SDR: Add option to set local oscillator (LO) offset

By default it is set to -1 MHz.

docs/sdr.html

@@ -77,9 +77,7 @@ In case of B-Netz, I use the following parameters:
 # bnetz --sdr-soapy \
         --sdr-tx-gain 50 \
         --sdr-rx-gain 30 \
-        --sdr-bandwidth 5000000 \
         --sdr-samplerate 5000000 \
-        --sdr-tune-args "OFFSET=1000000" \
         -s 100000 \
         -k 17
 
@@ -89,10 +87,10 @@ In case of B-Netz, I use the following parameters:
 In order to change from analog sound card to SDR, you need <b>--sdr-soapy</b> option.
 In my setup I use antennas directly connected to the SDR.
 Being about 1-10 meters away, I use the <b>gain</b> as defined above.
-The IF filter requires a minimum <b>bandwidth</b> of 5 MHz.
 The <b>sample rate</b> must be 5 MHz minimum.
+The default <b>bandwidth</b> follows the sample rate, if not specified using <b>--sdr-bandwidth</b>.
 Higher sample rate causes more CPU, RAM and USB load.
-The local oscillator frequency causes the transmitted signal to be noisy, so I shift it 1 MHz away, using an <b>offset</b>.
+The local oscillator frequency causes the transmitted signal to be noisy, so I shift it 1 MHz away, using the default <b>--sdr-lo-offset</b>.
 The audio processing rate of 100 KHz (<b>-s 100000</b>) is used to generate two channels: <b>17</b> and 19.
 Note that channel 19 is not given here, but will be used automatically.
 With B-Netz, the transmitter switches from any voice channel to the paging channel (19) whenever the phone gets paged.
@@ -174,9 +172,7 @@ Because C-Netz uses only odd channel numbers for 10 KHz spacing, we use channel
 # cnetz --sdr-soapy \
         --sdr-rx-gain 50 \
 	--sdr-tx-gain 30 \
-        --sdr-bandwidth 5000000 \
         --sdr-samplerate 5000000 \
-        --sdr-tune-args "OFFSET=1000000" \
 	-s 100000 \
 	-k 131 -k 135 \
 	-C 0,0
@@ -192,7 +188,7 @@ Give PAL 'FUBK' test image on TV channel 21.
 
 # osmotv --sdr-soapy \
          --sdr-tx-gain 60 \
-	 --sdr-tune-args "OFFSET=-3000000" \
+	 --sdr-bandwidth 60000000 \
 	 -r 13750000  \
 	 -c 21  \
 	 tx-fubk

src/libmobile/main_mobile.c

@@ -43,6 +43,8 @@
 #include "../libsdr/sdr_config.h"
 #endif
 
+#define DEFAULT_LO_OFFSET -1000000.0
+
 static int got_init = 0;
 
 /* common mobile settings */
@@ -77,7 +79,7 @@ void main_mobile_init(void)
 {
 	got_init = 1;
 #ifdef HAVE_SDR
-	sdr_config_init();
+	sdr_config_init(DEFAULT_LO_OFFSET);
 #endif
 }
 

src/libsdr/sdr.c

@@ -368,9 +368,11 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
 	display_iq_init(samplerate);
 	display_spectrum_init(samplerate, rx_center_frequency);
 
+	PDEBUG(DSDR, DEBUG_INFO, "Using local oscillator offseet: %.0f Hz\n", sdr_config->lo_offset);
+
 #ifdef HAVE_UHD
 	if (sdr_config->uhd) {
-		rc = uhd_open(sdr_config->channel, sdr_config->device_args, sdr_config->stream_args, sdr_config->tune_args, sdr_config->tx_antenna, sdr_config->rx_antenna, tx_center_frequency, rx_center_frequency, sdr_config->samplerate, sdr_config->tx_gain, sdr_config->rx_gain, sdr_config->bandwidth, sdr_config->uhd_tx_timestamps);
+		rc = uhd_open(sdr_config->channel, sdr_config->device_args, sdr_config->stream_args, sdr_config->tune_args, sdr_config->tx_antenna, sdr_config->rx_antenna, tx_center_frequency, rx_center_frequency, sdr_config->lo_offset, sdr_config->samplerate, sdr_config->tx_gain, sdr_config->rx_gain, sdr_config->bandwidth, sdr_config->uhd_tx_timestamps);
 		if (rc)
 			goto error;
 	}
@@ -378,7 +380,7 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
 
 #ifdef HAVE_SOAPY
 	if (sdr_config->soapy) {
-		rc = soapy_open(sdr_config->channel, sdr_config->device_args, sdr_config->stream_args, sdr_config->tune_args, sdr_config->tx_antenna, sdr_config->rx_antenna, tx_center_frequency, rx_center_frequency, sdr_config->samplerate, sdr_config->tx_gain, sdr_config->rx_gain, sdr_config->bandwidth);
+		rc = soapy_open(sdr_config->channel, sdr_config->device_args, sdr_config->stream_args, sdr_config->tune_args, sdr_config->tx_antenna, sdr_config->rx_antenna, tx_center_frequency, rx_center_frequency, sdr_config->lo_offset, sdr_config->samplerate, sdr_config->tx_gain, sdr_config->rx_gain, sdr_config->bandwidth);
 		if (rc)
 			goto error;
 	}

src/libsdr/sdr_config.c

@@ -32,13 +32,14 @@ static int got_init = 0;
 extern int use_sdr;
 sdr_config_t *sdr_config = NULL;
 
-void sdr_config_init(void)
+void sdr_config_init(double lo_offset)
 {
 	sdr_config = calloc(1, sizeof(*sdr_config));
 	memset(sdr_config, 0, sizeof(*sdr_config));
 	sdr_config->device_args = "";
 	sdr_config->stream_args = "";
 	sdr_config->tune_args = "";
+	sdr_config->lo_offset = lo_offset;
 
 	got_init = 1;
 }
@@ -65,6 +66,9 @@ void sdr_config_print_help(void)
 	printf("    --sdr-samplerate <samplerate>\n");
 	printf("        Sample rate to use with SDR. By default it equals the regular sample\n");
 	printf("        rate.\n");
+	printf("    --sdr-lo-offset <Hz>\n");
+	printf("        Give frequency offset in Hz to move the local oscillator away from the\n");
+	printf("        target frequency. (default = %.0f)\n", sdr_config->lo_offset);
 	printf("    --sdr-bandwidth <bandwidth>\n");
 	printf("        Give IF filter bandwidth to use. If not, sample rate is used.\n");
 	printf("    --sdr-rx-antenna <name>\n");
@@ -109,13 +113,14 @@ void sdr_config_print_hotkeys(void)
 #define	OPT_SDR_RX_GAIN		1508
 #define	OPT_SDR_TX_GAIN		1509
 #define	OPT_SDR_SAMPLERATE	1510
-#define	OPT_SDR_BANDWIDTH	1511
+#define	OPT_SDR_LO_OFFSET	1511
-#define	OPT_WRITE_IQ_RX_WAVE	1512
+#define	OPT_SDR_BANDWIDTH	1512
-#define	OPT_WRITE_IQ_TX_WAVE	1513
+#define	OPT_WRITE_IQ_RX_WAVE	1513
-#define	OPT_READ_IQ_RX_WAVE	1514
+#define	OPT_WRITE_IQ_TX_WAVE	1514
-#define	OPT_READ_IQ_TX_WAVE	1515
+#define	OPT_READ_IQ_RX_WAVE	1515
-#define	OPT_SDR_SWAP_LINKS	1516
+#define	OPT_READ_IQ_TX_WAVE	1516
-#define OPT_SDR_UHD_TX_TS	1517
+#define	OPT_SDR_SWAP_LINKS	1517
+#define OPT_SDR_UHD_TX_TS	1518
 
 struct option sdr_config_long_options[] = {
 	{"sdr-uhd", 0, 0, OPT_SDR_UHD},
@@ -125,6 +130,7 @@ struct option sdr_config_long_options[] = {
 	{"sdr-stream-args", 1, 0, OPT_SDR_STREAM_ARGS},
 	{"sdr-tune-args", 1, 0, OPT_SDR_TUNE_ARGS},
 	{"sdr-samplerate", 1, 0, OPT_SDR_SAMPLERATE},
+	{"sdr-lo-offset", 1, 0, OPT_SDR_LO_OFFSET},
 	{"sdr-bandwidth", 1, 0, OPT_SDR_BANDWIDTH},
 	{"sdr-rx-antenna", 1, 0, OPT_SDR_RX_ANTENNA},
 	{"sdr-tx-antenna", 1, 0, OPT_SDR_TX_ANTENNA},
@@ -184,6 +190,10 @@ int sdr_config_opt_switch(int c, int *skip_args)
 		sdr_config->samplerate = atoi(optarg);
 		*skip_args += 2;
 		break;
+	case OPT_SDR_LO_OFFSET:
+		sdr_config->lo_offset = atof(optarg);
+		*skip_args += 2;
+		break;
 	case OPT_SDR_BANDWIDTH:
 		sdr_config->bandwidth = atof(optarg);
 		*skip_args += 2;

src/libsdr/sdr_config.h

@@ -7,6 +7,7 @@ typedef struct sdr_config {
 			*stream_args,
 			*tune_args;
 	int		samplerate;		/* ADC/DAC sample rate */
+	double		lo_offset;		/* LO frequency offset */
 	double		bandwidth;		/* IF bandwidth */
 	double		tx_gain,		/* gain */
 			rx_gain;
@@ -22,7 +23,7 @@ typedef struct sdr_config {
 
 extern sdr_config_t *sdr_config;
 
-void sdr_config_init(void);
+void sdr_config_init(double lo_offset);
 void sdr_config_print_help(void);
 void sdr_config_print_hotkeys(void);
 extern struct option sdr_config_long_options[];

src/libsdr/soapy.c

@@ -62,7 +62,7 @@ static int parse_args(SoapySDRKwargs *args, const char *_args_string)
 	return 0;
 }
 
-int soapy_open(size_t channel, const char *_device_args, const char *_stream_args, const char *_tune_args, const char *tx_antenna, const char *rx_antenna, double tx_frequency, double rx_frequency, double rate, double tx_gain, double rx_gain, double bandwidth)
+int soapy_open(size_t channel, const char *_device_args, const char *_stream_args, const char *_tune_args, const char *tx_antenna, const char *rx_antenna, double tx_frequency, double rx_frequency, double lo_offset, double rate, double tx_gain, double rx_gain, double bandwidth)
 {
 	double got_frequency, got_rate, got_gain, got_bandwidth;
 	const char *got_antenna;
@@ -88,6 +88,13 @@ int soapy_open(size_t channel, const char *_device_args, const char *_stream_arg
 	if (rc < 0)
 		return rc;
 
+	if (lo_offset) {
+		char val[32];
+		snprintf(val, sizeof(val), "%.0f", lo_offset);
+		val[sizeof(val) - 1] = '\0';
+		SoapySDRKwargs_set(&tune_args, "OFFSET", val);
+	}
+
 	/* create SoapySDR device */
 	sdr = SoapySDRDevice_make(&device_args);
 	if (!sdr) {

src/libsdr/soapy.h

@@ -1,5 +1,5 @@
 
-int soapy_open(size_t channel, const char *_device_args, const char *_stream_args, const char *_tune_args, const char *tx_antenna, const char *rx_antenna, double tx_frequency, double rx_frequency, double rate, double tx_gain, double rx_gain, double bandwidth);
+int soapy_open(size_t channel, const char *_device_args, const char *_stream_args, const char *_tune_args, const char *tx_antenna, const char *rx_antenna, double tx_frequency, double rx_frequency, double lo_offset, double rate, double tx_gain, double rx_gain, double bandwidth);
 int soapy_start(void);
 void soapy_close(void);
 int soapy_send(float *buff, int num);

src/libsdr/uhd.c

@@ -49,7 +49,7 @@ static time_t			tx_time_secs = 0;
 static double			tx_time_fract_sec = 0.0;
 static int			tx_timestamps;
 
-int uhd_open(size_t channel, const char *_device_args, const char *_stream_args, const char *_tune_args, const char *tx_antenna, const char *rx_antenna, double tx_frequency, double rx_frequency, double rate, double tx_gain, double rx_gain, double bandwidth, int _tx_timestamps)
+int uhd_open(size_t channel, const char *_device_args, const char *_stream_args, const char *_tune_args, const char *tx_antenna, const char *rx_antenna, double tx_frequency, double rx_frequency, double lo_offset, double rate, double tx_gain, double rx_gain, double bandwidth, int _tx_timestamps)
 {
 	uhd_error error;
 	double got_frequency, got_rate, got_gain, got_bandwidth;
@@ -153,7 +153,7 @@ int uhd_open(size_t channel, const char *_device_args, const char *_stream_args,
 			uhd_close();
 			return -EIO;
 		}
-		if (fabs(got_rate - rate) > 0.001) {
+		if (fabs(got_rate - rate) > 1.0) {
 			PDEBUG(DUHD, DEBUG_ERROR, "Given TX rate %.0f Hz is not supported, try %.0f Hz\n", rate, got_rate);
 			uhd_close();
 			return -EINVAL;
@@ -182,7 +182,11 @@ int uhd_open(size_t channel, const char *_device_args, const char *_stream_args,
 		/* set frequency */
 		memset(&tune_request, 0, sizeof(tune_request));
 		tune_request.target_freq = tx_frequency;
-		tune_request.rf_freq_policy = UHD_TUNE_REQUEST_POLICY_AUTO;
+		if (lo_offset) {
+			tune_request.rf_freq_policy = UHD_TUNE_REQUEST_POLICY_MANUAL;
+			tune_request.rf_freq = tx_frequency + lo_offset;
+		} else
+			tune_request.rf_freq_policy = UHD_TUNE_REQUEST_POLICY_AUTO;
 		tune_request.dsp_freq_policy = UHD_TUNE_REQUEST_POLICY_AUTO;
 		tune_request.args = strdup(_tune_args);
 		error = uhd_usrp_set_tx_freq(usrp, &tune_request, channel, &tune_result);
@@ -219,7 +223,7 @@ int uhd_open(size_t channel, const char *_device_args, const char *_stream_args,
 			uhd_close();
 			return -EIO;
 		}
-		if (fabs(got_bandwidth - bandwidth) > 0.001) {
+		if (fabs(got_bandwidth - bandwidth) > 100.0) {
 			PDEBUG(DUHD, DEBUG_ERROR, "Given TX bandwidth %.0f Hz is not supported, try %.0f Hz\n", bandwidth, got_bandwidth);
 			uhd_close();
 			return -EINVAL;
@@ -337,7 +341,7 @@ int uhd_open(size_t channel, const char *_device_args, const char *_stream_args,
 			uhd_close();
 			return -EIO;
 		}
-		if (fabs(got_rate - rate) > 0.001) {
+		if (fabs(got_rate - rate) > 1.0) {
 			PDEBUG(DUHD, DEBUG_ERROR, "Given RX rate %.0f Hz is not supported, try %.0f Hz\n", rate, got_rate);
 			uhd_close();
 			return -EINVAL;
@@ -366,7 +370,11 @@ int uhd_open(size_t channel, const char *_device_args, const char *_stream_args,
 		/* set frequency */
 		memset(&tune_request, 0, sizeof(tune_request));
 		tune_request.target_freq = rx_frequency;
-		tune_request.rf_freq_policy = UHD_TUNE_REQUEST_POLICY_AUTO;
+		if (lo_offset) {
+			tune_request.rf_freq_policy = UHD_TUNE_REQUEST_POLICY_MANUAL;
+			tune_request.rf_freq = rx_frequency + lo_offset;
+		} else
+			tune_request.rf_freq_policy = UHD_TUNE_REQUEST_POLICY_AUTO;
 		tune_request.dsp_freq_policy = UHD_TUNE_REQUEST_POLICY_AUTO;
 		tune_request.args = strdup(_tune_args);
 		error = uhd_usrp_set_rx_freq(usrp, &tune_request, channel, &tune_result);
@@ -403,7 +411,7 @@ int uhd_open(size_t channel, const char *_device_args, const char *_stream_args,
 			uhd_close();
 			return -EIO;
 		}
-		if (fabs(got_bandwidth - bandwidth) > 0.001) {
+		if (fabs(got_bandwidth - bandwidth) > 100.0) {
 			PDEBUG(DUHD, DEBUG_ERROR, "Given RX bandwidth %.0f Hz is not supported, try %.0f Hz\n", bandwidth, got_bandwidth);
 			uhd_close();
 			return -EINVAL;

src/libsdr/uhd.h

@@ -1,5 +1,5 @@
 
-int uhd_open(size_t channel, const char *_device_args, const char *_stream_args, const char *_tune_args, const char *tx_antenna, const char *rx_antenna, double tx_frequency, double rx_frequency, double rate, double tx_gain, double rx_gain, double bandwidth, int _tx_timestamps);
+int uhd_open(size_t channel, const char *_device_args, const char *_stream_args, const char *_tune_args, const char *tx_antenna, const char *rx_antenna, double tx_frequency, double rx_frequency, double lo_offset, double rate, double tx_gain, double rx_gain, double bandwidth, int _tx_timestamps);
 int uhd_start(void);
 void uhd_close(void);
 int uhd_send(float *buff, int num);

src/tv/main.c

@@ -41,6 +41,8 @@ enum paging_signal;
 #include "tv_modulate.h"
 #include "channels.h"
 
+#define DEFAULT_LO_OFFSET -3000000.0
+
 void *sender_head = NULL;
 int use_sdr = 0;
 int num_kanal = 1; /* only one channel used for debugging */
@@ -454,7 +456,7 @@ int main(int argc, char *argv[])
 	debuglevel = 0;
 
 #ifdef HAVE_SDR
-	sdr_config_init();
+	sdr_config_init(DEFAULT_LO_OFFSET);
 #endif
 
 	skip_args = handle_options(argc, argv);