Analog Demod Carrier
The check box in the Markers > Calculation tab selects whether to show the carrier frequency of a signal for the active trace in the Markers window. is only available when the trace is the result of PM or FM Frequency Modulation demodulation.
When a demodulated trace is saved, the carrier frequency is saved with the trace. After recalling the trace, the carrier frequency can be viewed by selecting the checkbox.
Typically, the is used when Auto Carrier Frequency is selected. When no carrier frequency estimates are performed ( check box cleared), the demodulation algorithm uses the current center frequency as the carrier frequency. Hence, the the carrier frequency readout in the Markers Window will show the center frequency instead. When 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 is performed, the carrier frequency readout will show "Unavailable."
Averaging
When either time or rms averaging is selected, the carrier frequency for FM or carrier amplitude for AM is estimated for the current time record and fed into an exponential average. This provides an effect similar to loop bandwidth on a phase locked loop. Increasing the number of averages is equivalent to narrowing the loop bandwidth.
The current, averaged carrier estimate is used in the AM and FM algorithms.
See Also
