The idea of the twist in the line follows the old adage of the phone company
using a "twisted pair". This assisted in negating introduction of hum from
the AC power lines which were overhead on the poles. The same is true for
use on HF in two fold in that the twist will expose each side of the line
equally to any nearby object which contributes to unbalance of the line.
The second is to reduce the effects of the wind blowing against the line.
In my case the center fed wire is supported at the top of a 55 ft tower, the
line comes down the side to the tower to near ground level but is supported
every 10 ft by a 18" length of 1/2" PVC which serves as a stand-off. I
incorporate about 3 full twist or turns between each of the stand-offs. As
to balance, using a RF current probe at the point where the line attaches to
the output of the tuner, actually a 1:1 coaxial balun, the currents are
within 10% of less of the measured current on all bands 160M through 10M.
In measuring current at the feed point of the wire, the currents again are
within 10% or less. This is attributed to the legs being of slightly
unequal heights above ground at the ends and ground resistance under the
antenna being different.
I don't believe that a twist per 1/4 wave will be adequate. Perhaps I need
to make some measurements along these lines.
73
Bob, K4TAX
----- Original Message -----
From: "Lee A Crocker" <lee_crocker@yahoo.com>
To: <tentec@contesting.com>
Sent: Sunday, October 02, 2005 2:11 PM
Subject: [TenTec] Openwire fed differently
> The idea of twist is to maintain balance in the line.
> It was done in the old days of television with twin
> lead to try to get rid of ghosting. For low band
> operation it probably doesn't make much difference.
> If you do twist you probably only need one twist every
> 1/4 wave or so to maintain "balance".
>
> Personally I think the virtue of twisting is
> overblown.
>
> 73 W9OY
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|