User Manual

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:
In 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.
4.9. Pulse width modulation（PWM）
In PWM, the pulse width of the carrier varies with the instantaneous voltage of the modulating signal, and the
waveform shape of the carrier must be pulse. Before entering into PWM, users should firstly set the
frequency and amplitude of carrier wave under continuity function.
Press【PWM】key, the keyboard indicator of “PWM” will be on and the generator enter into pulse width
modulation function, the carrier wave is automatically set as pulse wave.
4.9.1. Modulation frequency:
Press【Menu】key to light “Mod_f” character and set modulation frequency value. In pulse width
modulation, modulation frequency is far lower than carrier frequency.
4.9.2. Pulse width deviation:
Press【Menu】key to light “Depth” indicator and set pulse width deviation value. It represents the variation
of carrier pulse width to the period of the pulse when the modulating waveform is with full amplitude during
PWM process, also the variation of the duty cycle. Name the maximum duty cycle of modulated carrier as
Dmax, and the minimum as Dmin, the pulse width deviation’s formula should be:
Pulse width deviation=Dmax-Dmin
If Dmax=80%, Dmin=20%, the pulse width deviation is 60％. If Dmax=50%, Dmin=50%, the pulse width
deviation should be 0%. That is to say, when pulse width deviation is 0, the duty cycle of pulse wave is 50%.
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