Bob,
I think a more accurate description of several coiled turns of coaxial
cable would be a RF Choke, serving to limit common mode currents on the outside
of the coax cable.
Norm W4QN
======================================
In a message dated 12/29/2010 3:01:05 P.M. Eastern Standard Time,
towertalk-request@contesting.com writes:
Message: 1
Date: Wed, 29 Dec 2010 06:00:35 -0600
From: Bob Alexander <realex@flash.net>
Subject: Re: [TowerTalk] 1/4 wave coax "Balun"?
To: _towertalk@contesting.com_ (mailto:towertalk@contesting.com)
=======================================
Norm,
A 75 ohm coaxial 2:1 impedance transformer does perform a BALUN function
when wound
into a coil or when several turns are wound on a suitable toroid.
73, Bob, W5AH
============== original ============================
On 12/28/2010 10:31 PM, W4QN wrote:
> Jim,
>
> The use of an ODD electrical quarter-wave of coaxial cable as a BAL-UN
is not
> correct. The correct description would be "series coaxial transformer".
And
> there are certain other conditions to be satisfied when constructing this
> impedance matching network. An odd quarter-wave of 75ohm coax is a
special case
> of the Series Transformer (which uses two different pieces of coax) and
is
> nominally a 2:1 impedance transformer. Its application for Cubical Quad
> antennas was popular as often the loop impedance of a quad was around
100 ohms,
> and required a 1:2 impedance change to match a 50 ohm source. It does
not
> perform a BALUN function (Balance to Unbalanced). Coaxial baluns can be
> constructed using electrical 1/2w piece of coax (Same Z)and connected so
that
> the shields are together, the feed coax center to terminal 1 of the
antenna and
> the 1/2w piece center from T1 to the other terminal of the antenna -
this also
> is a 4:1 impedance transformer as well.
===========================
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|