a fixed-tuned receiver in zero
span to provide time domain measurements.
Center frequency in the swept-tuned mode becomes the tuned
frequency in zero span. The horizontal axis of the screen becomes
calibrated in time only, rather than both frequency and time. Markers
display amplitude and time values.
The following functions establish a clear display of the waveform:
• Trigger stabilizes the waveform trace on the display by triggering on
the modulation envelope. If the modulation of the signal is stable,
video trigger synchronizes the sweep with the demodulated
waveform.
• Linear mode should be used in amplitude modulation (AM)
measurements to avoid distortion caused by the logarithmic
amplifier when demodulating signals.
• Sweep time adjusts the full sweep time from 5 ms to 2000 s. (20 µs to
2000 s if Option AYX is installed). The sweep time readout refers to
the full 10-division graticule. Divide this value by 10 to determine
sweep time per division.
• Resolution and video bandwidth are selected according to the signal
bandwidth.
Each of the coupled function values remains at its current value when
zero span is activated. Video bandwidth is coupled to resolution
bandwidth. Sweep time is not coupled to any other function.
NOTE
Refer to “Demodulating and Listening to an AM Signal” on page 88 for
more information on signal demodulation.
To obtain an AM signal, you can either connect a source to the analyzer
input and set the source for amplitude modulation, or connect an
antenna to the analyzer input and tune to a commercial AM broadcast
station.
Demodulating an AM Signal Example 1:
View the modulation waveform of an AM signal in the time domain.
1. Connect an RF signal source to the analyzer INPUT. For this
example, an Agilent E4433B Signal Generator was used with the
following settings:
a. RF Frequency 300 MHz
Chapter 1
59
Making Basic Measurements
Demodulating AM Signals (Using the Analyzer As a Fixed Tuned Receiver)
b. RF Output Power –10 dBm
c. AM On
d. AM Rate 1 kHz
e. AM Depth 80%
2. Set the analyzer as follows:
a. Press Preset, Factory Preset (if present).
b. Set the center frequency to 300 MHz by pressing FREQUENCY,
Center Freq, 300, MHz.
c. Set the span to 500 kHz by pressing SPAN, Span, 500, kHz.
d. Set the resolution bandwidth to 30 kHz by pressing BW/Avg,
Resolution BW, 30, kHz.
e. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
f. Change the analyzer sweep to 20 msec by pressing Sweep,
Sweep Time, 20, ms. See Figure 1-50.
Figure 1-50
Viewing an AM Signal
3. Set the Y-Axis Units to V by pressing AMPLITUDE, More, Y-Axis Units,
V.
4. Position the signal peak near the reference level by pressing
AMPLITUDE and rotating the front-panel knob.
5. Change the amplitude scale type to linear by pressing AMPLITUDE,
Scale Type (Lin).
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Demodulating AM Signals (Using the Analyzer As a Fixed Tuned Receiver)
6. Select zero span by either pressing SPAN, 0, Hz; or pressing SPAN,
Zero Span. See Figure 1-51.
7. Change the sweep time to 5 ms by pressing Sweep,
Sweep Time (Man), 5, ms.
8. Since the modulation is a steady tone, you can use video trigger to
trigger the analyzer sweep on the waveform and stabilize the trace,
much like an oscilloscope by pressing Trig, Video, and adjusting the
trigger level with the front-panel knob until the signal stabilizes. See
Figure 1-52.
If you are viewing an off-the-air signal you will not be able to
stabilize the waveform.
NOTE
Figure 1-51
If the Trigger Level is set too high or too low when this trigger mode is
activated, the sweep will stop. You will need to adjust the trigger level
up or down with the front-panel knob until the sweep begins again.
Measuring Modulation In Zero Span
Chapter 1
61
Making Basic Measurements
Demodulating AM Signals (Using the Analyzer As a Fixed Tuned Receiver)
Figure 1-52
Measuring Modulation In Zero Span
Figure 1-53
Measuring Modulation In Zero Span
9. Use markers and delta markers to measure the time parameters of
the waveform.
a. Press Marker and center the marker on a peak using Peak Search
or the front-panel knob.
b. Press Marker, Delta and center the marker on the next peak using
the front-panel knob or use Peak Search and Next Pk Right (or
Next Pk Left). See Figure 1-54.
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Demodulating AM Signals (Using the Analyzer As a Fixed Tuned Receiver)
Figure 1-54
Measuring Time Parameters
10. You can turn your analyzer into a % AM indicator as follows:
a. Set trigger to free run by pressing Trig, Free Run.
b. Set the sweep time to 5 seconds by pressing Sweep, Sweep Time, 5,
s.
c. Set the video filter to 30 Hz by pressing BW/Avg, Video BW , 30, Hz.
d. Change the reference level to position the trace at midscreen by
pressing AMPLITUDE, Ref Level, and adjacent the reference level
using the front-panel knob.
e. Reset the video filter to a high value. For example, press BW/Avg,
Video BW, 100, kHz.
f. Set the sweep time to 5 milliseconds by pressing Sweep, Sweep
Time, 5, ms.
The center horizontal line of the graticule now represents 0% AM;
the top and bottom lines, 100% AM. See Figure 1-55.
Chapter 1
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Making Basic Measurements
Demodulating AM Signals (Using the Analyzer As a Fixed Tuned Receiver)
Figure 1-55
Continuous Demodulation of an AM Signal
64
Chapter 1
Making Basic Measurements
Demodulating FM Signals
Demodulating FM Signals
As with amplitude modulation (see page 59) you can utilize zero span to
demodulate an FM signal. However, unlike the AM case, you cannot
simply tune to the carrier frequency and widen the resolution
bandwidth. The reason is that the envelope detector in the analyzer
responds only to amplitude variations, and there is no change in
amplitude if the frequency changes of the FM signal are limited to the
flat part of the resolution bandwidth.
On the other hand, if you tune the analyzer slightly away from the
carrier, you can utilize slope detection to demodulate the signal by
performing the following steps.
1. Determine the correct resolution bandwidth.
2. Find the center of the linear portion of the filter skirt (either side).
3. Tune the analyzer to put the center point at mid screen of the
display.
4. Select zero span.
The demodulated signal is now displayed; the frequency changes have
been translated into amplitude changes., see Figure 1-58. To listen to
the signal, turn on AM demodulation and the speaker.
In this example you will demodulate a broadcast FM signal that has a
specified 75 kHz peak deviation.
Demodulating a FM Signal Example:
Determine the correct resolution bandwidth. With a peak deviation of
75 kHz, your signal has a peak-to-peak excursion of 150 kHz. So we
must find a resolution bandwidth filter with a skirt that is reasonably
linear over that frequency range.
1. Perform a factory preset by pressing Preset, Factory Preset (if
present).
2. Turn on the internal 50 MHz reference signal of the analyzer as
follows:
• For the E7401A, use the internal 50 MHz amplitude reference
signal of the analyzer as the signal being measured. Press
Input/Output, Amptd Ref (On).
• For all other models connect a cable between the front-panel
AMPTD REF OUT to the analyzer INPUT, then press
Input/Output, Amptd Ref Out (On).
3. Set the center frequency to 50 MHz by pressing FREQUENCY,
Center Freq, 50, MHz.
Chapter 1
65
Making Basic Measurements
Demodulating FM Signals
4. Set the span to 1 MHz by pressing SPAN, Span, 1, MHz.
5. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
6. Set the reference level to –20 dBm by pressing AMPLITUDE, Ref Level,
–20, dB m.
7. Set the resolution bandwidth to 100 kHz by pressing BW/Avg,
Res BW , 100, kHz. The skirt is reasonably linear starting
approximately 5 dB below the peak.
8. Select a marker by pressing Marker, then move the marker
approximately 1/2 division down the right of the peak (high
frequency) using the front-panel knob.
9. Place a delta marker 150 kHz from the first marker by pressing
Delta, 150, kHz. The skirt looks reasonably linear between markers.
10. Determine the offset from the signal peak to the desired point on the
filter skirt by moving the delta marker to the midpoint. Press 75, kHz
to move the delta marker to the midpoint. See Figure 1-56.
Figure 1-56
Establishing the Offset Point
11. Press Delta to make the active marker the reference marker.
12. Press Peak Search to move the delta marker to the peak. The delta
value is the desired offset, for example 151 kHz. See Figure 1-57.
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Demodulating FM Signals
Figure 1-57
Determining the Offset
Demodulate the FM Signal
1. Connect an antenna to the analyzer INPUT.
2. Perform a factory preset by pressing Preset, Factory Preset (if
present).
3. Tune the analyzer to a peak the peak of one of your local FM
broadcast signals, for example 97.7 MHz by pressing FREQUENCY,
Center Freq, 97.7, MHz.
4. Set the span to 1 MHz by pressing SPAN, Span, 1, MHz.
5. Press AMPLITUDE, Ref Level, and use the front-panel knob to bring
the signal peak to the reference level.
6. Press Scale Type (Lin) to place the analyzer in linear scale mode.
7. Tune above or below the FM signal by the offset noted above in
step 12, in this example 151 kHz. Press FREQUENCY, CF Step, 151,
kHz, then press Center Freq and use the step-up key (↑) or step-down
key (↓).
8. Set the resolution bandwidth to 100 kHz, by pressing BW/Avg, Res
BW, 100, kHz.
9. Set the span to zero by pressing SPAN, Zero Span.
10. Turn off the automatic alignment by pressing System, Alignments,
Auto Align, Off.
11. Listen to the demodulated signal through the speaker by pressing
Det/Demod, Demod, AM, Speaker (On), then adjust the volume using
the front-panel volume knob.
Chapter 1
67
Making Basic Measurements
Demodulating FM Signals
12. Activate single sweep by pressing Single. See Figure 1-58.
Figure 1-58
Demodulating a Broadcast Signal
68
Chapter 1
2
Making Complex Measurements
69
Making Complex Measurements
What’s in This Chapter
What’s in This Chapter
This chapter provides information for making complex measurements.
The procedures covered in this chapter are listed below.
• “Making Stimulus Response Measurements” on page 71.
• “Making a Reflection Calibration Measurement” on page 84.
• “Demodulating and Listening to an AM Signal” on page 88.
To find descriptions of specific analyzer functions refer to the Agilent
Technologies EMC Series Analyzers User’s Guide.
Required Test Equipment
Test Equipment
Specifications
Recommended Model
Adapters
Type-N (m) to BNC (f) (2)
1250-0780
Cables
(3) BNC, 122-cm (48-in)
10503A
Miscellaneous
Bandpass Filter
Center Frequency:
200 MHz
Bandwidth: 10 MHz
Lowpass Filter
Cutoff Frequency:
10 MHz
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Chapter 2
Making Complex Measurements
Making Stimulus Response Measurements
Making Stimulus Response Measurements
What Are Stimulus Response Measurements?
Stimulus response measurements require a source to stimulate a device
under test (DUT), a receiver to analyze the frequency response
characteristics of the DUT, and, for return loss measurements, a
directional coupler or bridge. Characterization of a DUT can be made in
terms of its transmission or reflection parameters. Examples of
transmission measurements include flatness and rejection. Return loss
is an example of a reflection measurement.
A spectrum analyzer combined with a tracking generator forms a
stimulus response measurement system. With the tracking generator
as the swept source and the analyzer as the receiver, operation is the
same as a single channel scalar network analyzer. The tracking
generator output frequency must be made to precisely track the
analyzer input frequency for good narrow band operation. A narrow
band system has a wide dynamic measurement range. This wide
dynamic range will be illustrated in the following example.
Using An Analyzer With A Tracking Generator
There are three basic steps in performing a stimulus response
measurement, whether it is a transmission or a reflection
measurement. The steps are to set all the analyzer settings, normalize,
and measure.
The procedure below describes how to use a built in tracking generator
system to measure the rejection of a band pass filter, a type of
transmission measurement. Illustrated in this example are functions in
the tracking generator menu such as adjusting the tracking generator
output power. Normalization functions located in the trace menu are
also used. Making a reflection measurement is similar and is covered in
“Making a Reflection Calibration Measurement” on page 84.
Stepping Through a Transmission Measurement
1. To measure the rejection of a band pass filter, connect the equipment
as shown in Figure 2-1. This example uses a 200 MHz bandpass
filter as the DUT.
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71
Making Complex Measurements
Making Stimulus Response Measurements
Figure 2-1
Transmission Measurement Test Setup
2. Perform a factory preset by pressing Preset, Factory Preset
(if present).
3. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
4. Since we are only interested in the rejection of the bandpass filter,
tune the analyzer center frequency and span to center the bandpass
response and display the rejection ±50 MHz from the center of the
bandpass.
a. Set the span to 100 MHz by pressing SPAN, Span, 100, MHz.
b. Set the center frequency to 200 MHz by pressing FREQUENCY,
Center Freq, 200, MHz.
5. Set the resolution bandwidth to 3 MHz by pressing BW/Avg, Res BW,
3, MHz.
6. Turn on the tracking generator and if necessary, set the output
power to –10 dBm by pressing Source, Amplitude (On), –10, dBm .
See Figure 2-2.
CAUTION
Excessive signal input may damage the DUT. Do not exceed the
maximum power that the device under test can tolerate.
NOTE
To reduce ripples caused by source return loss, use 10 dB (E7401A) or
8 dB (all other models) or greater tracking generator output
attenuation. Tracking generator output attenuation is normally a
function of the source power selected. However, the output attenuation
may be controlled in the Source menu. Refer to specifications and
characteristics in your specifications guide for more information on the
relationship between source power and source attenuation.
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Chapter 2
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Making Stimulus Response Measurements
Figure 2-2
Tracking Generator Output Power Activated
7. Put the sweep time of the analyzer into stimulus response auto
coupled mode by pressing Sweep, Swp Coupling (SR). Auto coupled
sweep times are usually much faster for stimulus response
measurements than they are for spectrum analyzer (SA)
measurements. If necessary, adjust the reference level to place the
signal on screen.
NOTE
In the stimulus response mode, the Q of the DUT can determine the
fastest rate at which the analyzer can be swept. (Q is the quality factor,
which is the center frequency of the DUT divided by the bandwidth of
the DUT.) To determine whether the analyzer is sweeping too fast, slow
the sweep and note whether there is a frequency or amplitude shift of
the trace. Continue to slow the sweep until there is no longer a
frequency or amplitude shift.
8. Decrease the resolution bandwidth to increase sensitivity by
pressing BW/Avg, Res BW, and the step-down key (↓) until the
sensitivity is increased. In Figure 2-3, the resolution bandwidth has
been decreased to 30 kHz.
9. Narrow the video bandwidth to smooth the noise by pressing
BW/Avg, Video BW, and the step-down key (↓) until the noise is
reduced. In Figure 2-3, the video bandwidth has been decreased to
300 Hz.
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Making Complex Measurements
Making Stimulus Response Measurements
Figure 2-3
Decrease the Resolution Bandwidth to Improve Sensitivity
10.You might notice a decrease in the displayed amplitude as the
resolution bandwidth is decreased, (if the analyzer is an E7402A,
E7403A, E7404A, or E7405A). This indicates the need for
performing a tracking peak. Press Source, Tracking Peak. The
amplitude should return to that which was displayed prior to the
decrease in resolution bandwidth.
11.To make a transmission measurement accurately, the frequency
response of the test system must be known. Normalization is used to
eliminate this error from the measurement. To measure the
frequency response of the test system, connect the cable (but not the
DUT) from the tracking generator output to the analyzer input.
Press Trace/View, More, Normalize, Store Ref (1→3), Normalize (On).
The frequency response of the test system is automatically stored in
trace 3 and a normalization is performed. This means that the active
displayed trace is now the ratio of the input data to the data stored
in trace 3. (The reference trace is Trace 3 with firmware revision
A.04.00 and later)
When normalization is on, trace math is being performed on the
active trace. The trace math performed is (trace 1 − trace 3 + the
normalized reference position), with the result placed into trace 1.
Remember that trace 1 contains the measurement trace, trace 3
contains the stored reference trace of the system frequency response,
and normalized reference position is indicated by arrowheads at the
edges of the graticule.
NOTE
Since the reference trace is stored in trace 3, changing trace 3 to
Clear Write will invalidate the normalization.
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Chapter 2
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Making Stimulus Response Measurements
12.Reconnect the DUT to the analyzer. Note that the units of the
reference level have changed to dB, indicating that this is now a
relative measurement.
Press Trace/View, More, Normalize, Norm Ref Posn to change the
normalized reference position. Arrowheads at the left and right
edges of the graticule mark the normalized reference position, or the
position where 0 dB insertion loss (transmission measurements) or
0 dB return loss (reflection measurements) will normally reside.
Using the knob results in a change in the position of the normalized
trace, within the range of the graticule.
13.To measure the rejection of the filter 45 MHz above the center of the
bandpass, press Marker, 200, MHz (to ensure that the marker is in the
center of the signal), and then press Delta, 45, MHz . The marker
readout displays the rejection of the filter at 45 MHz above the
center of the bandpass. See Figure 2-4.
NOTE
Figure 2-4
Because the default trace is comprised of 401 discrete points, the
indicated marker frequency may differ slightly from the frequency that
you entered. Due to the horizontal resolution of the trace, the marker
frequency value will be rounded to within 0.25% of the span of the value
entered. If the analyzer is an ESA-E series with firmware revision
A.04.00 or later, the number of sweep points may be set to any value
between 101 and 8192.
Measure the Rejection Range
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Making Stimulus Response Measurements
Tracking Generator Unleveled Condition
When using the tracking generator, the message TG unleveled may
appear. The TG unleveled message indicates that the tracking
generator source power (Source, Amplitude) could not be maintained at
the selected level during some portion of the sweep. If the unleveled
condition exists at the beginning of the sweep, the message will be
displayed immediately. If the unleveled condition occurs after the sweep
begins, the message will be displayed after the sweep is completed. A
momentary unleveled condition may not be detected when the sweep
time is short. The message will be cleared after a sweep is completed
with no unleveled conditions.
The unleveled condition may be caused by any of the following:
• Start frequency is too low or the stop frequency is too high. The
unleveled condition is likely to occur if the true frequency range
exceeds the tracking generator frequency specification (especially
the low frequency specification).
• Source attenuation may be set incorrectly (select Attenuation (Auto)
for optimum setting).
• The source power may be set too high or too low, use Amplitude (Off)
then Amplitude (On) to reset it.
• The source power sweep may be set too high, resulting in an
unleveled condition at the end of the sweep. Use Power Sweep (Off)
then Power Sweep (On) to decrease the amplitude.
• Reverse RF power from the device under test detected by the
tracking generator ALC (automatic level control) system.
Measuring Device Bandwidth
It is often necessary to measure device bandwidth, such as when testing
a bandpass filter. There is a key in the Peak Search menu that will
perform this function. The device signal being measured must be
displayed before activating the measurement. The span must include
the full response.
Activate the measurement by toggling the N dB Points key to On. The
analyzer places arrow markers at the −3 dB points on either side of the
response and reads the bandwidth. For other bandwidth responses
enter the number of dB down desired, from −1 dB to −80 dB.
No other signal can appear on the display within N dB of the highest
signal. The measured signal cannot have more than one peak that is
greater than or equal to N dB. A signal must have a peak greater than
the currently defined peak excursion to be identified. The default value
for the peak excursion is 6 dB.
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Making Stimulus Response Measurements
Measurements are made continuously, updating at the end of each
sweep. This allows you to make adjustments and see changes as they
happen. The single sweep mode can also be used, providing time to
study or record the data.
The N dB bandwidth measurement error is typically ±1% of the span.
Example:
Measure the 3 dB bandwidth of a 200 MHz bandpass filter.
1. To measure the rejection of a bandpass filter, connect the equipment
as shown in Figure 2-5. This example uses a 200 MHz bandpass
filter.
Figure 2-5
Transmission Measurement Test Setup
2. Perform a factory preset by pressing Preset, Factory Preset (if
present).
3. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
4. Set the span to 100 MHz by pressing SPAN, Span, 100, MHz.
5. Set the center frequency to 200 MHz by pressing FREQUENCY,
Center Freq, 200, MHz.
6. Set the resolution bandwidth to 10 kHz by pressing BW/Avg, Res BW,
10, kHz.
7. Turn on the tracking generator and if necessary, set the output
power to –10 dBm by pressing Source, Amplitude (On), –10, dBm.
CAUTION
Excessive signal input may damage the DUT. Do not exceed the
maximum power that the device under test can tolerate.
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Making Stimulus Response Measurements
NOTE
To reduce ripples caused by source return loss, use 10 dB (E7401A) or 8
dB (all other models) or greater tracking generator output attenuation.
Tracking generator output attenuation is normally a function of the
source power selected. However, the output attenuation may be
controlled in the Source menu. Refer to specifications and
characteristics in your specifications guide for more information on the
relationship between source power and source attenuation.
8. Put the sweep time of the analyzer into stimulus response auto
coupled mode by pressing Sweep, then Swp Coupling (SR). Auto
coupled sweep times are usually much faster for stimulus response
measurements than they are for spectrum analyzer (SA)
measurements. Adjust the reference level if necessary to place the
signal on screen.
NOTE
In the stimulus response mode, the Q of the DUT can determine the
fastest rate at which the analyzer can be swept. (Q is the quality factor,
which is the center frequency of the DUT divided by the bandwidth of
the DUT.) To determine whether the analyzer is sweeping too fast, slow
the sweep and note whether there is a frequency or amplitude shift of
the trace. Continue to slow the sweep until there is no longer a
frequency or amplitude shift.
9. To activate the N dB bandwidth function press Peak Search, More,
then N dB Points (On). See Figure 2-6.
10.Read the measurement results displayed on the screen.
Figure 2-6
N dB Bandwidth Measurement at –3 dB
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Making Stimulus Response Measurements
11.The knob or the data entry keys can be used to change the N dB
value from −3 dB to −60 dB to measure the 60 dB bandwidth of the
filter. See Figure 2-7.
Figure 2-7
N dB Bandwidth Measurement at –60 dB
12.Press N dB Points (Off) to turn the measurement off.
Measuring Stop Band Attenuation Using Log Sweep
When measuring filter characteristics, it is useful to look at the
stimulus response over a wide frequency range. Setting the analyzer
x-axis (frequency) to display logarithmically provides this function.
Example:
Measure the stop band attenuation of a 10 MHz low pass filter.
1. To measure the response of a low pass filter, connect the equipment
as shown in Figure 2-8. This example uses a 10 MHz low pass filter.
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79
Making Complex Measurements
Making Stimulus Response Measurements
Figure 2-8
Transmission Measurement Test Setup
2. Perform a factory preset by pressing Preset, Factory Preset (if
present).
3. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
4. Set the start frequency to 100 kHz by pressing FREQUENCY,
Start Freq, 100, kHz.
5. Set the stop frequency to 1 GHz by pressing Stop Freq, 1, GHz.
6. Set the resolution bandwidth to 10 kHz by pressing BW/Avg, Res BW,
10, kHz.
7. Set the frequency scale to log by pressing FREQUENCY,
Scale Type (Log).
8. For E7405A analyzers with Option UKB, set the input coupling to
DC by pressing Input, Coupling (DC).
9. Turn on the tracking generator and if necessary, set the output
power to –10 dBm by pressing Source, Amplitude (On), –10, dBm .
CAUTION
Excessive signal input may damage the DUT. Do not exceed the
maximum power that the device under test can tolerate.
NOTE
To reduce ripples caused by source return loss, use 10 dB (E7401A) or 8
dB (all other models) or greater tracking generator output attenuation.
Tracking generator output attenuation is normally a function of the
source power selected. However, the output attenuation may be
controlled in the Source menu. Refer to specifications and
characteristics in your specifications guide for more information on the
relationship between source power and source attenuation.
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Making Stimulus Response Measurements
Figure 2-9
Tracking Generator Output Power Activated in Log Sweep
10.Put the sweep time of the analyzer into stimulus response auto
coupled mode by pressing Sweep, then Swp Coupling (SR). See
Figure 2-9. Auto coupled sweep times are usually much faster for
stimulus response measurements than they are for spectrum
analyzer (SA) measurements. Adjust the reference level if necessary
to place the signal on screen.
11.To make a transmission measurement accurately, the frequency
response of the test system must be known. Normalization is used to
eliminate this error from the measurement. To measure the
frequency response of the test system, connect the cable (but not the
DUT) from the tracking generator output to the analyzer input.
Press Trace/View, More, Normalize, Store Ref (1→3), Normalize (On).
This will activate the trace 1 minus trace 3 function and display the
results in trace 1. The normalized trace or flat line represents 0 dB
return loss. Normalization occurs each sweep.
NOTE
Since the calibration trace is stored in trace 3, changing trace 3 to
Clear Write, Max Hold, or Min Hold will invalidate the normalization.
12.Reconnect the DUT to the analyzer. Note that the units of the
reference level have changed to dB, indicating that this is now a
relative measurement. Refer to Figure 2-10.
13.Press Trace/View, More, Normalize, Norm Ref Posn to change the
normalized reference position. Arrowheads at the left and right
edges of the graticule mark the normalized reference position. Using
the knob results in a change in the position of the normalized trace,
within the range of the graticule. Refer to Figure 2-10.
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Making Complex Measurements
Making Stimulus Response Measurements
Figure 2-10
Normalized Trace After Reconnecting DUT
14.Press Marker, Delta Pair (Ref), 10, MHz to place the reference marker
at the specified cutoff frequency.
15.Press Delta Pair (∆), 20, MHz to place the second marker at the
20 MHz point. In this example, the attenuation over this frequency
range is 63.32 dB/octave (one octave above the cutoff frequency).
Figure 2-11
Determining Low Pass Filter Rolloff
16.Use the knob to place the marker at the highest peak in the stop
band to determine the minimum stop band attenuation. In this
example, the peak occurs at 708.76 MHz. The attenuation is
54.92 dB.
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Making Stimulus Response Measurements
Figure 2-12
Minimum Stop Band Attenuation
Chapter 2
83
Making Complex Measurements
Making a Reflection Calibration Measurement
Making a Reflection Calibration Measurement
The calibration standard for reflection measurements is usually a short
circuit connected at the reference plane (the point at which the device
under test (DUT) will be connected.) See Figure 2-13. A short circuit
has a reflection coefficient of 1 (0 dB return loss). It reflects all incident
power and provides a convenient 0 dB reference.
Figure 2-13
Reflection Measurement Short Calibration Test Setup
Example:
Measure the return loss of a filter. The following procedure makes a
reflection measurement using a coupler or directional bridge. This
example uses a 200 MHz bandpass filter as the DUT.
NOTE
The analyzer center frequency and span for this measurement can
easily be set up using the transmission measurement setup in “Making
Stimulus Response Measurements” on page 71. Tune the analyzer so
that the passband of the filter comprises a majority of the display, then
proceed with the steps outlined below.
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Making a Reflection Calibration Measurement
Reflection Calibration
1. Connect the DUT to the directional bridge or coupler as shown in
Figure 2-13. Terminate the unconnected port of the DUT.
NOTE
If possible, use a coupler or bridge with the correct test port connector
for both calibrating and measuring. Any adapter between the test port
and DUT degrades coupler/bridge directivity and system source match.
Ideally, you should use the same adapter for the calibration and the
measurement. Be sure to terminate the second port of a two port device.
2. Connect the tracking generator output of the analyzer to the
directional bridge or coupler.
3. Connect the analyzer input to the coupled port of the directional
bridge or coupler.
4. Perform a factory preset by pressing Preset, Factory Preset (if
present).
5. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
6. Turn on the tracking generator and if necessary, set the output
power to –10 dBm by pressing Source, Amplitude (On), –10, dBm.
CAUTION
Excessive signal input may damage the DUT. Do not exceed the
maximum power that the device under test can tolerate.
7. Set the span to 100 MHz by pressing SPAN, Span, 100, MHz.
8. Set the center frequency to 200 MHz by pressing FREQUENCY,
Center Freq, 200, MHz.
9. Set the resolution bandwidth to 3 MHz by pressing BW/Avg, Res BW,
3, MHz.
10.Replace the DUT with a short circuit.
11.Normalize the trace by pressing Trace/View, More, Normalize,
Store Ref (1→3), Normalize (On). See Figure 2-14.
This will activate the trace 1 minus trace 3 function and display the
results in trace 1. The normalized trace or flat line represents 0 dB
return loss. Normalization occurs each sweep. Replace the short
circuit with the DUT.
NOTE
Since the reference trace is stored in trace 3, changing trace 3 to
Clear Write will invalidate the normalization.
Chapter 2
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Making Complex Measurements
Making a Reflection Calibration Measurement
Figure 2-14
Short Circuit Normalized
Measuring the Return Loss
1. After calibrating the system with the above procedure, reconnect the
filter in place of the short circuit without changing any analyzer
settings.
2. Use the marker to read return loss. Press Marker and position the
marker with the knob to read the return loss at that frequency. Or
you can use the Min Search function to measure return loss by
pressing Peak Search, Min Search, the analyzer will place a marker at
the point where the return loss is maximized. See Figure 2-15.
Figure 2-15
Measuring the Return Loss of the Filter
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Chapter 2
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Making a Reflection Calibration Measurement
Converting Return Loss to VSWR
Return loss can be expressed as a voltage standing wave ratio (VSWR)
value using the following table or formula:
Table 2-1
Return
Loss
(dB)
Power to VSWR Conversion
VSWR
Return
Loss
(dB)
VSWR
Return
Loss
(dB)
VSWR
Return
Loss
(dB)
VSWR
Return
Loss
(dB)
VSWR
4.0
4.42
14.0
1.50
18.0
1.29
28.0
1.08
38.0
1.03
6.0
3.01
14.2
1.48
18.5
1.27
28.5
1.08
38.5
1.02
8.0
2.32
14.4
1.47
19.0
1.25
29.0
1.07
39.0
1.02
10.0
1.92
14.6
1.46
19.5
1.24
29.5
1.07
39.5
1.02
10.5
1.85
14.8
1.44
20.0
1.22
30.0
1.07
40.0
1.02
11.0
1.78
15.0
1.43
20.5
1.21
30.5
1.06
40.5
1.02
11.2
1.76
15.2
1.42
21.0
1.20
31.0
1.06
41.0
1.02
11.4
1.74
15.4
1.41
21.5
1.18
31.5
1.05
41.5
1.02
11.6
1.71
15.6
1.40
22.0
1.17
32.0
1.05
42.0
1.02
11.8
1.69
15.8
1.39
22.5
1.16
32.5
1.05
42.5
1.02
12.0
1.67
16.0
1.38
23.0
1.15
33.0
1.05
43.0
1.01
12.2
1.65
16.2
1.37
23.5
1.14
33.5
1.04
43.5
1.01
12.4
1.63
16.4
1.36
24.0
1.13
34.0
1.04
44.0
1.01
12.6
1.61
16.6
1.35
24.5
1.13
34.5
1.04
44.5
1.01
12.8
1.59
16.8
1.34
25.0
1.12
35.0
1.04
45.0
1.01
13.0
1.58
17.0
1.33
25.5
1.11
35.5
1.03
45.5
1.01
13.2
1.56
17.2
1.32
26.0
1.11
36.0
1.03
46.0
1.01
13.4
1.54
17.4
1.31
26.5
1.10
36.5
1.03
46.5
1.01
13.6
1.53
17.6
1.30
27.0
1.09
37.0
1.03
47.0
1.01
13.8
1.51
17.8
1.30
27.5
1.09
37.5
1.03
47.5
1.01
– RL
---------20
1 + 10
VSWR = ----------------------– RL
1 – 10
---------20
Where: RL is the measured return loss value.
VSWR is sometimes stated as a ratio. For example: 1.2:1 “one point two
to one” VSWR. The first number is the VSWR value taken from the
table or calculated using the formula. The second number is always 1.
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Making Complex Measurements
Demodulating and Listening to an AM Signal
Demodulating and Listening to an AM Signal
The functions listed in the menu under Det/Demod allow you to
demodulate and hear signal information displayed on the analyzer.
Simply place a marker on a signal of interest, activate AM
demodulation, turn the speaker on, and then listen.
Demodulating and Listening to an AM Signal
Example 1:
1. Connect an antenna to the analyzer input.
2. Perform a factory preset by pressing Preset, Factory Preset (if
present).
3. Set the Y-Axis Units to dBm by pressing AMPLITUDE, More,
Y-Axis Units, dBm.
4. Select a frequency range on the analyzer, such as the range for AM
radio broadcasts. For example, the frequency range for AM
broadcasts in the United States is 550 kHz to 1650 kHz. Press
FREQUENCY, Start Freq, 550, kHz, Stop Freq, 1650, kHz.
5. Place a marker on the signal of interest. Press Peak Search to place a
marker on the highest amplitude signal, or press Marker, Normal and
move the marker to a signal of interest. See Figure 2-16.
6. Press Det/Demod, Demod, AM. Use the front-panel volume knob to
control the speaker volume.
Figure 2-16
Demodulation of an AM Signal
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Chapter 2
Making Complex Measurements
Demodulating and Listening to an AM Signal
7. The signal is demodulated at the marker position only for the
duration of the demod time. Use the step keys, knob, or numeric
keypad to change the dwell time. For example, press the step up key
(↑) to increase the dwell time to 2 seconds.
8. The marker search functions can be used to move the marker to
other signals of interest. Press Peak Search to access Next Peak,
Next Pk Right, or Next Pk Left.
Demodulating and Listening to an AM Signal
Example 2:
1. Connect an antenna to the analyzer input.
2. Perform a factory preset by pressing Preset, Factory Preset (if
present).
3. Select a frequency range on the analyzer, such as the range for AM
radio broadcasts. For example, the frequency range for AM
broadcasts in the United States is 550 kHz to 1650 kHz. Press
FREQUENCY, Start Freq, 550, kHz, Stop Freq, 1650, kHz.
4. Place a marker on the signal of interest. Press Peak Search to place a
marker on the highest amplitude signal, or press Marker, Normal and
move the marker to a signal of interest.
5. Set the resolution bandwidth to spectrum analyzer by pressing
BW/Avg and Res BW (SA).
6. Set the frequency of the signal to center frequency by pressing
FREQUENCY then Signal Track (On) if the signal of interest is the
highest amplitude on screen signal. If it is not the highest amplitude
signal on screen, move the signal to center screen by pressing
Peak Search, Marker→, and Mkr→CF.
7. If the signal track function is on, press SPAN , 1, MHz to reduce the
span to 1 MHz. If signal track is not used, use the step down key (↓)
to reduce the span and use Mkr→CF to keep the signal of interest at
center screen.
8. Set the span to zero by pressing SPAN, Zero Span. Zero Span turns off
the signal track function.
9. Change the resolution bandwidth to 100 kHz by pressing BW/Avg,
Res BW, then enter 100, kHz.
10.Set the signal in the top two divisions of the screen by changing the
reference level. Press AMPLITUDE, and then the step down key (↓)
until the signal is in the top two divisions. Set the amplitude scale to
linear by pressing Scale Type (Lin). Keep the signal center displayed
by pressing AMPLITUDE, Ref Level and using the (↑) (↓) step keys.
Chapter 2
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Making Complex Measurements
Demodulating and Listening to an AM Signal
11.Press Det/Demod, Detector, Sample to set the detector mode of the
analyzer to Sample.
12.Press Det/Demod, Demod, AM. Use the front panel volume knob to
control the speaker volume.
13.You can turn your analyzer into a % AM indicator as follows:
a. Set trigger to free run by pressing Trig, Free Run.
b. Set the sweep time to 5 seconds by pressing Sweep,
Sweep Time, 5, s.
c. Set the video filter to 30 Hz by pressing BW/Avg, Video BW, 30, Hz.
d. Change the reference level to position the trace at midscreen by
pressing AMPLITUDE, Ref Level, and adjust the reference level
using the front-panel knob.
e. Reset the video filter to a high value. For example, press BW/Avg,
Video BW , 30, kHz.
f. Set the sweep time to 5 milliseconds by pressing Sweep, Sweep
Time, 5, ms.
The center horizontal line of the graticule now represents 0% AM;
the top and bottom lines, 100% AM. See Figure 2-17.
14.The signal to the speaker will be interrupted during retrace because
the analyzer is performing automatic alignment routines. To
eliminate the interruption and clicks between sweeps, turn the auto
alignment function off by pressing System, Alignments, Auto Align,
Off.
NOTE
Refer to the specifications for information about operating the analyzer
with the alignments turned off.
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Chapter 2
Making Complex Measurements
Demodulating and Listening to an AM Signal
Figure 2-17
Continuous Demodulation of an AM Signal
Chapter 2
91
Making Complex Measurements
Demodulating and Listening to an AM Signal
92
Chapter 2
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