[aprssig] Re: TM-271A data mod

Stephen H. Smith wa8lmf2 at aol.com
Wed Mar 16 04:15:02 CST 2005

scott at opentrac.org wrote:

>Anyway, good news... the pads for the data connection not only exist,
>they're conspicuous and clearly labeled.  Apparently the European version
>ships with a pigtail on it, presumably with a female mini-DIN.  There's only
>a small hole under the power lead grommet for the data cable, so it's not a
>bulkhead mount.  In the American version the hole just has some foam stuck
>in it.
>The silkscreen markings on the board are even listed in the manual (PKD =
>data in, PKS = standby, PR9 = 9600 out, PR1 = 1200 out, SQC = squelch, GND =
>ground).  (Standard disclaimer applies - this is all for TNC audio, not
>digital signals.)
>Close up:  <http://n1vg.net/images/tm271a_mod1.jpg>
>Whole board: <http://n1vg.net/images/tm271a_mod2.jpg>
>So... there IS at least one sub-$200 2-meter radio on the market with a
>9600-baud packet connector, if you don't mind 10 minutes of tweaking.
.You're not home yet!  The 1200 / 9600 contact pads are for RECEIVE -- 
not transmit!

The "9600 baud" output is non-de-emphasized raw receiver discriminator  
out, DC-coupled and typically 30-50 mV. 

The so-called 1200 baud point is (normally) de-emphasized and usually 
squelched RX audio just like the speaker but at a constant level. Use 
for low-speed TNCs, SSTV, Touch-Tone decoders, Echolink,and other voice 
apps, etc.  It's typically 100-300 mV ("line-level" ) audio out.  This 
is also the only pin that will be live on a multi-mode rig like a Yaesu  
FT100 or Icom 706 on SSB since the other line is unique to FM 

The standard minidin-6 "data/packet" connector has only a  --SINGLE--   
TX input that has to be switched between passing through the mic amp for 
1200 baud operation (i.e.1200/2200 Hz audio tones at 5-10 mV mic 
levels), and directly-DC-coupled to the TX modulator (typically at 0/5 
VDC TTL levels) for 9600. 


The real $179.95 question is:
        Does the U.S. version of the radio's firmware contain the menu 
entry for 1200 vs 9600 baud TX  select?

Or will you have to do the magic diode cutting or jumpering,  ala    
http://mods.dk  ,  to convert the radio to the Euro version to get the 
packet-speed-select menu option to appear? 

Stephen H. Smith             wa8lmf (at) aol.com
Home Page:                   http://wa8lmf.com

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