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[aprssig] Win APRS Mobile

Stephen H. Smith wa8lmf2 at aol.com
Thu Jun 2 06:54:06 UTC 2005

scott at opentrac.org wrote:

>Is the TNC board in the D700 the same as that in the DR-135?  Does anyone
>know how the APRS functions integrate with the TNC?
>I'm considering the possibility of building a version of my ARM-based TNC
>that'd work as a drop-in replacement for at least the TNC in the DR-135.  If
>the D700 is similar, I imagine it ought to be able to build an interface
>layer that would correct some of the APRS behavior of the radio.  It could
>be made to translate new message formats into those understood by the D700,
>for example.
>Just a thought...
There is no "TNC board" in the D700!  Everything, RF and digital except 
for the TX PA, is on a single big board. See some interior shots of the 
D700 on my web site at:

Look for "Interior Views of Kenwood TM-D700 146/440 Dual-Bander with 
built-in TNC" about 2/3rds of the way down the page.    Both RX front 
ends, both IF systems and both synthesizers are on this board along with 
the TNC, microprocessors,  8x8 audio crossbar switching matrix, etc.  
I've never seen a radio with all this co-existing on one board without 
mutual interference before.  

As for the difference between the Alinco and the Kenwoods, all are based 
on the same Tasco TNC-on-a-chip but the firmware is enormously 
different.  The Alinco is strictly a TNC somewhat similar to a TNC2 that 
requires an external terminal or computer to do anything useful. (It CAN 
act as a dumb NMEA-format tracker standalone, in a similar manner to 
plugging a GPS into the serial port of any TNC set to converse mode.)

The Kenwoods, by comparison,  have extensive APRS-specific firmware that 
allow the front panel dot-matrix displays to become ASCII displays to 
present incoming APRS packets in text form.  The Kenwoods will take 
incoming posits, compare them with the position your own GPS is 
reporting, and then display something like "W6XYZ-1 is 3.9 miles SE of 
you" along with a monochrome bitmap approximation of the APRS symbol the 
station is sending.   APRS messages and bulletins also get displayed on 
the front panel.   If you are a true masochist, you can even compose and 
send APRS messages by punching the buttons on the touch-tone mic about a 
bazillion times (similar to text messaging on a cell phone). This all 
happens in the "APRS" mode of these radios. 
     When the radio is placed in the "PACKET" mode, the internal 
interpretation of APRS data and the front panel presentation go away. 
The incoming packets are then sent out the serial port to an external 
computer or terminal, just like any other TNC.  
     In addition, local GPS data  (i.e. your own position) received by 
the radio on the dedicated GPS port is echoed out the main serial port, 
along with received packets. Nearly all current APRS applications can 
separate the the local GPS posits from received packets internally. Thus 
only one serial port is required on the PC to support both the TNC and 
the GPS (without the HSP hardware kludge).

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

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