AM Demodulation

The VSA uses the following algorithm to perform 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. demodulation:

$image\amdemodFormula1_wmf.jpg$

As shown in the following illustration, AM demodulation averages the carrier amplitude to derive the modulation index from the envelope.

$image\AMwaveform_wmf.jpg$

AM Demodulation and Averaging

Carrier amplitude estimates are always performed on AM calculations, as an estimate of the carrier amplitude is required to produce units of modulation depth.

For AM measurements, the carrier-amplitude estimate from the current time record is fed into an exponential average of estimates from prior time records. The resulting averaged carrier-amplitude is used as the carrier amplitude in the current time record's AM calculation.