Interactions With Other Features; Choosing Trigger Type With Analog Demodulation; Using Gating And Averaging With Analog Demodulation; Two-Channel Measurements And Analog Demodulation - Agilent Technologies 89410A Operator's Manual

Interactions with other features

Choosing trigger type with analog demodulation

The analog demodulator is located after the triggering circuits so it is not possible
to trigger on the demodulated signal. However, if the signal is AM modulated or
pulsed, IF trigger can be used to obtain a stationary time waveform.
External triggering (or triggering on the second input channel) can be used if the
original modulating signal is available.

Using gating and averaging with analog demodulation

When using analog demodulation, features such as gating, band power markers,
and averaging work as described for vector mode except that they work on the
demodulated signal, not the original signal. When demodulating, the entire time
record is demodulated.

Two-channel measurements and analog demodulation

Analog demodulation is performed on a channel-by-channel basis. This
architecture lets you independently select the type of demodulation, and, more
importantly, lets you demodulate one channel while measuring baseband signals on
the other. For example, you can use a PM demodulator to measure unintentional
phase modulation of an oscillator on channel one. At the same time you can
measure the signal thought to be causing the modulation by using channel two for a
baseband measurement. You can compare the two measurements visually by
observing their respective time and spectrum displays, or you can compare them
mathematically by using the coherence, cross-spectrum, frequency response, or
cross-correlation functions. You can use this two-channel capability to perform
tasks such as: tracking down the sources of phase-noise in an oscillator, or
computing the frequency response (magnitude and phase) of a modulator or
demodulator.
There are special considerations for using analog demodulation with two channels:
l
Both channels share the same center frequency when demodulators are
enabled for both channels.
l
When one channel has a demodulator enabled and the second does not, the
second channel makes baseband measurements with a span which is half of the
selected measurement span. This span matches the span of the demodulated
spectrum of the first channel.
Analog Demodulation Concepts
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