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[aprssig] APRS RFID reader?

Rudy Benner benner at vianet.ca
Mon Feb 1 21:56:07 UTC 2010

My hearing aid sets off the readers at the Mall-Wart store. Great fun.

----- Original Message ----- 
From: "Patrick" <winston at winston1.net>
To: "TAPR APRS Mailing List" <aprssig at tapr.org>
Sent: Monday, February 01, 2010 4:44 PM
Subject: Re: [aprssig] APRS RFID reader?

>A large part of the problem is the frequencies used.  They tend to be
> greatly affected by things in their read area, especially if the
> readers do not have auto-tuning antennas.  Again, the specialized ones
> are better at handling this but their cost increases.
> The setup I have for race results is self contained with ethernet and
> usb to computer (as well as a usb port for backup where all reads are
> written to a usb key), so pretty flexible..  I find around 90% read
> success of runners passing through the read area.  If nothing else its
> fun to make it go batty by throwing a couple dozen tags onto it.
> p
> Quoting Scott Miller <scott at opentrac.org>:
>> Passive RFID tags don't do long range very well... returned signal
>> decreases with the 4th power of the distance.
>> With the active tags I've got on my bench (somewhere in the $12 to
>> $20 range, I think) I can get a reading from across the warehouse,
>> maybe 70 feet, and with some work you can get a position estimate
>> using omni DF from multiple receivers - the tags are set up to send
>> their ID at several different power levels, since the receiver
>> doesn't have any sort of useful RSSI output.
>> Even the active tags don't have much penetrating power, though.  You
>> can put your hand around one and block off the signal when the
>> receiver's only a foot away.  I was hoping to use them to track
>> people and equipment in SAR vehicles, but I'm still not sure it's
>> reliable enough.
>> Scott
>> N1VG
>> Robert Bruninga wrote:
>>> 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
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