UHF antenna
 

What's the best feedline for UHF antenna, 75 ohm cable or 300 ohm
strap? The antenna is to be used for recieving 674 MHz (TV channel 48)

Hello,

If that's the case, why do all TV antenna installations use 75ohm coax? No
one uses 300ohm feeder at UHF!

Geoff

"Mark Keith" wrote in message
om...
(brian) wrote in message
. com...
What's the best feedline for UHF antenna, 75 ohm cable or 300 ohm
strap? The antenna is to be used for recieving 674 MHz (TV channel 48)

Unless the coax is very low loss, I'd have to put my money on the 300
ohm twinlead setup having the least overall loss, even counting the
little balun you will need. At least when dry... Or at least thats
what I found when I ran a large UHF TV antenna for 420 mhz ATV. I had
the least loss with the twinlead. MK

"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

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

===================================

Because it is much more convenient to install and easier to keep dry. And
TV receivers don't have 300-ohm antenna sockets.

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No-one uses 300ohm feeder at UHF!

===================================

Except when engineering economics and the appreciably lower loss of 300-ohm
line is less expensive than providing and running a higher power
transmitting station.

" Bank Managers wielding the Almighty Dollar Rule ! ". Terman and radio
hams have to take backseats.
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Reg, G4FGQ