[aprssig] APRS Multi-Mode Tracker

Stephen H. Smith wa8lmf2 at aol.com
Sun Mar 4 21:51:13 EST 2007

swdrumm at gmail.com wrote:
> I need some advice on building a multi-mode APRS tracker.
> The attached schematic illustrates what I'm trying to do.  In case the 
> list manager strips attachments, it shows that I want to build a 
> beacon-style tracker that will simultaneously feed the GPS position 
> and APRS network traffic to a laptop PC.  The GPS data would be used 
> for onboard vehicle navigation and the APRS feed is to monitor the 
> location of other stations.
> I'm using a dedicated radio (Yaesu FT-1500) for this purpose.  The 
> FT-1500 has a 6-pin DIN port on the back specifically for TNC 
> communications.
> My original design concept was to attach a Byonics TinyTrak3+ 
> <http://www.byonics.com/tinytrak/tt3plus.php> to the microphone 
> connector of the radio for the beacon.  An RS-232 splitter 
> <http://www.sfcable.com/store/d920-yy.html> would send the GPS 
> <http://www.deluoelectronics.com/customer/product.php?productid=99> 
> data to the TinyTrak and to the laptop simultaneously.  An Elcom USB 
> MicroTNT <http://www.elcom.gr/> in KISS / listen mode attached to the 
> radio's data port would send all of the APRS data to the laptop.  Will 
> this work?
> Alternatively, I just read a writeup about the PacComm 
> <http://www.paccomm.com/> dual-port PicoPacket...

1)   DON'T put up line art (like your schematic) as JPGs!!   JPG is only 
intended for continuous-tone images; i.e. photos. It applies image 
compression by looking for gradual gradients of brightness and color 
from groups of adjacent pixels.  When applied line art images like your 
block diagram that jump from 100% white to 100% black in a single pixel, 
you get the kind of squirmy, fuzzy compression artifacts that are 
showing in your diagram.   For any kind of non-continuous-tone images 
such as maps, schematic diagrams, architectural diagrams, line art, etc, 
that use a limited palette of colors, the  proper web-friendly formats 
are either GIF or PNG.

2)    What you are striving for is not a "multimode tracker" but a 
full-function APRS station that happens to be mobile.  The 
commonly-accepted usage of the term "Tracker" is for a dumb (or should I 
actually say deaf")  transmit-only mobile that spews out posits 
periodically and can't receive anything.

3)   The "GPS splitter" linked in your original post is nothing really.  
It's just three DB-9/DE-9 series connectors wired in parallel.  There 
are no active electronics inside.  The critical issue is whether only 
ONE of the connectors has it's TX data line connected.    Since RS-232 
outputs are low impedance and RS-232 inputs are relatively high 
impedance, it is no problem to have one output  (the GPS) feeding two or 
more inputs (the Tiny Track and a PC) in parallel. You just don't want 
twoRS-232  OUTPUTs wired in parallel.

4)    By far the simplest and tidiest way to do this is with a Kenwood 
D700 or TH-D7 which will do all of this automatically.  You connect the 
GPS receiver to a dedicated GPS port on the Kenwood and then connect the 
radio's main serial port to the PC.   When these radios are operated in 
standalone (i.e. without a PC) "APRS" mode, they send posits from the 
GPS , and SEND and RECEIVE  data (messages, bulletins, posits) and 
display them on it's control head screen. 

When the Kenwoods are placed in "TNC" mode, they automatically forward 
GPS data from the dedicated GPS port out the main serial port, along 
with off-air receive data from the TNC.      APRS-specific programs on 
the PC like UIview, APRSplus or APRSpoint generate maps showing both 
other stations posits from off-air reception, and your OWN position from 
your local GPS.     Additionally, UIview can optionally forward the 
received GPS data out a virtual (simulated) 2nd serial port for use by 
an external "civilian" mapping program like Streets & Trips or Delorme 
Street Atlas at the same time!

3)   Either the PacCom or a Kantronics KPC3+ can create the same effect 
for a non-Kenwood radio, i.e. the GPS pass-through function that can 
share a single serial port connection to the PC for both TNC RX and GPS 
data, or act as a standalone dumb tracker.  (Both devices have the 
dedicated GPS port with pass-though to the main serial port.)      In 
standalone mode, they are really dumb in that they transmit raw 
uncompressed NMEA strings as they come out out of the GPS, instead of 
the highly compressed Mic-E packets of the Kenwoods.  (The 
100-character-plus raw NMEA strings take much more air time to transmit, 
and are significantly less likely to be received successfully than the 
much shorter compressed Mic-E packets.)

The Elcom MicroTNC plug can also do this.  The difference is that while 
it accepts a serial GPS connection like the others, the main connection 
to the PC is via USB.  This is an advantage on today's "legacy-free" 
laptops that lack serial ports (saves you having to screw around with 
USB-to-serial cable "dongles").  It also reduces the mobile installation 
power cable rat's nest since the USB TNC can draw it's operating power 
from the laptop it is plugged into instead of needing a separate DC 
connection or wall wart.


Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com  --OR--   http://wa8lmf.net

NEW!   TNC Test CD

JavAPRS Filter Port 14580 Guide

"APRS 101"  Explanation of APRS Path Selection & Digipeating

Updated "Rev G" APRS            http://wa8lmf.net/aprs
Symbols Set for UI-View,
UIpoint and APRSplus:

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