Amplitude De-Modulation

Hello all,

I’m working on an Amplitude De-modulator. I have verified the received
signal is: x(t) = m(t)cos(2pibase_freq*t).

x(t) — |multiplier| — |lowpass filter| — km(t)
cos(2
pibase_freqt)

My difficulty is creating the lowpass_filter and complex/float
conversions.

channel_coeffs = gr.firdes.low_pass(1.0,
if_rate,
baseband_freq,
baseband_freq/2,
gr.firdes.WIN_HANN)

center_filter = gr.fir_filter_fff(2, channel_coeffs)

Here the filter is defined as fff, if I use ccf will the output be the
same? Also what does the first input parameter to gr.fir_filter_fff
mean?
In am_rcv.py, they set it to ‘2’, but do not show how to derive it.

Jonathan Shan

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