Topband: 160 Meter BALUNS

[Arne Gjerning]

Tom

As you suggested that 7 turns might be better, length of the coax strip
point and wire should be increased to about 140 inches to maintain same
diameter.  I use mine on a Cushcraft 2el 40M yagi (split dipole so balanced
feed point).  Thanks for info.

73 de Arne N7KA

----- Original Message -----
From: "Tom Rauch" <w8ji at contesting.com>
To: <topband at contesting.com>; <gjerning at flash.net>
Sent: Wednesday, December 24, 2003 5:25 AM
Subject: Re: Topband: 160 Meter BALUNS


>
> > On 160-40M the number of turns for both the coax and the wire should be
5
> > NOT 7.  The nominal dia is about 6.5 inches.  George used #10 or #12
wire
> > NOT #16 in his article in news letter I have.
>
> This design came when people thought voltage baluns were the desirable
type,
> just before Lewallen W7EL and others started doing balun analysis and
> changed the mindset of people to preferring current baluns.
>
> This was the same style used with some Telrex antennas from that time
> period. (I scrapped the one from my Telrex 40M Yagi and replaced it with a
> current balun).
>
>  It's important to know it is a voltage balun, not a current balun. It
does
> not isolate the shield for common mode problems unless the antenna is
nearly
> perfectly balanced, so it only should be used when the antenna is nearly
> perfectly balanced and nothing excites the cable shield. If you tried to
use
> it to decouple radials (in an elevated radial vertical), an off center fed
> antenna, or with a feedline that doesn't come straight away from a
balanced
> antenna it would actually hurt the system.
>
> It depends heavily on flux coupling between the single wire winding and
the
> coax shield for balance. The windings (the coax and the single wire) must
be
> coupled tightly. The winding must be as compacted as much as possible
> without turns being "spread out".
>
> 5 turns at 6.5" diameter (plus the continuation of five more turns of coax
> shield) would put about 300 ohms XL across the dipole terminals on 1.8,
> you'd get by with a slight change in feedpoint impedance. Bill's
suggestion
> of 7 turns might actually be better.
>
> 73 Tom
>
>
>
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