4.8 Phase modulation (PM)
In PM, the phase of the carrier is varied by the instantaneous voltage of the modulating waveform.
All the 16 waveforms could be used as carrier waveform.
Of course, it is invalid to use DC or noise.
Before entering into phase modulation, users should firstly set the waveform, frequency and amplitude of
carrier wave under continuity function.
Press
【
PM
】
key to light “PM”, the generator enters into PM function.
4.8.1. Modulation frequency:
Press
【
Menu
】
key to light “Mod_f” character and then set modulation frequency value.
In PM, modulation frequency is usually far lower than carrier frequency.
4.8.2. Phase deviation:
Press
【
Menu
】
key to light “Devia” character, and then set phase deviation value.
Phase deviation represents the variation of carrier phase while the modulating waveform is with full
amplitude in phase modulation. When the amplitude of the modulating waveform is at positive peak value,
the phase of the outputted signal increase one phase shift, and when it is at the negative peak value, the
phase of the outputted signal decrease one phase shift.
4.8.3. Modulation waveform:
Press
【
Menu
】
key to light “Shape” character, the current modulation waveform sequence No. is shown,
input modulation waveform No. with the numeric keys or adjusting knob to select modulation waveform,
the modulation waveform may be any one of the 16 kinds of waveforms listed in the waveforms table in
section 4.2.9.
4.8.4. Sync output:
I
n PM, the generator outputs a sync signal from the front panel “Sync” connector, which is a square wave
with TTL level and 50% duty cycle, its frequency is equal to modulating frequency and its phase is
referenced to the phase of the modulating signal.
In PM, press
【
PM
】
key, the “PM” keyboard light will be off, the generator exits PM function and returns
back to continuity function.
-47-
