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On Feb 13, 3:26*pm, bpnjensen wrote:
On Feb 13, 12:09*pm, dave 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. I don't quite picture this : mountains and canyons . Obviously-- no line of sight signals such as local AM and FM broadcasts, very poor groundwave propagation . Now, why is skywave affected as well ? What can possibly block HF signals ? |
#2
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#3
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On Feb 13, 3:59*pm, dave wrote:
On 02/13/2011 12:50 PM, wrote: On Feb 13, 3:26 pm, *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. * *I don't quite picture this : mountains and canyons . Obviously-- no line of sight signals such as local AM and FM broadcasts, *very poor groundwave propagation . Now, why is skywave affected as well ? What can possibly block HF signals ? The good skywaves come from 10 to 20 degrees up. The mountains are higher than that. I get no VHF/UHF TV. I get FM from Mt. Wilson, severely degraded. I get MW like gangbusters.- Hide quoted text - - Show quoted text - This must be a pretty good (quiet ) RF environment . When conditions are great, though . |
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