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B-Netz: Improved detection of tone/frame 

- Be less tollerant to levels when detcting tones.
- Squelch applies to tone detector also
pull/1/head
Andreas Eversberg 2021-08-08 17:44:37 +02:00
parent 4974e39999
commit 1b16029ac6
3 changed files with 33 additions and 18 deletions
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6
docs/b-netz.html
View File

@ -531,6 +531,12 @@ Then tune to actually up-link frequency 148.410 MHz.
The actual level is not yet relevant.
</p>
<p>
<font color="red">Hint: Use squelch on the receiver, to prevent noise from beeing detected as signaling information!</font>
<br><br>
If you use SDR, use the squelch option.
</p>
<pre>
# src/bnetz/bnetz -k 1

37
src/bnetz/dsp.c
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@ -55,6 +55,7 @@
#define METERING_HZ 2900 /* metering pulse frequency */
#define TONE_DETECT_CNT 7 /* 70 milliseconds to detect continuous tone */
#define TONE_LOST_CNT 14 /* we use twice of the detect time, so we bridge a loss of "TONE_DETECT_CNT duration" */
#define TONE_LEVEL_TH 0.20 /* threshold of low level to reject tone */
#define TONE_STDDEV_TH 0.2 /* threshold of bad quality (standard deviation) to reject tone */
/* carrier loss detection */
@ -147,7 +148,7 @@ static void fsk_receive_tone(bnetz_t *bnetz, int tone, int goodtone, double leve
/* set duration to TONE_DETECT_CNT, because it took that long to detect the tone */
bnetz->tone_duration = TONE_DETECT_CNT;
bnetz->tone_detected = tone;
PDEBUG_CHAN(DDSP, DEBUG_INFO, "Detecting continuous tone: F%d Level=%3.0f%% standard deviation=%.0f%% Quality=%3.0f%%\n", bnetz->tone_detected, level_avg * 100.0, level_stddev / level_avg * 100.0, quality_avg * 100.0);
PDEBUG_CHAN(DDSP, DEBUG_INFO, "Detecting continuous tone: F%d Level=%3.0f%% (threshold %3.0f%%) standard deviation=%.0f%% (threshold=%.0f%%) Quality=%3.0f%%\n", bnetz->tone_detected, level_avg * 100.0, TONE_LEVEL_TH * 100.0, level_stddev / level_avg * 100.0, TONE_STDDEV_TH * 100.0, quality_avg * 100.0);
bnetz_receive_tone(bnetz, bnetz->tone_detected);
}
}
@ -169,7 +170,7 @@ static void fsk_receive_bit(void *inst, int bit, double quality, double level)
{
double level_avg, level_stddev, quality_avg;
bnetz_t *bnetz = (bnetz_t *)inst;
int i;
int i, j;
/* normalize FSK level */
level /= TX_PEAK_FSK;
@ -200,18 +201,19 @@ static void fsk_receive_bit(void *inst, int bit, double quality, double level)
/* collect bits, and check for level and continuous tone */
bnetz->rx_tone = (bnetz->rx_tone << 1) | bit;
for (i = 0; i < TONE_DETECT_CNT; i++) {
for (i = 0, j = 0; i < TONE_DETECT_CNT; i++) {
if (((bnetz->rx_tone >> i) & 1) != bit)
break;
if (bnetz->rx_tone_level[i] < 0.05)
break;
continue;
if (bnetz->rx_tone_level[i] < TONE_LEVEL_TH)
continue;
j++;
}
/* continuous tone detection:
* 1. The quality must be good enough.
* 2. All bits must be the same (continuous tone).
*/
if (level_stddev / level_avg > TONE_STDDEV_TH || i < TONE_DETECT_CNT)
if (level_stddev / level_avg > TONE_STDDEV_TH || j < TONE_DETECT_CNT)
fsk_receive_tone(bnetz, bit, 0, level_avg, level_stddev, quality_avg);
else
fsk_receive_tone(bnetz, bit, 1, level_avg, level_stddev, quality_avg);
@ -243,16 +245,15 @@ static void fsk_receive_bit(void *inst, int bit, double quality, double level)
return;
/* collect bits, and check for level */
for (i = 0; i < 16; i++) {
if (bnetz->rx_telegramm_level[i] < 0.05)
break;
for (i = 0, j = 0; i < 16; i++) {
if (bnetz->rx_telegramm_level[i] >= TONE_LEVEL_TH)
j++;
}
if (i == 16)
PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "FSK Valid bits: %d / %d Level: %.0f%% Stddev: %.0f%%\n", i, 16, level_avg * 100.0, level_stddev / level_avg * 100.0);
PDEBUG_CHAN(DDSP, DEBUG_DEBUG, "FSK Valid bits: %d/%d Level: %.0f%% (threshold %.0f%%) Stddev: %.0f%% (threshold %.0f%%)\n", j, 16, level_avg * 100.0, TONE_LEVEL_TH * 100.0, level_stddev / level_avg * 100.0, TONE_STDDEV_TH * 100.0);
/* drop any telegramm that is too bad */
if (level_stddev / level_avg > TONE_STDDEV_TH || i < 16)
if (level_stddev / level_avg > TONE_STDDEV_TH || j < 16)
return;
/* update telegramm measurements */
@ -260,7 +261,7 @@ static void fsk_receive_bit(void *inst, int bit, double quality, double level)
display_measurements_update(bnetz->dmp_frame_stddev, level_stddev / level_avg * 100.0, 0.0);
display_measurements_update(bnetz->dmp_frame_quality, quality_avg * 100.0, 0.0);
PDEBUG_CHAN(DDSP, DEBUG_INFO, "Telegramm RX Level: average=%.0f%% standard deviation=%.0f%% Quality: %.0f%%\n", level_avg * 100.0, level_stddev / level_avg * 100.0, quality_avg * 100.0);
PDEBUG_CHAN(DDSP, DEBUG_INFO, "Telegramm RX Level: average=%.0f%% (threshold %.0f%%) standard deviation=%.0f%% (threshold %.0f%%) Quality: %.0f%%\n", level_avg * 100.0, TONE_LEVEL_TH * 100.0, level_stddev / level_avg * 100.0, TONE_STDDEV_TH * 100.0, quality_avg * 100.0);
/* receive telegramm */
bnetz_receive_telegramm(bnetz, bnetz->rx_telegramm);
@ -274,10 +275,7 @@ void sender_receive(sender_t *sender, sample_t *samples, int length, double rf_l
int pos;
int i;
/* fsk/tone signal */
fsk_demod_receive(&bnetz->fsk_demod, samples, length);
/* process signal mute/loss, without signalling tone / FSK frames */
/* process signal mute/loss, including removal of signalling tones / FSK frames */
switch (squelch(&bnetz->squelch, rf_level_db, (double)length / (double)bnetz->sender.samplerate)) {
case SQUELCH_LOSS:
bnetz_loss_indication(bnetz, LOSS_TIME);
@ -289,6 +287,9 @@ void sender_receive(sender_t *sender, sample_t *samples, int length, double rf_l
break;
}
/* fsk/tone signal */
fsk_demod_receive(&bnetz->fsk_demod, samples, length);
if ((bnetz->dsp_mode == DSP_MODE_AUDIO
|| bnetz->dsp_mode == DSP_MODE_AUDIO_METER) && bnetz->callref) {
int count;

8
src/bnetz/main.c
View File

@ -183,6 +183,14 @@ int main(int argc, char *argv[])
do_de_emphasis = 1;
}
/* use squelch */
if (!use_sdr || isinf(squelch_db)) {
fprintf(stderr, "*******************************************************************************\n");
fprintf(stderr, "I strongly suggest using squelch on your receiver! This prevents false channel\n");
fprintf(stderr, "allocation, due to received noise. For SDR, add '-S auto' to command line.\n");
fprintf(stderr, "*******************************************************************************\n");
}
/* create transceiver instance */
for (i = 0; i < num_kanal; i++) {
rc = bnetz_create(kanal[i], audiodev[i], use_sdr, samplerate, rx_gain, tx_gain, gfs, do_pre_emphasis, do_de_emphasis, write_rx_wave, write_tx_wave, read_rx_wave, read_tx_wave, loopback, squelch_db, paging, metering);