Neu structure for the paging process (B-Netz)

Paging tones are not created within sound_alsa.c
The audio API is now responsible to switch to paging channel.
In case of SDR, the sdr.c will switch frequency offset.

15 files changed, 238 insertions, 197 deletions

diff --git a/docs/b-netz.html b/docs/b-netz.html
index f7997e0..5524f46 100644
--- a/docs/b-netz.html
+++ b/docs/b-netz.html
@@ -536,7 +536,7 @@ The actual level is not yet relevant.
 ...
 bnetz.c:316 info   : Entering IDLE state, sending 'Gruppenfreisignal' 2 on channel 1.
 Base station ready, please tune transmitter to 153.010 MHz and receiver to 148.410 MHz.
-To call phone, switch transmitter (using pilot signal) to 153.370 MHz.
+To call phone, switch transmitter (using paging signal) to 153.370 MHz.
 on-hook: ..... (enter 0..9 or d=dial)
 
 </pre>
@@ -555,7 +555,7 @@ Set the selector for the base station ID ("Gruppenfreisignal") to 0.
 
 bnetz.c:351 info   : Entering IDLE state, sending 'Gruppenfreisignal' 2.
 Base station for channel 1 ready, please tune transmitter to 153.010 MHz and receiver to 148.410 MHz.
-To call phone, switch transmitter (using pilot signal) to 153.370 MHz.
+To call phone, switch transmitter (using paging signal) to 153.370 MHz.
 mncc_sock.c:137 notice : MNCC socket connected.
 dsp.c:159 info   : Detecting continous tone: 2070:Level= 80% Quality=100%
 bnetz.c:470 info   : Received signal 'Kanalbelegung' from mobile station, sending signal 'Wahlabruf'.
diff --git a/src/amps/amps.c b/src/amps/amps.c
index 8f9b1ad..fd8b03a 100644
--- a/src/amps/amps.c
+++ b/src/amps/amps.c
@@ -442,7 +442,7 @@ int amps_create(int channel, enum amps_chan_type chan_type, const char *audiodev
 	PDEBUG(DAMPS, DEBUG_DEBUG, "Creating 'AMPS' instance for channel = %d (sample rate %d).\n", channel, samplerate);
 
 	/* init general part of transceiver */
-	rc = sender_create(&amps->sender, channel, amps_channel2freq(channel, 0), amps_channel2freq(channel, 1), audiodev, samplerate, rx_gain, 0, 0, write_rx_wave, write_tx_wave, read_rx_wave, loopback, 0, PILOT_SIGNAL_NONE);
+	rc = sender_create(&amps->sender, channel, amps_channel2freq(channel, 0), amps_channel2freq(channel, 1), audiodev, samplerate, rx_gain, 0, 0, write_rx_wave, write_tx_wave, read_rx_wave, loopback, 0, PAGING_SIGNAL_NONE);
 	if (rc < 0) {
 		PDEBUG(DAMPS, DEBUG_ERROR, "Failed to init transceiver process!\n");
 		goto error;
diff --git a/src/anetz/anetz.c b/src/anetz/anetz.c
index 23ec592..539edf7 100644
--- a/src/anetz/anetz.c
+++ b/src/anetz/anetz.c
@@ -187,7 +187,7 @@ int anetz_create(int kanal, const char *audiodev, int samplerate, double rx_gain
 	PDEBUG(DANETZ, DEBUG_DEBUG, "Creating 'A-Netz' instance for 'Kanal' = %d (sample rate %d).\n", kanal, samplerate);
 
 	/* init general part of transceiver */
-	rc = sender_create(&anetz->sender, kanal, anetz_kanal2freq(kanal, 0), anetz_kanal2freq(kanal, 1), audiodev, samplerate, rx_gain, pre_emphasis, de_emphasis, write_rx_wave, write_tx_wave, read_rx_wave, loopback, loss_volume, PILOT_SIGNAL_NONE);
+	rc = sender_create(&anetz->sender, kanal, anetz_kanal2freq(kanal, 0), anetz_kanal2freq(kanal, 1), audiodev, samplerate, rx_gain, pre_emphasis, de_emphasis, write_rx_wave, write_tx_wave, read_rx_wave, loopback, loss_volume, PAGING_SIGNAL_NONE);
 	if (rc < 0) {
 		PDEBUG(DANETZ, DEBUG_ERROR, "Failed to init 'Sender' processing!\n");
 		goto error;
diff --git a/src/bnetz/bnetz.c b/src/bnetz/bnetz.c
index 6b8a6d9..fb92ef3 100644
--- a/src/bnetz/bnetz.c
+++ b/src/bnetz/bnetz.c
@@ -109,23 +109,23 @@ double bnetz_kanal2freq(int kanal, int unterband)
 	return freq * 1e6;
 }
 
-/* switch pilot signal (tone or file) */
+/* switch paging signal (tone or file) */
 static void switch_channel_19(bnetz_t *bnetz, int on)
 {
-	/* affects only if pilot signal is used */
-	sender_pilot(&bnetz->sender, on);
+	/* affects only if paging signal is used */
+	sender_paging(&bnetz->sender, on);
 
-	if (bnetz->pilot_file[0] && bnetz->pilot_is_on != on) {
+	if (bnetz->paging_file[0] && bnetz->paging_is_on != on) {
 		FILE *fp;
 
-		fp = fopen(bnetz->pilot_file, "w");
+		fp = fopen(bnetz->paging_file, "w");
 		if (!fp) {
-			PDEBUG(DBNETZ, DEBUG_ERROR, "Failed to open file '%s' to switch channel 19!\n", bnetz->pilot_file);
+			PDEBUG(DBNETZ, DEBUG_ERROR, "Failed to open file '%s' to switch channel 19!\n", bnetz->paging_file);
 			return;
 		}
-		fprintf(fp, "%s\n", (on) ? bnetz->pilot_on : bnetz->pilot_off);
+		fprintf(fp, "%s\n", (on) ? bnetz->paging_on : bnetz->paging_off);
 		fclose(fp);
-		bnetz->pilot_is_on = on;
+		bnetz->paging_is_on = on;
 	}
 }
 
@@ -141,11 +141,11 @@ static void bnetz_timeout(struct timer *timer);
 static void bnetz_go_idle(bnetz_t *bnetz);
 
 /* Create transceiver instance and link to a list. */
-int bnetz_create(int kanal, const char *audiodev, int samplerate, double rx_gain, int gfs, int pre_emphasis, int de_emphasis, const char *write_rx_wave, const char *write_tx_wave, const char *read_rx_wave, int loopback, double loss_factor, const char *pilot)
+int bnetz_create(int kanal, const char *audiodev, int samplerate, double rx_gain, int gfs, int pre_emphasis, int de_emphasis, const char *write_rx_wave, const char *write_tx_wave, const char *read_rx_wave, int loopback, double loss_factor, const char *paging)
 {
 	bnetz_t *bnetz;
-	enum pilot_signal pilot_signal = PILOT_SIGNAL_NONE;
-	char pilot_file[256] = "", pilot_on[256] = "", pilot_off[256] = "";
+	enum paging_signal paging_signal = PAGING_SIGNAL_NONE;
+	char paging_file[256] = "", paging_on[256] = "", paging_off[256] = "";
 	int rc;
 
 	if (!(kanal >= 1 && kanal <= 39) && !(kanal >= 50 && kanal <= 86)) {
@@ -163,34 +163,34 @@ int bnetz_create(int kanal, const char *audiodev, int samplerate, double rx_gain
 		return -EINVAL;
 	}
 	
-	if (!strcmp(pilot, "notone"))
-		pilot_signal = PILOT_SIGNAL_NOTONE;
+	if (!strcmp(paging, "notone"))
+		paging_signal = PAGING_SIGNAL_NOTONE;
 	else
-	if (!strcmp(pilot, "tone"))
-		pilot_signal = PILOT_SIGNAL_TONE;
+	if (!strcmp(paging, "tone"))
+		paging_signal = PAGING_SIGNAL_TONE;
 	else
-	if (!strcmp(pilot, "positive"))
-		pilot_signal = PILOT_SIGNAL_POSITIVE;
+	if (!strcmp(paging, "positive"))
+		paging_signal = PAGING_SIGNAL_POSITIVE;
 	else
-	if (!strcmp(pilot, "negative"))
-		pilot_signal = PILOT_SIGNAL_NEGATIVE;
+	if (!strcmp(paging, "negative"))
+		paging_signal = PAGING_SIGNAL_NEGATIVE;
 	else {
 		char *p;
 
-		strncpy(pilot_file, pilot, sizeof(pilot_file) - 1);
-		p = strchr(pilot_file, '=');
+		strncpy(paging_file, paging, sizeof(paging_file) - 1);
+		p = strchr(paging_file, '=');
 		if (!p) {
-error_pilot:
-			PDEBUG(DBNETZ, DEBUG_ERROR, "Given pilot file (to switch to channel 19) is missing parameters. Use <file>=<on>:<off> format!\n");
+error_paging:
+			PDEBUG(DBNETZ, DEBUG_ERROR, "Given paging file (to switch to channel 19) is missing parameters. Use <file>=<on>:<off> format!\n");
 			return -EINVAL;
 		}
 		*p++ = '\0';
-		strncpy(pilot_on, p, sizeof(pilot_on) - 1);
-		p = strchr(pilot_file, ':');
+		strncpy(paging_on, p, sizeof(paging_on) - 1);
+		p = strchr(paging_on, ':');
 		if (!p)
-			goto error_pilot;
+			goto error_paging;
 		*p++ = '\0';
-		strncpy(pilot_off, p, sizeof(pilot_off) - 1);
+		strncpy(paging_off, p, sizeof(paging_off) - 1);
 	}
 
 	bnetz = calloc(1, sizeof(bnetz_t));
@@ -202,11 +202,12 @@ error_pilot:
 	PDEBUG(DBNETZ, DEBUG_DEBUG, "Creating 'B-Netz' instance for 'Kanal' = %d 'Gruppenfreisignal' = %d (sample rate %d).\n", kanal, gfs, samplerate);
 
 	/* init general part of transceiver */
-	rc = sender_create(&bnetz->sender, kanal, bnetz_kanal2freq(kanal, 0), bnetz_kanal2freq(kanal, 1), audiodev, samplerate, rx_gain, pre_emphasis, de_emphasis, write_rx_wave, write_tx_wave, read_rx_wave, loopback, loss_factor, pilot_signal);
+	rc = sender_create(&bnetz->sender, kanal, bnetz_kanal2freq(kanal, 0), bnetz_kanal2freq(kanal, 1), audiodev, samplerate, rx_gain, pre_emphasis, de_emphasis, write_rx_wave, write_tx_wave, read_rx_wave, loopback, loss_factor, paging_signal);
 	if (rc < 0) {
 		PDEBUG(DBNETZ, DEBUG_ERROR, "Failed to init transceiver process!\n");
 		goto error;
 	}
+	bnetz->sender.ruffrequenz = bnetz_kanal2freq(19, 0);
 
 	/* init audio processing */
 	rc = dsp_init_sender(bnetz);
@@ -216,9 +217,9 @@ error_pilot:
 	}
 
 	bnetz->gfs = gfs;
-	strncpy(bnetz->pilot_file, pilot_file, sizeof(bnetz->pilot_file) - 1);
-	strncpy(bnetz->pilot_on, pilot_on, sizeof(bnetz->pilot_on) - 1);
-	strncpy(bnetz->pilot_off, pilot_off, sizeof(bnetz->pilot_off) - 1);
+	strncpy(bnetz->paging_file, paging_file, sizeof(bnetz->paging_file) - 1);
+	strncpy(bnetz->paging_on, paging_on, sizeof(bnetz->paging_on) - 1);
+	strncpy(bnetz->paging_off, paging_off, sizeof(bnetz->paging_off) - 1);
 	timer_init(&bnetz->timer, bnetz_timeout, bnetz);
 
 	/* go into idle state */
diff --git a/src/bnetz/bnetz.h b/src/bnetz/bnetz.h
index 10f5a6d..dcd3a87 100644
--- a/src/bnetz/bnetz.h
+++ b/src/bnetz/bnetz.h
@@ -53,10 +53,10 @@ typedef struct bnetz {
 	int			gfs;			/* 'Gruppenfreisignal' */
 
 	/* switch sender to channel 19 */
-	char			pilot_file[256];	/* if set, write to given file to switch to channel 19 or back */
-	char			pilot_on[256];		/* what to write to switch to channel 19 */
-	char			pilot_off[256];		/* what to write to switch back */
-	int			pilot_is_on;		/* set, if we are on channel 19. also used to switch back on exit */
+	char			paging_file[256];	/* if set, write to given file to switch to channel 19 or back */
+	char			paging_on[256];		/* what to write to switch to channel 19 */
+	char			paging_off[256];	/* what to write to switch back */
+	int			paging_is_on;		/* set, if we are on channel 19. also used to switch back on exit */
 
 	/* all bnetz states */
 	enum bnetz_state	state;			/* main state of sender */
@@ -100,7 +100,7 @@ typedef struct bnetz {
 
 double bnetz_kanal2freq(int kanal, int unterband);
 int bnetz_init(void);
-int bnetz_create(int kanal, const char *audiodev, int samplerate, double rx_gain, int gfs, int pre_emphasis, int de_emphasis, const char *write_rx_wave, const char *write_tx_wave, const char *read_rx_wave, int loopback, double loss_factor, const char *pilot);
+int bnetz_create(int kanal, const char *audiodev, int samplerate, double rx_gain, int gfs, int pre_emphasis, int de_emphasis, const char *write_rx_wave, const char *write_tx_wave, const char *read_rx_wave, int loopback, double loss_factor, const char *paging);
 void bnetz_destroy(sender_t *sender);
 void bnetz_loss_indication(bnetz_t *bnetz);
 void bnetz_receive_tone(bnetz_t *bnetz, int bit);
diff --git a/src/bnetz/main.c b/src/bnetz/main.c
index 7322ca3..409b574 100644
--- a/src/bnetz/main.c
+++ b/src/bnetz/main.c
@@ -36,8 +36,8 @@
 #include "ansage.h"
 
 int gfs = 2;
-int num_pilot = 0;
-const char *pilot[MAX_SENDER] = { "tone" };
+int num_paging = 0;
+const char *paging[MAX_SENDER] = { "tone" };
 double lossdetect = 0;
 
 void print_help(const char *arg0)
@@ -53,7 +53,7 @@ void print_help(const char *arg0)
 	printf("        Set to 19 in order to make the phone transmit at 100 mW instead of\n");
 	printf("        full 15 Watts. If supported, the phone uses the channel with low power\n");
 	printf("        (Kanal kleiner Leistung).\n");
-	printf(" -P --pilot tone | notone | positive | negative | <file>=<on>:<off>\n");
+	printf(" -P --paging tone | notone | positive | negative | <file>=<on>:<off>\n");
 	printf("        Send a tone, give a signal or write to a file when switching to\n");
 	printf("        channel 19. (paging the phone).\n");
 	printf("        'tone', 'positive', 'negative' is sent on second audio channel.\n");
@@ -63,7 +63,7 @@ void print_help(const char *arg0)
 	printf("        'negative' sends a negative signal for channel 19, else positive.\n");
 	printf("        Example: /sys/class/gpio/gpio17/value=1:0 writes a '1' to\n");
 	printf("        /sys/class/gpio/gpio17/value to switching to channel 19 and a '0' to\n");
-	printf("        switch back. (default = %s)\n", pilot[0]);
+	printf("        switch back. (default = %s)\n", paging[0]);
 	printf(" -L --loss <volume>\n");
 	printf("        Detect loss of carrier by detecting steady noise above given volume in\n");
 	printf("        percent. (disabled by default)\n");
@@ -79,7 +79,7 @@ static int handle_options(int argc, char **argv)
 
 	static struct option long_options_special[] = {
 		{"gfs", 1, 0, 'G'},
-		{"pilot", 1, 0, 'P'},
+		{"paging", 1, 0, 'P'},
 		{"loss", 1, 0, 'L'},
 		{0, 0, 0, 0},
 	};
@@ -109,7 +109,7 @@ static int handle_options(int argc, char **argv)
 			skip_args += 2;
 			break;
 		case 'P':
-			OPT_ARRAY(num_pilot, pilot, strdup(optarg))
+			OPT_ARRAY(num_paging, paging, strdup(optarg))
 			skip_args += 2;
 			break;
 		case 'L':
@@ -159,10 +159,10 @@ int main(int argc, char *argv[])
 		fprintf(stderr, "You need to specify as many sound devices as you have channels.\n");
 		exit(0);
 	}
-	if (num_kanal == 1 && num_pilot == 0)
-		num_pilot = 1; /* use defualt */
-	if (num_kanal != num_pilot) {
-		fprintf(stderr, "You need to specify as many pilot tone settings as you have channels.\n");
+	if (num_kanal == 1 && num_paging == 0)
+		num_paging = 1; /* use defualt */
+	if (num_kanal != num_paging) {
+		fprintf(stderr, "You need to specify as many paging tone settings as you have channels.\n");
 		exit(0);
 	}
 
@@ -187,13 +187,13 @@ int main(int argc, char *argv[])
 
 	/* create transceiver instance */
 	for (i = 0; i < num_kanal; i++) {
-		rc = bnetz_create(kanal[i], audiodev[i], samplerate, rx_gain, gfs, do_pre_emphasis, do_de_emphasis, write_rx_wave, write_tx_wave, read_rx_wave, loopback, (double)lossdetect / 100.0, pilot[i]);
+		rc = bnetz_create(kanal[i], audiodev[i], samplerate, rx_gain, gfs, do_pre_emphasis, do_de_emphasis, write_rx_wave, write_tx_wave, read_rx_wave, loopback, (double)lossdetect / 100.0, paging[i]);
 		if (rc < 0) {
 			fprintf(stderr, "Failed to create \"Sender\" instance. Quitting!\n");
 			goto fail;
 		}
 		printf("Base station for channel %d ready, please tune transmitter to %.3f MHz and receiver " "to %.3f MHz.\n", kanal[i], bnetz_kanal2freq(kanal[i], 0) / 1e6, bnetz_kanal2freq(kanal[i], 1) / 1e6);
-		printf("To call phone, switch transmitter (using pilot signal) to %.3f MHz.\n", bnetz_kanal2freq(19, 0) / 1e6);
+		printf("To call phone, switch transmitter (using paging signal) to %.3f MHz.\n", bnetz_kanal2freq(19, 0) / 1e6);
 	}
 
 	main_common(&quit, latency, interval, NULL);
diff --git a/src/cnetz/cnetz.c b/src/cnetz/cnetz.c
index f0a4ec5..71795da 100644
--- a/src/cnetz/cnetz.c
+++ b/src/cnetz/cnetz.c
@@ -274,7 +274,7 @@ int cnetz_create(int kanal, enum cnetz_chan_type chan_type, const char *audiodev
 
 	/* init general part of transceiver */
 	/* do not enable emphasis, since it is done by cnetz code, not by common sender code */
-	rc = sender_create(&cnetz->sender, kanal, cnetz_kanal2freq(kanal, 0), cnetz_kanal2freq(kanal, 1), audiodev, samplerate, rx_gain, 0, 0, write_rx_wave, write_tx_wave, read_rx_wave, loopback, 0, PILOT_SIGNAL_NONE);
+	rc = sender_create(&cnetz->sender, kanal, cnetz_kanal2freq(kanal, 0), cnetz_kanal2freq(kanal, 1), audiodev, samplerate, rx_gain, 0, 0, write_rx_wave, write_tx_wave, read_rx_wave, loopback, 0, PAGING_SIGNAL_NONE);
 	if (rc < 0) {
 		PDEBUG(DCNETZ, DEBUG_ERROR, "Failed to init transceiver process!\n");
 		goto error;
diff --git a/src/common/call.c b/src/common/call.c
index ab57390..50370ec 100644
--- a/src/common/call.c
+++ b/src/common/call.c
@@ -473,7 +473,7 @@ int call_init(const char *station_id, const char *audiodev, int samplerate, int
 		return 0;
 
 	/* open sound device for call control */
-	call.sound = sound_open(audiodev, NULL, NULL, 1, samplerate, 3700.0, 0.0);
+	call.sound = sound_open(audiodev, NULL, NULL, 1, 0.0, samplerate, 3700.0, 0.0);
 	if (!call.sound) {
 		PDEBUG(DSENDER, DEBUG_ERROR, "No sound device!\n");
 
@@ -671,7 +671,7 @@ void process_call(int c)
 			jitter_load(&call.dejitter, up, count);
 		}
 		spl_list[0] = up;
-		rc = sound_write(call.sound, spl_list, count, 1);
+		rc = sound_write(call.sound, spl_list, count, NULL, NULL, 1);
 		if (rc < 0) {
 			PDEBUG(DSENDER, DEBUG_ERROR, "Failed to write TX data to sound device (rc = %d)\n", rc);
 			if (rc == -EPIPE)
diff --git a/src/common/sdr.c b/src/common/sdr.c
index c2b38dc..527c291 100644
--- a/src/common/sdr.c
+++ b/src/common/sdr.c
@@ -17,12 +17,13 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
 #include <string.h>
 #include <math.h>
 #include "filter.h"
-#include "sdr.h"
+#include "sender.h"
 #ifdef HAVE_UHD
 #include "uhd.h"
 #endif
@@ -42,7 +43,9 @@ typedef struct sdr_chan {
 } sdr_chan_t;
 
 typedef struct sdr {
-	sdr_chan_t *chan;
+	sdr_chan_t *chan;	/* settings for all channels */
+	int paging_channel;	/* if set, points to paging channel */
+	sdr_chan_t paging_chan;	/* settings for extra paging channel */
 	double spl_deviation;	/* how to convert a sample step into deviation (Hz) */
 	int channels;		/* number of frequencies */
 	double samplerate;	/* IQ rate */
@@ -73,10 +76,10 @@ int sdr_init(const char *device_args, double rx_gain, double tx_gain)
 	return 0;
 }
 
-void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_frequency, double *rx_frequency, int channels, int samplerate, double bandwidth, double sample_deviation)
+void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_frequency, double *rx_frequency, int channels, double paging_frequency, int samplerate, double bandwidth, double sample_deviation)
 {
 	sdr_t *sdr;
-	double center_frequency;
+	double tx_center_frequency, rx_center_frequency;
 	int rc;
 	int c;
 
@@ -95,8 +98,14 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
 	sdr->spl_deviation = sample_deviation;
 	sdr->amplitude = 0.4 / (double)channels; // FIXME: actual amplitude 0.1?
 
+	/* special case where we use a paging frequency */
+	if (paging_frequency) {
+		/* add extra paging channel */
+		sdr->paging_channel = channels;
+	}
+
 	/* create list of channel states */
-	sdr->chan = calloc(sizeof(*sdr->chan), channels);
+	sdr->chan = calloc(sizeof(*sdr->chan), channels + (sdr->paging_channel != 0));
 	if (!sdr->chan) {
 		PDEBUG(DSDR, DEBUG_ERROR, "NO MEM!\n");
 		goto error;
@@ -105,43 +114,74 @@ void *sdr_open(const char __attribute__((__unused__)) *audiodev, double *tx_freq
 		PDEBUG(DSDR, DEBUG_INFO, "Frequency #%d: TX = %.6f MHz, RX = %.6f MHz\n", c, tx_frequency[c] / 1e6, rx_frequency[c] / 1e6);
 		sdr->chan[c].tx_frequency = tx_frequency[c];
 		sdr->chan[c].rx_frequency = rx_frequency[c];
-#warning check rx frequency is in range
 		filter_lowpass_init(&sdr->chan[c].rx_lp[0], bandwidth, samplerate);
 		filter_lowpass_init(&sdr->chan[c].rx_lp[1], bandwidth, samplerate);
 	}
+	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;
+	}
 
 	/* calculate required bandwidth (IQ rate) */
-	if (channels == 1) {
-		PDEBUG(DSDR, DEBUG_INFO, "Single frequency, so we use sample rate as IQ bandwidth: %.6f MHz\n", sdr->samplerate / 1e6);
-		center_frequency = sdr->chan[0].tx_frequency;
-	} else {
-		double low_frequency = sdr->chan[0].tx_frequency, high_frequency = sdr->chan[0].tx_frequency, range;
-		for (c = 1; c < channels; c++) {
-			if (sdr->chan[c].tx_frequency < low_frequency)
-				low_frequency = sdr->chan[c].tx_frequency;
-			if (sdr->chan[c].tx_frequency > high_frequency)
-				high_frequency = sdr->chan[c].tx_frequency;
-		}
-		range = high_frequency - low_frequency;
-		PDEBUG(DSDR, DEBUG_INFO, "Range between frequencies: %.6f MHz\n", range / 1e6);
-		if (range * 2 > sdr->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");
-			goto error;
-		}
-		center_frequency = (high_frequency + low_frequency) / 2.0;
+	double tx_low_frequency = sdr->chan[0].tx_frequency, tx_high_frequency = sdr->chan[0].tx_frequency;
+	double rx_low_frequency = sdr->chan[0].rx_frequency, rx_high_frequency = sdr->chan[0].rx_frequency;
+	double range;
+	for (c = 1; c < channels; c++) {
+		if (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)
+			tx_high_frequency = sdr->chan[c].tx_frequency;
+		if (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)
+			rx_high_frequency = sdr->chan[c].rx_frequency;
+	}
+	if (sdr->paging_channel) {
+		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)
+			tx_high_frequency = sdr->chan[sdr->paging_channel].tx_frequency;
 	}
-	PDEBUG(DSDR, DEBUG_INFO, "Using center frequency: %.6f MHz\n", center_frequency / 1e6);
+	/* range of TX */
+	range = tx_high_frequency - tx_low_frequency;
+	if (range)
+		PDEBUG(DSDR, DEBUG_INFO, "Range between all TX Frequencies: %.6f MHz\n", range / 1e6);
+	if (range * 2 > sdr->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", sdr->samplerate / 1e6, range * 2.0 / 1e6);
+		PDEBUG(DSDR, DEBUG_NOTICE, "Please increase samplerate!\n");
+		goto error;
+	}
+	tx_center_frequency = (tx_high_frequency + tx_low_frequency) / 2.0;
+	PDEBUG(DSDR, DEBUG_INFO, "Using TX center frequency: %.6f MHz\n", tx_center_frequency / 1e6);
+	/* range of RX */
+	range = rx_high_frequency - rx_low_frequency;
+	if (range)
+		PDEBUG(DSDR, DEBUG_INFO, "Range between all RX Frequencies: %.6f MHz\n", range / 1e6);
+	if (range * 2.0 > sdr->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");
+		goto error;
+	}
+	rx_center_frequency = (rx_high_frequency + rx_low_frequency) / 2.0;
+	PDEBUG(DSDR, DEBUG_INFO, "Using RX center frequency: %.6f MHz\n", rx_center_frequency / 1e6);
+	/* set offsets to center frequency */
 	for (c = 0; c < channels; c++) {
-		sdr->chan[c].offset = sdr->chan[c].tx_frequency - center_frequency;
-		sdr->chan[c].rx_rot = 2 * M_PI * -sdr->chan[c].offset / sdr->samplerate;
-		PDEBUG(DSDR, DEBUG_INFO, "Frequency #%d offset: %.6f MHz\n", c, sdr->chan[c].offset / 1e6);
+		double rx_offset;
+		sdr->chan[c].offset = sdr->chan[c].tx_frequency - tx_center_frequency;
+		rx_offset = sdr->chan[c].rx_frequency - rx_center_frequency;
+		sdr->chan[c].rx_rot = 2 * M_PI * -rx_offset / sdr->samplerate;
+		PDEBUG(DSDR, DEBUG_INFO, "Frequency #%d: TX offset: %.6f MHz, RX offset: %.6f MHz\n", c, sdr->chan[c].offset / 1e6, rx_offset / 1e6);
+	}
+	if (sdr->paging_channel) {
+		sdr->chan[sdr->paging_channel].offset = sdr->chan[sdr->paging_channel].tx_frequency - tx_center_frequency;
+		PDEBUG(DSDR, DEBUG_INFO, "Paging Frequency: TX offset: %.6f MHz\n", sdr->chan[sdr->paging_channel].offset / 1e6);
 	}
 	PDEBUG(DSDR, DEBUG_INFO, "Using gain: TX %.1f dB, RX %.1f dB\n", sdr_tx_gain, sdr_rx_gain);
 
 #ifdef HAVE_UHD
-#warning hack
-	rc = uhd_open(sdr_device_args, center_frequency, center_frequency - sdr->chan[0].tx_frequency + sdr->chan[0].rx_frequency, sdr->samplerate, sdr_rx_gain, sdr_tx_gain);
+	rc = uhd_open(sdr_device_args, tx_center_frequency, rx_center_frequency, sdr->samplerate, sdr_rx_gain, sdr_tx_gain);
 	if (rc)
 		goto error;
 #endif
@@ -168,12 +208,12 @@ void sdr_close(void *inst)
 	}
 }
 
-int sdr_write(void *inst, int16_t **samples, int num, int channels)
+int sdr_write(void *inst, int16_t **samples, int num, enum paging_signal __attribute__((unused)) *paging_signal, int *on, int channels)
 {
 	sdr_t *sdr = (sdr_t *)inst;
 	float buff[num * 2];
 	int c, s, ss;
-	double rate, phase, amplitude, dev;
+	double rate, offset, phase, amplitude, dev;
 	int sent;
 
 	if (channels != sdr->channels) {
@@ -186,11 +226,16 @@ int sdr_write(void *inst, int16_t **samples, int num, int channels)
 	amplitude = sdr->amplitude;
 	memset(buff, 0, sizeof(buff));
 	for (c = 0; c < channels; c++) {
-		/* modulate */
 		phase = sdr->chan[c].tx_phase;
+		/* switch offset to paging channel, if requested */
+		if (on[c] && sdr->paging_channel)
+			offset = sdr->chan[sdr->paging_channel].offset;
+		else
+			offset = sdr->chan[c].offset;
+		/* modulate */
 		for (s = 0, ss = 0; s < num; s++) {
 			/* deviation is defined by the sample value and the offset */
-			dev = sdr->chan[c].offset + (double)samples[c][s] * sdr->spl_deviation;
+			dev = offset + (double)samples[c][s] * sdr->spl_deviation;
 #ifdef FAST_SINE
 			phase += 256.0 * dev / rate;
 			if (phase < 0.0)
@@ -249,7 +294,6 @@ int sdr_read(void *inst, int16_t **samples, int num, int channels)
 			Q[s] = i * sin(phase) + q * cos(phase);
 		}
 		sdr->chan[c].rx_phase = phase;
-#warning eine interation von 2 führt zu müll (2. kanal gespiegeltes audio), muss man genauer mal analysieren
 		filter_lowpass_process(&sdr->chan[c].rx_lp[0], I, count, 1);
 		filter_lowpass_process(&sdr->chan[c].rx_lp[1], Q, count, 1);
 		last_phase = sdr->chan[c].rx_last_phase;
diff --git a/src/common/sdr.h b/src/common/sdr.h
index da3ccb0..ecbcbe4 100644
--- a/src/common/sdr.h
+++ b/src/common/sdr.h
@@ -1,8 +1,8 @@
 
 int sdr_init(const char *device_args, double rx_gain, double tx_gain);
-void *sdr_open(const char *audiodev, double *tx_frequency, double *rx_frequency, int channels, int samplerate, double bandwidth, double sample_deviation);
+void *sdr_open(const char *audiodev, double *tx_frequency, double *rx_frequency, int channels, double paging_frequency, int samplerate, double bandwidth, double sample_deviation);
 void sdr_close(void *inst);
-int sdr_write(void *inst, int16_t **samples, int num, int channels);
+int sdr_write(void *inst, int16_t **samples, int num, enum paging_signal *paging_signal, int *on, int channels);
 int sdr_read(void *inst, int16_t **samples, int num, int channels);
 int sdr_get_inbuffer(void *inst);
 
diff --git a/src/common/sender.c b/src/common/sender.c
index a579388..f610dbc 100644
--- a/src/common/sender.c
+++ b/src/common/sender.c
@@ -32,7 +32,7 @@ static sender_t **sender_tailp = &sender_head;
 int cant_recover = 0;
 
 /* Init transceiver instance and link to list of transceivers. */
-int sender_create(sender_t *sender, int kanal, double sendefrequenz, double empfangsfrequenz, const char *audiodev, int samplerate, double rx_gain, int pre_emphasis, int de_emphasis, const char *write_rx_wave, const char *write_tx_wave, const char *read_rx_wave, int loopback, double loss_volume, enum pilot_signal pilot_signal)
+int sender_create(sender_t *sender, int kanal, double sendefrequenz, double empfangsfrequenz, const char *audiodev, int samplerate, double rx_gain, int pre_emphasis, int de_emphasis, const char *write_rx_wave, const char *write_tx_wave, const char *read_rx_wave, int loopback, double loss_volume, enum paging_signal paging_signal)
 {
 	sender_t *master, *slave;
 	int rc = 0;
@@ -49,12 +49,7 @@ int sender_create(sender_t *sender, int kanal, double sendefrequenz, double empf
 	sender->de_emphasis = de_emphasis;
 	sender->loopback = loopback;
 	sender->loss_volume = loss_volume;
-#ifdef HAVE_SDR
-	if (!strcmp(audiodev, "sdr"))
-		pilot_signal = PILOT_SIGNAL_NONE;
-#endif
-	sender->pilot_signal = pilot_signal;
-	sender->pilotton_phaseshift = 1.0 / ((double)samplerate / 1000.0);
+	sender->paging_signal = paging_signal;
 
 	PDEBUG_CHAN(DSENDER, DEBUG_DEBUG, "Creating 'Sender' instance\n");
 
@@ -73,13 +68,13 @@ int sender_create(sender_t *sender, int kanal, double sendefrequenz, double empf
 			break;
 	}
 	if (master) {
-		if (master->pilot_signal != PILOT_SIGNAL_NONE) {
-			PDEBUG(DSENDER, DEBUG_ERROR, "Cannot share audio device with channel %d, because second channel is used for pilot signal!\n", master->kanal);
+		if (master->paging_signal != PAGING_SIGNAL_NONE && !!strcmp(master->audiodev, "sdr")) {
+			PDEBUG(DSENDER, DEBUG_ERROR, "Cannot share audio device with channel %d, because its second audio channel is used for paging signal! Use different audio device.\n", master->kanal);
 			rc = -EBUSY;
 			goto error;
 		}
-		if (pilot_signal != PILOT_SIGNAL_NONE) {
-			PDEBUG(DSENDER, DEBUG_ERROR, "Cannot share audio device with channel %d, because we need a stereo channel for pilot signal!\n", master->kanal);
+		if (paging_signal != PAGING_SIGNAL_NONE && !!strcmp(audiodev, "sdr")) {
+			PDEBUG(DSENDER, DEBUG_ERROR, "Cannot share audio device with channel %d, because we need a second audio channel for paging signal! Use different audio device.\n", master->kanal);
 			rc = -EBUSY;
 			goto error;
 		}
@@ -95,10 +90,6 @@ int sender_create(sender_t *sender, int kanal, double sendefrequenz, double empf
 		/* link audio device */
 #ifdef HAVE_SDR
 		if (!strcmp(audiodev, "sdr")) {
-			if (pilot_signal != PILOT_SIGNAL_NONE) {
-				PDEBUG(DSENDER, DEBUG_ERROR, "No pilot signal allowed with SDR, please fix!\n");
-				abort();
-			}
 			sender->audio_open = sdr_open;
 			sender->audio_close = sdr_close;
 			sender->audio_read = sdr_read;
@@ -169,6 +160,7 @@ int sender_open_audio(void)
 {
 	sender_t *master, *inst;
 	int channels;
+	double paging_frequency = 0.0;
 	int i;
 
 	for (master = sender_head; master; master = master->next) {
@@ -188,10 +180,12 @@ int sender_open_audio(void)
 				rx_f[i] = inst->sendefrequenz;
 			else
 				rx_f[i] = inst->empfangsfrequenz;
+			if (inst->ruffrequenz)
+				paging_frequency = inst->ruffrequenz;
 		}
 
 		/* open device */
-		master->audio = master->audio_open(master->audiodev, tx_f, rx_f, channels, master->samplerate, master->bandwidth, master->sample_deviation);
+		master->audio = master->audio_open(master->audiodev, tx_f, rx_f, channels, paging_frequency, master->samplerate, master->bandwidth, master->sample_deviation);
 		if (!master->audio) {
 			PDEBUG(DSENDER, DEBUG_ERROR, "No audio device!\n");
 			return -EIO;
@@ -226,27 +220,6 @@ void sender_destroy(sender_t *sender)
 	jitter_destroy(&sender->dejitter);
 }
 
-static void gen_pilotton(sender_t *sender, int16_t *samples, int length)
-{
-	double phaseshift, phase;
-	int i;
-
-	phaseshift = sender->pilotton_phaseshift;
-	phase = sender->pilotton_phase;
-
-	for (i = 0; i < length; i++) {
-		if (phase < 0.5)
-			*samples++ = 30000;
-		else
-			*samples++ = -30000;
-		phase += phaseshift;
-		if (phase >= 1.0)
-			phase -= 1.0;
-	}
-
-	sender->pilotton_phase = phase;
-}
-
 static void gain_samples(int16_t *samples, int length, double gain)
 {
 	int i;
@@ -271,16 +244,12 @@ void process_sender_audio(sender_t *sender, int *quit, int latspl)
 
 	/* count instances for audio channel */
 	for (num_chan = 0, inst = sender; inst; num_chan++, inst = inst->slave);
-	if (sender->pilot_signal != PILOT_SIGNAL_NONE) {
-		if (num_chan != 1) {
-			PDEBUG(DSENDER, DEBUG_ERROR, "Software error, please fix!\n");
-			abort();
-		}
-		num_chan = 2;
-	}
 	int16_t buff[num_chan][latspl], *samples[num_chan];
-	for (i = 0; i < num_chan; i++)
+	enum paging_signal paging_signal[num_chan];
+	int on[num_chan];
+	for (i = 0; i < num_chan; i++) {
 		samples[i] = buff[i];
+	}
 
 	count = sender->audio_get_inbuffer(sender->audio);
 	if (count < 0) {
@@ -321,41 +290,12 @@ cant_recover:
 			/* do pre emphasis towards radio, not wave_write */
 			if (inst->pre_emphasis)
 				pre_emphasis(&inst->estate, samples[i], count);
-		}
-		switch (sender->pilot_signal) {
-		case PILOT_SIGNAL_TONE:
-			/* tone if pilot signal is on */
-			if (sender->pilot_on)
-				gen_pilotton(sender, samples[1], count);
-			else
-				memset(samples[1], 0, count << 1);
-			break;
-		case PILOT_SIGNAL_NOTONE:
-			/* tone if pilot signal is off */
-			if (!sender->pilot_on)
-				gen_pilotton(sender, samples[1], count);
-			else
-				memset(samples[1], 0, count << 1);
-			break;
-		case PILOT_SIGNAL_POSITIVE:
-			/* positive signal if pilot signal is on */
-			if (sender->pilot_on)
-				memset(samples[1], 127, count << 1);
-			else
-				memset(samples[1], 128, count << 1);
-			break;
-		case PILOT_SIGNAL_NEGATIVE:
-			/* negative signal if pilot signal is on */
-			if (sender->pilot_on)
-				memset(samples[1], 128, count << 1);
-			else
-				memset(samples[1], 127, count << 1);
-			break;
-		case PILOT_SIGNAL_NONE:
-			break;
+			/* set paging signal */
+			paging_signal[i] = sender->paging_signal;
+			on[i] = sender->paging_on;
 		}
 
-		rc = sender->audio_write(sender->audio, samples, count, num_chan);
+		rc = sender->audio_write(sender->audio, samples, count, paging_signal, on, num_chan);
 		if (rc < 0) {
 			PDEBUG(DSENDER, DEBUG_ERROR, "Failed to write TX data to audio device (rc = %d)\n", rc);
 			if (rc == -EPIPE) {
@@ -406,8 +346,8 @@ transmit_later:
 	}
 }
 
-void sender_pilot(sender_t *sender, int on)
+void sender_paging(sender_t *sender, int on)
 {
-	sender->pilot_on = on;
+	sender->paging_on = on;
 }
 
diff --git a/src/common/sender.h b/src/common/sender.h
index c655ca6..5dbdf52 100644
--- a/src/common/sender.h
+++ b/src/common/sender.h
@@ -11,13 +11,13 @@
 
 #define MAX_SENDER	16
 
-/* how to send a 'pilot' signal (trigger transmitter) */
-enum pilot_signal {
-	PILOT_SIGNAL_NONE = 0,
-	PILOT_SIGNAL_TONE,
-	PILOT_SIGNAL_NOTONE,
-	PILOT_SIGNAL_POSITIVE,
-	PILOT_SIGNAL_NEGATIVE,
+/* how to send a 'paging' signal (trigger transmitter) */
+enum paging_signal {
+	PAGING_SIGNAL_NONE = 0,
+	PAGING_SIGNAL_TONE,
+	PAGING_SIGNAL_NOTONE,
+	PAGING_SIGNAL_POSITIVE,
+	PAGING_SIGNAL_NEGATIVE,
 };
 
 /* common structure of each transmitter */
@@ -30,15 +30,16 @@ typedef struct sender {
 	int			kanal;			/* channel number */
 	double			sendefrequenz;		/* transmitter frequency */
 	double			empfangsfrequenz;	/* receiver frequency */
+	double			ruffrequenz;		/* special paging frequency used for B-Netz */
 	double			bandwidth;		/* max NF frequency to be transmitted unaffected by filtering */
 	double			sample_deviation;	/* frequency deviation of one sample step (after pre-emphasis) */
 
 	/* audio */
 	void			*audio;
 	char			audiodev[64];		/* audio device name (alsa or sdr) */
-	void			*(*audio_open)(const char *, double *, double *, int, int, double, double);
+	void			*(*audio_open)(const char *, double *, double *, int, double, int, double, double);
 	void 			(*audio_close)(void *);
-	int			(*audio_write)(void *, int16_t **, int, int);
+	int			(*audio_write)(void *, int16_t **, int, enum paging_signal *, int *, int);
 	int			(*audio_read)(void *, int16_t **, int, int);
 	int			(*audio_get_inbuffer)(void *);
 	int			samplerate;
@@ -67,11 +68,9 @@ typedef struct sender {
 	double			loss_volume;
 	loss_t			loss;
 
-	/* pilot tone */
-	enum pilot_signal	pilot_signal;		/* if pilot signal is used and how it is performed */
-	int			pilot_on;		/* 1 or 0 for on or off */
-	double			pilotton_phaseshift;	/* phase to shift every sample */
-	double			pilotton_phase; 	/* current phase */
+	/* paging tone */
+	enum paging_signal	paging_signal;		/* if paging signal is used and how it is performed */
+	int			paging_on;		/* 1 or 0 for on or off */
 
 	/* display wave */
 	dispwav_t		dispwav;		/* display wave form */
@@ -81,11 +80,11 @@ typedef struct sender {
 extern sender_t *sender_head;
 extern int cant_recover;
 
-int sender_create(sender_t *sender, int kanal, double sendefrequenz, double empfangsfrequenz, const char *audiodev, int samplerate, double rx_gain, int pre_emphasis, int de_emphasis, const char *write_rx_wave, const char *write_tx_wave, const char *read_rx_wave, int loopback, double loss_volume, enum pilot_signal pilot_signal);
+int sender_create(sender_t *sender, int kanal, double sendefrequenz, double empfangsfrequenz, const char *audiodev, int samplerate, double rx_gain, int pre_emphasis, int de_emphasis, const char *write_rx_wave, const char *write_tx_wave, const char *read_rx_wave, int loopback, double loss_volume, enum paging_signal paging_signal);
 void sender_destroy(sender_t *sender);
 int sender_open_audio(void);
 void process_sender_audio(sender_t *sender, int *quit, int latspl);
 void sender_send(sender_t *sender, int16_t *samples, int count);
 void sender_receive(sender_t *sender, int16_t *samples, int count);
-void sender_pilot(sender_t *sender, int on);
+void sender_paging(sender_t *sender, int on);
 
diff --git a/src/common/sound.h b/src/common/sound.h
index 313a559..a352f06 100644
--- a/src/common/sound.h
+++ b/src/common/sound.h
@@ -1,7 +1,9 @@
 
-void *sound_open(const char *audiodev, double *tx_frequency, double *rx_frequency, int channels, int samplerate, double bandwidth, double sample_deviation);
+enum paging_signal;
+
+void *sound_open(const char *audiodev, double *tx_frequency, double *rx_frequency, int channels, double paging_frequency, int samplerate, double bandwidth, double sample_deviation);
 void sound_close(void *inst);
-int sound_write(void *inst, int16_t **samples, int num, int channels);
+int sound_write(void *inst, int16_t **samples, int num, enum paging_signal *paging_signal, int *on, int channels);
 int sound_read(void *inst, int16_t **samples, int num, int channels);
 int sound_get_inbuffer(void *inst);
 
diff --git a/src/common/sound_alsa.c b/src/common/sound_alsa.c
index c8d0668..4eef893 100644
--- a/src/common/sound_alsa.c
+++ b/src/common/sound_alsa.c
@@ -21,11 +21,13 @@
 #include <stdint.h>
 #include <alsa/asoundlib.h>
 #include "debug.h"
-#include "sound.h"
+#include "sender.h"
 
 typedef struct sound {
 	snd_pcm_t *phandle, *chandle;
 	int pchannels, cchannels;
+	double paging_phaseshift;	/* phase to shift every sample */
+	double paging_phase;	 	/* current phase */
 } sound_t;
 
 static int set_hw_params(snd_pcm_t *handle, int samplerate, int *channels)
@@ -128,7 +130,7 @@ static int sound_prepare(sound_t *sound)
 	return 0;
 }
 
-void *sound_open(const char *audiodev, double __attribute__((unused)) *tx_frequency, double __attribute__((unused)) *rx_frequency, int channels, int samplerate, double __attribute__((unused)) bandwidth, double __attribute__((unused)) sample_deviation)
+void *sound_open(const char *audiodev, double __attribute__((unused)) *tx_frequency, double __attribute__((unused)) *rx_frequency, int channels, double __attribute__((unused)) paging_frequency, int samplerate, double __attribute__((unused)) bandwidth, double __attribute__((unused)) sample_deviation)
 {
 	sound_t *sound;
 	int rc;
@@ -144,6 +146,8 @@ void *sound_open(const char *audiodev, double __attribute__((unused)) *tx_freque
 		return NULL;
 	}
 
+	sound->paging_phaseshift = 1.0 / ((double)samplerate / 1000.0);
+
 	rc = snd_pcm_open(&sound->phandle, audiodev, SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK);
 	if (rc < 0) {
 		PDEBUG(DSOUND, DEBUG_ERROR, "Failed to open '%s' for playback! (%s)\n", audiodev, snd_strerror(rc));
@@ -200,7 +204,51 @@ void sound_close(void *inst)
 	free(sound);
 }
 
-int sound_write(void *inst, int16_t **samples, int num, int channels)
+static void gen_paging_tone(sound_t *sound, int16_t *samples, int length, enum paging_signal paging_signal, int on)
+{
+	double phaseshift, phase;
+	int i;
+
+	switch (paging_signal) {
+	case PAGING_SIGNAL_NOTONE:
+		/* no tone if paging signal is on */
+		on = !on;
+		// fall through
+	case PAGING_SIGNAL_TONE:
+		/* tone if paging signal is on */
+		if (on) {
+			phaseshift = sound->paging_phaseshift;
+			phase = sound->paging_phase;
+			for (i = 0; i < length; i++) {
+				if (phase < 0.5)
+					*samples++ = 30000;
+				else
+					*samples++ = -30000;
+				phase += phaseshift;
+				if (phase >= 1.0)
+					phase -= 1.0;
+			}
+			sound->paging_phase = phase;
+		} else
+			memset(samples, 0, length << 1);
+		break;
+	case PAGING_SIGNAL_NEGATIVE:
+		/* negative signal if paging signal is on */
+		on = !on;
+		// fall through
+	case PAGING_SIGNAL_POSITIVE:
+		/* positive signal if paging signal is on */
+		if (on)
+			memset(samples, 127, length << 1);
+		else
+			memset(samples, 128, length << 1);
+		break;
+	case PAGING_SIGNAL_NONE:
+		break;
+	}
+}
+
+int sound_write(void *inst, int16_t **samples, int num, enum paging_signal *paging_signal, int *on, int channels)
 {
 	sound_t *sound = (sound_t *)inst;
 	int16_t buff[num << 1];
@@ -208,15 +256,22 @@ int sound_write(void *inst, int16_t **samples, int num, int channels)
 	int i, ii;
 
 	if (sound->pchannels == 2) {
-		if (channels < 2) {
+		if (paging_signal && on && paging_signal[0] != PAGING_SIGNAL_NONE) {
+			int16_t paging[num << 1];
+			gen_paging_tone(sound, paging, num, paging_signal[0], on[0]);
 			for (i = 0, ii = 0; i < num; i++) {
 				buff[ii++] = samples[0][i];
+				buff[ii++] = paging[i];
+			}
+		} else if (channels == 2) {
+			for (i = 0, ii = 0; i < num; i++) {
 				buff[ii++] = samples[0][i];
+				buff[ii++] = samples[1][i];
 			}
 		} else {
 			for (i = 0, ii = 0; i < num; i++) {
 				buff[ii++] = samples[0][i];
-				buff[ii++] = samples[1][i];
+				buff[ii++] = samples[0][i];
 			}
 		}
 		rc = snd_pcm_writei(sound->phandle, buff, num);
diff --git a/src/nmt/nmt.c b/src/nmt/nmt.c
index db764ec..5076fd6 100644
--- a/src/nmt/nmt.c
+++ b/src/nmt/nmt.c
@@ -334,7 +334,7 @@ int nmt_create(int channel, enum nmt_chan_type chan_type, const char *audiodev,
 	PDEBUG(DNMT, DEBUG_DEBUG, "Creating 'NMT' instance for channel = %d (sample rate %d).\n", channel, samplerate);
 
 	/* init general part of transceiver */
-	rc = sender_create(&nmt->sender, channel, nmt_channel2freq(channel, 0), nmt_channel2freq(channel, 1), audiodev, samplerate, rx_gain, pre_emphasis, de_emphasis, write_rx_wave, write_tx_wave, read_rx_wave, loopback, 0, PILOT_SIGNAL_NONE);
+	rc = sender_create(&nmt->sender, channel, nmt_channel2freq(channel, 0), nmt_channel2freq(channel, 1), audiodev, samplerate, rx_gain, pre_emphasis, de_emphasis, write_rx_wave, write_tx_wave, read_rx_wave, loopback, 0, PAGING_SIGNAL_NONE);
 	if (rc < 0) {
 		PDEBUG(DNMT, DEBUG_ERROR, "Failed to init transceiver process!\n");
 		goto error;