Related Special Functions; Low Distortion Fm/*M On - HP 8642A Operating Manual

Operation
Model 8642A/B
Modulation, $M (cont'd)
Selecting Heterodyne Band Operation
Special Function 8 (Prefer Het Band) can be used to cause the Signal Generator to oper­
ate in the heterodyne band regardless of $ M deviation, whenever RF frequency is less
than 132.187501 MHz. This function prevents the Signal Generator from switching
from the heterodyne band when it would be possible to use the divide bands. Refer to
"How to Select the Het Band" on page 3 - 4 1 .
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 FM and <t>M. $M is allowed in the following combinations:
Any one of these types:
• Internal $M,
• External a c - or dc-coupled $M, or
• Internal + external a c - or dc-coupled $ M
With any one of the following:
• Internal AM,
• External a c - or dc-coupled AM,
• Internal + external a c - or dc-coupled AM,
• Internal pulse modulation, or
• External dc-coupled pulse modulation.
NOTE
All internal modulation sources use the internal modulation
oscillator, therefore all internal modulation, as well as MOD
OUTPUT, have the same modulation frequency.
Spurious Signals (Spurs) That Occur with the Internal Source
Internally generated spurs (with levels specified less than - 1 0 0 dBc) 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 o u t ­
put (MOD OUT) is off.
HP-IB. Sequence Dependency
$ M settings are sometimes coupled with other functions. Therefore, HP-IB codes may
need to be entered in a particular sequence when accessing combinations of these func­
tions. Refer to the discussion about Sequence Dependency, which begins on page 3-12 in
the HP-IB portion of this Section III.
Related
Special
Functions 7. Low Distortion FM/€>M On. In the $ M mode, the low distortion function is
limited by the actual frequency deviation. Therefore, to use Special Function 7 for $M,
you need to calculate frequency deviation as the phase deviation (in radians) times the
modulation frequency (in Hz). Frequency deviation must be less than 7% of the maxi­
mum allowable frequency deviation for the RF frequency chosen.
207. Low Distortion FM/4>M Off. This special function switches out the shaper cir­
cuitry inserted with Special Function 7.
3-124