Ext Ac, Ext Dc; How To Set Fm With An External Source - HP 8642A Operation And Calibration Manual

Operation
Model 864 2A/B
Modulation, FM (cont'd)
How to Set FM with an External Source
3-108
EXT AC, EXT DC
Source
Do not apply more than 15 Vpk maximum external voltage to the
FM/wM INPUT or damage to the Signal Generator's circuitry could
result.
The external modulation source connects to the FM/wM INPUT connector (input
impedance of 600 ohms).
The external modulation signal level should be adjusted to a 1 Vpk (0.707 Vrms)
sinewave input to the Signal Generator to get the displayed FM deviation. With an
external I Vpk signal applied, the Signal Generator modulates its RF output to achieve
the deviation setting. For example, if a I Vpk external modulation source is provided,
with the Signal Generator's FM deviation set to 50.0 kHz per volt, the output has 50.0
kHz FM deviation.
(If
the source voltage is reduced to 0.5 Vpk, and no other settings are
changed, the output has 25.0 kHz FM deviation.)
If the HI and La annunciators are not displayed then the externaly modulation signal is
between 0.95 Vpk and 1.05 Vpk. The HI, La annunciators only apply to sinewave
mputs. The HI, LO detectors do not monitor dc voltage input levels.
External Coupling
Anyone of the following functions can be used to couple the external FM/<i>M INPUT to
the FM circuitry:
AC-Coupled Source
., (EXT AC )
This function selects the external, ac-coupled FM source (displaying the EXT and AC
ann uncia tors).
o INT
+
(EXT AC) ([ SHIFT ) ( EXT AC ) )
This function selects the external, ac-coupled FM source and internal FM source
summed together (displaying the INT, EXT, and AC annunciators).
e EXTERNAL LOW RATE FM (Special Function 5)
This function selects the external, ac-coupled FM source for 0.4 Hz to 200 kHz rates
(displaying the EXT annunciator).
(Refer to page 3-112 for more information about this specia 1 function.)
9
INTERNAL + EXTERNAL LOW RATE FM (Special Function 112)
This function selects the external, ac-cQupled FM source (for 0.4 Hz to 200 kHz
rates) and internal FM source summed together (displaying the INT and EXT
annunciators). (Refer to page 3-112 for more information about this special
function)
e AC-COUPLED DC FM
Note: AC-Coupled DC FM is listed under DC-Coupled Source on page 3-109.