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.
In a message dated 12/29/2010 3:01:05 P.M. Eastern Standard Time,
Date: Wed, 29 Dec 2010 06:00:35 -0600
From: Bob Alexander <email@example.com>
Subject: Re: [TowerTalk] 1/4 wave coax "Balun"?
To: firstname.lastname@example.org_ (mailto:email@example.com)
A 75 ohm coaxial 2:1 impedance transformer does perform a BALUN function
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:
> The use of an ODD electrical quarter-wave of coaxial cable as a BAL-UN
> correct. The correct description would be "series coaxial transformer".
> there are certain other conditions to be satisfied when constructing this
> impedance matching network. An odd quarter-wave of 75ohm coax is a
> of the Series Transformer (which uses two different pieces of coax) and
> nominally a 2:1 impedance transformer. Its application for Cubical Quad
> antennas was popular as often the loop impedance of a quad was around
> and required a 1:2 impedance change to match a 50 ohm source. It does
> perform a BALUN function (Balance to Unbalanced). Coaxial baluns can be
> constructed using electrical 1/2w piece of coax (Same Z)and connected so
> the shields are together, the feed coax center to terminal 1 of the
> the 1/2w piece center from T1 to the other terminal of the antenna -
> is a 4:1 impedance transformer as well.
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