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diff --git a/docs/amps.html b/docs/amps.html
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@@ -32,6 +32,7 @@ Dr. Martin Cooper produced the first handheld phone "DynaTAC8000x", the famous B
</p>
<center><img src="amps-dynatac.jpg"/></center>
+<center><a href="https://en.wikipedia.org/wiki/Motorola_DynaTAC">Image taken from Wikipedia</a></center>
<p>
<ul>
@@ -57,11 +58,10 @@ Dr. Martin Cooper produced the first handheld phone "DynaTAC8000x", the famous B
</p>
<p>
-The detailed communication between base station and mobile station is described in <a href="TIA_EIA_553_A.compressed.pdf">TIA/EIA-553 standard</a>. Click for reading the PDF file. <i>Reproduced under written permission from Telecommunications Industry Association.</i>
-</p>
-
-<p>
-*TBD*
+The detailed communication between base station and mobile station is described in <a href="TIA_EIA_553_A.compressed.pdf">TIA/EIA-553 standard</a>.
+Click for reading the PDF file.
+Thanx to TIA for allowing me to add the standard document to this project's documentation.
+<i>Reproduced under written permission from Telecommunications Industry Association.</i>
</p>
<p>
@@ -81,7 +81,43 @@ Setup of a base station
</p>
<p>
-*TBD*
+<font color="red">Importaint: We need to connect to PLL and discriminator!</font>
+</p>
+
+<p>
+AMPS does not use a modulated tone to carry bits of information, instead it modulates the radio carrier directly.
+This image shows a signal generated by this software, which is similar to a received signal from the phone:
+</p>
+
+<center><img src="amps-burst.png"/></center>
+
+<p>
+Generally a receiver will do de-emphasis and filtering after demodulating the signal.
+We don't want that.
+It may work, but be sure to use a receiver with discriminator output.
+This output gives direct signal of the frequency deviation of the received signal.
+The signal on the sound card represents the frequency shift of the received signal.
+Many receivers can be modified, so search the Web for more info.
+</p>
+
+<p>
+On the transmitter we don't want to have filtering and pre-emphasis.
+It may work, but be sure to use a transmitter that allows to disable emphasis.
+I took the schematics of my transmitter and connected the sound card directly to the PLL.
+The transmitter will now shift frequency according the the level of the sound card.
+</p>
+
+<p>
+<font color="red">Importaint: We need to transmit correct polarity, use auto polarity detection always!</font>
+</p>
+
+<p>
+In my case, my sound card is connected to a transmitter, where a positive sample value causes a negative frequency deviation.
+This is why I need to flip the polarity of the signal, so I generate a negative sample value that causes a positive frequency deviation.
+I use the '-f yes' option or '--flip-polarity yes'.
+Also it is essential to use a transmitter with direct access to the modulator and and a receiver with direct access to the disciminator.
+I use '-p -d' or '--pre-emphasis --de-emphasis' to process emphasis for audio signal in software.
+I use the calling channel (control channel) 334, which could also be used as traffic channel (voice channel).
</p>
<pre>
@@ -113,6 +149,13 @@ The actual level is not yet relevant.
(You may check the quality using '-l 2' or '--loopback 2' command line option and build a radio loop by tuning the receiver to the transmitter.)
</p>
+<p>
+If the polarity is correct and the volume of the signal (frequency deviation) is about right, you will make the phone register.
+The phone will transmit on the uplink.
+If not, try other polarity.
+This is how my phone registers to my network:
+</p>
+
<pre>
frame.c:3630 info : RX RECC: DCC=0