[OZAPRS] Homebrew HF APRS transmitter

[Peter Schrader]

A few have asked what I put together.

I built a Small Wonder Labs PSK31-30 kit, changed the main LO crystal to 
suit the 10147.6 kHz dial frequency, with a 4MHz IF, the LO becomes 
6147.6 kHz.  The crystal came from Hy-Q in Melbourne.  Unfortunately 
Small Wonder Labs have discontinued production of these kits, 
http://www.smallwonderlabs.com/.

Used a Communications Concepts 20W driver amp module for the PA, setup a 
pi attenuator to drop the PSK31 RF output power to 100mW to suit the PA 
input.   http://www.communication-concepts.com/an779L.htm

An Argent Data Opentracker2 does the encoding, I had all sorts of 
trouble using a OT1+, it is much more susceptible to conducted RF.  I 
did try all sorts of techniques to stop the RF travelling up the control 
wires, ending up giving up and using the OT2.  Using the ADM1 GPS from 
Argent Data.

I constructed a standard LPF from Amidon cores and silver mica 
capacitors to keep the output clean.

All packaged in a metal instrument box I bought from Jaycar.  I 
installed a set of powerpoles under the dash which are energised once 
the engine is running.  The box sits under the drivers seat.

Antenna is a surplus tapped helical whip to which I hard wired a wander 
lead to make it resonant on 10147 kHz, it sits on the bull bar on a 
heavy duty Codan spring base.

I guess it would have been easier to use something like a Codan, but 
would have not been not as much fun :-)

73,
Peter
VK4EA