HP ESA-L1500A Spectrum Analyzer Measurment Guide

HP ESA-L1500A Spectrum Analyzer Measurment Guide
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Measurement Guide
HP ESA-L1500A Spectrum Analyzer
[email protected]
PACKARD
HP Part No. E4411-90022
Supersedes E4411-90001
Printed in: USA
June 1997
Hewlett-Packard Company 1997 All Rights Reserved. Reproduction, adaptation, or
translation without prior written permission is prohibited, except as allowed under the
copyright laws.
1400 Fountaingrove Parkway, Santa Rosa, CA 95403-1799, USA
Notice
The information contained in this document is subject to change without notice.
Hewlett-Packard 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. Hewlett-Packard 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 Notice
The following safety notes are used throughout this manual.
Familiarize yourself with the notes and their meaning before operating
this instrument.
CAUTION
Caution denotes a hazard. It calls attention to a procedure that, if not
correctly performed or adhered to, would result in damage to or
destruction of the instrument. Do not proceed beyond a caution until
the indicated conditions are fully understood and met.
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.
WARNING
This is a Safety Class 1 Product (provided with a protective
earthing ground incorporated in the power cord). The mains
plug shall only be inserted in a socket outlet provided with a
protective 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.
2
Contents
1. Instrument Overview
FrontPanelFeatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Rear Panel Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Screen Annotation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2. Making Basic Measurements
What’s in This Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Comparing Signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Resolving Signals of Equal Amplitude. . . . . . . . . . . . . . . . . . . . . . . . .
Resolving Small Signals Hidden by Large Signals . . . . . . . . . . . . . . .
Making Better Frequency Measurements . . . . . . . . . . . . . . . . . . . . . .
Decreasing the Frequency Span Around the Signal . . . . . . . . . . . . . .
Tracking Unstable Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Measuring Low Level Signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Identifying Distortion Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Demodulating AM Signals (Using the Analyzer As a Fixed Tuned
Receiver) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
19
23
26
29
31
33
37
44
49
3. Making Measurements
What’s in This Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Making Stimulus Response Measurements. . . . . . . . . . . . . . . . . . . . .
Making a Reflection Calibration Measurement. . . . . . . . . . . . . . . . . .
Demodulating and Listening to an AM Signal. . . . . . . . . . . . . . . . . . .
Measuring Device Bandwidth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Measuring Percent Amplitude Modulation . . . . . . . . . . . . . . . . . . . . .
Measuring Third Order Intermodulation Distortion. . . . . . . . . . . . . .
54
55
62
65
68
70
72
4. Using Instrument Features
What’s in this Chapter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Saving and Loading Files from Analyzer Memory. . . . . . . . . . . . . . . .
Creating Limit Lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Entering Amplitude Correction Factors. . . . . . . . . . . . . . . . . . . . . . . .
76
77
81
92
Index
3
1
Instrument Overview
l
Front Panel
l
Rear Panel
l
Screen Annotation
5
Instrument Overview
Front Panel Features
Front Panel Features
Figure l-l
Front Panel Feature Overview
1
Brightness keys allow you to change the brightness of
the display.
2
Menu keys are the unlabeled keys next to the screen.
The menu key labels are the annotation on the screen
next to the unlabeled keys. Most of the labeled keys on
the spectrum analyzer front panel (also called front
panel keys) access menus of related function keys.
3
Measure accesses a menu of keys that make some
common spectrum analyzer measurements.
4
Frequency, Span, and Amplitude are the three large keys
that activate the primary spectrum analyzer functions
and access menus of related functions.
6
Chapter 1
Instrument Overview
Front Panel Features
5
6
CONTROL functions access menus that allow you to
adjust the resolution bandwidth, adjust the sweep time,
and control the instrument display They also set other
spectrum analyzer parameters needed for making
measurements.
SYSTEM functions affect the state of the entire
spectrum analyzer. Printer setup and alignment
routines are accessed with the System key The green
Preset key resets the spectrum analyzer to a known
state.
The File key menu allows you to save and load traces,
states, limit-line tables and amplitude correction
factors to or from spectrum analyzer memory.
Print sends a copy of the screen data to a printer. Use
the Printer menu keys under System before using the
Print key See the user’s guide for more details.
CAUTION
7
MARKER functions control the markers, read out
frequencies and amplitudes along the spectrum
analyzer trace, automatically locate the signals of
highest amplitude, and keep a signal in the center of
the screen.
8
EARPHONE. The EARPHONE connector (located behind
the door on the right side of the front panel) provides a
connection for an earphone jack instead of using the
internal speaker. The speaker is turned on and off with
the Speaker On Off key in the Det/Demod menu.
9
VOLUME. The VOLUME knob can adjust the volume of
the internal speaker. The speaker is turned on and off
with the Speaker On Off key in the Det/Demod menu.
10
DATA keys, which include the step keys, knob, and
numeric keypad, allow you to change the numeric value
of an active function.
11
EXT KEYBOARD. The EXT KEYBOARD connector is a
6-pin mini-DIN connector that is compatible with most
PC key boards. The external keyboard is not included
with the spectrum analyzer. The external keyboard can
be used to enter screen titles and remote commands.
Turn off the spectrum analyzer before connecting an external keyboard
to the spectrum analyzer.
12
Chapter 1
PROBE POWER provides power for high-impedance ac
probes or other accessories.
7
Instrument Overview
Front Panel Features
CAUTION
13
Est. The Esc (escape) key deactivates the active
function and blanks the active function text from the
display Esc will abort a print (if one is in progress) and
clear error messages from the analyzer display
14
More. The More key accesses other pages of a multi-page
menu. A 1 of 2 type message is displayed just above the
key if there is more than one page.
15
INPUT 50n (INPUT 75~ for Option 1DP) is the signal
input for the spectrum analyzer.
16
RF OUT 50a (for Option 1DN) or RF OUT 75~ (for Option
If the tracking generator output power is too high, it may damage the
device under test. Do not exceed the maximum power that the device
under test can tolerate.
17
NOTE
1DQ) is the source output for the built-in tracking
generator. Option 1DN or 1DQ only
The I (On) key turns the analyzer on, while the 0
(Standby) key turns most of the analyzer off An
instrument alignment is performed every time the
analyzer is turned on. After applying power, allow 5
minutes of warm-up time to ensure the analyzer will
meet all specifications.
The instrument continues to draw power when it is plugged into the ac
power source even if the line power switch is in standby
Data Controls
Data controls are used to change values for functions such as center
frequency, start frequency, resolution bandwidth, and marker position.
The data controls will change the active function in a manner
prescribed by that function. For example, you can change center
frequency in fine steps with the knob, in discrete steps with the step
keys, or to an exact value with the numeric keypad. Resolution
bandwidth, however, which can be set to discrete values in a 1,3, 10
sequence only, is changed to the closest allowed value with any of the
data controls.
Knob
The knob allows continuous change of functions such as center
frequency, reference level, and marker position. It also changes the
values of many functions that change in increments only Clockwise
rotation of the knob increases values. For continuous changes, the
8
Chapter 1
Instrument Overview
Front Panel Features
extent of alteration is determined by the size of the measurement
range; the speed at which the knob is turned affects the rate at which
the values are changed.
The knob enables you to change the center frequency, start or stop
frequency, or reference level. In slow sweep times, the analyzer uses a
smooth scrolling feature which is designed to move the trace display to
the latest function value as the knob is turned. When either center
frequency or reference level is adjusted, the signal will shift right or left
or up or down with the rotation of the knob before a new sweep is
actually taken. An asterisk is placed in the message block (the upper
right hand corner of the spectrum analyzer display) to indicate that the
data on-screen does not reflect data at the current setting.
Numeric Keypad
The numeric keypad allows entry of exact values for many of the
spectrum analyzer functions. You may include a decimal point in the
number portion. If not, the decimal point is placed at the end of the
number.
Numeric entries must be terminated with a units key. The units keys
change depending on what the active function is. They are labeled on
the right edge of the display For example, the units keys for frequency
span are GHr, MHz, kHz, and Hz, whereas the units for reference level
are +dBm, -dBm, mV, and pV.
NOTE
If an entry from the numeric keypad does not coincide with an allowed
function value (for example, that of a 12 MHz bandwidth), the spectrum
analyzer defaults to the nearest allowable value.
Step Keys
The step keys allow discrete increases or decreases of the active
function value. The step size depends upon the spectrum analyzer
measurement range or on a preset amount. Each press results in a
single step change. For those parameters with fixed values, the next
value in a sequence is selected each time a step key is pressed. Changes
are predictable and can be set for some functions. Out-of-range values
or out-of-sequence values will not occur using these keys.
Chapter 1
9
Instrument Overview
Rear Panel Features
Rear Panel Features
Figure 1-2
Rear Panel Feature Overview
CC 0
0
8.
A
,_
\
I;
i _..........._i 0
bn7lOa
Power input is the input for the line power source.
Make sure that the line power source outlet has a
protective ground contact.
Line Fuse. The fuse is removed by twisting l/4 turn.
Replace only with a fuse of the same rating. See the
label on the rear panel.
Standard Inputs/Outputs
3a
10
VGA OUTPUT drives an external VGA
compatible monitor with a signal that
has 31.5 kHz horizontal, 60 Hz vertical
synchronizing rate, non-interlaced.
Chapter 1
Instrument Overview
Rear Panel Features
4
3b
EXT TRIG IN (TTL) accepts the positive
edge of an external voltage input that
triggers the spectrum analyzer internal
sweep source.
3c
HI SWP OUT (TTL) indicates when the
spectrum analyzer is sweeping.
(Shown) HP-IB and parallel (Option A4H) are optional
interfaces. HP-IB supports remote instrument
operation and direct printing of screen data. The
parallel port is for printing only
(Not Shown) RS-232 and parallel (Option 1AX) are
optional interfaces. RS-232 supports remote instrument
operation and direct printing of screen data. The
parallel port is for printing only
Only one optional interface can be installed at a time.
Option 1AX or Option A4H must be installed in slot 1
on the rear panel. Option A4H is shown installed in slot
1 in the figure.
5
Spectrum Analyzer Inputs/outputs (Option A4J):
SWP OUT provides a voltage ramp corresponding to the
sweep of the spectrum analyzer (0 V to 10 V).
HI SWP OUT (TTL) indicates when the spectrum analyzer
is sweeping.
HI SWP IN (TTL) can be grounded to stop sweeping.
AUX VIDEO OUT provides detected video output (before
the analog to digital conversion) proportional to vertical
deflection of the trace. Output is from 0 V to 1 V.
Amplitude correction factors are not applied to this
signal. The output signal will be blanked occasionally
during retrace by the automatic alignment routine.
Select a very long sweep time to minimize this, or turn
off the Auto Align All function (and use Align Now All
manually to maintain calibration.) Refer to the user’s
guide for more information on alignment key functions.
AUX IF OUT is a 5OQ 21.4 MHz IF output that is the
down-converted signal of the RF input of the spectrum
analyzer. Amplitude-correction factors are not applied
to this signal. This output is taken after the resolution
bandwidth filters and step gains and before the log
amplifier. The output signal will be blanked
occasionally during retrace by the automatic alignment
routine. Select a very long sweep time to minimize this,
or turn off the Auto Align All function (and use Align
Chapter 1
11
Instrument Overview
Rear Panel Features
Now All manually to maintain calibration.) Refer to the
user’s guide for more information on alignment key
functions.
10 MHz REF IN accepts an external frequency source to
provide the 10 MHz, -15 to +lO dBm frequency
reference used by the spectrum analyzer.
10 MHz FIEF OUT provides a 10 MHz, 0 dBm minimum,
timebase reference signal.
Service Connector. The service connector is for service
use only
Power On Selection selects a preference for when
power is applied to the analyzer’s rear panel power
connector. The analyzer can be set to be always off or
always on when power is connected. This is useful when
the analyzer is used at an unattended location to
ensure that the analyzer powers on after a power
outage.
9
DC Fuse. Protects against too much power to the DC
10
DC Power is the input for the DC power source. Refer
12
power connector on the rear panel of the spectrum
analyzer.
to “Power Requirements” in the specifications chapter
of the user’s guide.
Chapter 1
Instrument Overview
Screen Annotation
Screen Annotation
Here is an example of the annotation that may appear on a spectrum
analyzer screen. The screen annotation is referenced by numbers which
are listed in the following table. The Function Key column indicates
which key activates the function related to the screen annotation. Refer
to the user’s guide for more information on a specific function key.
Figure 1-3
Screen Annotation
2
’ -12.0
01
,dBm
f+a
,100
WA SB
..- _....__ -..
flu&
0
14
CF Step
Man
Freq Offset
t
soan 70.00 MHz -
n1744a
Chapter 1
13
Instrument Overview
Screen Annotation
Screen Annotation
External keyboard entry
Refer to the external keyboard
ation in the Measurement
Auto alignment routine is
14
Chapter 1
Instrument Overview
Screen Annotation
Item 24 refers to the trigger and sweep modes of the spectrum analyzer.
The first letter (“F”) indicates the spectrum analyzer is in free run
trigger mode. The second letter (“(3”) indicates the spectrum analyzer is
in continuous sweep mode.
Item 25 refers to the trace modes of the spectrum analyzer. ‘I’he first
letter (“W”) indicates that the spectrum analyzer is in clear-write mode.
The second letter is “A,” representing trace A. The trace B trace mode is
“SB”, indicating trace B (“B”) is in the store-blank mode (“S”). The trace
mode annotation for trace C is displayed under the trace mode
annotation of trace A. The trace C trace mode is “SC”, indicating trace C
(“C”) is in the store blank mode (‘73”).
Refer to the following table for the screen annotation codes for trace,
trigger, and sweep modes.
Table l-l
Screen Annotation for Trace, Trigger, and Sweep Modes
Trace Mode
Trigger Mode
Sweep Mode
W clear write (traces A/B/C)
F free run
C continuous
M maximum hold (traces A/B)
L line
S single sweep
V view (traces A/B/C)
V video
S store blank (traces A/B/C)
E external
M minimum hold (trace C)
Chapter 1
15
2
Making Basic Measurements
17
Making Basic Measurements
What’s in This Chapter
What’s in This Chapter
This chapter demonstrates basic spectrum analyzer measurements
with examples of typical measurements; each measurement focuses on
different functions. The measurement procedures covered in this
chapter are listed below.
l
“Comparing Signals” on page 19
l
“Resolving Signals of Equal Amplitude” on page 23
l
“Resolving Small Signals Hidden by Large Signals” on page 26
l
“Making Better Frequency Measurements” on page 29
l
“Decreasing the Frequency Span Around the Signal” on page 31
l
“Tracking Unstable Signals” on page 33
l
“Measuring Low Level Signals” on page 37
l
“Identifying Distortion F’roducts” on page 44
l
“Demodulating AM Signals (Using the Analyzer As a Fixed Tuned
Receiver)” on page 49
To find descriptions of specific spectrum analyzer functions, refer to the
user’s guide.
18
Chapter 2
Making Basic Measurements
Comparing Signals
Comparing Signals
Using the spectrum analyzer, you can easily compare frequency and
amplitude differences between signals, such as radio or television
signal spectra. The spectrum 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.
Example 1:
Measure the differences between two signals on the same display
screen.
1. Use the spectrum analyzer’s internal 50 MHz alignment signal as
the signal being measured. Press Preset, System, 50 MHz osc On Off
(On). Set the center frequency to 75 MHz and the span to 200 MHz:
press Frequency, 75 MHz, Span, 200 MHz.
The alignment signal and its harmonics appear on the display
2. Press 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 50 MHz
alignment signal. See Figure 2-l.
The signal that appears to the left of the 50 MHz signal, is the
spectrum analyzer local oscillator (LO) and represents 0 Hz.
Chapter 2
19
Making Basic Measurements
Comparing Signals
Figure 2-1
Placing a Marker on the 50 MHz Signal
ua 06:01:20 AUG 05, 2012
Ref 107.0 dBuU
Atten 10 dB
I
Mkr 50.0 MHz
80.17 dBuV
WA SB
SC FC
RA
Center 75.0 MHz
Res BW 1.0 MHz
VBW 300 kHz
SDan 200.0 MHz
Swkep 5.00 msec
3. Press Marker, Marker A, to activate a second marker at the position of
the first marker. Move the second marker to another signal peak
using the knob, or by pressing Search and Next Pk Right or Next Pk
Left.
4. The amplitude and frequency difference between the markers is
displayed in the active function block and in the upper left corner of
the screen. See Figure 2-2. The resolution of the marker readings
can be increased by turning on the frequency count function. Press
Freq Count.
Press Marker, Marker All Off to turn the markers off.
20
Chapter 2
Making Basic Measurements
Comparing Signals
Figure 2-2
Using the Marker Delta Function
Ea 06:03:09
RUG 05, 2012
Ref 107.0 dBuU
Peak
Mkrb 50.0 ME
-24.6? 43
Rtten 10 dB
kg
dB/
WA SB
SC FC
AA
I
I
Center 75.0 MHz
Res BW 1.0 MHz
I
I
I
VBW 300 kHz
I
I
I
I
I
I
Span 200.0 MHz
Sweep 5.00 msec
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. Turn on the spectrum analyzer’s internal 50 MHz alignment signal
(if you have not al ready done so). Press Preset, System, 50 MHz osc
On Off (On). Then press Frequency, 50 MHz, Span and the step down
key (4) to narrow the frequency span until only one signal appears
on the screen.
2. Press Peak Search to place a marker on the peak.
3. Press Marker, Marker A to anchor the position of the first marker and
activate a second marker.
4. Press Frequency, CF Step Auto Man (Man) to activate the center
frequency step size function, and enter 50 MHz. Press Center Freq
and the (?) key to increase the center frequency by 50 MHz. The first
marker remains on the screen at the amplitude of the first signal
peak.
Chapter 2
21
Making Basic Measurements
Comparing Signals
NOTE
Changing the reference level changes the marker delta amplitude
readout.
The annotation in the upper right corner of the screen indicates the
amplitude and frequency difference between the two markers. See
Figure 2-3.
5. To turn the markers off, press Marker, Marker All Off.
Figure 2-3
Frequency and Amplitude Difference Between Signals
@a 06:06:10 AUG 05, 2012
Ref 107.0 dBuV
Peak
Atten 10 dB
Mkrd. 50.00 MHz
-25.63 dB
kg
dB/
WFI SB
SC FC
RA
Center 100.00 MHz
Res BW 300 kHz
22
VBW 100 kHz
Span 50.00 MHz
Swkep 5.00 msec
Chapter 2
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 one on the spectrum analyzer display Responding to a single.
frequency signal, a swept-tuned spectrum analyzer traces out the shape
of its internal IF (intermediate frequency) filters. As we change the
filter bandwidth, we 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 appear as one. Thus, signal
resolution is determined by the IF filters inside the spectrum 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 (Res BW) function selects an IF filter setting for a
measurement. Resolution bandwidth is defined as the 3 dB 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, 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 2-5.
In order to keep the spectrum analyzer measurement calibrated, sweep
time is automatically set to a value that is inversely proportional to the
square of the resolution bandwidth. 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
proportional to l/BW2.) For fastest measurement times, use the widest
resolution bandwidth that still permits discrimination of all desired
signals. The spectrum analyzer allows you to select from 1 kHz to
3 MHz resolution bandwidths in a 1,3, 10 sequence for maximum
measurement flexibility.
Example:
Resolve two signals of equal amplitude with a frequency separation of
100 kHz.
1. Connect two sources to the spectrum analyzer input as shown in
Figure 2-4.
Chapter 2
23
Making Basic Measurements
Resolving Signals of Equal Amplitude
Figure 2-4
Setup for Obtaining Two Signals
bn71 a
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.
3. On the spectrum analyzer, press Preset. Set the center frequency to
300 MHz, the span to 2 MHz, and the resolution bandwidth to 300
kHz by pressing Frequency 300 MHz, Span 2 MHz, then BW/Avg
300 kHz. A single signal peak is visible.
NOTE
If the signal peak cannot be found, increase the span to 20 MHz by
pressing Span 20 MHz. The signal should be visible. Press Peak Search,
Frequency, Signal Track On Off (On is underlined), then Span 2 MHz to
bring the signal to center screen. Then press Signal Track On Off so that
Off is underlined to turn the signal track function off.
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 100 kHz. Two signals are now visible as shown
in Figure 2-5. Use the knob or step keys to further reduce the
resolution bandwidth and better resolve the signals.
24
Chapter2
Making Basic Measurements
Resolving Signals of Equal Amplitude
Figure 2-5
Resolving Signals of Equal Amplitude
pa 06:43:47 RUG 24, 2012
Ref .0 dBm
0
Rtten 10 dB
WA SB
SC FC
FIR
"IV'WWJ
I
I
Center 300.000 MHz
NRes BW100 kHz
I
VBW 30 kHz
Span 2.000 MHz
Sweep 5.00 msec
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 preset conditions, the resolution bandwidth is “coupled” (or
linked) to the span.
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. (Also see
the Auto Couple key description in the 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 2
25
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 spectrum
analyzer’s IF filter as well as its 3 dB bandwidth. (See “Resolving
Signals of Equal Amplitude” on page 23 example for more information.)
The shape of a filter is defined by the shape factor, which is the ratio of
the 60 dB bandwidth to the 3 dB bandwidth. (Generally, the IF filters in
this spectrum analyzer have shape factors of 15:l or less.) 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 band width such that k is less than a. See Figure 2-6.
Figure 2-6
Resolution Bandwidth Requirements for Resolving Small
Signals
.
-a+
7
.
kif
k
< a
The separation between the two signals (a) must be greater than half
the filter width of the larger signal at the amplitude level of the smaller
signal (k).
Example:
Resolve two input signals with a frequency separation of 200 kHz and
an amplitude separation of 60 dB.
1. To obtain two signals with a 200 kHz separation, connect the
equipment as shown in the previous section, “Resolving Signals of
Equal Amplitude” on page 23. Set one source to 300 MHz at
-20 dBm.
2. Set the analyzer center frequency to 300 MHz and the span to
2 MHz: press Frequency, 300 MHz, then Span 2 MHz.
26
Chapter 2
Making Basic Measurements
Resolving Small Signals Hidden by Large Signals
NOTE
If the signal peak cannot be found, increase the span to 20 MHz by
pressing Span, 20 MHz. The signal should be visible. Press Peak Search,
Frequency, Signal Track On Off so that On is underlined, then Span,
2 MHz to bring the signal to center screen. Then press Signal Track On
Off to Off to turn the signal track function off
3. Set the second source to 300.2 MHz, so that the signal is 200 kHz
higher than the first signal. Set the amplitude of the signal to
-80 dBm (60 dB below the first signal).
4. Set the 300 MHz signal to the reference level by pressing Peak
Search, Search, then Mkr -> RL.
If a 10 kHz filter with a typical shape factor of 15:l is used, the filter
will have a band width 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 2-7.
Figure 2-7
Signal Resolution with a 10 kHz Resolution Bandwidth
@a 06:52:25 RUG 24, 2012
011
Atten 10 dB
Ref .0 dBm
Peak -
1
Res BW
Ctltlz
WFI SB
SC FC
AA
I
I
I
Center 300.000 MHz
xRes BW 10 kHz
I
I
VBW 10 kHz
I
I
I
I
I
I
Span 2.000 MHz
Sweep 60.0 msec
If 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 2-8. (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.)
Chapter 2
27
Making Basic Measurements
Resolving Small Signals Hidden by Large Signals
Figure 2-8
Signal Resolution with a 30 kHz Resolution Bandwidth
&)a 06:53:44 FIIIC 76 7617
Ref .0 dBm
Peak m
kg
dB/
I
Atten 10 dB
I
I
I
I
I
I
WA SB
SC FC
Afl
I
Center 300.000 MHz
NRes BW 30 kHz
28
I
I
UBW 30 kHz
I
I
I
I
I
1
Span 2.000 MHz
Sweep 10.0 msec
Chapter 2
Making Basic Measurements
Making Better Frequency Measurements
Making Better Frequency Measurements
The 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 O.OOZ>, the
Marker Count Widen Res BW message appears on the display It
indicates that the resolution bandwidth is too narrow.
Example:
Increase the resolution and accuracy of the frequency readout on the
signal of interest.
1. This example uses the internal 50 MHz alignment signal. Turn it on
by pressing System, 50 MHz osc On Off and place a marker on the
signal.
2. Set the center frequency to 50 MHz and the span to 80 MHz.
3. Press Freq Count. (Notice that Marker Count On Off has On
underlined turning the frequency counter on.) The frequency and
amplitude of the marker and the word Counter will appear in the
active function area.
4. Increase the counter resolution by pressing Resolution Auto Man and
then entering the desired resolution using the step keys or the
numbers keypad. For example, press 1 kHz. The marker counter
readout is in the upper-right corner of the screen. The resolution can
be set from 1 Hz to 100 kHz.
5. The marker counter remains on until turned off. Turn off the marker
counter by pressing Freq Count, then Marker Count On Off (until Off is
underlined). (Marker All Off also turns the marker counter off.)
Chapter 2
29
Making Basic Measurements
Making Better Frequency Measurements
Figure 2-9
Using the Marker Counter
Ew
Ref .0 dBm
Peak
Log
0
Atten 10 dB
Cntr 49.9999 MHz
-26.61dBm
i!/
wfl SI
SC FI
Al
Center 50.00 MHz
Res BW 1.0 MHz
30
UBW 300 kHz
SDan 80.00
Span
80.00 MHz
Sweep
Swkep 30.0
30.0 msec
Chapter 2
Making Basic Measurements
Decreasing the Frequency Span Around the Signal
Decreasing the Frequency Span Around the
Signal
Using the spectrum 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.
Example:
Examine a signal in a 200 kHz span.
1. Press Preset and use the internal signal as the test signal. To turn it
on, press System, 50 MHz osc On Off.
2. Press Peak Search to place a marker at the peak.
3. Press Frequency, Signal Track On Off (On) and the signal will move to
the center of the screen, if it is not already positioned there. (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.
4. Press Span, 200 kHz. The span decreases in steps as automatic zoom
is completed. See Figure 2-10. You can also use the knob or step keys
to decrease the span or use the Span Zoom function under Span.
Press Signal Track On Off again (so that Off is underlined) to turn off the
signal track function.
Chapter 2
31
Making Basic Measurements
Decreasing the Frequency Span Around the Signal
NOTE
When you are finished with the example, turn off the signal tracking
function.
Figure 2-10
After.Zooming In on the Signal
&a 07:10:32 RUG 05, 2012
Ref 107.0 dBuV
P e a k
WA SB
SC FC
AA
1
I
I
I
Center 50.0005 MHz
Res BW 3.0 kHz
32
Sig-Trk 50.0005 MHz
80.19 dBuV
Fltten 10 dB
I
I
UBW 3 kHz
\
\..
I
I
I
I
Span 200.0 kHz
Sweep 100 msec
Chapter2
Making Basic Measurements
Tracking Unstable Signals
Tracking Unstable Signals
The signal track function is useful for tracking unstable signals that
drift with time. The maximum hold function is useful for displaying
modulated signals which appear unstable, but have an envelope that
contains the information bearing portion of the signal.
Signal Track On Off may be used to track these unstable signals. Use
Peak Search to place a marker on the highest signal on the display
Pressing Frequency, Signal Track On Off (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. (Span Zoom, in the
Span menu, is a quick way to perform the Peak Search, Frequency, Signal
Track On Off, Span key sequence.)
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
spectrum 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.
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 modulated signal. An acceptable signal can be
easily found by connecting an antenna to the spectrum analyzer input
and tuning to the FM broadcast band (88 to 108 MHz). Set the
spectrum analyzer center frequency to one of the signals, the span to
20 MHz, the attenuator setting to 0 dB, and the reference level setting
to approximately -30 dBm. Your circumstances may be slightly
different, depending on building shielding and proximity to
transmitters.
1. Connect an antenna to the spectrum analyzer input.
2. Press Preset, Marker and move the marker to the peak of one of your
local FM broad cast signals. Set the span to 20 MHz.
NOTE
Use a different FM signal source if no FM broadcast signals are
available in your area.
3. Press Amplitude, 30 -dBm, Attenuation Auto Man (Man), 0 +dBm.
4. Press Marker, Marker A, to fix a marker on the signal peak.
5. Press Span, Span Zoom, 500 kHz.
Notice that the signal has been held in the center of the display.
Chapter 2
33
Making Basic Measurements
Tracking Unstable Signals
NOTE
If the signal you selected drifts too quickly for the spectrum analyzer to
keep up with, use a wider span.
6. The signal frequency drift can be read from the screen if both the
signal track and mark er delta functions are active. Press Frequency,
Signal Track On Off (On). The marker readout indicates the change in
frequency and amplitude as the signal drifts. See Figure 2-11.
Figure 2-11
Using Signal Tracking to Track an Unstable Signal
@a 07:36:19 AUG 05, 2012
R e f-30.0 dBm
Peak
aRtten 0 dB
II
Sig a-Trk -17.5 kHz
-1.49 dB
kg
dB/
Center 100.0963 MHz
Res BW 10 kHz
UBWlQ kHz
Span 500.0 kHz
Sweep 30.0 msec
The spectrum 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 an FM
signal occupies.
Example 2:
Using the maximum-hold functions, monitor the envelopes of an FM
modulated signal.
1. Connect an antenna to the spectrum analyzer input to display the
FM broadcast band 88 to 108 MHz.
2. Press Preset, Frequency, (enter your local FM broadcast signal
frequency), and Span, 20 MHz.
34
Chapter 2
Making Basic Measurements
Tracking Unstable Signals
3. Press Amplitude, 30 -dBm, Attenuation Auto Man, (Man), 0 +dBm,
Span, Span Zoom, 500 kHz.
4. Turn off the signal track function by pressing Frequency, Signal Track
On Off (Off).
5. To measure the excursion of the signal, press Trace then Max Hold A.
As the signal varies, maximum hold maintains the maximum
responses of the input signal, as shown in Figure 2-12.
Figure 2-12
Viewing an Unstable Signal Using Max Hold A
ma 07:42:13 AUG 05, 2012
Ref -30.0 dBm
Peak
II
Mkr100.1225 MHz
-31.90 dBm
Atten 0 dB
kg
dB/
Mi=i SB
SC FC
Afl
I
I
I
Center100.1188 MHz
Res BW1O kHz
I
I
UBW 10 kHz
I
I
I
I
I
I
Span 500.0 kHz
Sweep 30.0 msec
Annotation on the left side of the screen indicates the trace mode.
For example, MA SB SC indicates trace A is in maximum-hold mode,
trace B and trace C are in store- blank mode. See “Screen
Annotation” in Chapter 1.
6. Press Trace, Trace A B C, to select trace B. (Trace B is selected when B
is underlined.) Press Clear Write B to place trace B in clear-write
mode, which displays the current measurement results as it sweeps.
Trace A remains in maximum hold mode, showing the frequency
shift of the signal.
Chapter 2
35
Making Basic Measurements
Tracking Unstable Signals
Figure 2-13
Viewing an Unstable Signal With Max Hold and Clear Write
Ref -30.0 dBm
Peak 1
I
Atten 0 dB
Mkr 100.0912 MHz
-32.16 dBm
I
I
MA WB
MC FS
Afl
Center 100.0962 MHz
Res BW 10 kHz
36
UBW 10 kHz
Span 500.0 kHz
Sweep 30.0 msec
Chapter 2
Making Basic Measurements
Measuring Low Level Signals
Measuring Low Level Signals
The spectrum analyzer’s ability to measure low level signals is limited
by the noise generated inside the spectrum 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 spectrum 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.
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 spectrum analyzer.
CAUTION
The total power of all input signals at the spectrum analyzer input
must not exceed the maximum power level for the spectrum analyzer.
1. Connect an antenna to the spectrum analyzer input. Press Preset.
2. Reduce the frequency range to locate a low level signal of interest.
Narrow the frequency span to a range of 88 MHz to 108 MHz, the
FM broadcast range. Press Frequency, Start Freq, 88 MHz, Stop Freq,
108 MHz.
3. Place a marker on the low level signal of interest. Press Marker and
use the knob to position the marker at the signal’s peak.
4. Place the signal at center frequency by pressing Search, then Marker
-> CF.
5. Reduce the span to 10 MHz. Press Span, and then use the step-down
key (J). See Figure 2-14.
Chapter 2
37
Making Basic Measurements
Measuring Low Level Signals
Figure 2-14
Low-Level Signal
r#J
Ref .0 dBm
Peak
Log L
0
fltten 10 dB
Mkr 96.50 ME
-64.38 dBm
2,
WA SB
SC FC
RA
Center 96.50 MHz
Res BW 100 kHz
VBW 30 kHz
SDan 10.00 MHz
Swkep 10.0 msei
6. Press Amplitude, Attenuation Auto Man. Press the step-up key (‘l’)
twice 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
spectrum analyzer settings.
7. To see the signal more clearly, enter 0 dB. Zero attenuation makes
the signal more visible. Note that the reference level changed to
-10 dBm, the highest level allowed with 0 dB attenuation. See
Figure 2-15.
Before connecting other signals to the spectrum analyzer input,
increase the RF attenuation to protect the spectrum analyzer input:
press Attenuation Auto Man so that Auto is underlined or press Auto
Couple.
38
Chapter 2
Making Basic Measurements
Measuring Low Level Signals
Figure 2-15
Using 0 dB Attenuation
ma
I¶
Ref -10.0 dBm
Peak
*Atten 0 dB
Mkr 96.50 MHz
-64.32 dBm
kg
dB/
WA SB
SC FC
AA
ti
Center 96.50 MHz
Res BW1OO kHz
I I I I I I I
VBW 30 kHz
I
Soan 10.00 MHz
Swkep 10.0 msec
Example 2:
The resolution bandwidth can be decreased to view low level signals.
1. As in the previous example, connect an antenna to the spectrum
analyzer input. Set the spectrum analyzer to view a low level signal.
2. Press BW/Avg, then 1. The low level signal appears more clearly
because the noise level is reduced. See Figure 2-16.
Chapter 2
39
Making Basic Measurements
Measuring Low Level Signals
Figure 2-16
Decreasing Resolution Bandwidth
Ed
Ref .0 dBm
Peak I
I
Log
Atten 10 dB
I
I
I
Mkr 96.50 MHz
-71.39
-.-_ dF
- 3m
2,
WA SB
SC FS
AA
Center 96.50 MHz
*Res BW 3.0 kHz
VBW 3 kHz
Span 10.00 MHz
Sweep 3.33 set
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.
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 spectrum 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 spectrum analyzer
calibrated.)
Using the video bandwidth function, measure the amplitude of a low
level signal.
1. As in the first example, connect an antenna to the spectrum analyzer
input. Set the spectrum analyzer to view a low level signal.
2. Narrow the video bandwidth by pressing BW/Avg, Video BW Auto
Man, and the step-down key (L). This clarifies the signal by
smoothing the noise, which allows better measurement of the signal
amplitude.
40
Chapter 2
Making Basic Measurements
Measuring Low Level Signals
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 2-17.
Instrument preset conditions couple the video bandwidth to the
resolution bandwidth so that the video bandwidth is equal to, or
narrower than, the resolution bandwidth. If the bandwidths are
uncoupled when video bandwidth is the active function, pressing
Video BW Auto Man (so that Auto is underlined) recouples the
bandwidths.
NOTE
The video bandwidth must be set wider than the resolution bandwidth
when measuring impulse noise levels.
Figure 2-17
Decreasing Video Bandwidth
r!%a
Ref .Q dBm
Peak
Atten 10 dB
Mkr 96.50 MHz
-64.66 dBm
kg
dB/
Wfi SB
SC FS
AA
Center 96.50 MHz
Res BW 100 kHz
xVBW100 Hz
Span 10.00 MHz
Sweep 3.00 set
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.
Chapter 2
41
Making Basic Measurements
Measuring Low Level Signals
Video averaging is a digital process in which each trace point is
averaged with the previous trace-point average. Selecting video
averaging 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 spectrum analyzer takes
sweeps, you can watch video averaging smooth the trace.
1. Position a low-level signal on the spectrum analyzer screen.
2. Press BW/Avg, then Video Average On Off. When On is underlined,
the video averaging routine is initiated. As the averaging routine
smooths the trace, low level signals be come more visible. Vid Avg
100 appears in the active function block. The number represents the
number of samples (or sweeps) taken to complete the averaging
routine.
3. To set the number of samples, use the numbers keypad. For example,
press Video Average On Off (so that On is underlined), 25 Enter. Turn
video averaging off and on again by pressing Video Average On Off
(Oft), Video Average On Off (On). The number of samples equals the
number of sweeps in the averaging routine.
During averaging, the current sample number appears at the left
side of the graticule. Changes in active functions 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.
Once the set number of sweeps has been completed, the spectrum
analyzer continues to provide a running average based on this set
number.
42
Chapter 2
Making Basic Measurements
Measuring Low Level Signals
Figure 2-18
Using the Video Averaging Function
CF..
Ref .0 dBm
Smpl
Log
0
Atten 10 dB
Mkr 96.50 MHz
Ai/
UBW 30 kHz
Chapter 2
Span 10.00 MHz
SweeplO.O msec
43
Making Basic Measurements
Identifying Distortion Products
Identifying Distortion Products
Distortion from the Analyzer
High level input signals may cause spectrum analyzer distortion
products that could mask the real distortion measured on the input
signal. Using trace B and the RF attenuator, you can determine which
signals, if any, are internally generated distortion products.
Example:
Using a signal from a signal generator, determine whether the
harmonic distortion products are generated by the spectrum analyzer.
1. Connect a signal generator to the spectrum analyzer INPUT. Set the
signal generator frequency to 200 MHz and the amplitude to 0 dBm.
Set the center frequency of the spectrum analyzer to 400 MHz and
the span to 500 MHz: press Frequency, 400 MHz, Span 500 MHz. The
signal shown in Figure 2-19 produces harmonic distortion products
in the spectrum analyzer input mixer.
Figure 2-19
Harmonic Distortion
@a 07:13:17 AUG 24, 2012
Ref .0 dBm
:ten 10 dB
;E:k ,+
WFI SB
SC FC
RR
Center 400.0 MHz
Res BW 3.0 MHz
VBWl MHz
Soan 500.0 MHz
Swkep 5.00 msec
2. Change the center frequency to the value of one of the observed
harmonics.
44
Chapter 2
Making Basic Measurements
Identifying Distortion Products
3. Change the span to 200 MHz: press Span, 200 MHz.
4. Change the attenuation to 0 dB: press Amplitude, Attenuation Auto
Man, 0 dBm.
5. To determine whether the harmonic distortion products are
generated by the spectrum analyzer, first save the screen data in
trace B.
Press Trace, Trace A B C (until trace B is underlined), then Clear Write
B. Allow the trace to update (two sweeps) and press View B, Peak
Search, Marker, Marker A. The spectrum analyzer display shows the
stored data in trace B and the measured data in trace A.
6. Next, increase the RF attenuation by 10 dB: press Amplitude,
Attenuation Auto Man, and the step-up key (?) twice. See
Figure 2-20.
Figure 2-20
RF Attenuation of 10 dB
@a 07:26:51 RUG 24, 2012
Ref -10.0 dBm
Peak
13
Mkrb 0 Hz
-20.24 dB
*Atten 20 dB
kg
dB/
I
*
WFI VB
SC FC
Afl
I
I
I
Center 600.0 MHz
Res BW 1.0 MHz
I
I
UBW 300 kHz
I
I
I
I
Span 200.0 MHz
Sweep 5.00 msec
7. Compare the response in trace A to the response in trace B. If the
distortion product de creases as the attenuation increases, then it is
caused by the spectrum analyzer.
The change in the distortion product is shown by the marker A
value. The high level input signals that are overloading the input
and causing the internal distortion, must be attenuated.
If the responses in trace A and trace B differ, as in Figure 2-20, then
attenuation is required. If there is no change in the signal level, the
distortion is not caused internally For example, the signal that is
Chapter 2
45
Making Basic Measurements
Identifying Distortion Products
causing the distortion shown in Figure 2-21 is not high enough in
amplitude to cause internal distortion in the spectrum analyzer so any
distortion that is displayed is present on the input signal.
Figure 2-21
No Harmonic Distortion
@.a
24, 2012
@a 07:30:40
07:30:40 AUG 24,
2012
Ref -10.0 dBm
Peak
Log
*Atten 0 dB
0
Mkra 0 Hz
-.S4 dB
Ai/
WA VB
SC FC
AR
Center 600.0 MHz
Res BW 1.0 MHz
VBW 300 kHz
Span 200.0 MHz
Sweep 5.00
Sweep
5.00 msec
Third-Order Intermodulation Distortion
Two-tone, third-order intermodulation distortion is a common problem
in communication systems. When two signals are present in a system,
they can mix with the second harmonics generated and create
third-order inter-modulation distortion products, that are located close
to the original signals. These distortion products are generated by
system components such as amplifiers and mixers.
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 2-22.
46
Chapter 2
Making Basic Measurements
Identifying Distortion Products
Figure 2-22
Third-Order Intermodulation Equipment Setup
I
LOWPASS
FILTER
MIXER
Input
I
I
J
LOWPASS
FILTER
bn72a
2. Set one source to 300 MHz and the other source to 301 MHz, for a
frequency separation of 1 MHz. Set the sources equal in amplitude
(in this example, they are set to -5 dBm).
3. Tune both signals onto the screen by setting the center frequency
between 300 and 301 MHz. Then, using the knob, center the two
signals on the display Reduce the frequency span to 5 MHz. This
should be wide enough to include the distortion products on the
screen. To be sure the distortion products are resolved, reduce the
resolution bandwidth until the distortion products are visible.
4. For best dynamic range, set the mixer input level to -40 dBm and
move the signal to the reference level: press Amplitude, More, Max
Mixer Lvl, 40 -dBm.
The spectrum analyzer automatically sets the attenuation so that a
signal at the reference level will be a maximum of -40 dBm at the
input mixer. Press BW/Avg, Resolution BW, and then use the
step-down key (J) to reduce the resolution bandwidth until the
distortion products are visible.
5. To measure a distortion product, press Marker to place a marker on a
source signal. To activate the second marker, press Marker A. Using
the knob, adjust the second marker to the peak of the distortion
product that is beside the test signal. The difference between the
markers is displayed in the active function block.
Chapter 2
47
Making Basic Measurements
Identifying Distortion Products
To measure the other distortion product, press Search, Next Peak.
This places a marker on the next highest peak, which, in this case, is
the other source signal. To measure the difference between this test
signal and the second distortion product, press Marker A and use the
knob to adjust the second marker to the peak of the second distortion
product. See Figure 2-23.
Figure 2-23
Measuring the Distortion Product
1I
Mkra 1.000 MH;
-65.29 d:
mfl 07:39:00 RUG 24, 2012
Rtten 10 dB
Ref .0 dBm
Peak
Log I
I
i
I
2,
WA SB
SC FC
AA
1
ri
+A w&&
Center 300.000 MHz
SRes BW 3.0 kHz
48
UBW 3 kHz
I
I
I
Span 5.000 MHz
Sweep 1.67 set
Chapter2
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 spectrum 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, rather than frequency Markers display amplitude
and time values.
The following functions establish a clear display of the waveform:
l
l
l
l
Trigger stabilizes the waveform trace on the display by triggering on
the modulation envelope. If the signal’s modulation 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. The
sweep time readout refers to the full lo-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 65 for
more information on signal demodulation.
Example:
View the modulation waveform of an AM signal in the time domain.
1. To obtain an AM signal, you can either connect a source to the
spectrum analyzer input and set the source percent modulation, or
connect an antenna to the spectrum analyzer input and tune to a
commercial AM broadcast station. This example uses a source. (If
you are using a commercial broadcast station as your signal, press
Det/Demod, Demod, and AM to turn on AM demodulation. Then press
Done, Speaker On Off (On), and the spectrum analyzer will operate as
a radio.)
Chapter 2
49
Making Basic Measurements
Demodulating AM Signals (Using the Analyzer As a Fixed Tuned Receiver)
2. First, center and zoom in on the signal in the frequency domain. See
“Decreasing the Frequency Span Around the Signal” on page 31. Be
sure to turn off the signal track function, since it must be off for zero
span operation. See Figure 2-24.
Figure 2-24
Viewing an AM Signal
Ea 075253 RUG 24, 2012
Ref .0 dBm
E"
Atten 10 dB
l - l - r
WR SB
SC FS
AA
Center 300.00 MHz
#Res BW 1.0 MHz
VBW 300 kHz
Span 20.00 MHz
Sweep 5.00 msec
3. To demodulate the AM, press BW/Avg. Increase the resolution
bandwidth to include both sidebands of the signal within the
passband of the spectrum analyzer.
4. Next, position the signal peak near the reference level and select a
linear voltage display Press Amplitude, and change the reference
level, then press Scale Log Lin to underline Lin.
5. To select zero span, either press Span, 0 Hz, or press Zero Span. See
Figure 2-25. If the modulation is a steady tone, for example from a
signal generator, use video trigger to trigger on the waveform and
stabilize the display (If you are viewing an off-the-air signal you will
not be able to stabilize the waveform.) Adjust the sweep time to
change the horizontal scale.
Use markers and delta markers to measure the time parameters of the
waveform.
50
Chapter 2
Making Basic Measurements
Demodulating AM Signals (Using the Analyzer As a Fixed Tuned Receiver)
Figure 2-25
Measuring Modulation In Zero Span
pa 07:57:15 AUG 24, 2012
Ref -13.0 dBm
Peak
Lin
Fltten 0 dB
WA SI
SC FI
Al
Cents:r 300.000 MHz
#Res BW 1.0 MHz
Chapter 2
UBW 300 kHz
Span 0 Hz
Sweep 5.00 msec
51
3
Making Measurements
53
Making Measurements
What’s in This Chapter
What’s in This Chapter
l
“Making Stimulus Response Measurements” on page 55
l
“Demodulating and Listening to an AM Signal” on page 65
l
“Measuring Third Order Inter-modulation Distortion” on page 72
l
“Measuring Percent Amplitude Modulation” on page 70
l
“Measuring Percent Amplitude Modulation” on page 70
l
“Measuring Third Order Intermodulation Distortion” on page 72
To find descriptions of specific spectrum analyzer functions refer to the
user’s guide.
54
Chapter 3
Making 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. 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 spectrum analyzer as the receiver,
operation is the same as a single channel scalar network analyzer. The
tracking generator’s output frequency must be made to precisely track
the spectrum 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 A Spectrum 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 spectrum analyzer settings,
normalize, and measure.
The procedure below describes how to use a built in tracking generator
system to measure the rejection of a low pass filter, which is 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 62. Refer to
the HP Spectrum Analyzer Seminar (HP part number 5958-6564) for
more information.
Stepping Through a Transmission Measurement
1. To measure the rejection of a low pass filter, connect the equipment
as shown in Figure 3-2. This example uses a filter with a cut off
frequency of 300 MHz as the DUT.
Chapter 3
55
Making Measurements
Making Stimulus Response Measurements
Figure 3-1
Transmission Measurement Test Setup
SPECTRUM ANALYZER
RF Out
bn73a
2. Access the tracking generator functionality using the source key on
the spectrum analyzer. To activate the tracking generator power
level, press Source Amptd. See Figure 3-2.
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 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 Amptd
menu. Refer to specifications and characteristics in your user’s and
calibration guide for more information on the relationship between
source power and source attenuation.
56
Chapter 3
Making Measurements
Making Stimulus Response Measurements
Figure 3-2
Tracking Generator Output Power Activated
Pia
Ref .0 dBm
Peak
Atten 10 dB
kg
dB/
WF1 SB
SC FC
Center 750 MHz
Res BW 3.0 MHz
VBWl MHz
Span 1.500
Soan
1.500 GHz
Sweep 75.0 msec
3. Put the sweep time of the analyzer into stimulus response auto
coupled mode by pressing Sweep, then Swp Coupling SR SA until SR
(stimulus response mode) is underlined. Auto coupled sweep times
are usually much faster for stimulus response measurements than
they are for spectrum analyzer measurements.
NOTE
In the stimulus response mode, the Q of the DUT can determine the
fastest rate at which the spectrum analyzer can be swept. (Q is the
quality factor, which is reactance versus resistance.) To determine
whether the analyzer is sweeping too fast, slow the sweep time and
note whether there is a frequency or amplitude shift of the trace.
Continue to slow the sweep time until there is no longer a frequency or
amplitude shift.
4. Since we are only interested in the rejection of the low pass filter,
tune the spectrum analyzer center frequency and span so that the
roll-off of the filter comprises the majority of the trace on the display
See Figure 3-3.
Chapter 3
57
Making Measurements
Making Stimulus Response Measurements
Figure 3-3
Spectrum Analyzer Settings According to the Measurement
Requirement
r!!..
r
Ref .0 dBm
Peak
I nn
iS
Atten 10 dB
dB/
WA SB
SC FC
Start 100.0 MHz
Res BW 3.0 MHz
UBW 1MHz
I
Stop 800.0 MHz
Sweep 35.0 msec
5. Decrease the resolution bandwidth to increase sensitivity, and
narrow the video bandwidth to smooth the noise. In Figure 3-4, the
resolution bandwidth has been decreased to 10 kHz.
58
Chapter 3
Making Measurements
Making Stimulus Response Measurements
Figure 3-4
Decrease the Resolution Bandwidth to Improve Sensitivity
c!ia
fltten 10 dB
Ref .0 dBm
%
Wfl SB
SC FC
I
I
Start 100.0 MHz
*Res BW 10 kHz
I
I
I
VBW 10 kHz
I
I
I
I
I
I
Stop 800.0 MHz
Sweep 200 msec
6. To make a transmission measurement accurately, the frequency
response of the test system must be known. Normalization is then
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 spectrum analyzer
input. Press Trace, Normalize, Normalize On Off so that On is
underlined. The frequency response of the test system is
automatically stored in trace B 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 B.
When normalization is on, trace math is being performed on the
active trace. The trace math performed is (trace A - trace B + the
normalized reference position), with the result placed into trace A.
Remember that trace A contains the measurement trace, trace B
contains the stored calibration trace of the system frequency
response, and normalized reference position is indicated by
arrowheads at the edges of the graticule.
NOTE
Since the calibration trace is stored in trace B, changing trace B to
Clear Write will invalidate the normalization.
7. Reconnect the DUT to the spectrum analyzer. Note that the units of
the reference level have changed to dB, indicating that this is now a
relative measurement. Press 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
Chapter 3
59
Making Measurements
Making Stimulus Response Measurements
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.
8. To measure the rejection of the filter at a given frequency, press
Marker, and enter the frequency For example, enter 350 MHz. The
marker readout displays the rejection of the filter at 350 MHz. See
Figure 3-5.
NOTE
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.
Figure 3-5
Measure the Rejection Range
Ii!..
Ref .0 dB
0
Atten 10 dB
Mkr 350.3 MHz
Peak I
WFI-SB
SC FC
Start 100.0 MHz
*Res BW 10 kHz
VBW 10 kHz
Stop 800.0 MHz
Sweep 200 msec
Tracking Generator Unleveled Condition
When using the tracking generator, the message TO unleveled may
appear. The TO unleveled message indicates that the tracking
generator source power (Source Amptd, Amplitude On Off) 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 small. 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:
60
Chapter 3
Making Measurements
Making Stimulus Response Measurements
l
l
l
l
l
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
Man (Auto) for optimum setting).
The source power may be set too high or too low, use Amplitude On Off
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 On Off
to decrease the amplitude.
Reverse RF power from the device under test detected by the
tracking generator ALC (automatic level control) system.
Chapter 3
61
Making 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 test
device will be connected.) See Figure 3-6. A short circuit has a reflection
coefficient of l(0 dB return loss). It reflects all incident power and
provides a convenient 0 dB reference.
Figure 3-6
Reflection Measurement Short Calibration Test Setup
TG Output
RF Input
Reference Plane
Port
DIRECTIONAL
BRIDGE/COUPLER
Example:
Measure the return loss of a filter. The following procedure makes a
reflection measurement using a coupler or directional bridge.
Reflection Calibration
NOTE
The spectrum 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 55. Tune
the spectrum analyzer so that the passband of the filter comprises a
majority of the display, then proceed with the steps outlined below.
62
Chapter 3
Making Measurements
Making a Reflection Calibration Measurement
1. Connect the DUT to the directional bridge or coupler as shown in
Figure 3-6. 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 spectrum analyzer to
the input port of a directional bridge or coupler.
3. Connect the spectrum analyzer input to the coupled port of a
directional bridge or coupler.
4. Set center frequency, span, and other spectrum analyzer settings.
Turn on the tracking generator and set the amplitude level by
pressing Source Amptd, Amplitude On Off (On).
5. Replace the DUT with a short circuit.
6. Normalize the trace by pressing Trace, Normalize. Then set Normalize
On Off to On, to activate the trace A minus trace B function and
display the results in trace A. 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 calibration trace is stored in trace B, changing trace B to
Clear Write will invalidate the normalization.
Measuring the Return Loss
l
l
After calibrating the system with the above procedure, reconnect the
filter in place of the short circuit without changing any spectrum
analyzer settings.
Use the marker to read return loss. Press Marker and position the
marker with the knob to read the return loss at that frequency. See
Figure 3-7.
Chapter 3
63
Making Measurements
Making a Reflection Calibration Measurement
Figure 3-7
Measuring the Return Loss of the Filter
&a 08:12:15 RUG 24, 2012
q
Mkr 232.1 MHz
-1.91 dB
Atten 10 dB
Ref .0 dB
Peak
Log
t&
/
Y
>
Mark;er
L
I
I
Start 5.0 MHz
Res BW 3.0 MHz
64
I
I
I
I
I
UBWl MHz
Yi
/
I
I
I
I
I
I
I
I
Stop 400.0 MHz
Sweep 19.8 msec
Chapter 3
Making 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 spectrum
analyzer. Simply place a marker on a signal of interest, activate AM
demodulation, turn the speaker on, and then listen.
Example:
1. Connect an antenna to the spectrum analyzer input.
2. Select a frequency range on the spectrum 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
Preset, Frequency, Start Freq, 550 kHz, Stop Freq, 1650 kHz.
3. Place a marker on the signal of interest by using Peak Search to place
a marker on the highest amplitude signal, or by pressing Marker,
Marker Normal and moving the mark er to a signal of interest.
4. Press Det/Demod, Demod, AM. Use the front panel volume knob to
control the speaker’s volume. (Speaker On Off is set to On by the
preset function.)
NOTE
The AM demodulation function can also be used to listen to an FM
signal.
a. First find an FM signal in the FM band (88 to 108 MHz, in the
US.)
b. Make sure that the resolution bandwidth is set to 100 kHz by
either setting the span to 10 MHz, or by directly setting the
resolution bandwidth.
c. Adjust the reference level until FM broadcast signals can be seen
on the display
d. Place the marker on the skirt (off of the peak) of a strong FM
signal.
e. Turn on the speaker and the AM demodulation. The FM signal
can be heard on the speaker. This example uses an AM detector to
do slope detection on an FM signal.
Chapter 3
65
Making Measurements
Demodulating and Listening to an AM Signal
Figure 3-8
Demodulation of an AM Signal
&?!a
Ref si 1Bm
Smpl
Log
Mkr 1.350 MHz
-39.14 dBm
Atten 310 dB
~~,
I
I
OWE
?a
Q
P
A
A
WA SB
SC FC
Start 48 kHz
Res BW 10 kHz
UBW 10 kHz
Stop 1.650 MHz
Sweep 50.0 msec
5. ‘I’he signal is demodulated at the marker’s position only for the
duration of the dwell time. Use the step keys, knob, or numbers
keypad to change the dwell time. For example, press the step up key
(?> to increase the dwell time to 2 seconds. Notice that you can hear
the demodulated signal for a longer period of time.
6. The marker search functions can be used to move the marker to
other signals of interest. Press Search to access Next Peak, Next Pk
Right, or Next Pk Left.
Example:
1. Place the marker on a signal of interest as in steps 1 through 3 of the
previous example.
2. If the signal of interest is the highest amplitude on screen signal, set
the frequency of the signal to center frequency by pressing Frequency
then Signal Track On Off (On). If it is not the highest amplitude signal
on screen, move the signal to center screen by pressing Search and
Marker -> CF.
3. If signal track function is on, press Span and 1 MHz to reduce the
span to 1 MHz. If signal track is not used, use the step down key CL>
to reduce the span and use Marker - > CF to keep the signal of interest
at center screen.
4. Set the span to zero by pressing Zero Span. Zero Span turns off the
marker track function.
66
Chapter 3
Making Measurements
Demodulating and Listening to an AM Signal
5. Change the resolution bandwidth to 100 kHz by pressing BW/Avg
and entering 100 kHz.
6. Set the signal in the top two divisions of the screen by changing the
reference level. Press Amplitude, and then the step down key (J> until
the signal is in the top two divisions. Set the amplitude scale to
linear by pressing Scale Log Lin so that Lin is under lined.
7. Press DetlDemod, Demod, AM. Use the front panel volume knob to
control the speaker’s volume. (Speaker On Off is set to On by the
preset function.)
NOTE
The signal to the speaker will be interrupted during retrace because the
analyzer is performing automatic alignment routines. You can turn off
the alignment by pressing System, Alignments, Auto Align, Off. Refer to
the specifications for information about operating the analyzer with the
alignments turned off.
8. To eliminate the clicks between sweeps, turn the auto alignment
function off by pressing System, Alignments, Auto Align, Off.
Figure 3-9
Continuous Demodulation of an AM Signal
riw
Ref -30.0 dBm
Smpl
Log
Atten 0 dB
Mkr 15.075 msec
-43.29 dBm
2%
WA SB
SC FS
Center 1.3498 MHz
*Res BW 100 kHz
Chapter 3
UBW 30 kHz
Span 0 Hz
Sweep 30.0 msec
67
Making Measurements
Measuring Device Bandwidth
Measuring Device Bandwidth
It is often necessary to measure device bandwidth, such as when testing
a band pass filter. There is a key in the Measure 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 turning the N dB Points On Off key (On).
The spectrum 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.
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 about +l% of the
span.
68
Chapter 3
Making Measurements
Measuring Device Bandwidth
Figure 3-10
N dB Bandwidth Measurement
B..
Ref .0 dBm
reaK
Atten 10 dB
kg
dB/
.
.
_I
SC FC AA
I
I
Center 50.00 MHz
*Res BW 1.0 MHz
I
I
I
VBW 300 kHz
I
I
I
I
I
1
Span 10.00 MHz
Sweep 5.00 msec
Example: Measure the 3 dB bandwidth of the spectrum analyzer’s
1 MHz resolution bandwidth filter using the internal 50 MHz signal.
1. On the spectrum analyzer, press Preset, System, 50 MHz Osc On Off
(On) to turn on the internal signal.
2. Press Frequency, 50 MHz, to center the signal.
3. Press Span, 10 MHz, to narrow the displayed span.
4. Press BW/Avg and T until the 1 MHz resolution bandwidth is
selected.
5. Press Measure and N dB Points On Off (On) to activate the N dB
bandwidth function.
6. Read the measurement results in the upper left corner of the screen.
7. The knob or the data entry keys can be used to change the N dB
value from 3 dB to 6 dB to measure the 6 dB bandwidth of the filter.
8. Press N dB Points On Off (OfI’) to turn the measurement off.
Chapter 3
69
Making Measurements
Measuring Percent Amplitude Modulation
Measuring Percent Amplitude Modulation
Percent amplitude modulation (AM) can be measured quickly and
easily using the front panel % AM On Off key The signal and both its
sidebands must be on the display before the measurement is activated.
The signal sidebands are assumed to be entirely from amplitude
modulation. The spectrum analyzer places arrow markers on the three
signals to be used to compute percent amplitude modulation, and
displays the value. If the sidebands are not in the frequency span or
their frequency spacing is not equal, the measurement stops and an
error message is displayed.
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.
Percent AM measurement accuracy:
Figure 3-11
l
Typically about +O.l%, for log mode
l
Typically about +3%, for linear mode
Percent Amplitude Modulation Measurement
pa 08:41:52 RUG 25, 2012
0
Ref .0 dBm
Atten 10 dB
Peak
,% AM:- 8!26-%
kg
dB/
4
A
III
WA SB
SC FC
AA
1
Center 300.0000 MHz
Res BW 3.0 kHz
70
VBW 3 kHz
Span 200.0 kHz
Sweep 100 msec
Chapter 3
Making Measurements
Measuring Percent Amplitude Modulation
Example:
1. Press Preset. Connect a signal with amplitude modulation, to the
INPUT connector. The modulation frequency should be 210 kHz.
2. Press Frequency and enter the frequency of your input signal to place
the signal at the analyzer center frequency.
3. Press Span. Change the span until only the signal and its two
sidebands appear on the display.
4. Press Measure and % AM On Off (On) to activate the percent
amplitude modulation function.
5. Read the measurement results in the upper left corner of the screen.
6. Press % AM On Off (Off) to turn the measurement off.
Chapter 3
71
Making Measurements
Measuring Third Order Intermodulation Distortion
Measuring Third Order Intermodulation
Distortion
There is a front panel TO1 (third order intercept) measurement key to
make quick and easy inter-modulation measurements on mixers or
converters. Before the TO1 measurement is turned on there must be
four signals on the display, two test signals and their two associated
distortion products. All of the signals must have peaks greater than the
peak excursion value that is currently defined. (The default value for
the peak excursion is 6 dB.) The two highest amplitude signals are
assumed to be the test signals for the third order intercept
measurement.
The spectrum analyzer computes and displays the third order intercept
of the displayed signals, marking all four signals with arrows to confirm
the correct signal selection. The measurement updates at the end of
every sweep, which enables real time optimization of devices or systems
under test. The single sweep mode can also be used to provide time to
study or record the data.
Third Order Intercept: Third order intercept is defined as the absolute
power level at which the third order distortion products intercept the
level of two equal level test signals. If the distortion products are due to
true third order distortion, then the measurement result will be
independent of the level of the test signals.
The third order intermodulation is calculated as follows (all amplitude
values are expressed in dBm):
TO1 =
2 ’ Am&gnal A - Ampldistortion product A + Am&ignal B
2
where the frequency of distortion product A is:
Freqdistortion product A = 2 ’ Freqsignal A - Freqsignal B
The measurement algorithm used by TOI On Off (see above equation)
corrects for the two test signals being different amplitudes. The result
is a calculated value for the two test signals being equal amplitude, and
is independent of the absolute level of either test signal. In order to
minimize the measurement error, it is best to keep the test signals as
close as possible to the same level and to the top of the screen.
72
Chapter 3
Making Measurements
Measuring Third Order Intermodulation Distortion
Figure 3-12
Third Order Intermodulation Measurement
0
@a 07:41:34 AUG 24, 2012
Ref .0 dBm
Peak
TO1
Rtten 10 dB
kg
dB/ t
WO SB
SC FC
RR
Center 300.000 MHz
xRes BW 3.0 kHz
UBW 3 kHz
Span 5.000 MHz
Sweep 1.67 set
Example:
Use the TO1 function to make a measurement.
1. Press Preset. Connect two equal amplitude signals with different
frequencies, to the spectrum analyzer INPUT.
2 . Press Frequency and enter the frequency of one of your input signals
to place the signal at the spectrum analyzer center frequency
3. Press Span. Change the span until only the two signals and their two
distortion products appear on the display
4. Press Measure and TOI On Off (On) to activate the third order
intercept measurement function.
5. Read the measurement results in the upper left corner of the screen.
6. Press TOI On Off (Off) to turn the measurement off.
It is important to verify that the TO1 being measured is coming from
the device under test and not from the spectrum analyzer. An easy way
to do this is as follows:
1. Set up the TO1 measurement and turn it on.
2. Press Amplitude, Attenuation Auto Man (Auto) and increase the
attenuation +lO dB by pressing ‘T’ twice.
Chapter 3
73
Making Measurements
Measuring Third Order Intermodulation Distortion
3. If the displayed result of the TO1 measurement remains constant,
then the value is the result of the device under test.
4. If the displayed result of the TO1 measurement increases, then the
value is due to spectrum analyzer distortion and not the device
under test. In this case, continue to increase the attenuator setting
until the measurement result no longer changes as the attenuator is
changed. When the value remains constant, the result is from the
device under test.
Increasing the attenuator setting of the spectrum analyzer decreases
the level of the signal internal to the spectrum analyzer and
therefore decreases the distortion generated by the analyzer.
However, it also increases the noise floor of the instrument, which
decreases the measurement range and the ability to see low level
distortion products. Refer to the information in the specifications
and characteristics chapter of your user’s and calibration guide for a
graph of the distortion performance of the spectrum analyzer.
74
Chapter 3
4
Using Instrument Features
75
Using Instrument Features
What’s in this Chapter
What’s in this Chapter
This chapter introduces features of the spectrum analyzers. These
features can be used to manipulate measurement data and to make
measurements more easily In this chapter you will be:
“Saving and Loading Files from Analyzer Memory” on page 77
l
l
“Creating Limit Lines” on page 81
l
“Entering Amplitude Correction Factors” on page 92
l
“Using the External Keyboard” on page 99
76
Chapter 4
Using instrument Features
Saving and Loading Files from Analyzer Memory
Saving and Loading Files from Analyzer
Memory
This section explains how to save and load state, trace, limit line, and
amplitude correction factor data files to and from spectrum analyzer
memory using the functions in the File menu.
Saving state data saves the spectrum analyzer settings, but not the
trace data. Saving trace data saves the trace data and the state data.
States, traces, limit line tables, and amplitude correction factors are
retained in spectrum analyzer memory even if the instrument is turned
off or Preset is pressed. Files cannot be saved if the Internal Lock On Off
softkey function is set to On.
Refer to Table , “Summary of Save and Recall Operations to Analyzer
Memory,” on page 78 at the end of this section for a summary of saving
and loading data to and from spectrum analyzer memory. Refer to page
79 for the rules for naming a file.
To Save a File in Memory
1. Several different types of files can be saved in analyzer memory:
l
Saving a
saved.
l
l
l
state: Set up the spectrum analyzer settings to be
Saving a trace: Set the analyzer to display the trace to be
saved. (Enter a screen title, if desired, by using Display and Title,
Change Title.) Saving trace data saves both the trace data and the
state data in the same file.
lines: Set up the limit line table to be saved.
See page 81 in this chapter. Limit line data can be entered using
the remote programming commands as well as through the front
panel keys.
Saving limit
Saving amplitude correction data: Setupthetableof
correction data to be saved. See page 92 in this chapter for more
information. Amplitude correction data can be entered using the
remote programming commands as well as through the front
panel keys.
2. Press File, Save.
3. Press the key for the desired type of file to be saved. (for example,
State). The files of the selected type, that are currently in memory,
will be displayed on the spectrum analyzer.
NOTE
If a trace is being saved, press the Trace A B C softkey until you have
underlined the trace that you want to save.
Chapter 4
77
Using Instrument Features
Saving and Loading Files from Analyzer Memory
4. The analyzer will create a unique name for the file to be saved, with
the proper suffix. ( . STA for a state) To select a different file name,
press New Filename and use the alpha editor keys to enter a name.
The correct suffix is automatically attached to the file name.
5. Press Save Now to save the file in memory.
To Load a File from Memory
1. Press File, Load.
2. Select the desired type of file to load (for example, State).
If a trace is being loaded, press Trace A B C so that the desired
destination for the trace data is underlined.
NOTE
3. Use the Up/Down arrows or the knob to select the desired file.
4. Press Load Now.
To Protect Data From Being Overwritten
If you want to protect all state, trace, limit line, and amplitude
correction data from being overwritten, press File, then Internal Lock On
Off so that On is under lined. page 78 summarizes the functions when
saving and loading data to and from spectrum analyzer memory.
Summary of Save and Recall Operations to Analyzer Memory
Operation
Screen
Title
Available?
Key Sequence
Save state
No
File, Save, State, New Filename (enter file name), Save Now
Load state
No
File, Load, State, (select desired file name), Load Now
Save trace
Yes
File, Save, Trace, Trace A B C (select desired source trace),
New Filename (enter file name), Save Now
Load trace
Yes
File, Load, Trace, Trace A B C (select desired destination
trace), (select desired file name), Load Now
Save limit line
table
Yes
File, Save, Limits, New Filename (enter file name), Save
Now
78
Chapter 4
Using Instrument Features
Saving and Loading Files from Analyzer Memory
Screen
Title
Available?
Operation
Key Sequence
Load limit line
table
No
File, Load, Limits, (select desired file name), Load Now
Save amplitude
correction factors
Yes
File, Save, Ampcor, New Filename (enter file name), Save
Now
Load amplitude No
correction factors
File, Load, Ampcor, (select desired file name), Load Now
File Naming Rules
File names for storing states, traces, limit lines or amplitude correction
data files in the analyzer should follow the conventions as indicated
below:
l
l
They can be up to eight characters long. In addition, they can have a
file extension up to three characters long. The analyzer assigns the
extension.
They are not case sensitive. It does not matter whether you use
upper case or lower case letters when you type them.
l
They can contain only the letters A through Z, the number 0 through
9, and the following special characters:
l
underscore _
l
carat *
l
dollar sign $
l
tilde -
l
exclamation point !
l
number sign #
l
percent sign %
l
ampersand &
l
hyphen -
l
braces (1
l
at sign @
l
single quotation mark ‘
l
apostrophe ’
l
parenthesis (>
No other characters are valid.
Chapter 4
79
Using Instrument Features
Saving and Loading Files from Analyzer Memory
l
l
80
They cannot contain spaces, commas, backslashes, or periods.
(except the period that separates the name from the extension.)
They cannot be identical to the name of another file in the same
directory.
Chapter 4
Using Instrument Features
Creating Limit Lines
Creating Limit Lines
Limit lines provide an easy way to compare trace data to a set of
amplitude and frequency parameters while the spectrum analyzer is
sweeping the measurement range. An upper and/or lower limit line can
be displayed. Every measurement sweep of trace A is compared to the
limit lines. If trace A is at or within the bounds of the limit lines, LIMIT
PASS is displayed. If trace A is out of the limit line boundaries, LIMIT
FAIL is displayed. Figure 4-l shows a sample limit line display.
Limit lines are constructed from a table of frequency and amplitude
coordinate pairs. Limit line segments are created by connecting these
points. Everything except the segment length is defined by the entry for
the beginning point. Limit lines can be entered as coordinates of
frequency and amplitude, or in terms of time and amplitude for zero
span measurements.
This section provides a procedure for creating a sample upper limit line
and descriptions of the limit line functions. Refer to the user’s guide for
more information on a specific limit line function.
Procedure for Creating an Upper Limit Line
This procedure demonstrates how to create a sample upper limit line
for the internal alignment signal and then activate testing. Detailed
descriptions of the limit line functions follow this procedure.
1. Press Preset.
2. Set the center frequency and span by pressing Frequency, 50 MHz,
and Span, 90 MHz.
3. Turn on the internal alignment signal by pressing System and
50 MHz osc On Off, so that On is underlined. (The alignment signal is
used as the “test” signal for this demonstration.) The amplitude
units are in dBm.
4. Press Measure, Limits to access the limit line menus.
NOTE
To clear an existing limit-line table, you must press Delete Limits two
times. The Preset key turns limit-line testing off (if it is on), but does not
clear an existing limit-line table.
5. Select the type of limit line needed.
a. Limits Fixed Rel specifies whether or not the limit line values are
fixed values, or are values relative to the spectrum analyzer
center frequency and reference level settings. Press Limits Fixed
Rel so that fixed is underlined. The table will be labeled
limits=FIXEDorlimits=RELATIVE.
Chapter 4
81
Using Instrument Features
Creating Limit Lines
b. X Axis Units Freq Time allows you to select frequency (or time, for
zero span) units for the horizontal axis. Press X Axis Units Freq
Time so that Freq is under lined. The table column will be labeled
START-FREQ or START-TIME.
When time parameters are used, the RELATIVE format only
affects the amplitude part of the coordinate pairs. The time
parameters are always fixed beginning at the left edge of the
graticule.
6. Press Edit Limits. Notice that Upper is selected on the Select Line
Upper Lower key Press Edit Line to create an upper limit line.
7. The limit line table will be displayed. The table type defaults are
frequency parameters (the second column is labeled START-FREQ)
and fixed parameters (the table is labeled Limits=FIXED).
Figure 4-1
Typical Limit Line Display
3 0
P
hP
Ref .0 dBm
Peak I
I
I
dB/II
I
Atten 10 dB
I
I
I
I
/
I I IMIT PASS
I
I
WA SBW
Center50. 00 MHz
Res BW 1.0 MHz
VBW 300 kHz
SDan 90.00 MHz
Swkep 5.00 msec
Table 4-1
Item
82
Description of Items in Figure 4-1
1
Upper limit line
2
Lower limit line
3
Screen message
Chapter 4
Using Instrument Features
Creating Limit Lines
8. Specify the first limit line segment to begin at 5 MHz and have an
amplitude of -60 dBm by using the following key sequence. (Use the
Frequency menu key that is labeled on the display, not the
permanent key on the right side of the front panel.):
l
Frequency, 5 MHz
l
60 -dBm
l
NOTE
Flat
When entering a limit line segment, the frequency (or time) and
amplitude values will be listed as asterisks (* * *> until new values are
entered. The new segment will be listed last until the frequency (time),
amplitude, and type of line segment have been entered. Once the values
are entered, the segment will be sorted into the limit line table
according to frequency or time. The coordinates for the second point
must be entered before the first limit line segment is displayed.
9. Enter the second limit line segment by pressing the following keys:
l
Frequency, 40 MHz
l
60 -dBm
l
Slope
Table entries can be edited if you make a mistake. To edit an existing
segment, use Segment in the Edit Line menu to specify the segment.
Use Frequency, Amplitude, or Select Type to specify the column you
wish to edit.
lO.Specify the third limit line segment by pressing the following keys:
l
Frequency, 45 MHz
l
30 -dBm
l
Flat
You may notice that the end coordinate of segment three is drawn to
a point off the top of the spectrum analyzer display This assures
that no trace data beyond the end of the limit line will cause the test
to fail.
ll.Specify the fourth limit line segment by pressing the following keys:
l
Frequency, 100 MHz
l
30-dBm
l
Point
Since the limit line in this procedure has only four segments
specified, the frequency value of segment four (the last segment) is
set to 100 MHz, which is greater than the stop frequency of the
display
Chapter 4
83
Using Instrument Features
Creating Limit Lines
12.Press Done twice when all the segments have been entered.
13.Press Limit Test On Off so that On is underlined. This turns the limit
testing on. For example, LIMIT FAIL is displayed because the signal
exceeds the limit line. See Figure 4-2.
Figure 4-2
The Completed Limit Line Table
Ref .0 dBm
Peak
Atten 10 dB
:ig -Limit Line= UPPER
Segments= 4 of 30
Amp1 Scale= LOG Limits= FIXED
Freq Scale= LIN
dB/
I
rSEG START-FREQ UPPERAMP TYPE
A
SEG#
-5
1 5.000 MHz
2
40.00 MHz
-6
-6
WA SB
SC FC
corr
Center 50.00 MHz
Res BW 1.0 MHz
Span 90.00 MHz
Sweep 5.00 msec
UBW 300 kHz
14Press System and 50 MHz osc Off.
signal exceeds the limit line.
LIMIT
PASS is displayed since no
15.At this point you may want to try the following:
a. To remove the limit line from the display without deleting it, use
Limit Display Y N Auto. Underlining Y displays the limit lines,
while N turns them off. Selecting Auto allows them to be
displayed if limit line testing is turned on, or it turns the limit
lines off if testing is turned off.
b. To clear an existing limit line table, press Delete Limits.
c. To save the current limit line table, press File, Save, Limits. Press
Edit File Name to enter the file name, or use the default file name
assigned by the analyzer. Then press Save Now.
16.You may need to have limit lines above and below your test signal.
Follow the same procedure above to generate the upper limit line.
Then press Select Line Upper Lower so that Lower is underlined and
enter in the desired values for the lower limit line. See Figure 4-3.
84
Chapter 4
Using instrument Features
Creating Limit Lines
Figure 4-3
Upper and Lower Limit Line Testing
q
fF
Ref .0 dBm
Peak I
I
I
Atten 10 dB
I
I
I
I
I
I IMfT PRSS
I
WA SBSC FC
corr
I
I
Center 50.00 MHz
Res BW 1.0 MHz
VBW 300 kHz
Span 90.00 MHz
Sweep 5.00 msec
Limit Line Functions
This section describes the limit line functions in the order that they are
usually used.
Editing, Creating, or Viewing a Limit Line
Pressing Measure, then Limits accesses the softkey menus used for
creating a limit line.
Press Edit Limits, Edit Line to edit an existing limit line table. If no limit
line table currently exists, this will allow you to create one.
If a limit line exists currently, and you would like to purge it and create
a new one, press Select Line Upper, and Done, Done. Then press Delete
Limits two times to clear the existing limit line table and press Edit
Limits, Edit Line to access the limit line editing menu.
Chapter 4
85
Using Instrument Features
Creating Limit Lines
Selecting the Type of Limit Line Table
The X Axis Units Freq Time key selects the type of limit line parameters
for the horizontal axis. Parameters can be entered as
frequency/amplitude coordinates, or as time/amplitude coordinates. Use
the X Axis Units Freq Time key, to underline the desired choice of either
frequency or time parameters. Frequency is the default selection. If
Time is selected Time will replace Frequency in the Edit Line menu.
The second column of the limit line table is labeled START-FREQ when
frequency is selected. It is labeled START-TIME when time is selected.
The Limits Fixed Ret key selects the type of limit line. There are two
types of limit lines: fixed and relative. Fixed limit lines contain only
absolute amplitude and frequency (or time) values. Relative limit lines
consist of frequency values that are referenced to the spectrum
analyzer center frequency and amplitude values that are relative to the
analyzer reference level. The relative setting does not affect time
values. Time values always begin at the left edge of the graticule.
As an example of fixed versus relative limit lines, if a limit line is
specified as fixed, entering a limit line segment with a frequency
coordinate of 300 MHz displays a limit line segment at 300 MHz. If the
same limit line table is specified as relative, it is displayed relative to
the spectrum analyzer center frequency and reference level. If the
analyzer center frequency is at 900 MHz, a relative limit line segment
with a frequency coordinate of 300 MHz will display a limit line
segment at 1.2 GHz. If the amplitude component of a relative limit line
segment is -10 dB and the spectrum analyzer reference level is
-15 dBm, then -10 dB is added to the reference level value and the
amplitude component of the limit line will be at -25 dBm.
Limits=RELATIVE is displayed in the limit line table when the limit
line type is relative; Limits=FIXED is displayed when the limit line
type is fixed. A limit line entered as fixed may be changed to relative,
and one entered as relative may be changed to fixed. When the limit
line type is changed, the frequency and amplitude values in the limit
line table are modified by the current center frequency and reference
level settings to keep the limit line in the same position on the
spectrum analyzer.
Selecting the Limit Line Table Format
Press Select Line Upper Lower and underline either Upper or Lower to
edit or create the desired type of limit line table. You can use an upper
limit line only, or a lower limit line only, or both an upper and a lower
limit line. The upper and lower limit lines are each edited separately,
but activated together.
86
Chapter 4
Using Instrument Features
Creating Limit Lines
Selecting the Segment Number and Entering Coordinates
Pressing the Segment key specifies the segment number to be entered or
edited. Up to 30 segments can be specified for an upper or lower limit
line table. Limit lines are constructed from left to right.
Limit line segments are created by entering frequency (time) values
and amplitude values into a limit line table. The frequency(time) and
amplitude values specify a coordinate point from which a limit line
segment is drawn. The segment is defined by its beginning point, that is
the coordinate point that is the lowest frequency or time point of the
line segment. See Figure 4-4.
The segment coordinates are entered by pressing Frequency (or Time)
and entering the value. Regardless of the table format, a frequency
(time) coordinate must be specified. Pressing the Amplitude key allows
you to enter the amplitude value of the coordinate.
NOTE
When entering a limit line segment, the frequency (or time) and
amplitude values will be listed as asterisks (* * *) until new values are
entered. The new segment will be listed last until the frequency (time),
amplitude, and type of line segment have been entered. Once the values
are entered, the segment will be sorted into the limit line table
according to frequency or time.
Chapter 4
87
Using Instrument Features
Creating Limit Lines
Figure 4-4
Limit Line Segments
Ref.0 dBm\
Peak
Log
In
Atten\ dB
I
I
I
SA SB
SC FC
corr
Center 50.00 MHz
Res BW 1.0 MHz
UBW 300 kHz
Span 90.00 MHz
Sweep 5.00 msec
Table 4-2
Item
Description of Items in Figure 4-4
1
Frequency and amplitude coordinate that starts the first
segment
2
First segment
3
Frequency and amplitude coordinate that starts the second
segment
4
Second segment
5
Frequency and amplitude coordinate that starts the third
segment
6
Third segment
7
Frequency and amplitude coordinate that starts the fourth
segment
8
Fourth segment
9
Frequency and amplitude coordinate that starts the fifth
segment
10
Fifth segment
11
Frequency and amplitude coordinate that starts the sixth
segment
88
Chapter 4
Using Instrument Features
Creating Limit Lines
Selecting the Segment Type
After entering the frequency (time) and amplitude coordinates, press
Type and Flat, Slope, or Point to specify the segment type. The segment
type determines how to connect the coordinate point of the current line
segment with the coordinate point of the next line segment. The
segment type determines whether the line segment is horizontal,
sloped, or a single point. The three segment types are:
1. Flat draws a zero slope line between the coordinate point of the
current segment and the coordinate point of the next segment,
producing limit line values equal in amplitude for all frequencies or
times between the two points. If the amplitude values of the two
segments differ, the limit line will “step” to the value of the second
segment at the frequency coordinate of the second segment. See
Figure 4-5.
2. Slope draws a straight line between the coordinate point of the
current segment and the coordinate point of the next segment,
producing limit line values for all frequencies between the two
points.
3. Point specifies a limit value for the coordinate point. It specifies a
limit at a single frequency or time, and for no other frequency/time
points. For an upper limit line, a point segment is indicated by a line
drawn from the coordinate point, vertically off the top of screen. For
a lower limit line, a point segment is indicated by a line drawn from
the co ordinate point, vertically off the bottom of screen. The line will
continue to the right edge of the display, but testing stops at the
defined point.
The point segment type should be used as the last segment in the
limit line table. However, if the last segment in the table is not
specified, an implicit point is automatically used. If a point segment
at the right edge of the display is not desired, add a last point
segment to the limit line table that is higher in frequency than the
displayed stop frequency.
Figure 4-5 demonstrates the different segment types.
Chapter 4
89
Using Instrument Features
Creating Limit Lines
Figure 4-5
Segment Types
dB/
1
SA SB
SC FC
I
I
,-
I
hl
I
I
I
/f\
IN
corrY I
bn76a
Table 4-3
Item
Segment Types
1
Flat (upper limit line)
2
Slope (upper limit line)
3
Point (upper limit line)
4
Point (lower limit line)
5
Slope (lower limit line)
6
Flat (lower limit line)
Completing Table Entry and Activating Limit Line Testing
Pressing Done blanks the limit line table from the screen and accesses
the menu with Limit Test On Off and Limit Display Y N Auto softkeys.
Pressing Limit Test On Off turns on the testing of the current trace
against the limit line values.
90
Chapter 4
Using Instrument Features
Creating Limit Lines
Pressing Limit Display Y N Auto (Y or N) turns display of the limit lines
on and off. Pressing Limit Display Y N Auto (Auto) sets the limit line
display to match the limit line test function. With Auto underlined the
limit lines are only displayed when limit line testing is turned on.
Chapter 4
91
Using Instrument Features
Entering Amplitude Correction Factors
Entering Amplitude Correction Factors
This section provides an overview of amplitude correction, a procedure
for creating amplitude correction data, and descriptions of the
amplitude correction functions. Refer to the key descriptions in the
user’s guide for more information on a specific amplitude correction
function.
Amplitude corrections provide an easy way to adjust trace data with a
set of amplitude and frequency parameters while the spectrum
analyzer is sweeping the measurement range. Every measurement
sweep of data is adjusted by the amplitude correction values. When
using the amplitude correction functions, an A is displayed at the left
hand side of the graticule edge. See Figure 4-6.
Figure 4-6
Amplitude Correction Display
Ref .0 dBm
Peak
Atten 10 dB
kg
dB/
VA WB
SC FC
&orr
Center 300.0 MHz
Res BW 3.0 MHz
VBW 1 MHz
Span 500.0 MHz
Sweep 5.00 msec
bn75a
92
Chapter 4
Using Instrument Features
Entering Amplitude Correction Factors
Table 4-4
Item
I
1
Description of Items in Figure 4-6
I
Indicates amplitude correction factors are
on
2
Amplitude corrections ON
3
Amplitude corrections OFF
Procedure for Creating Amplitude Correction
Factors
This procedure demonstrates how to create and activate amplitude
correction data. Detailed descriptions of the amplitude correction
functions follow this procedure.
1. Press Preset.
NOTE
A signal is not used in this procedure for demonstrating how to create
amplitude correction data. Disconnect any cable on the spectrum
analyzer input.
2. Set the center frequency to 300 MHz and the span to 500 MHz by
pressing:
l
Frequency, 300 MHz
l
Span, 500 MHz
3. Press Amplitude, More, Ampcor to access the amplitude correction
functions.
4. Press Modify Ampcor to access the editing menus for amplitude
correction factors.
5. To clear any existing amplitude correction data, press Purge Ampcor
twice.
6. Specify the first amplitude correction point by pressing the following
keys:
l
Select Freq
l
50MHz
l
12dB
7. Specify the second amplitude correction point by pressing the
following keys:
l
l
250 MHz
10dB
Chapter 4
93
Using Instrument Features
Entering Amplitude Correction Factors
Table entries can be edited if you make a mistake. To edit an existing
point, use Select Point to specify the point. Then use Select Freq or Select
Amptd to specify the entry that you wish to edit.
8. Specify the third and fourth amplitude correction points by using the
following key sequence:
Figure 4-7
l
300 MHz, 15 dB
l
350 MHz, 22 dB
Completed Amplitude Correction Table
0
ma 06:33:23 RUG 05, 2012
Ref 107.0 dBpU
Peak *
Atten 10 dB
:ig -AMPCOR USER
dB/
Points= 4 of 80
Freq Scale=
-PT FREQUENCY AMPLITUDE
I
I
WA SB
SC FC
A RR
Center 300.0 MHz
Res BW 3.0 MHz
VBWl MHz
ban 500.0 MHz
Swkep 5.00 msec
9. Press Done when all the points have been entered.
Use step 10 and step 11 to display corrected versus uncorrected
amplitude trace data for trace comparison.
lO.Display the amplitude corrected trace in trace A by pressing the
following keys:
94
l
Trace
l
Clear Write A
l
View A
Chapter 4
Using Instrument Features
Entering Amplitude Correction Factors
ll.Display the uncorrected amplitude trace in trace B by pressing the
following keys. See Figure 4-8.
l
Figure 4-8
Trace A B C until B is selected
l
Clear Write B
l
Amplitude, More, Ampcor
l
Ampcor On Off until Off is selected
Uncorrected and Amplitude Corrected Trace
@a 06:27:50 AUG 05, 2012
Ref 107.0 dBpU
Peak
I nn
‘CbR
0
Atten 1 0 dB
I
‘Points; 0 ofl 80-l
Freq Seal e=
FREQUENCY AMPLITUDE
U&R
’
’
I
Getiter 300.0 MHz
Res BW 3.0 MHz
UBW 1 MHz
I
Span 500.0 MHz
Sweep 5.00 msec
Amplitude Correction Functions
This section describes the amplitude correction functions in the order
they are usually used.
Editing or Viewing the Amplitude Correction Tables
Pressing Amplitude, More, Ampcor accesses the softkey menus for
creating an amplitude correction table.
NOTE
Preset turns amplitude correction factors off (if it is on), but does not
clear an existing amplitude correction table. Use Purge Ampcor to clear
an existing amplitude correction table.
Chapter 4
95
Using Instrument Features
Entering Amplitude Correction Factors
Press Modify Ampcor to edit an existing amplitude correction table or, if no
amplitude correction table currently exists, to create an amplitude correction
table.
Selecting the Amplitude Correction Point
Pressing Select Point specifies the amplitude correction point to be
entered or edited. Amplitude correction data is constructed from left to
right and is created by entering frequency and amplitude values into an
amplitude correction table. The frequency and amplitude values specify
a coordinate point from which amplitude corrections are interpolated.
See Figure 4-9. Up to 80 points can be specified for the amplitude
correction table.
Table 4-5
Amplitude Correction data for Figure 4-9
1 Point ) Frequency 1 Amplitude 1
I1
I .O dB
I
250.0 MHz
I~
I 15.0 dB
I
I 20.0 dB
I -10.0 dB
I
4
I 300.0 MHz
I 300.0 MHz
I 5
350.0 MHz
I 25.0 dB
I
I-2
I3
96
I
200.0 MHz
I
Chapter4
Using Instrument Features
Entering Amplitude Correction Factors
Figure 4-9
Amplitude Correction Points
WR SB
SC FC
A RA
I
I
Start 150.0 MHz
Res BW 3.0 MHz
UBWl MHz
I
I
1
I
I
I
Stop 400.0 MHz
Sweep 5.00 msec
n1746a
Table 4-6
Item
Description of Items in Figure 4-9
1
Frequencies below first point use first amplitude level
2
First segment interpolated with the 15 dB amplitude correction
3
Frequency and amplitude coordinate that starts the second
segment
4
Third segment interpolated with the -10 dB amplitude correction
5
Frequency and amplitude coordinate that starts the fourth
segment
Chapter 4
97
Using Instrument Features
Entering Amplitude Correction Factors
Selecting the Frequency Coordinate
Press Select Freq, then enter a frequency value for the point.
NOTE
Only two entries per frequency are used. If more points with the same
frequency are entered, only the first and last entries are used. All other
amplitude values are ignored. See Figure 4-9 for an example of two
entries at the same frequency
NOTE
When entering amplitude correction data, the frequency and amplitude
values will be listed as asterisks (* * * ) until new values are entered.
Once the frequency value is entered, the segment is immediately sorted
into the table according to this value.
Selecting the Amplitude Coordinate
The amplitude value is entered by pressing Select Amptd, entering an
amplitude value, and pressing a units key
Completing Table Entry and Activating Amplitude
Corrections
Pressing Done blanks the amplitude correction table from the screen
and accesses the menu with Ampcor On Off. This turns the amplitude
corrections on and off.
Saving or Loading Amplitude Correction Tables
Pressing File accesses Save and Load. These softkey functions provide
an easy way to save or load current amplitude correction tables. Save,
Ampcor saves the current amplitude correction table in the spectrum
analyzer memory, Press Edit File Name to enter a file name, then press
Save Now to save the cur rent amplitude correction table.
Press File, Load, Ampcor to load amplitude correction tables from the
spectrum analyzer memory. Scroll through the displayed amplitude
correction files to select the desired one and press Load Now to load the
table.
98
Chapter 4
Using Instrument Features
Using the External Keyboard
Using the External Keyboard
The HP C1405B keyboard is an IBM AT compatible keyboard (with a
mini-DIN connector) that can be connected to the external keyboard
connector on the front panel of the spectrum analyzer. The external
keyboard allows a convenient way to enter screen titles and remote
programming commands directly into the spectrum analyzer or to
access the softkey functions. Detailed information on using the external
keyboard can be found in the programmer’s guide.
The function keys of the external keyboard control the spectrum
analyzer as follows:
External Keyboard Functions
Table 4-7
Description
Key
~Replaces the analyzer Esc key. Turns off the
currently active function, but will not abort a printer
operation.
Esc
Shows what the current operation mode is, either
command mode or enter title mode on the analyzer
screen.
Num Lock
F
Scroll Lock
Retrieves the present screen title for editing.
Fl-F7
Softkeys 1 through 7 (respectively) of the current
analyzer menu.
F8
Replaces the analyzer More key. Accesses other
pages of the current menu, for multi-page menus.
I F9
I
Accesses the Measure menu.
FlO
Accesses the Frequency menu.
Fll
Accesses the Span menu.
F12
1 Accesses the Amplitude menu.
Print Screen
Copies the analyzer screen display to the active copy
device.
Pause
Toggles operation between the command mode and
the enter title mode.
Delete
Deletes the character over the cursor.
Insert
Toggles between the insert and replace mode at the
Backspace
Erases the previous character to the left of the
Alt-Delete
Clears the keyboard line.
Chapter 4
I
I
99
Using Instrument Features
Using the External Keyboard
Description
Key
Ctrl-Delete
Clears to end of line.
[+I
Moves the cursor to the left.
I-11
Moves the cursor to the right.
PI
Moves from earlier items to later items in the recall
buffer.
Moves from later items to earlier items in the recall
buffer.
I
Ctrl- C
I End-of-text.
I
1 Ctrl- J -ILine feed.
1
PI
I
I Ctrl- M
I Carriage return.
1 Ctrl- N
1 Turns on inverse video.
Ctrl- 0
I
Turns enhancements (inverse video, underlining)
Off.
Ctrl- P
Turns on underlining.
Ctrl- (space)
Escape.
The dash between keys indicates that both keys should be pressed
at the same time.
The external keyboard operation with the spectrum analyzer is similar
to its operation with a computer except for the following:
Pause, Num Lock and Scroll Lock are fixed and cannot be changed.
Pressing Pause toggles between the keyboard’s command mode and title
mode. Pressing Num Lock displays the current keyboard mode on the
spectrum analyzer screen. Pressing Scroll Lock retrieves the current
title for editing.
The keyboard supports a 244 character recall buffer. The longest single
item is limited to 243 characters; subsequent characters are ignored.
Using the (1‘) or (J) keys of the external keyboard to recall an item does
not change the buffer contents. Recalling an item and then pressing the
Enter key does not store a new copy of the item in the recall buffer. If an
item is recalled and then modified, a new copy will be made in the recall
buffer. Adding new data into the keyboard line deletes the oldest data
automatically.
When in command mode, the active line will append a semicolon to the
keyboard entry if the line does not end with a semicolon and it is fewer
than 243 characters long.
100
Chapter 4
Using Instrument Features
Using the External Keyboard
Using the External Keyboard
The following three example procedures demonstrate how to use an
external key board to enter a screen title and programming commands.
However, a brief procedure on installing your external keyboard is
described first. More detailed information on using the external
keyboard is found in the programmer’s guide.
External Keyboard Installation
1. Turn off the spectrum analyzer.
CAUTION
The spectrum analyzer must be turned off before connecting an
external keyboard to it.
2. Connect the HP C1405B keyboard cable to the spectrum analyzer
front panel connector EXT KEYBOARD.
3. Turn the spectrum analyzer on.
4. The external keyboard is now ready to use for entering a screen title
or programming commands.
To Enter a Screen Title
Refer to the programmer’s guide for more information.
1. Press Pause on the external keyboard to enter the title mode.
2. Type in a screen title using the external keyboard. The entry
appears at the top line of the spectrum analyzer display as it is
entered.
3. Press Enter on the external keyboard. Pressing Enter moves the
characters to the position on the display for screen title annotation.
NOTE
To view more than 31 characters per line, turn off the time and date
display by pressing the following keys: System, Time/Date, Time/Date On
off (OflJ.
To Enter Programming Commands
Refer to the programmer’s guide for more information.
1. Press Pause on the external keyboard to enter the mode for
executing remote commands.
2. Type in a programming command (for example, type
IP).
3. Press Enter on the external keyboard to execute the command.
Chapter 4
101
Using Instrument Features
Using the External Keyboard
NOTE
Unlike entering a remote programming command using an external
controller, entering the remote programming commands with the
external keyboard does not require including the spectrum analyzer
address. It is also not necessary to terminate the programmrng line
with a semicolon. However, semicolons are necessary for separating the
programming commands. For example, a program line is entered via
theexternalcontrolleras: OUTPUT 718;"CF 300MHZ;SP lMHZ;".The
same program line is entered using the external keyboard as: CF
3OOMHZ;SP 1MHz; Enter.
After Pause is pressed, the spectrum analyzer remains in command
mode. To return to the title entry mode, press Pause (on the external
keyboard).
102
Chapter 4
Index
Symbols
%AM,6
%AMOnOff, 70
Numerics
10 MHz REF INPUT, 12
10 MHz REF OUTPUT, 12
A
AM signal demodulation, 49
Ampcor On Off, 94, 98
amplitude correction
amplitude coordinate, 98
point, 96
amplitude correction factors, 92
amplitude correction functions,
95
amplitude corrections
creating, 93, 94
editing, 94
frequency coordinate, 98
testing, 98
turning on/off, 94
using, 98
Amplitude key, 6
analyzer distortion products, 44
annotation, 13
arrow keys, 9
AUX IF OUT, 12
AUX VIDEO OUT, 11
B
bandwidth measurement, 6,68
brightness keys, 6
BWlAvg key, 7
C
compare two signals, 19
connector
10 MHz ref input, 12
10 MHz ref output, 12
aux if output, 12
aux video output, 11
ext ale input, 10
ext trig input, 11
external keyboard, 7
hi sweep in, 11
hi sweep out, 11
HP-IB, 11
INPUT 50 ohm, 8
parallel interface, 11
probe power, 7
RF OUT 50 ohm, 8
RS-232, 11
service, 12
Index
COPY, 7
counter resolution, 29
creating amplitude correction
factors, 93
creating limit lines, 81
D
data controls, 8
data entry keys, 7
data keys, 9
data protection, 78
Delete Limits, 85
delta marker, 19, 20
Demod key, 65
demodulating AM, 49
demodulation
AM, 65
continuous, 66
DetJDemod key, 7
Display key, 7
display limit lines, 90
distortion products, 44
down arrow key, 9
drifting signals, 33
E
earphone connector, 7
Edit Ampcor, 95
Edit Limits, 85
Edit Lower, 86
Edit Upper, 86
editing amplitude corrections, 94
editing limit lines, 83
Esc key, 8
escape key, 8
EXT TRIG IN, 11
external keyboard
keyboard, 99
programming command entry,
101
screen title entry, 101
external keyboard connector, 7
external keyboard installation,
101
external keyboard operation, 101
F
features
front panel, 6
File key, 7
file name rules, 79
file protection, 78
fixed limit lines, 82, 86
fix-tuned receiver, 49
Flat, 89
Freq Count key, 29
Frequency
amplitude correction, 98
frequency counter function, 7
Frequency key, 6
frequency limit lines, 86
frequency readout resolution
increased, 29
front panel features, 6
fuse holder, 10
fuse location, 10
H
HI SWEEP IN, 11
HI SWEEP OUT, 11
hold key, 8
hold, maximum, 33
HP-IB connector, 11
I
identifying distortion products, 44
impulse noise measurement, 4 1
INPUT 50 ohm, 8
installation, external keyboard
attaching external keyboard,
101
instrument preset, 7
intermodulation distortion, third
order, 46
Internal Lock On Off, 78
K
key functions, external keyboard,
99
keyboard
external connector, 7
keyboard operation, external, 101
keys labeled on display, 6
knob, 8
L
Limit Display Y N Auto, 90
limit line functions, 85
limit lines, 6, 85, 87
creating, 81
displaying, 90
editing, 83
fixed, 86
freq time, 82
frequency or time, 86
relative, 86
segment number, 87
segment type, 89
table format, 86
table type, 86
testing, 90
using, 81
103
Index
Limit Test On Off, 81, 84, 90
Limits, 85
Limits Fixed Rel, 82, 86
LINE front panel key, 8
line fuse, 10
line power connector, 10
LINE switch, 8
LO feedthrough, 19
Load key, 7
loading a state from analyzer
memory, 78
loading amplitude correction
factors from analyzer
memory, 78
loading files from memory, 77
loading limit lines from analyzer
memory, 78
local oscillator signal, 19
lock files in memory, 78
low level signals
reducing attenuation, 37
reducing resolution bandwidth,
39
reducing video BW, 40
video averaging, 41
low-level signals, 37
M
Marker Count key, 29
marker counter example
marker frequency resolution, 29
Marker Delta key, 20
marker keys, 7
Marker to peak-to-peak key, 2 1
Max Hold A key, 35
maximum hold, 33
Measure key, 6
measurement
%AM, 70
bandwidth, 68
stimulus response, 55
TOI, 72
measuring low-level signals, 37
measuring return loss, 63
memory
saving and loading files, 77
menu keys, 6
monitor output, 10
More key, 8
moving signals, 33
N
N dB Points key, 68
naming a file, 79
normalization, 59
Normalize On Off key, 59
number/units keypad, 9
104
0
on/off switch, 8
P
parallel interface connector, 11
Peak Search key, 7
percent AM, 6
percent AM measurement, 70
Point, 89, 96
power connector, 10
power input, 10
power on key, 8
Preset key, 7
presetting the analyzer, 7
Print key, 7
printer control, 7
probe power connector, 7
programming command entry,
external keyboard, 101
protect files in memory, 78
R
rear panel features, 10
reflection calibration and
measurement, 62
relative limit lines, 82, 86
resolution bandwidth
resolving signals, 23
resolving signals using resolution
bandwidth, 27
return loss measurement, 63
RF OUT 50 ohm, 8
RPG knob, 8
RS-232 interface connector, 11
S
Save key, 7
saving a state in analyzer
memory, 77
saving files in memory, 77
screen annotation, 13
screen title, using an external
keyboard
title, create with external
keyboard, 101
Segment, 87
sensitivity
spectrum analyzer, 37
service connector, 12
signal tracking
marker tracking, 31
Slope, 89
softkeys, 6
source power control, 56
Span key, 6
Span Zoom key, 33
speaker on/off control, 7
speaker volume control, 7
step keys, 9
stimulus response
measurements, 55
sweep coupling
stimulus response
measurements, 57
Sweep key, 7
sweep modes, 14
sweep output connector
SWEEP OUT, 11
Swp Coupling SR SA, 57
System key, 7
T
testing with limit lines, 81
third order intermodulation
distortion example, 46
third order intermodulation
measurement, 72
verification of, 73
time limit lines, 86
TOI, 6
TO1 On Off key, 72
Trace key, 7
trace modes, 15
tracking generator
measurement, 55
normalization, 60
stimulus response, 55
tracking unstable signals, 33
Trig key, 7
trigger modes, 14
U
unstable signals, 33
up arrow key, 9
using limit lines, 81
V
VGA connector, 10
video averaging example, 41
video BW example, 40
video connector, 10
volume control, 7
W
write-protect files, 78
X
X Axis Units Freq Time, 82, 86
Index
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