
Model 8640B
TM 9-4935-601-14-7&P
ADJUSTMENTS
5-32. AM SENSITIVITY ADJUSTMENT (Cont'd)
PROCEDURE:
1. Connect equipment as shown in Figure 5-2 after setting Signal Generator's controls as follows:
Meter Function ................................................................................................AM
COUNTER MODE: EXPAND .......................................................................... Off
LOCK.............................................................................................................. Off
Source ........................................................................................................... INT
AM .................................................................................................................. AC
MODULATION .......................................................................................... Full cw
FM ................................................................................................................OFF
RANGE ......................................................................................... 256 - 512 MHz
FREQUENCY TUNE .............................................................................. 512 MHz
OUTPUT LEVEL .....................................................................................-27 dBm
.................................................. (switch 5 steps ccw from full cw, vernier full cw)
RF ON/OFF ....................................................................................................ON
2. Set test oscillator for a 1 kHz, 353.6 mVrms signal as, read on DVM (50% AM). Disconnect DVM from test
oscillator (leave oscillator connected to generator). Connect the DVM to spectrum analyzer's vertical output. Set
calibrated step attenuator to 0 dB.
3. Set spectrum analyzer's resolution bandwidth to 300 kHz, input attenuation to 20 dB, frequency span per division
(scan width) to 20 kHz (tuning stabilizer on), scale to linear, and adjust center frequency and scale reference
level controls to center the 512 MHz signal on the display. Set frequency span per division to 0 Hz and display
smoothing (video filter) to 10 kHz. Peak the trace on the display with center frequency controls; set trace to
center of display with reference controls.
NOTE
Step 4 measures the analyzer's dc offset (
V
off) and must be performed to ensure the accuracy of this
test. However if
V
off for the analyzer being used has recently been measured and noted, skip step 4 and
go on to step 5 (and eliminate the calibrated step attenuator from the test setup).
4. Measure analyzer's dc offset (
V
off) by performing steps "a" through "f".
a.
Set generator's controls as follows:
Meter Function .......................................................................................... LEVEL
AM ................................................................................................................OFF
RANGE .................................................................................................2 - 4 MHz
FREQUENCY TUNE ..................................................................................3 MHz
b.
Set analyzer's center frequency controls to 3 MHz.
c.
Adjust analyzer's reference level controls for -500 mVdc indicated on DVM (
V
DET 1)-
d.
Set step attenuator to 20 dB. Note DVM reading (
V
DET 2)-
5-18
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