Related Special Functions; External Low Rate Fm On; Internal + External Low Rate Fm On - HP 8642A Operating Manual

Operation
Model 8642A/B
Modulation, FM (cont'd)
How to Obtain Low Residual FM
At high FM deviation settings, the residual FM performance of the Signal Generator can
be limited by ground loops set up between the external FM source and the Signal
Generator. For minimum residual FM, a floating external FM source should be used.
How to Obtain Maximum FM Stereo Separation
Maximum stereo separation (at least 50 dB) is achieved in the heterodyne band with
dc-coupled FM. Low Distortion FM (Special Function 7) may be selected to further
reduce total harmonic distortion.
HP-IB. Sequence Dependency
FM 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
functions. Refer to the discussion about Sequence Dependency, which begins on page
3-12 in the HP-IB portion of this Section III.
Table 3 - 2 0 . Maximum FM Deviation Settings with only an External Source
Band
10
9
8
7
6
5
4
3
2
1
Het
Frequency Range (MHz)
1057.500001 to 2115.00000
(8642B only)
528.750001 to 1057.500000
264.375001 to 528.750000
132.187501 to 264.375000
66.093751 to 132.187500
33.046876 to 66.093750
16.523438 to 33.046875
8.261719 to 16.523437
4.130860 to 8.261718
0.100000 to 4.130859
0.100000 to 132.187500*
Maximum FM Deviation Settings
(kHz
Pre-Emphasis Off
3000.000
1500.000
750.000
375.000
187.500
93.750
46.875
23.437
11.718
93.750
1500.000
per Volt)
Pre-Emphasis On
(Special Function 6)
420.498
210.249
105.124
52.562
26.281
13.140
6.570
3.285
1.642
13.140
210.249
"When FM deviations exceed limits listed for Bands 1 through 6, the Signal Generator automatically switches
to the Hetero dyne Band.
Related
Special
Functions 5. External Low Rate FM On
112. Internal + External Low Rate FM On
These special functions typically provide 0.4 Hz to 200 kHz external-FM ac coupling
with the Signal Generator remaining in a phase locked state. Input coupling required for
these functions makes the Signal Generator especially sensitive to dc voltage fluctuations.
Relatively small dc voltage changes can cause the Signal Generator to lose phase lock,
requiring one to two seconds to regain the locked condition. These functions will be
turned off when another FM modulation source is selected.
205. External Low Rate FM Off. This special function turns off the FM modulation
source selected with Special Function 5. When Special Function 5 is turned off in this
way, the Signal Generator selects external, ac-coupled FM.
3-112