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[aprssig] APRS RFID reader?

Patrick winston at winston1.net
Mon Feb 1 21:44:20 UTC 2010

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.


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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