[Elecraft] OT: pwr rating of RG6, etc

[n2ey at aol.com]

-----Original Message-----
From: Samuel Strongin <kf4yox at embarqmail.com>

>RG6 is 75 ohm cable. Why would you buy a great radio and worry about 
performance,then go use the wrong cable. You >start out at a 1.5:1 swr.

Because RG-6 may not be the "wrong cable", and the SWR may not be 1.5 
to 1.

IMHO, the question of what cable to use requires evaluating the entire 
antenna/transmission line *system* and taking all the issues into 
account. Depending on the antenna impedance, frequency, length of line 
and comparison coax, RG-6 might be lower loss than 50 ohm line (say, 
RG-58 or even RG-8X).

For example, suppose I had a wire dipole at a height such that the 
feedpoint Z was 75 ohms, and it needed a long feedline to reach the 
shack. Feed it with RG-6 and the SWR on the line will be 1:1. All I 
need to do is match that 75 ohms to 50 ohms at the shack, which can be 
done with an unun or the ATU in the rig. With 50 ohm cable the load SWR 
will be 1.5 to 1, and I'll probably still need to match it at the shack 
end - but the shack-end Z can be anything inside the 1.5 to 1 SWR 
circle on the Smith Chart. Depending on the line used, the loss with 50 
ohm cable may be greater, too.

73 de Jim, N2EY


 
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