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[aprssig] RFID antennas

Bob Bruninga bruninga at usna.edu
Mon Jul 21 03:13:00 UTC 2008


Regarding APRS RFID Name Tags:

>> Why not use those little 433mhz data transmitters?

> I hooked an early prototype SMT OpenTracker 
> to one of those ...  Frequency drifted a bit 
> with temperature extremes, but it was standard 
> APRS decoded with a 70cm rig.

Great to hear of such testing...

That is the ideal approach, but I just figured the full APRS AX..25 was overkill and would take more power.  THe winning application here is the one that is either complete passive (meaning it always works) or is a 1 year battery replacement (meaning it almost always works mostly)...

If it takes a battery per full day or weekend of operation, then I think it is a non-starter, since it simply will not be a 100% passive detector of the wearer's presence... everywhere and always...

I figured the DATA key-chain FSK transmitrers that have companion receivers and are immune to the effects of drift and all they have to send is a callsign/SSID (40 bits).  Everything else is added by the RFID sensor.

Now I would like to know ideas on what additional bits might be needed?.  Bout the only additional info I can imagine is an SSID or SYMBOL byte so that one ham can wear different name tags to convey slight differences...

CALLSIGN
SYMBOL  (can be a very reduced subset)

But since almost everything that is germane to the event or situation is known and can be added by the RFID DOORWAY READER, I still have not come up with much other than callsign/ssid is all that is needed.  Ideas?

in fact, SSID is not really needed since again, the doorway-reader can flag it as a RFID and not any other use under that persons call...

And that makes it work perfectly under the KISS principle!

Bob, WB4APR






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