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John Passaneau · April 11th 08, 02:38 PM posted to rec.radio.amateur.antenna

"Robert11" wrote in news:SK-
:

Hello,

For the scanner frequencies around 118 MHz, e.g., I realize FM is
essentially line of sight.

Are AM transmissions also line of sight ?

Same question, but for the higher freq's around 800 MHz ?

Thanks,
Bob

Hi Bob

The propagation of radio signals is frequency dependent, not modulation
mode dependent. That is not to say that some modulation modes are not
better over long distances than others, SSB is better than AM and AM is
better than FM. To say that VHF frequencies are always line of sight is
also not completely correct. They are propagation modes that can extend
the range of VHF signals quite a bit. I have worked stations on 144MHz
that were more than 500 miles away. But these are not an everyday thing
so it safe to say that most of the time VHF is line of sight. 800MHz is
in the UHF band and is even more just line of sight than VHF but they are
still propagation modes that can extend the range out to 100’s of miles.
Line of sight propagation is the reason that VHF and UHF antennas are put
up high as it extends the line of sight.

John Passaneau W3JXP