[aprssig] simple digipeater

Stephen H. Smith WA8LMF2 at aol.com
Tue Aug 17 02:49:58 EDT 2004

Christopher A. Kantarjiev wrote on 8/16/2004, 8:31 PM:

 > I've been looking at the PocketTracker and considering how that could
 > be the
 > right model - a receiver and transmitter that are focused on APRS,
 > rather than
 > using an HT. A Picpac or something similar is about the right hardware
 > for what
 > I have in mind.

1)  The PocketTracker has no receiver!  It only transmits.

2)  2W telemetry link transceivers are commercially available and would 
be perfect for this application.  These devices, typically housed in a 
small diecast box, normally don't have any mic amp or RX audio power 
amp/speaker.  You would connect the RX and TX audio and PTT line of a 
TNC to this device.

For the ultimate low power consumption, use a Kantronics KPC3+ ( this is 
the only TNC with the capability to do WIDEn-N digipeating out of the 

To do it cheaply, use a TNC2 clone such as an MFJ-1270 or Paccom, and 
replace it's standard firmware EPROM with one containing the freeware 
UI-Digi firmware.  This code essentially gives a TNC2 a "brain 
transplant" and converts it into a dedicated intelligent APRS digipeater 
  with sophisticated dupe suppression and WIDEn-N callsign substitution 
capability.  Before programming the eprom, the souce code is customized 
to include your call sign, beacon intervals, paths and messages, etc. 
The result is that your personalized settings are literally "frozen in 
stone" (silicon actually) when you program the eprom so they can't be 
lost from a power failure, accidental reset, etc.  Something to consider 
if the digi is going to be in a remote, inaccessble location.

The downside of the TNC2/UI-Digi appoach is that a TNC2 consumes a lot 
more power (300mA at 12VDC) than a KPC3+ (less than 9mA).   A 
consideration if you want to power this thing on batteries and solar 

Stephen H. Smith                   wa8lmf (at) aol.com

Home Page:                            http://wa8lmf.com

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