[aprssig] RFID antennas

Bob Bruninga bruninga at usna.edu
Mon Jul 14 10:33:51 EDT 2008

> The RFID tags that are cheap are pre-programmed 
> with unique serial numbers.  We'd need some way...

GOod point.  I wonder if we want to roll our own. Besides readers are expensive.  But if we do our own, then it becomes a nice ham club kit project.

I think of an IR link.  The reader uses lots of IR LED's to interrogate as the ham walks through the door.  His tag responds in IR with his callsign ID.

THe reader than sends out an APRS packet for that ham with his callsign and a vicinity plot in the vicinity of the reader.

All it takes is a PIC, an IR transistor and an IR LED.  Done.

A great ARRL project!


 (ie central server) to register your unique serial number and map it to a callsign.  There are RFID tags that are programmable, and they would be slick for this application...  I suppose you'd want a RFID reader to send data to a PIC processor that would combine a canned GPS location with the serial number of the RFID tag.  Perhaps you'd want the PIC processor to randomize the position it used with the RFID tag serial number?  
Hmm... many aprs clients will display a tactical callsign, so if the RFID pic processor were to construct a 3rd party APRS packet using the RFID serial number as the "callsign" we could manually assign it a tactical call of the user's actual callsign on our aprs client (like xastir).  But aren't we limited to 9 digits for a callsign in the aprs spec?  I think the RFID serial numbers are longer than that.  Of course the serial numbers would be serial in a sequence, so perhaps we could truncate the RFID number and just use the last 9 digits?
I've thought about indoor tracking.... have a tiny track or open track (what have you) and program it so that it will transmit w/o a GPS fix.  Have a pic processor above the doorway into a room sending via IR either a fixed GPS position string (ie fake GPRMC), or a fake GPRMC that chooses random coords with set boundaries.  If you randomize the coordinates it will prevent everyone in the room from appearing to "stack up".  your tracker is able to receive serial data from a 38khz IR photo transistor or from your personal GPS unit.
It goes like this....   When you walk indoors, the GPS will loose lock and begin to transmit (serially) that it is out of lock.  The pic processor in the opentracker should ignore this data.  The GPS data is fed to the open tracker via a 10k series resistor.  The data from the IR photo transistor is fed via no resistor and is easily able to "over power" the serial signal from the real GPS unit.  

If it were me, I'd place one of the fake GPRMC sentence generators over a doorway shining down at a 45 degree angle into the room.  One on each side of a door header to catch you entering the room and leaving the room.

On Sun, Jul 13, 2008 at 11:05 AM, Bob Bruninga <bruninga at usna.edu> wrote:

> "The Texas Instrument HF Antenna Cookbook."
> The designs are for RFID at 13.56 MHz.

I seriously want to see the ARRL/Ham radio invest in RFID for ham radio ops.  Embed the chip in the ARRL name tag.
Then we can have gateways to APRS...

Put one at each venu or checkpoint or clubhouse, or whatever.
Range should be about 100 feet...


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