"Geoff" wrote in message ...
Hello,

If that's the case, why do all TV antenna installations use 75ohm coax?

They don't. It is more common these days due to practical installation
reasons, but people ran 300 ohm line to TV antennas for years. Some
still do. It's the best choice usually for feeding a TV antenna,
unless the extra loss of coax is not enough to get you a snowy
picture. In the city, many times coax will be good enough. Out in the
country, I would always use low loss ladder line or twin lead. I
prefer that over using coax and a mast mounted preamp to make up for
the extra losses. In bad cases, you might even need a preamp with twin
lead..:/ But in that case, I prefer a bigger better antenna.


No one uses 300ohm feeder at UHF!

Sure they do. I did. It blew 75 ohm coax out of the water as far as
loss on that freq. I compared them on the local ATV repeater. And I
used beldon dual shield coax, which was fairly decent.
Look up the specs for each. What is lowest loss at UHF be be fairly
obvious. My 25 element corner reflector yagi/log thingy is set up for
direct connection to twin lead. You would have to use a
transformer/balun to run coax. And that adds a bit more loss... Yes,
the twin lead does get lossy when it gets wet, but dry it's quite
good. Also some 300 ohm twinleads are better than others. The ones
with the thickest wire size are usually best. MK