[Elecraft] Baluns and 450 ohm line

[N2EY@aol.com]

In a message dated 6/4/02 2:53:58 AM Eastern Daylight Time, 
kc4kgu@ENTERZONE.NET writes:

> I currently feed my
>  75m doublet with twin pieces of RG8X.  This presents a line impedence of
>  about 100 ohms.  Prior to feeding with twin pieces of coax, I cut the
>  doublet for resonance at 3.875Mhz.  It showed a 1:1 match at 50 Ohms
>  according to the MFJ-269 analyzer.

I'm a little confused with your setup.

Are there two pieces of RG-8X "side by side", with the center conductors 
going to the feedpoint of the dipole? 

Is there a balun in the setup somewhere?
  
>  Now, since the MFJ-269 is designed to give readings based on 50Ohms, what
>  should I be looking for when I check one of my antennas that is being fed
>  with twin coax with a 100 Ohm feedline impedence?

That depends entirely on the length of the coax. A basic example:

If the electrical coax length (don't forget velocity factor) is an integral 
multiple of a half wavelength, the impedance at the feedpoint will be 
"repeated" at the other end - regardless of the transmission line used! 

73 de Jim, N2EY