
Model 8640B
TM 9-4935-601-14-7&P
FRONT PANEL FEATURES
15 FM:
selects frequency modulation and source.
OFF: no FM.
INT: FM by internal oscillator.
AC: FM by external source through FM INPUT
jack (>20 Hz, ac + dc <5 Vpk).
DC: FM by external source through FM INPUT
jack (ac + dc <5 Vpk).
CAL: used to calibrate external modulation
input (do not use when phase locked).
16 PEAK DEVIATION:
switch and concentric vernier
vary FM frequency deviation (as indicated on the
meter). Vernier range is from zero to the peak
deviation selected by the switch.
17 FM INPUT/OUTPUT:
600 ohm input for external
FM; nominally 1 Vpk (0.7071 Vrms) required for full
peak deviation selected by PEAK DEVIATION
switch (never more than 5 Vpk). Output for internal
oscillator whenever FM selector is set to
INT (600 ohm source impedance); level controlled by
AUDIO OUTPUT LEVEL.
18 MODULATION FREQUENCY:
switch selects 400
Hz or 1000 Hz. With Option 001 Variable
Modulation Oscillator (shown), switch also selects
multiplier. Vernier, with multiplier, sets frequency
from 20 Hz to 600 kHz.
19 AM INPUT/OUTPUT:
600 ohm input for external
AM; 1 Vpk (0.7071 Vrms) required for 100%
modulation (never more than 5 Vpk). Input for pulse
modulation (50 ohm): >1 Vpk positive pulse
required to turn on RF. Output for internal oscillator
whenever AM selector is set to INT (600 ohm source
impedance); level controlled by AUDIO OUTPUT
LEVEL.
NOTE
With the Option 001 Variable
Modulation Oscillator, AM OUTPUT
and FM OUTPUT are in parallel.
Parallel load should be ->600 ohms.
Figure 3-2. Front Panel Controls, Indicators, and Connectors (3 of 4)
3-4
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