[Elecraft] open wire feeders

[Don Wilhelm]

George,

Short question, long answer follows --

Do to constraints at home, I no longer use open wire or ladder line 
feeders, but when I did use them, I found several things were true if 
you did not want them to radiate (and create RF in the Shack).
My first rule is to use balanced antennas - off center fed antennas are 
famous for feedline radiation and RF in the shack.
The second rule is to run the feedline away from the antenna at right 
angles for as great a length as you can manage, but certainly for a 
quarterwavelength - The feedline can pick up radiation from the antenna 
if this rule is not followed.
Third is to run the feedline correctly - use nice gentle bends if you 
must change direction, support it using as few hangers as possible (if 
you can put the feedline under tension, you can get away with very few 
supports) but support it so it is stable even in the wind.  Do not run 
it parallel to other conductors, but you may cross a conductor at right 
angles if necessary.  The line should be spaced away from other objects 
by at least 3 times the spacing of the conductors.

Lastly, If I could, use a true balanced tuner, link coupled is best, so 
if you see a Johnson Matchbox at a hamfest, get it.  If you must use an 
unbalanced tuner, use a good balun at the output (see K9AY's info on 
baluns).  BTW, do not assume that a 4:1 balun is the thing to use, the 
feedpoint impedance in the shack can vary wildly from very low to very high.

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

On 12/31/2011 11:25 AM, W2bpi1 at aol.com wrote:
> Those of you using open wire feed lines. How do you keep RF out of the
> shack? 73 George/W2BPI K2/100
>