2008/4/28 <[EMAIL PROTECTED]>: > On Mon, Apr 28, 2008 at 11:56:26AM -0700, Ralph Shumaker spake thusly: > > band bouncing off the upper atmosphere? And why would small planes > > interfere? Is it their radio equipment? Or are they just "blocking" > > the signal? > > They wouldn't. How close are these planes that you are seeing? If you live > in La Mesa and look outside when you notice interference and happen to see > a plane in the air it is because there are always planes in the air over > La Mesa. Small planes carry VHF radios and each plane spends very little > time transmitting. As a pilot I can't conceive of how they would affect > your TV reception. > > -- > Tracy Reed http://www.ultraviolet.org > >
Multipath reflections. Over the air TV signals have a pretty short wavelength in comparison to a passenger jet, or even a small airplane. You have this metal clad tube flying through the air, probably at a low altitude. Most over the air TV broadcasting comes from Mt Soledad, so what happens is the TV signal goes straight to your outdoor/indoor TV antenna, and another signal bounces off the aircraft, also arriving at your antenna. Once that happens, there's enough of a delay in the signal from the aircraft that it interferes with the signal arriving directly at your antenna. When this happens, the signals add/subtract from each other, causing multiple images to appear, or parts of the signal actually getting canceled out and getting snow for part of the video. It's also possible to get very long distance TV stations during this time of year due to tropospheric ducting. Think of layers of clouds in the atmosphere, they form a kind of 'electronic tube', that acts like duct in your home. When it's the correct diameter, it'll pass radio signals through it for very long distances. Some amateurs park near the glider port close to UCSD listening for VHF beacons from Hawaii... -- Mark Schoonover, CMDBA http://www.linkedin.com/in/markschoonover http://marksitblog.blogspot.com [EMAIL PROTECTED] -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
