Modulation, Fm - HP 8642A Operating Manual

Model 8642A/B
Operation
MODULATION, FM
Description The Signal Generator can frequency modulate its RF output either with a variable
internal modulation oscillator, and/or with an ac- or dc-coupled external source applied
to the FM/$M INPUT.
Depending on the RF frequency selected, the 8642A/B has different limits on the
possible FM deviation that can be selected. (See Figures 3-12 and 3-13 on the following
page.) The Signal Generator normally selects a divide band to obtain its FM deviation.
However, if the divide band's maximum internal FM deviation boundaries are crossed, the
Signal Generator can automatically switch to the heterodyne band which allows wider
FM deviation at RF frequencies less than 132.187 501 MHz. (Refer to RF Frequency,
page 3-39, for more information about these different bands.) If FM Pre-emphasis is
selected, more limitations are placed on FM deviation and modulation frequency. (Refer
to the discussion about FM Pre-emphasis starting on page 3-113 under "6. FM
Pre-emphasis On".)
Table 3-19. FM Operating Characteristics
Electrical Characteristics
FM Deviation Limitations
Indicator Accuracy
(Rates from 20 Hz to 100 kHz)
Resolution
FM Distortion
(Rates from 20 Hz to 100 kHz)
FM 3 dB Bandwidth
Performance Limits
See Figures 3-12 and 3-13
±(5% of setting +10 Hz)
0.7% of setting or 0.0004%
of maximum deviation
(whichever is larger)
4%
2%
0.4%
dc to 200 kHz
20 Hz to 200 kHz
20 Hz to 100 kHz
0.4 Hz to 200 kHz (with
Special Function 5)
Conditions
For maximum dc-coupled deviation
For
1
/2 maximum dc-coupled deviation
For
1
/is maximum dc-coupled deviation
External dc source
External ac source
Internal source
3-105