[aprssig] 433 MHz operation
scott at opentrac.org
Wed Feb 15 12:12:14 CST 2012
I've been playing with some half-watt 70 cm data transceivers lately.
I'm currently testing at 434 MHz, and with the standard crystal they
should cover about 430 to 439 MHz. I'm not really familiar with the 70
cm band plan and figured I'd check here and see if people consider that
a reasonable part of the band to be working in.
I've got another small batch of them coming soon and might start selling
a board based around it for people who want to experiment. Right now
I'm using an OpenTracker USB variant. It's currently running at 4800
baud with some basic FEC - a (7,4) Hamming code with interleaving, not
fancy but easy to implement. The transceivers will go up to 115200 bps.
When I have time, I'll see if they can be made to inter-operate with
G3RUH TNCs, but for now I'm going to assume that won't work.
The really attractive part is that they're cheap - retail price should
be not more than 1/3 what we're selling the half-watt transmit-only
2-meter modules from SRB for, and they're about the same size.
There are still some bugs to be worked out, but the OpenTracker USB (and
by extension the Tracker3) will presently work transparently with these
radios, doing APRS at 4800 baud with error correction. I'll be working
some more on them to improve mesh routing and channel access control to
try to make them more suitable than vanilla APRS for short range, high
rate tracking applications.
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