What Is Analog Demodulation; Applications; Using Analog Demodulation For Zero Span Measurements - Agilent Technologies 89410A Operator's Manual

Analog Demodulation Concepts

What is Analog Demodulation?

Analog demodulation demodulates amplitude modulated (AM), frequency
modulated (FM), and phase modulated (PM) signals.

Applications

AM, PM, and FM signals commonly consist of a high-frequency carrier signal
modulated by a lower-frequency audio, video, or data signal. For these signals,
analog demodulation removes the carrier frequency leaving the modulating signal
which is contained in the sidebands of the carrier signal. An example of this
application is included in "Demodulating an Analog Signal" earlier in this book.
The most obvious use for analog demodulation is analyzing intentionally modulated
signals as noted above. However, analog demodulation is also useful in analyzing
signals which are not intentionally modulated. For example, you may choose to:
l
Apply phase and frequency demodulation to oscillator or synthesizer designs
to examine phase and frequency trajectories during frequency hops or to
establish phase-lock-loop lock-up time. For an example of this type of
application see "Characterizing a Transient Signal" earlier in this book.
l
Demodulate a burst signal to evaluate wait time to determine when a signal
stabilizes.
l
Amplitude and phase demodulate sidebands to determine the type of
modulation present in phase noise.
l
Demodulate bearing noise in mechanical measurements to examine
frequency instability.

Using analog demodulation for zero span measurements

If you are accustomed to making zero span measurements, you can use AM
demodulation to make similar measurements. The information bandwidth of other
analyzers is limited by the resolution bandwidth filters, but in 89400 series
analyzers the information bandwidth is only limited by span. Therefore, AM
demodulated signals appear similar to zero span measurements with a wider choice
of information bandwidth.
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