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Robert Bruninga wrote:
<blockquote cite="mid:A157E36FEE4148BA8E233DF9A2DB0EF9@ewlab.usna.edu"
type="cite">
<pre wrap="">
OK, PL. Should be easy to decode in a pic... Just count the
frequency...
Bob, WB4aPR
</pre>
</blockquote>
<br>
If you are envisioning this as some sort of external add-on gadget
(otherwise I assume you wouldn't be talking about programming PIC
processors), this may not be as simple an undertaking as you assume.
"PL" ("Private Line") is the Motorola trademark for the signaling
system known generically as "continuous tone-coded subaudible squelch"
(CTCSS). The key is *SUBAUDIBLE*, more or less -- in the frequency
range from about 60 Hz to around 180 Hz. <br>
<br>
Trying to take these tones off the speaker output (or inject them into
the mic jack) of most radios will not work very well since the audio
amps on both RX and TX intentionally roll off the low frequency
response to keep these low tones out of the speaker. [The RX audio
channel typically starts with a 200-250 Hz audio high-pass filter.]<br>
<br>
You will need a direct connection to the receiver discriminator, with
it's "down-to-DC" frequency response for these add-ons to work
reliably. [The connection point for OEM internal PL options is
normally a separate audio channel with a 200-Hz cutoff audio low-pass
filter tapped directly off the RX discriminator.] If the radio has
one of the 6-pin mini-DIN "data" or "packet" jacks, then no problem --
one can get at the raw discriminator audio easily. <br>
<br>
<br>
Otherwise you will encounter the same issue that prevented 9600 baud
packet from being widely accepted by the average ham "end-user" -- the
need to cut into the radio to tap the RX discriminator and TX
modulator. [And when was the last time you saw a hand-held with a
6-pin miniDIN data jack?]<br>
<br>
<hr size="2" width="100%"><br>
--<br>
<br>
Stephen H. Smith wa8lmf (at) aol.com <br>
EchoLink Node: WA8LMF or 14400 [Think bottom of the 2M band]<br>
Skype: WA8LMF<br>
Home Page: <a class="moz-txt-link-freetext" href="http://wa8lmf.net">http://wa8lmf.net</a><br>
<br>
NEW! *** HF APRS over PSK63 ***<br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/APRS_PSK63/index.htm">http://wa8lmf.net/APRS_PSK63/index.htm</a><br>
<br>
Universal HF/VHF/UHF Antenna Mounting System<br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/mobile/UniversalAntMountSystem.htm">http://wa8lmf.net/mobile/UniversalAntMountSystem.htm</a><br>
<br>
"APRS 101" Explanation of APRS Path Selection & Digipeating <br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/DigiPaths">http://wa8lmf.net/DigiPaths</a> <br>
<br>
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