HP 8642A Operation And Calibration Manual page 158

Operation
Model 8642A/B
Modulation,
~M
(cont'd)
3-122
If the HI and LO annunciators are not riisptayed thcn the external modulation signal is
between 0.95 Vpk. and 1.05 Vpk. The HI, LO annunciators only apply to sinewave
inputs. The HI, LO detectors do not monitor dc voltage input levels.
External Coupling
Anyone of tht following
f
ldlctions can be used to couple the external FM/<PM INPUT to
the <l>M circuitry:
AC-Coupled Source
$
mr
AC I
This function selects the external, ac-coupled <PM source (displaying the EXT and AC
annunciators).
e
INT
+
(EXT AC) ((
SHIFT I ( EXT AC ) )
This function selects the external, ac-coupled q>!\1 source and internal
pM
source
summed together (displaying the INT, EXT, and AC annunciators).
DC-Coupler! Source
o (EXT DC )
This function selects the external, dc-coupled <l>M source for de to 15 kHz rates
(displaying the EXT and DC annunciators).
$
INT+ (EXT DC)
([§BJED I EXT DC ) )
This function selects the external, dc-coupled !pM source and internal PM source
summed together (displaying the INT, EXT, and DC annunciators).
Rate
Determined by the external modulation source frequency.
NOTE
Fxternal modulation frequency is not monitored by the Signal
Generator. The Signal Generator's mod\llation frequency display
I efers to the internal modulation oscillator only.
Deviation
<l>M
(r-[
S"' R rrl " ' " F ..... T-,j
crnJ )
and the desired value of
<PM
deviation in radians ( [
RAD
%
(per volt).
When using an external source, the 1>M deviation setting does not set the actual
deviation, It sets the input sensitiVity per volt. A linear relationship exists between the
<l>M
deviation setting and the external voltage applied (for voltages less than
approxima tely 1.2 V pk).
NOTE
With simultaneous internal ane! external modulation, the sum of the
internal and external signals sllLluld not cause the 1>M deviation to
exceed the limits mentioned on page 3-119. If these limits are
exceeded, the Signal Generator could go out of lock which causes
queued up Hardware Error messages. Also, the external FM/1>M
lNPUT
d~,es
not respond linearly to inputs greater than
approximately
J
2 \'pk