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authorAndreas Eversberg <jolly@eversberg.eu>2019-05-30 18:20:25 +0200
committerAndreas Eversberg <jolly@eversberg.eu>2019-05-30 21:07:41 +0200
commit831b68401a4e2e6f7e1b8b1e9d9c1b834a6da988 (patch)
treec1dd960dad76a93dfd4a04693e785bd1c1111bfa /src
parent37406db7e3a0e9cf90d02de84b6c99c4d85afac1 (diff)
SDR: Move center frequenc (DC) away from channels
If one channel is used, shift the center frequency down by half of the bandwidth. If more channels are used, select a center frequency between two channels close to the center, but equal distance. Show the spectum layout on startup. This patch reverts f1292a985bf8f19d9538e6337c229db1b463a547
Diffstat (limited to 'src')
-rw-r--r--src/libsdr/sdr.c123
1 files changed, 81 insertions, 42 deletions
diff --git a/src/libsdr/sdr.c b/src/libsdr/sdr.c
index 39f2c92..dd89cea 100644
--- a/src/libsdr/sdr.c
+++ b/src/libsdr/sdr.c
@@ -101,6 +101,36 @@ typedef struct sdr {
sample_t *wavespl1;
} sdr_t;
+static void show_spectrum(const char *direction, double halfbandwidth, double center, double *frequency, double paging_frequency, int num)
+{
+ char text[80];
+ int i, x;
+
+ memset(text, ' ', 79);
+ text[79] = '\0';
+
+ // FIXME: better solution
+ if (num > 9)
+ num = 9;
+
+ for (i = 0; i < num; i++) {
+ x = (frequency[i] - center) / halfbandwidth * 39.0 + 39.5;
+ if (x >= 0 && x < 79)
+ text[x] = '1' + i;
+ }
+ if (paging_frequency) {
+ x = (paging_frequency - center) / halfbandwidth * 39.0 + 39.5;
+ if (x >= 0 && x < 79)
+ text[x] = 'P';
+ }
+
+ PDEBUG(DSDR, DEBUG_INFO, "%s Spectrum:\n%s\n---------------------------------------+---------------------------------------\n", direction, text);
+ for (i = 0; i < num; i++)
+ PDEBUG(DSDR, DEBUG_INFO, "Frequency %c = %.4f MHz\n", '1' + i, frequency[i] / 1e6);
+ if (paging_frequency)
+ PDEBUG(DSDR, DEBUG_INFO, "Frequency P = %.4f MHz (Paging Frequency)\n", paging_frequency / 1e6);
+}
+
void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_frequency, double *rx_frequency, int channels, double paging_frequency, int samplerate, int latspl, double max_deviation, double max_modulation)
{
sdr_t *sdr;
@@ -227,23 +257,17 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
if (tx_frequency) {
/* calculate required bandwidth (IQ rate) */
+
+ double tx_low_frequency = 0.0, tx_high_frequency = 0.0;
for (c = 0; c < channels; c++) {
- PDEBUG(DSDR, DEBUG_INFO, "Frequency #%d: TX = %.6f MHz\n", c, tx_frequency[c] / 1e6);
sdr->chan[c].tx_frequency = tx_frequency[c];
- }
- if (sdr->paging_channel) {
- PDEBUG(DSDR, DEBUG_INFO, "Paging Frequency: TX = %.6f MHz\n", paging_frequency / 1e6);
- sdr->chan[sdr->paging_channel].tx_frequency = paging_frequency;
- }
-
- double tx_low_frequency = sdr->chan[0].tx_frequency, tx_high_frequency = sdr->chan[0].tx_frequency;
- for (c = 1; c < channels; c++) {
- if (sdr->chan[c].tx_frequency < tx_low_frequency)
+ if (c == 0 || sdr->chan[c].tx_frequency < tx_low_frequency)
tx_low_frequency = sdr->chan[c].tx_frequency;
- if (sdr->chan[c].tx_frequency > tx_high_frequency)
+ if (c == 0 || sdr->chan[c].tx_frequency > tx_high_frequency)
tx_high_frequency = sdr->chan[c].tx_frequency;
}
if (sdr->paging_channel) {
+ sdr->chan[sdr->paging_channel].tx_frequency = paging_frequency;
if (sdr->chan[sdr->paging_channel].tx_frequency < tx_low_frequency)
tx_low_frequency = sdr->chan[sdr->paging_channel].tx_frequency;
if (sdr->chan[sdr->paging_channel].tx_frequency > tx_high_frequency)
@@ -251,9 +275,15 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
}
tx_center_frequency = (tx_high_frequency + tx_low_frequency) / 2.0;
+ /* show spectrum */
+ show_spectrum("TX", (double)samplerate / 2.0, tx_center_frequency, tx_frequency, paging_frequency, channels);
+
/* 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);
+ double low_side, high_side, range;
+ low_side = (tx_center_frequency - tx_low_frequency) + bandwidth / 2.0;
+ high_side = (tx_high_frequency - tx_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 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);
@@ -301,47 +331,56 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
if (rx_frequency) {
/* calculate required bandwidth (IQ rate) */
+ double rx_low_frequency = 0.0, rx_high_frequency = 0.0;
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];
- }
-
- 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)
+ if (c == 0 || sdr->chan[c].rx_frequency < rx_low_frequency)
rx_low_frequency = sdr->chan[c].rx_frequency;
- if (sdr->chan[c].rx_frequency > rx_high_frequency)
+ if (c == 0 || 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;
+ /* prevent channel bandwidth from overlapping with the center frequency */
+ if (channels == 1) {
+ /* simple: just move off the center by half of the bandwidth */
+ rx_center_frequency -= bandwidth / 2.0;
+ /* Note: rx_low_frequency is kept at old center.
+ Calculation of 'low_side' will become 0.
+ This is correct, since there is no bandwidth
+ below new center frequency.
+ */
+ PDEBUG(DSDR, DEBUG_INFO, "We shift center frequency %.0f KHz down (half bandwidth), to prevent channel from overlap with DC level.\n", bandwidth / 2.0 / 1e3);
+ } else {
+ /* find two channels that are aside the center */
+ double low_dist, high_dist, dist;
+ int low_c = -1, high_c = -1;
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;
+ dist = fabs(rx_center_frequency - sdr->chan[c].rx_frequency);
+ if (round(sdr->chan[c].rx_frequency) >= round(rx_center_frequency)) {
+ if (high_c < 0 || dist < high_dist) {
+ high_dist = dist;
+ high_c = c;
+ }
+ } else {
+ if (low_c < 0 || dist < low_dist) {
+ low_dist = dist;
+ low_c = c;
+ }
+ }
}
- 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;
+ /* new center = center of the two frequencies aside old center */
+ if (low_c >= 0 && high_c >= 0) {
+ rx_center_frequency =
+ ((sdr->chan[low_c].rx_frequency) +
+ (sdr->chan[high_c].rx_frequency)) / 2.0;
+ PDEBUG(DSDR, DEBUG_INFO, "We move center freqeuency between the two channels in the middle, to prevent them from overlap with DC level.\n");
}
- rx_center_frequency += offset;
- rx_low_frequency += offset;
- rx_high_frequency += offset;
}
+ /* show spectrum */
+ show_spectrum("RX", (double)samplerate / 2.0, rx_center_frequency, rx_frequency, 0.0, channels);
+
/* range of RX */
double low_side, high_side, range;
low_side = (rx_center_frequency - rx_low_frequency) + bandwidth / 2.0;