[Elecraft] open wire feeders

[Ron D'Eau Claire]

I have often had a voltage loop at the rig end of my open wire feed line and
have never experienced a problem with stray RF, even though a neon bulb
lying near the ATU blinked as I sent CW. 

HOWEVER - I do use a homebrew link-coupled ATU with open wire line. It lacks
the dual-differential tuning capacitors that Johnson used to adjust virtual
coil taps for the feed line in the Matchbox, but mine has a much wider
matching range using actual taps on the coil. (The Johnson Matchbox is only
rated to match balanced lines with impedances up to 1200 ohms).  

Link coupling has a number of advantages including a high order of
suppression of stray signals since there is no direct electrical connection
between the antenna and the rig. Everything coming in (or going out) has to
pass magnetically across the link coupling and through the tuned circuit.
That's especially handy if you live near a broadcast station. 

And of course, you can use the same tuner with unbalanced lines (e.g. coax).
Just connect the shield to the center of the coil and tap the center
conductor out to either side.

WZ5Q has a great example of a beautifully link coupled tuner at:

http://www.wz5q.net/index/shack_data/tuna.htm

It's bigger and neater than mine but the circuit is the same right down to
the RF current sensors. 

Ron AC7AC

-----Original Message-----

If you do encounter a high impedance feedpoint on any band, that will 
place a high RF voltage point at the shack end - add or subtract some 
feedline to bring the feedpoint impedance down.
If you do not understand how the  feedpoint impedance changes with the 
length, take a look at the Antenna article on my website www.w3fpr.com

73,
Don W3FPR