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Old 19-Jan-2012, 9:04 PM   #1
Badfish740
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Effect of weather/atmospheric conditions on OTA TV?

I was wondering what I can expect from a well designed OTA TV system during different weather conditions? The Dish we have now basically works fine except in really driving rains (and I mean coming down in sheets-normal rainfall doesn't phase it), and of course when it gets covered with snow. What kinds of weather and/or atmospheric conditions can affect TV transmissions? Are sunspots, solar flares, and other atmospheric conditions typically a factor? I had a neighbor growing up who was a CB enthusiast who had a 60' tower in his backyard, etc... I remember him talking about something called "the skip" that happened either during a certain time of year (or during certain kinds of weather-I don't really remember), but basically whatever this condition was it allowed the waves to bounce of certain parts of the atmosphere, allowing them to travel much much farther than usual. Is anyone familiar with this phenomenon and does it apply to television waves?
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Old 19-Jan-2012, 11:07 PM   #2
Dave Loudin
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There are a couple of mechanisms that will affect VHF and UHF propagation. The first involves weather, specifically temperature. For several reasons (fronts, heating over a cold surface, etc.) a layer of air of one temperature will trap a layer of a different temperature. Since the density of air depends on temperature, at the boundary between the two layers will be a rapid change in density. TV and FM signals approaching this region will get bent back towards earth instead of continuing out to space. This is tropospheric scattering. Sometimes, signals can get trapped in this region until another abrupt change knocks them out. The signal has travelled a lot farther than normal, and this is called ducting. Both tropo scatter and ducting affect a wide range of frequencies at the same time.

The other mechanism involves the ionosphere. Normally, ion density is not sufficient to bend VHF/UHF signals back down to earth. Occasionally, extra clouds of ionization form at the bottom of what's called the E-layer that are sufficient to bend back these signals. This effect is called sporadic-E propagation, and sets up very long distance reception, as in getting Kansas stations here. Often, local stations will be wiped out by the distant one, as the distant one has suffered very little loss along the way. This tends to be a VHF only event, and cuts off very abruptly above a certain frequency.

Rain and snow will affect UHF propagation.
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Old 20-Jan-2012, 7:47 AM   #3
phone man
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All my major network channels are 40 to 65 miles away and two edge at that. Rain, snow, fog etc haven't been an issue at all. I make a point of checking when it's pouring rain or snowing very hard. For my location, weird tropospheric conditions have far more impact on UHF TV reception, ranging from complete loss of normally reliable TV stations to reception of stations far beyond normal line of sight.
Here's a website that provides forecasts for such events. http://www.dxinfocentre.com/tropo.html
I'm not a serious DXer by any means but I did start a log of oddball stations that show up during these tropo events.
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Old 20-Jan-2012, 1:55 PM   #4
Electron
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Tv antennas and Tv reception

Thank you Phone Man for the practical and useful information that you provide. You provide information about what is actually happening not what theory says should happen.

Last edited by Electron; 21-Jan-2012 at 12:19 AM.
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Old 21-Jan-2012, 1:53 PM   #5
Dave Loudin
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Nothing theoretical about what I wrote. Tropo scatter gives me reception of Hampton Roads, VA, stations and stations across the Chesapeake Bay. The enhanced bending also brings Baltimore in.
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