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SDR: Move channel away from center frequency, to avoid bad RX

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pull/1/head
Andreas Eversberg 4 years ago
parent 5311f44daa
commit f1292a985b
1 changed files with 37 additions and 5 deletions
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  1. 42
      src/libsdr/sdr.c

42
src/libsdr/sdr.c
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@ -249,6 +249,8 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
if (sdr->chan[sdr->paging_channel].tx_frequency > tx_high_frequency)
tx_high_frequency = sdr->chan[sdr->paging_channel].tx_frequency;
}
tx_center_frequency = (tx_high_frequency + tx_low_frequency) / 2.0;
/* range of TX */
double range = tx_high_frequency - tx_low_frequency + bandwidth;
PDEBUG(DSDR, DEBUG_INFO, "Total bandwidth for all TX Frequencies: %.0f Hz\n", range);
@ -259,7 +261,6 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
PDEBUG(DSDR, DEBUG_NOTICE, "*******************************************************************************\n");
goto error;
}
tx_center_frequency = (tx_high_frequency + tx_low_frequency) / 2.0;
PDEBUG(DSDR, DEBUG_INFO, "Using center frequency: TX %.6f MHz\n", tx_center_frequency / 1e6);
/* set offsets to center frequency */
for (c = 0; c < channels; c++) {
@ -299,12 +300,12 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
}
if (rx_frequency) {
/* calculate required bandwidth (IQ rate) */
for (c = 0; c < channels; c++) {
PDEBUG(DSDR, DEBUG_INFO, "Frequency #%d: RX = %.6f MHz\n", c, rx_frequency[c] / 1e6);
sdr->chan[c].rx_frequency = rx_frequency[c];
}
/* calculate required bandwidth (IQ rate) */
double rx_low_frequency = sdr->chan[0].rx_frequency, rx_high_frequency = sdr->chan[0].rx_frequency;
for (c = 1; c < channels; c++) {
if (sdr->chan[c].rx_frequency < rx_low_frequency)
@ -312,9 +313,41 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
if (sdr->chan[c].rx_frequency > rx_high_frequency)
rx_high_frequency = sdr->chan[c].rx_frequency;
}
rx_center_frequency = (rx_high_frequency + rx_low_frequency) / 2.0;
/* prevent channel from being at the center */
for (c = 0; c < channels; c++) {
double abs = fabs(rx_center_frequency - sdr->chan[c].rx_frequency);
if (abs < 1.0)
break;
}
if (c < channels) {
/* find second closest frequency */
double second_frequency = 0, offset;
for (c = 0; c < channels; c++) {
double abs = fabs(rx_center_frequency - sdr->chan[c].rx_frequency);
/* must be off center AND closer to the center than last one found */
if (abs > 1.0 && (second_frequency == 0 || abs < fabs(rx_center_frequency - second_frequency)))
second_frequency = sdr->chan[c].rx_frequency;
}
if (second_frequency == 0) {
/* just some offset, if single frequency */
offset = 20000;
} else {
/* offset between center frequency and second closest frequency */
offset = (rx_center_frequency - second_frequency) / 2.0;
}
rx_center_frequency += offset;
rx_low_frequency += offset;
rx_high_frequency += offset;
}
/* range of RX */
double range = rx_high_frequency - rx_low_frequency + bandwidth;
PDEBUG(DSDR, DEBUG_INFO, "Total bandwidth for all RX Frequencies: %.0f Hz\n", range);
double low_side, high_side, range;
low_side = (rx_center_frequency - rx_low_frequency) + bandwidth / 2.0;
high_side = (rx_high_frequency - rx_center_frequency) + bandwidth / 2.0;
range = ((low_side > high_side) ? low_side : high_side) * 2.0;
PDEBUG(DSDR, DEBUG_INFO, "Total bandwidth (two side bands) for all RX Frequencies: %.0f Hz\n", range);
if (range > samplerate * USABLE_BANDWIDTH) {
PDEBUG(DSDR, DEBUG_NOTICE, "*******************************************************************************\n");
PDEBUG(DSDR, DEBUG_NOTICE, "The required bandwidth of %.0f Hz exceeds %.0f%% of the sample rate.\n", range, USABLE_BANDWIDTH * 100.0);
@ -322,7 +355,6 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
PDEBUG(DSDR, DEBUG_NOTICE, "*******************************************************************************\n");
goto error;
}
rx_center_frequency = (rx_high_frequency + rx_low_frequency) / 2.0;
PDEBUG(DSDR, DEBUG_INFO, "Using center frequency: RX %.6f MHz\n", rx_center_frequency / 1e6);
/* set offsets to center frequency */
for (c = 0; c < channels; c++) {

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