[Elecraft] SWR Question

[Vic K2VCO]

Bob Fish wrote:

> I added some ferrite beads at the feedpoint to ensure that it isn't 
> common mode currents on the outside of the coax sheild causing this. I 
> always thought that SWR doesn't change along a transmission line. What 
> is causing this I wonder, and should I just tune the antenna for lowest 
> SWR at the transmitter regard less of feedpoint SWR?

I presume you're using a link-coupled tank circuit? Or did you just tap 
it for the coax?

The bobtail curtain has a very high impedance at the feedpoint, as you 
know. It's like an endfed zepp in that regard.  So it doesn't need a 
low-impedance ground connection, but it does need some kind of ground 
return. My guess is that you, with the MFJ tuner in your hand, were it, 
especially if you were not using a link-coupled tuner.  So when you 
walked away, everything changed!

Possibly a 1/4 wave radial connected to the bottom of the tuner would 
tame it a bit.

A link-coupled tuner will be much better at isolating the coax than a 
tapped tank.

This is my experience with other antennas fed this way -- I never tried 
a BC and maybe I'm all wet!
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco