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February 13th 11, 09:57 PM
posted to rec.radio.shortwave
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Mountains don't simply block HF
On 02/13/2011 12:26 PM, bpnjensen wrote:
On Feb 13, 12:09 pm, wrote: The signals don't travel; a field is set up around the transmitter antenna, like turning on a lamp. When the field encounters an obstruction it "knife-edges" and Fresnel zones are created, which may help or totally prevent reception, depending on the math (distance from transmitter to obstruction, from obstruction to receiver, blah blah). I am in a box canyon, open only to the South. If mountains stopped the signals completely, all I'd get would be penguins. A sort of diffraction effect. Makes sense. - however, I would bet some RF is blocked by either reflection or absorption, and the probable chaotic diffraction from irregular edges likely results in a pretty unpredictable pattern. That's what Fresnel zones are. |
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