About Analog Demod

Analog Demod (Analog Demodulation) demodulates the following analog-modulated signals.

Amplitude modulated (AM Amplitude Modulation - CW modulation using amplitude variation in proportion to the amplitude of the modulating signal. Usually taken as DSB-LC for commercial broadcast transmissions and DSB-SC for multiplexed systems.)
Frequency modulated (FM Frequency Modulation)
Phase modulated (PM)

Selecting Analog Demod

To enable Analog Demod, select the analog demodulator (click MeasSetup > Measurement Type > General Purpose > Analog Demod). Then open the demod properties dialog box and set the analog demodulation parameters (click MeasSetup > Analog Demod Properties).

Overview

Analog Demodulation characterizes amplitude modulated, frequency modulated, and phase modulated signals in both the frequency domain and the time domain. The VSA determines the amplitude, phase, or frequency deviation of the modulating signal relative to the carrier.

If averaging is enabled, the carrier amplitude obtained by averaging across the current time record is fed into an exponential average of estimates from prior time records. The resulting averaged carrier amplitude estimate is used for the above AM calculation.

PM and FM demodulation selects automatic carrier-frequency estimation algorithms. For PM and FM demodulated traces, the estimated carrier frequency can be shown using Analog Demod Carrier. Averaged measurements also average the estimated carrier frequency for FM and estimated carrier amplitude for AM.

Modulated signals commonly consist of a high frequency carrier-signal modulated by lower frequency audio, video, or data signals. These may also be contaminated with unintentional sources of modulation.

Analog Demod recovers the baseband-modulating signal, which is contained in the sidebands of the carrier signal. One example is a VCO turn-on transient, in which the stable oscillating frequency can be considered a carrier, and overshoot an FM or PM modulation of the carrier.