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14. Gain Compression
Gain Compression is measured by applying two signals, separated by 3 MHz. First, the test places a -30 dBm signal at the input of the spectrum analyzer (the spectrum analyzer reference level is also set to -30 dBm). Then, a 0 dBm signal is applied to the spectrum analyzer, overdriving its input. The decrease in the first signal’s amplitude (gain compression) caused by the second signal is the measured gain compression.
There are no related adjustment procedures for this performance test.
Equipment Required
Synthesized sweeper
Synthesizer/level generator
Measuring receiver (used as a power meter)
Power sensor
Directional bridge
Adapter, Type N (f) to BNC (m)
Adapter, Type N (m) to BNC (m)
Adapter, Type N (f) to APC 3.5 (f)
Adapter, Type N (m) to BNC (f)
Cable, BNC, 120 cm (48 in) (2 required)
Additional Equipment for Option 001
Power sensor, 75 D
Adapter, Type N (f) to BNC (m), 75 62
Adapter, BNC (m) to BNC (m), 75 D
l-60 Calibrating HP 8590D Spectrum Analyzer
14. Gain Compression
Caution
Use only 75 Q cables, connectors, or adapters on the 75 61 input of an Option
001 or damage to the input connector will occur.
SYNTHESIZED SWEEPER
LW
R F O U T P U
MEASURING RECEIVER r-1
ADAPTER
SPECTRUM ANALYZER
POWER SENSOR
B
ADAPTER
I
SYNTHESIZER/LEVEL
GENERATOR
ADAPTER
SOURCE
I
XY121
Figure l-20. Gain Compression Test Setup
Procedure
1. Zero and calibrate the measuring receiver and the power sensor in log mode so the power reads out in dBm. Enter the power sensor’s 50 MHz Cal Factor into the measuring receiver.
Option 001 only:
Calibrate the 75 62 power sensor.
2. Connect the equipment as shown in Figure l-20, with the load (reflected) of the directional coupler connected to the power sensor.
Option 001 only:
The power measured at the output of the 50 D directional bridge by the
75 6) power sensor, is the equivalent power “seen” by the 75 61 spectrum analyzer. Use the
75 D power sensor with a Type N (f) to BNC (m) 75 62 adapter and use a BNC (m) to BNC
(m) 75 62 adapter in place of the 50 Q adapter.
3. Press INSTRUMENT PRESET on the synthesized sweeper then set the controls as follows:
CW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53 MHz
POWERLEVEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..6dBm
4. Set the synthesizer/level generator controls as follows:
CW.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..50MH z
AMPLITUDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -14 dBm
50 O/75 Q SWITCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
75 Q (no RF output)
HP 859OD Spectrum Analyzer Calibrating l-61
14. Gain Compression
5. On the spectrum analyzer, press (j-1 and wait for the preset to finish then set the controls as follows:
FREQUENCY]
50 IhnHz) h2om
Option 001:
Press
(
AMPLITUDE
],
More 1 of 2 , Amptd Units , then dEm
.
6. On the synthesized sweeper, adjust the power level for a 0 dBm reading on the measuring receiver. Set RF to OFF On the synthesizer/level generator, set the 50 O/75 62 switch to
50 0.
Note that the power level applied to the spectrum analyzer input is 10 dB greater than the specification to account for the 10 dB attenuation setting. A power level of 0 dBm at the spectrum analyzer input yields -10 dBm at the input mixer.
7. Disconnect the power sensor from the directional coupler and connect the directional coupler to the INPUT 50 Q connector of the spectrum analyzer using an adapter and not a cable.
Option 001 only:
Use a 75 D adapter, BNC (m) to BNC (m).
8. On the spectrum analyzer, press the following keys:
SPEAK S E A R C H )
(MKRFCTN) MK
TRACK OM OFF (ON)
[SPAN) 100
Wait for the AUTO ZOOM message to disappear.
9. On the synthesizer/level generator, adjust the Amplitude to place the signal 1 dB below the spectrum analyzer reference level.
19. On the spectrum analyzer, press
[SGLSWP), [PEAK
SEARCH
),
then MARKER A .
11. On the synthesized sweeper, set RF to ON.
12. On the spectrum analyzer, press
f,jsGL], (
PEAK SEARCH
),
NEXT PEAK. The active marker should be on the lower amplitude signal and not on the signal that is off the top of the screen. If it is not on the lower amplitude signal, reposition the marker to this peak using the spectrum analyzer knob.
13. Read the MKR A amplitude and record as TR Entry 14-1 in the performance test record.
The absolute value of this amplitude should be less than or equal to 0.5 dB.
1-62 Calibrating
HP 859OD Spectrum Analyzer
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