5.4.3. Modulation waveform
Press
【
Menu
】
key and select “Shape” option, set modulation waveform by setting waveform No., the
modulation waveform may be any one of the 16 kinds of waveforms listed in the waveforms table.
5.4.4. Modulation source
Press
【
Menu
】
key, select “Source” option and then set modulation source, there are only two values to
choose: 0 and 1. Set the value as 0 to choose internal modulation source, and set it as 1 to choose external
modulation source. If external modulation source is chosen, connect a modulation signal to the
《
Modulation
In
》
port on the rear panel of the generator. When external modulation signal reaching to full amplitude as
±5 V, the display of frequency deviation accords with its real value. Or the display of frequency deviation is
incorrect.
5.4.5. Sync output
In FM, 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 wave frequency and its phase is
referenced to the phase of the modulating wave.
In FM, press
【
FM
】
key, the keyboard indicator of “FM” will be off, the generator will exit frequency
modulation function and return back to continuous function.
5.5. Amplitude modulation (AM)
In AM, the amplitude of the carrier is varied by the instantaneous voltage of the modulating waveform, all the
16 kinds of waveforms listed in the waveforms table could be used as carrier waveform. Before entering into
amplitude modulation, the users should set the waveform, frequency and amplitude value of the carrier wave
first under CHA continuous function.
Press
【
AM
】
key, the keyboard indicator of “AM” will be on and CHA output amplitude modulation signal.
5.5.1. Modulation depth
Press
【
Menu
】
key and select “Depth” option, and then set modulation depth value. Modulation depth
represents the percentage of variation of the carrier amplitude to the amplitude setting value while the
modulating wave is with full amplitude during AM process. If the maximum amplitude of the modulated carrier
waveform is called as Amax, the minimum amplitude as Amin, the amplitude setting value as A, the
modulation depth as M, then the relationship between the four values is:
Amax
＝
(1+M)×A÷2.2 Amin
＝
(1-M)×A÷2.2
Then the modulation depth is M
＝
(Amax
－
Amin)×1.1÷A
If modulation depth is 120%, Amax=A, Amin=-0.09A. If modulation depth is 100%, Amax=0.909A, Amin=0. If
modulation depth is 50%, Amax=0.682A, Amin=0.227A. If modulation depth is 0
％
, Amax=0.455A,
Amin=0.455A. That is to say, when modulation depth is 0, carrier amplitude is about half of the amplitude
setting.
3.5.2. Modulation frequency
Press
【
Menu
】
key and select “Mod_f” option, and then set modulation frequency value. In AM, modulation
frequency is usually far lower than carrier frequency.
3.5.3. Modulation waveform
Press
【
Menu
】
key and select “Shape” option, set modulation waveform by setting waveform no. The
modulation waveform may be any one of the 16 kinds of waveforms listed in the waveforms table.
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