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[aprssig] RFID antennas

Robert Bruninga bruninga at usna.edu
Wed Jul 16 12:54:28 UTC 2008


> "Cheap" will probably be the biggest issue, 
> as [the wi-fi RFID tags] are meant for commercial 
> and enterprise applications....
> ...If we can't get a deal on them, perhaps one 
> could be fashioned from one of those cheap USB 
> Wi-Fi sticks, and a PIC processor?
> 
> I guess my point in all of this is to not assume 
> we need to use 1200/9600 baud AFSK AX.25 stuff 
> to accomplish this job.

Thanks. Yes, I am not suggesting AX.25.  I'm suggesting simple
key-chain xmtrs (about $9 each).  After the "RFID reader"
receives this simple FSK, then the reader translates the
information into APRS and transmits it on 144.39 using AX.25...
Bob, WB4APR
> 
> 
> ----------------------------------------
> > From: bruninga at usna.edu
> > To: aprssig at lists.tapr.org
> > Date: Tue, 15 Jul 2008 19:04:47 -0400
> > Subject: Re: [aprssig] RFID antennas
> > 
> >> Sounds like what you need are the RFID tags 
> >> that run the Wi-Fi protocol. ... They can 
> >> be worn by people, or attached to equipment.
> > 
> > But I doubt they are cheap and more importantly, can run for
> > hours or days on tiny battery cell that would fit on a
nametag?
> > A passive device with 10 foot range would be even better...

> > 
> > I cant resist!  I started a WEB page:
> > http://www.ew.usna.edu/~bruninga/aprs-rfid.html
> > 
> > Lets see.  A $89 microwave oven with the door off....  That
> > could beam plenty of power.... (JOKE!)  but seriously, what
is
> > the lowest power microprocessor we have readilly available?
> > 
> > Lets see.  The ARRL exposure limits are about 1 mW/sqcm at
900
> > MHz so a 3 x 10 cm nametag could conceivably capture about
30 mW
> > ... Lets go to 10% of that amount to be safe..  Store up 3mw
> > over one second and then tx at 30 mW for 100 mS at the
end...
> > Hummh... To get that much power into the name tag, through a
6x6
> > foot door would need 100 W though!  Maybe I'm doing
something
> > wrong...
> > 
> > A safer approach would be a few sqcm of solar cells would
give
> > over 100mw in the sun, you'd get only 10mw indoors.  But if
you
> > charge up a cap over a few minutes in the light, you could
power
> > a burst?
> > 
> > Remember, from a CALLSIGN, we would get all of the following
> > when that station walked through the door:
> > 
> > CALL, DATE, TIME, LOCATION
> > 
> > In addition, the door system would add these:
> > FREQUENCY in use in that arena
> > FUNCTION being performed there...
> > 
> > Of course the location is offset-and plotted as a list...
See
> > the web page...
> > 
> > And that is pretty much what APRS is all about.
> > 
> > Bob, WB4APR
> >> 
> >> 
> >> ----------------------------------------
> >>> From: bruninga at usna.edu
> >>> To: aprssig at lists.tapr.org
> >>> Date: Mon, 14 Jul 2008 23:43:32 -0400
> >>> Subject: Re: [aprssig] RFID antennas
> >>> 
> >>>> I would question the need for such a device. 
> >>>> I can see it being used at something like Dayton...
> >>>> but I wonder if there is a significant enough 
> >>>> collection of Hams in other avenues to justify the cost.
> >>>> Where do you see this system used?
> >>> 
> >>> First thoughts that come to mind are at the door to the 
> >> clubhouse, the EOC (we have 3, county, city and state).  At

> >> the mobile comm vans, the HQ and other gathering points for

> >> emergency comms.  At each checkpoint in any ham supported 
> >> event.  At hamfests..
> >>> 
> >>> Then there are applications where we loan our badges to 
> >> things or people that need to be tracked.  Not just hams.  
> >>> 
> >>> By rolling our own systems, my guess is we could get the 
> >> readers down to the price of a tracker or so.  The point
is, 
> >> that it would be a new capability that we have never had 
> >> before, so we dont really know what all the applications 
> >> would be.  Kinda like barcodes invented for grocerystores, 
> >> but then they became to be used everywhere for all kinds of

> >> applications...
> >>> 
> >>> Bob, WB4APR
> >>> -- 
> >>> 
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> >>> https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig
> >> 
> >>
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