[aprssig] Homebrew transmitter

scott at opentrac.org scott at opentrac.org
Tue Aug 29 12:19:59 CDT 2006

> Ramsey occasionally has an SMT xtal transmitter listed, the "Rocket 
> Tracker".  I think it's $75 assembled, about $50 kit, and has around 
> 25mW or so output power.  The crystal will put the unit at or near 
> 146.565 for T-hunt purposes, so you'd have to get crystals made for 
> 144.390 to get it on the APRS freq.

I've used the MR6, and built a clone board of my own, and even one with an
integrated OpenTracker chip.  I got bored one evening and launched it with a
few 12" helium balloons, though.

The MR6 design is awful in terms of spurious emissions.  It's basically a
broadband comb generator - I took one to a buddy at a local radio shop and
we checked out both the MR6 and my clone on his spectrum analyzer, and it
puts out AT LEAST as much power 12 MHz up from the intended frequency.  I
think it was actually about 1 dB higher.

I could sell complete kits at a profit for under $20, but I can't in good
conscience market something that as far as I can tell doesn't meet FCC
requirements.  I don't know how Ramsey gets away with it.

As for putting other crystals on it, I'd say do so at your own risk.  A
crystal that gives you a frequency in the 2 meter band could also give you a
strong carrier on 121.5 - and 25 mW is enough power to risk a visit from
your local Civil Air Patrol squadron or search and rescue team.


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