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Uladzimir KarpenkaandClaude Opus 4.8
65cb3c386e
Model the pair on fmd.c / fmmod.c, but with the parts that a 75 kHz
deviation forces:
- the demodulator discriminates with arg(x[n] * conj(x[n-1])) rather
than a PLL; an omegaN in the tens of kHz cannot track 75 kHz.
- emphasis is a one-pole RC (tau 75 us) on both ends, not fmd's 1/f
fc_impulse FIR. A 1/f FIR from f_low = 20 Hz would sit ~+57 dB at
20 Hz, where broadcast FM specifies flat below the corner.
- TXA_WFM leaves the shared preemph block off; wfmmod carries its own.
- wfmmod clamps bp_fc = deviation + f_high to 0.45 * samplerate, since
+/-90 kHz exceeds Nyquist at the rates the narrowband modes use.
Scope is mono: no 19 kHz pilot, no 38 kHz stereo subcarrier, no RDS.
Both mode enums are appended to so the ABI stays stable for clients.
The JNI bindings are deliberately left alone.
Verified against a wfmmod -> wfmd loopback: the discriminator is exact,
the dc-removal one-pole tracks |H_lp(f)| * ain * sdelta to ratio 1.000,
and a 700 + 1900 Hz two-tone comes back with THD+N ~ 3e-5 % at +/-37.5
kHz deviation. Note the demodulator aliases unless samplerate exceeds
2 * deviation * |aud|max, so 192 kHz is the practical floor.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
104 lines
2.8 KiB
C
104 lines
2.8 KiB
C
/* wfmd.h
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This file is part of a program that implements a Software-Defined Radio.
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Copyright (C) 2013 Warren Pratt, NR0V
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License
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as published by the Free Software Foundation; either version 2
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of the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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The author can be reached by email at
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warren@wpratt.com
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*/
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#ifndef _wfmd_h
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#define _wfmd_h
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#include "firmin.h"
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#include "wcpAGC.h"
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typedef struct _wfmd
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{
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int run;
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int size;
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double* in;
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double* out;
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double rate;
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double f_low; // audio low cutoff
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double f_high; // audio high cutoff
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// quadrature discriminator
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double deviation; // peak deviation, Hz
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double again; // discriminator output gain
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double pre_i; // previous sample, I
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double pre_q; // previous sample, Q
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// for dc removal
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double tau;
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double mtau;
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double onem_mtau;
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double fmdc;
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// de-emphasis, single-pole RC
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int deemph_run;
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double tau_de; // 75.0e-6 (Americas) or 50.0e-6 (elsewhere)
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double mde;
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double onem_mde;
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double deemph_z;
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// for audio filter
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double* audio;
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FIRCORE paud;
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int nc_aud;
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int mp_aud;
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double afgain;
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// detector limiter
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WCPAGC plim;
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int lim_run;
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double lim_gain;
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double lim_pre_gain;
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} wfmd, *WFMD;
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extern WFMD create_wfmd ( int run, int size, double* in, double* out, int rate, double deviation,
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double f_low, double f_high, double tau, int deemph_run, double tau_de, double afgain,
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int nc_aud, int mp_aud);
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extern void destroy_wfmd (WFMD a);
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extern void flush_wfmd (WFMD a);
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extern void xwfmd (WFMD a);
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extern void setBuffers_wfmd (WFMD a, double* in, double* out);
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extern void setSamplerate_wfmd (WFMD a, int rate);
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extern void setSize_wfmd (WFMD a, int size);
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// RXA Properties
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extern __declspec (dllexport) void SetRXAWFMDeviation (int channel, double deviation);
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extern __declspec (dllexport) void SetRXAWFMNCaud (int channel, int nc);
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extern __declspec (dllexport) void SetRXAWFMMPaud (int channel, int mp);
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extern __declspec (dllexport) void SetRXAWFMAFFilter (int channel, double low, double high);
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extern __declspec (dllexport) void SetRXAWFMDeemphRun (int channel, int run);
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extern __declspec (dllexport) void SetRXAWFMDeemphTau (int channel, double tau);
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extern __declspec (dllexport) void SetRXAWFMLimRun (int channel, int run);
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extern __declspec (dllexport) void SetRXAWFMLimGain (int channel, double gaindB);
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#endif
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