Quadrature Demod

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This can be used to demod FM, FSK, GMSK, etc. The input is complex baseband, output is the signal frequency in relation to the sample rate, multiplied with the gain.

Mathematically, this block calculates the product of the one-sample delayed-&-conjugated input and the undelayed signal, and then calculates the argument (a.k.a. angle, in radians) of the resulting complex number:

Let x be a complex sinusoid with amplitude A>0, (absolute) frequency and phase sampled at f_s>0 so, without loss of generality,

then

is real, and so is , and hence only scales, therefore is invariant: = arg

This block does not support C++ output, so it cannot be used when the output language of a flowgraph in GRC is C++.

Parameters[edit]

Gain
Gain setting to adjust the output amplitude. Set based on converting the phase difference between samples to a nominal output value. Default: "samp_rate/(2*math.pi*fsk_deviation_hz)".

Example Flowgraph[edit]

This flowgraph shows the Quadrature Demod block as a Frequency Shift Keying detector.

RTTY rcv.png

Source Files[edit]

C++ files
[1]
Header files
[2]
Public header files
[3]
Block definition
[4]