|author||Andreas Eversberg <email@example.com>||2016-05-28 19:40:19 +0200|
|committer||Andreas Eversberg <firstname.lastname@example.org>||2016-06-17 17:03:27 +0200|
work on docs
Diffstat (limited to 'docs')
3 files changed, 31 insertions, 12 deletions
diff --git a/docs/b-netz.html b/docs/b-netz.html
index bfab791..c3346a8 100644
@@ -61,6 +61,10 @@ How it works
+Note that the following protocol description is based on my research. It may be incomplete or wrong on certain details.
Two tones are used for signalling:
@@ -397,6 +401,7 @@ The transceiver of the base station switches to channel 19 and sends a paging se
Then the base station returns to the ordered channel and waits 2 seconds for the mobile station to send the call acknowledge signal ("Rufbestätigung").
If it is not received, the base station repeats the paging sequence again.
If there is still no call acknowledge signal, it returns to idle state and indicates announcenemnt to the calling party that the mobile station is (currently) not available.
+(German announcement sais: "Dieser Anschluß ist vorrübergehend nicht erreichbar!")
@@ -410,7 +415,7 @@ The base station receives the call acknowledge signal and sends the call hold si
When the mobile station receives the call hold signal, it indicates ringing tone to the mobile subscriber.
-Additionally the car's siren is turned on, if the mobile subscriber is outside the car.
+Additionally the car's siren is turned on (if connected to the phone), if the mobile subscriber is outside the car.
diff --git a/docs/c-netz.html b/docs/c-netz.html
index 0bf8a8f..78a8475 100644
@@ -59,10 +59,25 @@ We need to calibrate the speed of our transmit signal (and receive signal as wel
First of all, we need a reference clock.
Since most systems have standard crystals, we cannot use our system clock as reference without any help.
I decided to use the NTP daemon.
-After running the system for one day, the clock speed should be accurate enough for our needs.
+After running the system for several days, the clock speed should be accurate enough for our needs.
Be sure to choose a place with constant temperature.
+In /etc/ntp.conf define one or more servers to geht the time from. I suggest to use the German atom clock of the PTB:
+This clock provides time base for European radio clocks and most German clocks.
+It is perfect for this project, so please use this clock.
netbook ~ # ntptime
@@ -96,7 +111,7 @@ To minimize this effect, don't use extension cables.
Since we have precise system clock now, we can measure the speed of our sound adapter.
Later we will use the measurement result to adjust our signal processor.
-Be sure to have your machine running for at least 24 hours (with your sound adapter attached).
+Be sure to have your machine running for at least 3-4 days (with your sound adapter attached, in case you have USB sound adapter).
The machine must have network connection to the NTP server.
I suggest to use 'ntp1.ptb.de' and 'ntp2.ptb.de' as reference.
Use command line option '-M' or '--measure' to measure my sound adapter.
@@ -123,8 +138,7 @@ dsp.c:218 notice : Clock: RX=19.44 TX=19.49; Signal: RX=19.35 TX=19.43 ppm
One can see that the measured clock from the sound card (sample rate) differs about +19.45 PPM.
Because I did not do any correction to the signal processing, the same error applies to the signal.
Use command line option '-S 19.45,19.45' or '--clock-speed 19.45,19.45' to compensate the clock error by adjusting the signal processor.
-Let it run again for one hour and you will see that signal is now below 1 PPM.
-(Or close to it.)
+Let it run again for one hour and you will see that clock deviation is below 1 PPM.
@@ -142,13 +156,13 @@ Let it run again for one hour and you will see that signal is now below 1 PPM.
-<font color="red">Importaint: We need to transmit correct polarity!</font>
+<font color="red">Importaint: We need to transmit correct polarity, use auto polarity detection always!</font>
-C-Netz uses FSK (Frequency Shift Keying) by directly modulating the carrier, rather than modulating a transmitted tone.
+C-Netz uses FSK (Frequency Shift Keying) by directly modulating the carrier, rather than modulating a tone, which is then transmitted via FM.
The advantage is much higher data rate.
The base station's carrier frequency is raised by 2.5 KHz to transmit a logical "1" and lowered by 2.5 KHz to transmit a logial "0".
(The mobile station transmits reversed polarity.)
@@ -158,7 +172,7 @@ In the picture above, the polarity is wrong.
(The logical "1" points down and the logical "0" points up.)
You must check, with what polarity your transmitter is doing a positive frequency deviation.
Also you must check your sound card's polarity on positive value beeing sent.
-To change polarty, use command line option '-F' or '--flip-polarity'.
+To change polarty, use command line option '-F yes' or '--flip-polarity yes'.
(Note: don't confuse with '-P'!)
diff --git a/docs/software.html b/docs/software.html
index 53f82c9..80f4b61 100644
@@ -149,7 +149,7 @@ Some adapters have mono input, especially on microphone jack.
In this case you will always receive audio, no matter if you cross the channels or not.
If you cross the channels, the left channel of your sound adapter is used.
I use mono cables with only one channel on the tip of the plug.
-My sound adapter uses left channel on the tip, so i need to swap channels.
+Usual sound adapters connect left channel on the tip of the plug, so we need to swap channels to use mono plugs.
Use the command line option '-x' or '--cross':
@@ -170,7 +170,7 @@ Emphasis
Pre-emphasis is used on the transmitter and de-emphasis is used on the receiver side.
The nature of FM causes noise amplitude to be proportional to the transmitted frequency.
(double frequency = double noise volume)
-To compensate this, most FM radios, as well as all analog mobile networks emphasis.
+To compensate this, most FM radios, as well as all analog mobile networks use emphasis.
@@ -266,7 +266,7 @@ bnetz.c:528 notice : Round trip delay is 0.001 seconds
-If command line option '-L 1' or '--loopback 2' is given, an external loopback is performed.
+If command line option '-L 2' or '--loopback 2' is given, an external loopback is performed.
The receiver needs to be tuned to transmitter, so the software receives its own signal.
The received quality level is relevant. It should be not less than 90 for B-Netz.
@@ -274,7 +274,7 @@ The received quality level is relevant. It should be not less than 90 for B-Netz
If command line option '-L 3' or '--loopback 3' is given, the audio from the input is sent back to the output.
It can be used to check a headset.
-Everything that is spoken into the microphone should be appear in the headphone.
+Everything that is spoken into the microphone should appear on the headphone.
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