On Sun, 11 Mar 2007 15:12:13 -0400, Rick Smith wrote > no, 900 mhz rfid would be 20mhz bands. They MUST be exceeding EIRP, > tho, because I've never seen problems with rfid at close ranges like > that, and not having good reads with normal, or even less than > normal power. Problem is, rfid is 100% tx/rx 100% of the time. > > How far away is this from you ? > > I guarantee it's a piece of bad equipment - cable or such - on their > end, "leaking". > > Certified letter or bb gun, your choice... ;) >
Actually, that may not be true. I did a lot of reading up on RFID, and the loading doc version that Walmart uses requires full EIRP to work, because they are intending to read all theindividual tags inside of cartons, containers, etc, and these are passive devices, needing the RF field to create the power for the tag to transmit. Additionally, some of the systems are FHSS and use the full spectrum, including being maximum eirp at the same time. Walmart won't talk to you, because they've been assured by the RFID maker that there's nothing you can do to them. However, that doesn't preclude the more weighty matters of retailing... Like bad publicity. Like, getting your local paper to carry a story about how WalMart installed an RFID inventory tracking control and it took X number of people's internet connections away due to interference, and they won't even discuss mitigation with you. Mitigation of interference is a big thing, actually, because they need to install several of these devices in some instances, within a single building. They accomplish this by sheilding - metal shielding to "curtain" off the rf emissions, so that each station can work isolated form the others. Walmart is aware of this, as is the maker of the RFID system. I would suggest that after some negative publicity, they might be willing to talk to you about sheilding, especially since you could point a focused beam at them and cause serious inventory control problems for them, as well. The problem they will have, is that the RFID tag outputs are measured in a few microwatts, and even at a few feet, interference need not be all that strong to cause problems. I would approach them at this angle, explaining it's in their interest to sheild their system, because your equipment, if moved, can definitely interfere with them. -------------------------------------------- Mark Koskenmaki <> Neofast, Inc Broadband for the Walla Walla Valley and Blue Mountains 541-969-8200 -- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
