HP 8642A Operation And Calibration Manual page 137

Model 8642A/B Operation
Modulation, AM (cont'd)
Comments Specified AM Rates Can Be Increased by Selecting the Het Band
AM depths are specified for depths less than or equal to 90% at a maximum rate of 20
kHz in bands 2, 3, and 4 (4130860 to 33046875 MHz). You can increase specified
AM rates in this RF frequency range from a maximum of 20 kHz to a maximum of
100 kHz by selecting Special Function 8 (Prefer Het Band). Refer to "How to Select
the Het Band" on page 3-41.
Spurious Signals (Spurs) That Occur With the Internal Source
Internally generated spurs (with levels specified less than -100 dEc) might be present
when the internal modulation oscillator is in use. These spurs will be eliminated when
no internal modulation source is modulating the carrier, and the modulation oscillator
(MOD OUT) is off.
Modulation Switching Time
The time required to turn on the internal modulation oscillator or to switch between
modulation frequencies can be reduced by approximately 200 ms (depending on
modulation frequency), with a loss in modulation frequency accuracy, by selecting
Modulation Frequency Correction Off (Special Function 113). For more information,
refer to "Speeding Up Modulation Switching Time" on page 3-132.
The time required to turn on the internal modulation oscillator is increased by
approximately 200 ms if DC FM Update Mode (Special Function 117) is active. For
more information, refer to "117 DC FM Update Mode On" (page 3 -116).
Modulation Restrictions with Other Functions
AM and pulse modulation are not possible during amplitude sweep. Also, AM and
pulse modulation are not possible when ALC Off (Special Function 4) is selected.
Mixed Modulation
The Signal Generator can simultaneously modulate the RF signal with more than one
modulation type. The Signal Generator does not allow simultaneous AM and pulse
modulation or simultaneous PM and <PM.
AM is allowed in the following
combinations:
Anyone of these types:
e In ternal AM,
o External ac- or dc-coupled AM, or
~ Internal
+
external ac- or dc-coupled AM
With anyone of the following:
o Internal FM,
$
External ac- or dc-coupled FM,
e Internal + external ac- or dc-coupled FM,
e
External low-rate FM (Special Function 5),
• Internal + external low-rate FM (Special Function 112),
e Internal
~M,
~ External ac- or dc-coupled ~M, or
• Internal + external ac- or dc-coupled
~M.
NOTE
All internal modulation sources use the
modulation oscillator, therefore all
modulation, as well as MOD OUTPUT, have
modulation frequency.
internal
internal
the same
3-101