An implementation of Analog cellular networks like A-Netz, B-Netz, C-Netz, NMT, AMPS, TACS, JTACS, Radiocom 2000, IMTS, MPT1327, Eurosignal and more http://osmocom-analog.eversberg.eu/
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osmocom-analog/docs/b-netz.html

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<h2><center>B-Netz</center></h2>
<center><img src="b-netz.jpg"/></center>
<p align='justify'>
Before testing this software, power on your B-Netz.
Refer to the manual how to dial a number.
Start dialing and after some seconds you should hear a busy signal.
This means that the phone sweeps over all channels to find a base startion.
If no free base station is found, you will get a busy signal.
</p>
<center><img src="b-netz-display.jpg"/></center>
<p align='justify'>
Now run your base station on channel 1.
Tune the transmitter to 153.010 MHz and the receiver to 148.410.
You should tune the receiver to 153.010 first, to check if you hear the idle signal from the base station.
Then tune to actually uplink frequency 148.410 MHz.
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<font size='4'><pre>
# src/bnetz/bnetz -k 1
...
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.
on-hook: ..... (enter 0..9 or d=dial)
</pre></font>
<p align='justify'>
Now dial again on the phone and watch the base station receiving the call:
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<font size='4'><pre>
bnetz.c:471 info : Received signal 'Kanalbelegung' from mobile station, sending signal 'Wahlabruf'.
bnetz.c:561 info : Received station id from mobile phone: 50993
bnetz.c:569 info : Received number from mobile phone: 800330100
bnetz.c:571 info : Sending station id back to phone: 50993.
bnetz.c:631 info : Dialing complete 50993-&gt;0800330100, call established.
bnetz.c:637 info : Setup call to network.
call.c:574 info : Incomming call from '50993' to '0800330100'
bnetz.c:669 notice : Received 'Schlusssignal' from mobile station
bnetz.c:352 info : Entering IDLE state, sending 'Gruppenfreisignal' 2.
call.c:695 info : Call has been released with cause=16
</pre></font>
<p align='justify'>
The first thing the phone does is to find the channel 1.
Then it transmits a signal tone, called 'Kanalbelegung'.
The base station responds and sends a signal tone, called 'Wahlabruf'.
Then the phone sends caller ID + number.
The base station replies the caller ID to prevent false transmissions.
After establishment, you can use the headset, if present, for speech communication with the phone.
If you hangup the phone, the call gets released by a message, called 'Schlusssignal'.
The base station returns to idle.
</p>
<p align='justify'>
In order to call the phone from the base station, you need to transmit channel 19.
Your transmitter must tune to 153.370 MHz in order to page the phone.
The phones listens to incomming signals from the base station.
In order to transmit on channel 19, you may use a second transmitter or re-tune your single transmitter.
There are many ways todo that, but it is actually up to your own how to couple it and how to control your transmitter.
I use an optocoupler to tell my transmitter to switch to channel 19.
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<center><img src="trigger-1.jpg"/></center>
<br>
<center><img src="trigger-2.jpg"/><img src="trigger-3.jpg"/></center>
<p align='justify'>
I measure about 3 Volts peak on the ouput of the USB chip I use.
Since my optocoupler triggers at arround 1 Volts, I have two Volts on the Resistor, which results in 10 mA current.
In order to check and change the voltage, use '-P positive' or '-P negative' option to select trigger level on one audio channel.
Run the base station and enter a 5 digit number.
Measure the voltage on both audio output channels.
Once you press 'd' for dialing, the base station triggers the channel using positive or negative level.
See if and where the voltage changes.
The trigger is just about two seconds long, so check your meter quickly after pressing 'd'.
Once the base station timed out, press 'h' for hangup and try again.
</p>
<font size='4'><pre>
./bnetz/bnetz -k 1 -P positive
...
on-hook: 55555 (enter 0..9 or d=dial)
call.c:437 info : Outgoing call to 55555
bnetz.c:757 info : Call to mobile station, paging station id '55555'
bnetz.c:375 info : Entering paging state (try 1), sending 'Selektivruf' to '55555'.
bnetz.c:411 info : Paging mobile station 55555 complete, waiting for answer.
</pre></font>
<p align='justify'>
Now again it is up to your own to make the transmitter switch to channel 19 on trigger level.
If you use a second transmitter, use the tigger to press the PTT button.
</p>
[<a href="index.html">Back to main page</a>]
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