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SDG7000A User Manual
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AM
AM is amplitude modulation, a modulation method that uses the amplitude of the modulating
waveform to control the amplitude of the carrier.
The parameters that can be set for AM are listed in the table below.
Table 10-4 Description of AM modulation parameters
AM
Modulation depth
Also known as amplitude modulation factor (m), determined by the
maximum and minimum amplitude of the envelope:
𝑚 =
U
cm,max
− U
cm,min
U
cm,max
+ U
cm,min
When source = internal or channel, this value can be set directly. When
source = external, it is determined by the amplitude of the external
modulation input.
AM frequency
The frequency of the modulating waveform.
When source = internal, the value can be set directly. When source =
external or channel, it is determined by the frequency of the external
modulation input or another channel.
Shape
The shape of the modulating waveform.
When source = internal, the value can be set directly. When source =
external or channel, it is determined by the external modulation input or
the waveform of another channel.
The AM amplitude strategy is to keep the power of the carrier the same as when it is unmodulated,
i.e.: the power of the carrier is independent of the modulation depth. This will result in the AM
waveform peaking beyond the set value, which is normal. The figure below shows a comparison
of the amplitude of a 100 MHz, 0 dBm carrier with no modulation and at 100% modulation depth,
and it can be seen that the peaks in the time domain become larger when modulation is turned
on, but the power of the carrier remains the same in the frequency domain.
Unmodulated time-domain diagram
100% modulation depth time-domain diagram
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