[aprssig] APRS RFID reader?

[Robert Bruninga]

I still think APRS-RFID... Is a next thing for APRS
experimenting

Every ham hat could have a $2 chip in it.

Then we can tell who enters the clubhouse or EOC... (it gets
converted to APRS...)
See http://www.aprs.org/aprs-rfid.html

Problem is, the maximum range reader I can find is only good for
10 inches max and it costs about $24:
http://www.sparkfun.com/datasheets/Sensors/ID-12-Datasheet.pdf

It has provisions for a  wind your own antenna but still can
only get to about 10 " (25cm).  But since hams are RF
experimenters, it would seem that we could improve on this.  One
sentence in the limited docs says that there has to be enough
energy to activate the chip.  This implies to me that the limit
is on the energy transmitted to the chip, not necessarily the
read range.  Frequency is 125 KHz.

To get reliable coverage for people walking through a door, I
think we need about 48" range...

Does anyone want to fill us in on the details?  I assume a 125
KHz carrier in the antenna coil provides the energy for the RFID
chip (this can be scaled up... Just needs more power)...  But
then I guess it has some off cycles so the chip can send back
the 32 bit code?

Bob, WB4APR