[Antennas] Hardline Questions
Cletus W Whitaker
[email protected]
2003年10月28日 17:48:51 -0500
de WB2CPN South Central Pennsylvania 2003年10月28日
Greeting all,
Where the 75 Ohm TV coax, which is fairly low loss in
its own right, is used to replace a run of more
conventional coax which has a higher loss at the frequency
to be used, there is a length where the loss of the
mis-matched 75 Ohm coax is less than the loss of the
coax it's replacing. That is, the longer the run beyond
this critical length, the better the 75 Ohm coax looks.
I have a lot of 3/4 and 1" 75 Ohm TV coax here.
Also, be careful with Bird-type watt meters who are
dependent on the voltages and currents found in a 50-Ohm
environment. And, 60 Ohm, more or less, quarter waves are
likely to be the best way to transform 75 to 50 if you
go that way. Fewer moving parts, but frequency sensitive.
(My Ringo Ranger does 70 Ohm feed very well. Also, most
free space simple dipoles are 72 Ohms (+/-) at the middle.)
Comments ?
73 Clete