
Model 8640B
TM 9-4935-601-14-7&P
SETTING MODULATION
NOTES
1. The REDUCE FM VERNIER annunciator (4) lights whenever an FM input causes peak deviation
to exceed its limits. When it lights, reduce either the PEAK DEVIATION vernier or the external
signal level.
2. Do not apply FM signals that are less than 50 Hz when using the generator in the phase lock
mode. Doing so will cause either the FM deviation to be uncalibrated or the generator to break
phase lock (thereby causing the counter display to flash). Also do not use FM CAL after locking.
Simultaneous AM and FM
a. Simultaneous AM and FM, or pulse modulation and FM, can be accomplished using the procedures described
above. The internal modulation oscillator can be used for either one or both, AM and FM.
NOTE
On Signal Generators with the Option 001 Variable Modulation Oscillator, don't load both AM
OUTPUT (19) and FM OUTPUT (17) when the oscillator is providing both modulating signals.
The outputs are in parallel and the parallel load should be greater than 600 ohms.
Figure 3-6. Setting the Modulation Controls (4 of 4)
3-18
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