Related Special Functions; Modulation Frequency Correction Off; Calibrate The Modulation Frequency Bands Again - HP 8642A Operating Manual
Synthesized signal generator
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- Service manual (326 pages) ,
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Model 8 6 4 2 A / B
Operation
Modulation Oscillator (cont'd)
Special Function 213. When modulation frequency correction is disabled, the Signal
Generator does not automatically recalibrate at each modulation frequency when one is
selected. Instead, the instrument uses, as its calibration data, the previously calculated
calibration factor for each frequency band. The accuracy of previously calculated
calibration factors depends on variations in temperature from the time the calibration
factor was selected. Typically, 2% accuracy can be degraded to 5% if recalibration is not
performed when the Signal Generator is subjected to temperature changes of 50°C.
DC FM Update Mode (Special Function 117) also increases modulation frequency
switching by up to 200 ms. (Refer to Special Function 117 description in Modulation,
FM on page 3-116).
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
output (MOD OUT) is off.
Modulation Output Phase
The phase of the modulation output (MOD OUTPUT) is 180° out-of-phase with the
internal use of the modulation oscillator.
Underranging Specified Modulation Oscillator Frequency
Modulation oscillator frequencies as low as 10 Hz can be selected.
However, the
modulation oscillator's signal characteristics are not specified below 20 Hz.
Related
Special
Functions
113.
Modulation Frequency Correction Off.
This special function
disables the
single-band calibration of the modulation frequency oscillator that normally occurs
whenever the modulation oscillator frequency is set or the internal modulation oscillator
is put into use. When this calibration is disabled, the typical modulation frequency
switching time is decreased by approximately 200 ms. For more information, refer
"Speeding Up Modulation Switching Time" on page 3-1 32.
213.
Modulation Frequency Correction On.
This special function re-enables the
modulation frequency correction disabled with Special Function 1 1 3.
248. Calibrate the Modulation Frequency Bands Again. This special function enables
you to initiate the calibration sequence that normally only occurs during instrument
power-up.
This function can be used, for example, to recalibrate the modulation
oscillator frequency bands if normal modulation frequency correction has been disabled
with Special Function 11 3. Calibration typically takes one to two seconds.
3-133
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