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SDR: Add DC offset removal (DC bias)

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This commit is contained in:
Andreas Eversberg
2017-11-26 08:53:09 +01:00
parent 9e75e64787
commit 417151e9a3
5 changed files with 46 additions and 1 deletions
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37
src/libsdr/sdr.c
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@@ -391,6 +391,39 @@ error:
return NULL;
}
double bias_I, bias_Q; /* calculated bias */
int bias_count = -1; /* number of calculations */
void calibrate_bias(void)
{
bias_count = 0;
bias_I = 0.0;
bias_Q = 0.0;
}
static void sdr_bias(float *buffer, int count)
{
int i;
if (bias_count < sdr_config->samplerate) {
for (i = 0; i < count; i++) {
bias_I += *buffer++;
bias_Q += *buffer++;
}
bias_count += count;
if (bias_count >= sdr_config->samplerate) {
bias_I /= bias_count;
bias_Q /= bias_count;
PDEBUG(DSDR, DEBUG_INFO, "DC bias calibration finished.\n");
}
} else {
for (i = 0; i < count; i++) {
*buffer++ -= bias_I;
*buffer++ -= bias_Q;
}
}
}
static void *sdr_write_child(void *arg)
{
sdr_t *sdr = (sdr_t *)arg;
@@ -461,6 +494,8 @@ static void *sdr_read_child(void *arg)
if (sdr_config->soapy)
count = soapy_receive(sdr->thread_read.buffer2, num);
#endif
if (bias_count >= 0)
sdr_bias(sdr->thread_read.buffer2, count);
if (count > 0) {
#ifdef DEBUG_BUFFER
printf("Thread read %d samples from SDR and writes them to read buffer.\n", count);
@@ -767,6 +802,8 @@ int sdr_read(void *inst, sample_t **samples, int num, int channels, double *rf_l
if (sdr_config->soapy)
count = soapy_receive(buff, num);
#endif
if (bias_count >= 0)
sdr_bias(buff, count);
if (count <= 0)
return count;
}