Post by Carlos E.R.]> Can a 500 mile TV antenna work for radio?
]> TV is digital and the signals are separated, but how will you
]> separate radio stations that have the same frequency?
It can and does. I have listened to shortwave radio transmissions across
the Atlantic.
You can not separate them, except by using a directional antena. So
stations have to use different frequencies, or different time slots.
Notice that to reach those distances they bounce the signal on the
ionosphere (yes, the earth is round). They choose a frequency that
bounces on one or another of the layers, according to their intended
listener target (the distance, and direction).
Notice that there is a distance where there is no reception: there is
first the area in sight of the antena, with good reception. Then the
waves go a bit down the curve of the earth, then they get into space. In
this area there is no reception, which could be precisely 500 miles.
Then the first ionosphere bounce area starts.
Look for "skip zone".
Yup.
A similar thing *can* happen occasionally, for higher frequencies (VHF
and UHF television and radio signals). In those frequencies it's
usually referred to as "ducting" in the troposphere - the creation
of a refractive channel which can propagate these signals well
beyond their normal line-of-sight range.
Under exceptional ducting conditions, VHF signals can travel from
(e.g.) California to Hawaii - there are a few such 2-meter radio
contacts on record.
The same phenomenon can allow TV and FM-radio signals to be
picked up, occasionally, well beyond their usual range limit
(100 miles or so on VHF).
It's not something to count on, though. It's relatively rare, depends
on the season and weather and atmospheric conditions, usually fairly
short-lived, and you can be utterly certain that the duct will fall
apart (and you'll lose the TV signal) just before the Big Reveal at
the end of the episode :-)
When there's no tropo-ducting taking place, the chance of a
so-called "thousand-mile antenna" picking up a useful TV
signal from 1000 miles away is probably about as good as your
chance of winning the Powerball lottery using a grease-soiled
receipt from your local hamburger shack.