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SDR: Check if the required bandwidth can be handled by given sample rate

This commit is contained in:
Andreas Eversberg 2017-10-16 12:26:13 -04:00
parent b32e0ab602
commit 2c4d0ee687
1 changed files with 16 additions and 14 deletions
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30
src/common/sdr.c
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@ -49,6 +49,8 @@ enum paging_signal;
/* enable to test without oversampling filter */
//#define DISABLE_FILTER
/* usable bandwidth of IQ rate, because no filter is perfect */
#define USABLE_BANDWIDTH 0.75
typedef struct sdr_thread {
int use;
@ -122,7 +124,7 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
}
bandwidth = 2.0 * (max_deviation + max_modulation);
PDEBUG(DSDR, DEBUG_INFO, "Require bandwidth of 2 * (%.1f + %.1f) = %.1f\n", max_deviation / 1000, max_modulation / 1000, bandwidth / 1000);
PDEBUG(DSDR, DEBUG_INFO, "Require bandwidth of each channel is 2 * (%.1f deviation + %.1f modulation) = %.1f KHz\n", max_deviation / 1e3, max_modulation / 1e3, bandwidth / 1e3);
if (channels < 1) {
PDEBUG(DSDR, DEBUG_ERROR, "No channel given, please fix!\n");
@ -243,14 +245,13 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
tx_high_frequency = sdr->chan[sdr->paging_channel].tx_frequency;
}
/* range of TX */
double range = tx_high_frequency - tx_low_frequency;
if (range)
PDEBUG(DSDR, DEBUG_DEBUG, "Range between all TX Frequencies: %.6f MHz\n", range / 1e6);
if (range * 2 > samplerate) {
// why that? actually i don't know. i just want to be safe....
PDEBUG(DSDR, DEBUG_NOTICE, "The sample rate must be at least twice the range between frequencies.\n");
PDEBUG(DSDR, DEBUG_NOTICE, "The given rate is %.6f MHz, but required rate must be >= %.6f MHz\n", samplerate / 1e6, range * 2.0 / 1e6);
double range = tx_high_frequency - tx_low_frequency + bandwidth;
PDEBUG(DSDR, DEBUG_INFO, "Total bandwidth for all TX 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);
PDEBUG(DSDR, DEBUG_NOTICE, "Please increase samplerate!\n");
PDEBUG(DSDR, DEBUG_NOTICE, "*******************************************************************************\n");
goto error;
}
tx_center_frequency = (tx_high_frequency + tx_low_frequency) / 2.0;
@ -306,12 +307,13 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
rx_high_frequency = sdr->chan[c].rx_frequency;
}
/* range of RX */
double range = rx_high_frequency - rx_low_frequency;
if (range)
PDEBUG(DSDR, DEBUG_DEBUG, "Range between all RX Frequencies: %.6f MHz\n", range / 1e6);
if (range * 2.0 > samplerate) {
// why that? actually i don't know. i just want to be safe....
PDEBUG(DSDR, DEBUG_NOTICE, "The sample rate must be at least twice the range between frequencies. Please increment samplerate!\n");
double range = rx_high_frequency - rx_low_frequency + bandwidth;
PDEBUG(DSDR, DEBUG_INFO, "Total bandwidth 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);
PDEBUG(DSDR, DEBUG_NOTICE, "Please increase samplerate!\n");
PDEBUG(DSDR, DEBUG_NOTICE, "*******************************************************************************\n");
goto error;
}
rx_center_frequency = (rx_high_frequency + rx_low_frequency) / 2.0;