->  It's possible to lose power out (ERP) with signals reflected
->  back to the transmitter feeding a waveguide, just like those
->  standing waves on a transmission like reflecting back to a
->  radio/TV transmitter.

 And that is why the Nalleys Beef Stew Can works better then the
Pringles can. Althopugh I hear that the Hunts Spagetti Can is pretty
good also for a WiFi Waveguide antenna.          
One web site I visited on this subject even had an online Calcualtor
determine antenna position and length for the antenna for various sizes
of Cans. 
 But in real world testing the Nalleys Can beat the Pringles Can by
quite a bit. In fact of several sizes of cans tested it was the lowest
gain antenna. But for close in work for sniffing out hot Spots the
Pringles can dosen't attract as much attention. It is tricky to build
though as the can has a metal foil lining covered with plastic and
getting a good connection for the ground on the Coax connector is
tricky.

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