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Fred McKenzie

In article ,
wrote:

I was just wondering about this and perhaps someone knows the answer. We're
about 60 miles North of Boston, which is where most of our OTA TV comes from.
I use an old Channel Master 5 foot parabolic, (unfortunately NLA) along with
a Winegard low noise mast mounted Preamplifier. The parabolic beats the pants
off the yagi that I was previously using. There is also a rotor. Our
elevation is rather low, however regardless of the season we can usually get
the networks, PBS and a few old movie channels, however every once in awhile
we might get a day where the signal will break up, and then after that it's
good again for weeks. We're not big TV watchers so it's nothing we can't live
with.

There is a strange phenomenon though that seems to occur at times, generally
when its very cold and clear. During some of those periods, but not all the
time it seems like the band just opens up and I get all these additional
stations, both low and high frequency ones, and some with 75 to 85% relative
signal strength indicated as well. Sometimes these additional stations will
be gone the next day, and other times they might hang around for a week or so
and then, just as quickly as they appeared they're gone again until the next
time they mysteriously reappear.

Sometimes I have thought that snow might be a factor, that is not when it's
snowing but after it's on the ground and the temperature is cold. I used to
DX VHF TV with just a Vbeam when I was a kid in New York City but It's been
my experience that UHF doesn't usually skip. Could this be ground wave, but
on UHF?

If anyone has any thoughts on this and how and why it seems to relate to
weather I would be very interested in hearing them. Lenny

Its called "ducting". Signals are reflected between layers of the
ionosphere, traveling long distances. It is sort of a "waveguide in the
sky".

I understand it is a kind of weather phenomenon, sometimes called a
temperature inversion. I found one article about it at:

http://en.wikipedia.org/wiki/Troposp...ospheric_ducti
ng.

Fred