
Model 8640B
TM 9-4935-601-14-7&P
ADJUSTMENTS
5-32. AM SENSITIVITY ADJUSTMENT (Cont'd)
e.
Calculate
V
off where
V
DET 2
-
a
V
DET 1
V
off=
1
-
a
and
a
=
V
RF 2/
V
RF 1 (i.e.,
a
= attenuation; for 20 dB it is 0.1).
therefore
V
DET 2 + 50 mVdc
V
off =
0.9
f.
Reset step attenuator to 0 dB, Signal Generator as specified in step 1, and spectrum analyzer as specified
in step 3.
5. To calibrate spectrum analyzer for percent of AM measurement, use analyzer's reference level controls to set -
282.8 mV +
V
off at vertical output (as measured on the DVM). For example, if
V
off is +50.0 mV, then set -282.8
mV + (+50.0 mV) or -232.8 mV at vertical output. (Check that trace is peaked on analyzer display.)
6. Set DVM to measure mVrms (ac only). Adjust % AM adjustment, A26A2R19, for a DVM indication of 100
mVrms.
5-33. PEAK DEVIATION AND RANGE SWITCH ADJUSTMENT
REFERENCE:
Service Sheets 6, 7, and 8.
DESCRIPTION:
The switches are adjusted so that the FM gain switch (i.e., A9S3, the switch that is controlled by both the peak deviation
and the frequency range switch) is correctly positioned. This procedure should be performed whenever the A9 assembly
has been disassembled.
PROCEDURE:
1. Set RANGE and PEAK DEVIATION switches full cw. Loosen setscrews in the knobs and position RANGE switch
knob so that 512 - 1024 MHz is under the cursor on front panel. Position PEAK DEVIATION switch knob so that
5.12 MHz is under the cursor on front panel. Tighten setscrews.
5-19
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