[TenTec] Open-Wire Feeders

[Martin, AA6E]

It's not only a matter of electrical degrees.  There are at least two
other reasons to keep spacing moderate at any frequency: 1.  The more
spread out the lines are, the more susceptible they are to coupling
with nearby (asymmetrically positioned) metallic objects, leading to
imbalance and power coupled into the wrong places (like downspouts and
power lines) on xmit and to more noise susceptiblity on receive.  2.
The electric and magnetic fields are strong within a certain radius,
roughly twice the line spacing, leading to dielectric losses and
coupling problems, even with symmetrically placed foreign objects. 
You want to keep the spacing reasonably small to minimize these
problems.  So, the customary 4-6" seems reasonable to me, also.  You
do want enough spacing to avoid arcing due to high voltage and to keep
the impedance fairly high, but an inch or more is probably enough for
that.

Another small point is that smaller line spacing means you have to
control the wire spacing more accurately -- i.e., observe a certain
maximum percentage deviation from constant spacing -- to keep the
impedance constant.  Wider spacing may be easier in this regard.

Lots of things to think about if you are inclined to worry.  I'd just
use the standard stuff for HF and get on with it!

73 Martin AA6E

On 2/5/06, Allan H. Kaplan <w1ael at mindspring.com> wrote:
> Catfish wrote: ..."the wider the space the better",
> but I urge a more moderate approach.   Getting the lines more than a few
> electrical degrees apart will allow them to radiate some of the power we
> would like to transmit to the antenna.   Art Collins held his
> engineering staff to a very demanding tolerance of  one electrical
> degree -- about an inch at 30 MHz..   I believe that a 3 to 6 inch
> spacing is reasonable.   I use line supplied by W7FG, spaced at about 4
> inches.  It has held up well in the hills of east Tennessee.  73, Allan
> W1AEL.
>
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