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Filter improvement: LP and HP filters, added test function

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The -3 dB level at cut-off frequency is now maintained for multiple
iterations.
This commit is contained in:
Andreas Eversberg
2017-01-15 11:08:42 +01:00
parent 799b96c801
commit ac0da3f76e
10 changed files with 186 additions and 32 deletions
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10
src/common/sdr.c
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@@ -39,7 +39,7 @@ typedef struct sdr_chan {
double rx_rot; /* rotation step per sample to shift rx frequency (used to shift) */
double rx_phase; /* current rotation phase (used to shift) */
double rx_last_phase; /* last phase of FM (used to demodulate) */
filter_lowpass_t rx_lp[2]; /* filters received IQ signal */
filter_t rx_lp[2]; /* filters received IQ signal */
} sdr_chan_t;
typedef struct sdr {
@@ -123,8 +123,8 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
PDEBUG(DSDR, DEBUG_INFO, "Frequency #%d: TX = %.6f MHz, RX = %.6f MHz\n", c, tx_frequency[c] / 1e6, rx_frequency[c] / 1e6);
sdr->chan[c].tx_frequency = tx_frequency[c];
sdr->chan[c].rx_frequency = rx_frequency[c];
filter_lowpass_init(&sdr->chan[c].rx_lp[0], bandwidth, samplerate);
filter_lowpass_init(&sdr->chan[c].rx_lp[1], bandwidth, samplerate);
filter_lowpass_init(&sdr->chan[c].rx_lp[0], bandwidth, samplerate, 1);
filter_lowpass_init(&sdr->chan[c].rx_lp[1], bandwidth, samplerate, 1);
}
if (sdr->paging_channel) {
PDEBUG(DSDR, DEBUG_INFO, "Paging Frequency: TX = %.6f MHz\n", paging_frequency / 1e6);
@@ -378,8 +378,8 @@ int sdr_read(void *inst, int16_t **samples, int num, int channels)
Q[s] = i * sin(phase) + q * cos(phase);
}
sdr->chan[c].rx_phase = phase;
filter_lowpass_process(&sdr->chan[c].rx_lp[0], I, count, 1);
filter_lowpass_process(&sdr->chan[c].rx_lp[1], Q, count, 1);
filter_process(&sdr->chan[c].rx_lp[0], I, count);
filter_process(&sdr->chan[c].rx_lp[1], Q, count);
last_phase = sdr->chan[c].rx_last_phase;
for (s = 0; s < count; s++) {
phase = atan2(Q[s], I[s]);