Frequency Mod

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This block is an input amplitude controlled complex sine. It outputs a signal, which has a momentary phase increase that is proportional to sensitivity and input amplitude.

More specifically, takes a real, baseband signal (x_m[n]) and output a frequency modulated signal (y[n]) according to:

Freq-mod-1.png

Where x[n] is the input sample at time n and is the frequency deviation. Common values for are 5 kHz for narrowband FM channels such as for voice systems and 75 kHz for wideband FM, like audio broadcast FM stations. In this block, the input argument is sensitivity, not the frequency deviation. The sensitivity specifies how much the phase changes based on the new input sample. Given a maximum deviation , and sample rate , the sensitivity is defined as:

Freq-mod-2.png

Parameters

(R): Run-time adjustable

Sensitivity (R)
Sensitivity = (2 * math.pi * deviation) / sample_rate
where 'deviation' is the change of the frequency when the input is at the values of -1 or +1. If the input is outside [-1, +1], it can deviate more.

Example Flowgraph

NFM xmt 2 fg.png

Source Files

C++ files
frequency_modulator_fc_impl.cc
Header files
frequency_modulator_fc_impl.h
Public header files
frequency_modulator_fc.h
Block definition
analog_frequency_modulator_fc.block.yml