Model 8640B TM 9-4935-601-14-7&P
ADJUSTMENTS
5-39. FM LINEARITY ADJUSTMENT (Cont'd)
PROCEDURE:
1. Connect equipment as shown in Figure 5-7 after setting Signal Generator's controls as follows:
Meter Function .............................................................................................................................. FM
COUNTER MODE: EXPAND......................................................................................................... Off
LOCK ........................................................................................................................................... Off
Source .......................................................................................................................................... INT
AM ............................................................................................................................................... OFF
FM ................................................................................................................................................ .AC
PEAK DEVIATION ................................................................................................................ 2.56 M Hz
PEAK DEVIATION Vernier ....................................................................................................... Full cw
RANGE ........................................................................................................................ 256 - 512 MHz
FREQUENCY TUNE.............................................................................................................. 360 MHz
OUTPUT LEVEL ....................................................................................................................... -7 dBm
RF ON/OFF................................................................................................................................... . ON
NOTE
If it is desired to optimize FM linearity at a frequency other than mid-band, proceed as follows:
a. Set RANGE and FREQUENCY TUNE to the desired frequency.
b. Set RANGE to 256 - 512 MHz.
c. Set the reference signal generator 5 MHz below the test generator's output frequency.
2. reference signal generator for a 355 MHz, CW signal at + 7 dBm.
3. Calibrate the discriminator; prepare a 25 kHz filter (from the filter kit) and install it in the discriminator. Set FM
linearity circuit's output switch to ref ∅. Adjust variable-phase generator's variable phase output's amplitude and
the oscilloscope's horizontal gain for full screen deflection on the display. Adjust reference signal generator for 5
MHz on the discriminator.
4. Set variable-phase generator's reference phase output for a 1 kHz signal at an amplitude that gives a 2.56 MHz
peak deviation indication on the Signal Generator's panel meter. Set linearity circuit's voltage divider switch to
100. Adjust generator's variable phase output's phase for a straight line on the display as shown in Figure 5-8.
Adjust oscilloscope's vertical gain for ± 1 division at edge of display.
5-31
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