[FoxHunt] ARDF Transmitter Kit

[Dave Willey]

> Date: Wed, 12 Jun 2002 22:48:44 -0700
> From: Marvin Johnston <marvin@rain.org>
> To: foxhunt@mailman.qth.net
> Subject: Re: [FoxHunt] Fox Transmitter Plans?

(SNIP)
....
> The standard program takes a CW message (MOE, MOI, MOS, 
> MOH, or MO5), repeats it 10 times, and the callsign ends the 
> transmission. The cycle
> will repeat itself in about 4 seconds. Depending on the length of the
> callsign and the CW message, the cycle for MO? signals runs between 55
> seconds to perhaps 65 seconds. Because all of the above is hard
> programmed in, user modifications are not possible.

(SNIP)

> The PIC processor uses the internal RC clock. Because of that and some
> program limitations, it would be difficult to get the exact same cycle
> on multiple transmitters. And of course there will most likely be some
> timing drift although that hasn't been measured or checked yet.

(SNIP)

> Marvin, KE6HTS

Hi Marvin,

Your transmitter kit sounds just like what I've been looking for.
I'm trying to get a bunch of the local hams into foxhunting, particular
more of the ARDF style of hunting rather than mobile (car) hunts.

My only concern is the cycle timing of the of the individual units as 
a group.  I would be interested in hearing from you when you have a 
chance to test this.  

How much does the RC timing vary between units? Could one
use a xtal instead? (but then the development time & unit cost would
also go up.)

On a related note:
Is there enough programming room to put a "sleep" cycle of  "N" 
seconds at the top of the portion of the program.
(i.e. Staggered start.
 MOE would sleep 0 seconds then go into it's normal 60 sec 
loop. While MOI would be coded to sleep 60 seconds before 
dropping into it's 60 second normal loop.  And MOS would
sleep 120 seconds before it starts. etc.) 

Then again I guess you'd need another sleep cycle of 4 minutes
at the bottom of the main loop to keep each unit "in phase"
of the other 4 units.

You hinted that RAM is limited.  (GRIN) You probably have
the same problem I do.  Your object code  is ALWAYS 1 byte
over what's available on the microprocessor RAM.

I'll be interested in what the first production units look like.


Happy hunting.


Dave Willey