[BC] Commercial Station Feeding A Commercial Translator Question

[Richard Fry]

More comments on this based on the data in the OP...

The radio horizon for an antenna at 300 feet AGL is about 24.5 miles over a 
smooth earth (4/3 radius).  So even if the translator receive antenna was 
at 300 feet AGL, that still leaves a lot of a ~90 mile direct path needing 
to travel through the earth.

It can't do that, so whatever signal arrives at the translator site has to 
refract over the terrain elevation peaks along the path, in line-of-sight 
segments.  Each refraction can reduce the signal by 15 dB or more, so it 
doesn't take many of them before the signal is too weak to be usable.  Also 
the signal strengths over long paths have a lot of time variability.

For some insight, I use a 10-element FM receiving antenna at about 35 feet 
AGL to listen to St. Louis FM stations, using a  McIntosh tuner.  The path 
is about 90 miles long, over fairly flat terrain to Quincy, IL.  The 
stations using 100 kW at ~1,000 feet AGL will vary over large blocks of a 
24-hr period from being rather quiet (maybe 40 dB SNR) to being totally 
unlistenable.

RF