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[aprssig] APRS and RF data modules

Jason Winningham jdw at eng.uah.edu
Thu Apr 28 12:52:55 UTC 2005


On Apr 28, 2005, at 7:23 AM, Andrew Rich wrote:

> can u get just 2m tx ?

I haven't seen any.  There is a 70cm ISM band that coincides with the 
70cm ham band (at least in the US), and that's why we see these little 
tx/rx devices.

I've seen several variations - AM, FM, etc - on several different 
frequencies: 315MHz, 433MHz, somewhere in the 900MHz range, and maybe 
1.2GHz (I could be hallucinating that last one).  I think these 
correspond to ISM (Industrial, Scientific, Medical) device frequencies.

The only thing I've seen on 2m is the Ramsey Rocket beacon (almost as 
much $$ as an HT) and a few fox transmitters that are as much or more 
than an HT.

I'd think that a simple low power 2m transmitter, either crystal 
controlled or even a direct synthesis DAC type arrangement would be 
doable for fairly cheap, but I haven't seen one.  I don't have the time 
or experience to try it myself.

I have thought about building a circuit similar to the Ramsey. but add 
support for a PIC so it would be a useful 2m tracking beacon.  Maybe a 
DC-DC converter, so the thing would run off a single 1.5V AA lithium?  
It would need 3 or 5 volts for the PIC and 9 or 12 for the transmitter. 
  I think maxim has a beastie that does both.  Yet another project for 
my copious spare time...

-Jason
kg4wsv





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