[aprssig] Automatic omni DF query
scott at opentrac.org
Mon Feb 9 13:44:08 CST 2009
My new T2-301 trackers are frequency-agile and can measure incoming
signal strength, so it occurred to me that it'd be useful to define an
APRS query that'd cause all capable stations to QSY their receive side
to the specified frequency for a second, take a reading, and then come
back and report what they heard in omni-DF format.
Before anyone asks, these particular units won't work for 121.5 - I've
only been able to get them to receive as low as 127 MHz.
Based on some experimentation with a service monitor, it looks like the
usable RSSI range is roughly -128 dBm to -68 dBm. If I'm reading my
conversion chart right, for a 50-ohm system that's a little more than
the standard S0-S9 range. Seems kind of low at the top end, but I'll
have to do some field testing and see what I get.
What I'm thinking of is something like this:
The response should be a DFSshgd omni-DF extension followed by the
frequency. I'd prefer the frequency to be a standard part of that
response, so clients could be made smart enough to separate out multiple
Comments or suggestions?
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