
Model 8640B
TM 9-4935-601-14-7&P
PERFORMANCE TESTS
4-22. RESIDUAL FM TEST (Cont'd)
DESCRIPTION:
An FM discriminator is used to measure FM deviation (a reference signal generator and a mixer are used to down-
convert the test Signal Generator's RF output to within the range of the discriminator). The discriminator output is filtered
and amplified and then measured with a voltmeter. The voltmeter reading, in mVrms, is proportional to the rms
frequency deviation of the residual FM.
NOTE
This test measures the total residual FM of both generators. Therefore, the reference generator
must have residual FM that is less than or equal to the specification for the test generator.
Figure 4-9. Residual FM Test Setup
EQUIPMENT:
FM Discriminator ......................................................................................................HP 5210A
Filter Kit..................................................................................................................HP 10531A
RMS Voltmeter .........................................................................................................HP 3400A
40 dB Amplifier ...........................................................................................................HP 465A
Capacitor 5 pF ................................................................................................... HP 0180-2211
Reference Signal Generator .....................................................................................HP 8640A
Mixer ......................................................................................................................HP 10514A
3 kHz Low-Pass Filter (LPF) ........................................................................ CIR-Q-TEL 5 Pole
15 kHz Low-Pass Filter (LPF) ...................................................................... CIR-Q-TEL 7 Pole
50 Ohm Load..........................................................................................................HP 11593A
4-22
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