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authorAndreas Eversberg <jolly@eversberg.eu>2017-10-09 20:49:14 +0200
committerAndreas Eversberg <jolly@eversberg.eu>2017-10-22 19:23:08 +0200
commitb32e0ab6025a025850dc0079fa6596a96d7295a6 (patch)
tree199098e532a80417d5a3a18e80172280ccb84cad /docs
parentf7a0e4622bed9551bb0999d3c54bb69249065d38 (diff)
Implementation of RX level squelch (for A-Netz and B-Netz)
Use -S <dB> for setting RF level or use -S auto for auto level. When squelch closes, audio is muted. If squelch is closed for some seconds (depending on network), call is released. (RF loss condition) The previous loss detection has been removed
Diffstat (limited to 'docs')
-rw-r--r--docs/a-netz.html6
-rw-r--r--docs/b-netz.html58
2 files changed, 29 insertions, 35 deletions
diff --git a/docs/a-netz.html b/docs/a-netz.html
index d91534c..b0bf9ee 100644
--- a/docs/a-netz.html
+++ b/docs/a-netz.html
@@ -259,6 +259,9 @@ Be sure that the phone turns off the transmitter and indicates the (green) light
<p>
Level adjustment:
+</p>
+
+<p>
We see a receive level of around 140%.
Then start the base station using '-l 2' option for loop-back and tune receiver to the transmitter.
The base station generates a 1750 Hz test signal, just like the mobile phone.
@@ -308,6 +311,9 @@ Be sure to check: Does your transmitter has enough frequency deviation (15 KHz i
<p>
Detecting loss of carrier signal:
+</p>
+
+<p>
To automatically release the call, when the carrier signal gets lost, look at the B-Netz page.
It is the same principle.
</p>
diff --git a/docs/b-netz.html b/docs/b-netz.html
index 4dfaf19..6bdb18e 100644
--- a/docs/b-netz.html
+++ b/docs/b-netz.html
@@ -638,6 +638,9 @@ The base station returns to idle.
<p>
Level adjustment:
+</p>
+
+<p>
We see a receive level of around 85%.
Tune your receiver to the up-link frequency, so you get loop-back of base station broadcast.
Use the variable resistor (connecting your transmitter) to adjust the volume until the received level matches the same level of your previously received message.
@@ -703,53 +706,38 @@ dsp.c:159 info : Detecting continous tone: 2070:Level= 104% Quality=100%
<p>
Detecting loss of carrier signal:
-We do not have any RSSI (Received Signal Strength Indicator) signal from our radio, so we cannot directly find out if the signal is lost.
-But we have a constant noise level when the signal is lost.
-Be sure to have squelch on your receiver all the way open, so that noise reaches the base station.
-In order to see this level, use command line option '-L 100 -v 0' or '--loss 100 --verbose 0'.
-The noise level (relative to the sound card's input level) is shown:
+</p>
+
+<p>
+This works with SDR only, because we do not have any RSSI (Received Signal Strength Indicator) signal from a radio connected to the sound card.
+With SDR we know the RX level, so we can define a threashold value for a lost signal.
+Use '-S &lt;db&gt;' or '--squelch &lt;db&gt;' to define the squelch threshold level.
+To measure the noise floor, use the 'm' key to get a bar graph of the current RSSI. (RF level)
+Add some dB to the noise floor for the squelch threshold value.
+An easier way is to use '-S auto' or '--squelch auto' to automatically measure the noise floor level and then automatically use a threshold level that is some dB above this measured level.
+This level is then used to detect loss of carrier.
+Also this level is used to mute the audio path, whenever the signal gets lost for a short time.
+After about 12 seconds of signal loss, a call is released - similar to the real network.
</p>
<pre>
...
-loss.c:74 debug : Noise level = 22%
+squelch.c:94 info : RF signal measurement: -69.2 dB noise floor, using threshold of -63.2 dB
...
</pre>
<p>
-Since we have a noise level of about 20%, we can use a threshold of 10%.
-Use command line option '-L 10' in this case.
-To see the process, keep debugging on by using command line option '-v 0'.
-Whenever the noise level is above the given percentage, loss of carrier is assumed, if the noise level is constant.
-If the noise level changes (due to speech), the noise is ignored and the loss counter is reset.
-After a system specific duration of signal loss, the call is released.
-</p>
-
-<p>
-In this example I cut the power off the phone and waited for the base station to time out.
+In the following example I cut off the power of the phone beeing in a call and waited 12 seconds for the base station to time out:
</p>
<pre>
...
-loss.c:74 debug : Noise level = 1%
-loss.c:74 debug : Noise level = 2%
-loss.c:74 debug : Noise level = 1%
-loss.c:74 debug : Noise level = 22%
-loss.c:74 debug : Noise level = 21%
-loss.c:84 debug : Detected signal loss 1 for intervals level change 6% (below 10%).
-loss.c:74 debug : Noise level = 21%
-loss.c:84 debug : Detected signal loss 2 for intervals level change 2% (below 10%).
-...
-loss.c:74 debug : Noise level = 22%
-loss.c:84 debug : Detected signal loss 11 for intervals level change 7% (below 10%).
-loss.c:74 debug : Noise level = 21%
-loss.c:84 debug : Detected signal loss 12 for intervals level change 3% (below 10%).
-bnetz.c:448 notice : Detected loss of signal, releasing.
-bnetz.c:363 info : Entering release state, sending 'Trennsignal'.
-call.c:706 info : Call has been released with cause=41
-bnetz.c:439 debug : Sending telegramm 'Trennsignal/Schlusssignal'.
-bnetz.c:439 debug : Sending telegramm 'Trennsignal/Schlusssignal'.
-bnetz.c:439 debug : Sending telegramm 'Trennsignal/Schlusssignal'.
+squelch.c:114 info : RF signal weak: Muting audio (RF -77.6 dB &lt; -70.7 db)
+bnetz.c:392 notice : Detected loss of signal after 12 seconds, releasing.
+bnetz.c:297 info : Entering release state, sending 'Trennsignal' (4 times).
+call.c:933 info : Call has been released with cause=41
+bnetz.c:279 info : Entering IDLE state on channel 17, sending 'Gruppenfreisignal' 2.
+call.c:637 info : Call hangup
...
</pre>