I used gamma matchs and 1:1 baluns made up of solenoid wound coax for each
band. This arrangement allowed me to use horizontal AND vertical feedpoints on
the TEN Meter driven loop and obtain 20dB isolation. The gamma match will
permit you to tune a perfect match. The 1:1 balun isolated the shield nicely.
If you would like to see a picture of the quad, and have a few links to the
dual polarity quad... go to QRZ and type my call AB2KC.
My quad is 3-elements on 20 and 15, 4-elements on 10. Only 3-bander.
I too was concerned about the other bands with interference/beam shape, and
front to back ratio deterioration.
Have fun,
73,
George
Ab2KC
----- Original Message -----
From: Michael Baker
Date: Monday, May 24, 2010 7:10 am
Subject: Re: [TowerTalk] Quad questions
To: 'Martin Sole' , TowerTalk@contesting.com
> Hello Martin,
>
> One sure way to break any common connection to the other
> elements is
> to use a line isolator/ 1:1 in line with each elements feed
> line. There is
> NO common ground connection at that point. You have a balanced antenna
> element to start with and an unbalanced feed line so putting a
> balun in each
> line would make sense and with the feed impedance being about
> 100 ohms a
> matching transformer would be prudent and would save the
> matching problem
> unless you used a 1/4 wave 75 Ohm stub on each feed element. You
> would still
> have an unbalanced stub to a balanced load issue. Interesting
> conundrum.
> Michael Baker K7DD
> k7dd@cox.net
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Martin Sole
> Sent: Sunday, May 23, 2010 10:05 PM
> To: TowerTalk@contesting.com
> Subject: [TowerTalk] Quad questions
>
> I am about to start work on re-installing my Lightning Bolt 2
> element quad.
> Since we were granted access to 10, 18 and 24MHz I have decided
> to add these
> bands back on to the spreaders but I am mindful of the issues in
> having 5
> bands on 1 quad. From what I have read I believe the first important
> requirement is to feed each band separately. To do this I intend
> to use a
> boom mounted remote coaxial switch but have a few questions.
>
> 1. I plan to have coaxial baluns on each feed point but am
> unclear if
> this will provide sufficient isolation for the common connected
> shield at
> the switch box? Do I need to isolate the entire feed to each
> element or is
> switching the centre of the coax sufficient?
>
> 2. Cebik states that it is beneficial, especially for the
> 20m and 10m
> loops, to ensure the 20m loop is open when operating on 10m.
> With the length
> of open coax from the 20m feed point to the switch box acting as a
> transmission line transformer the length would seem critical to
> ensure an
> open circuit feedpoint? Presumably it needs to be a multiple of half
> wavelengths at 10m?
>
> 3. What about the other bands? It seems prudent to ensure
> feeding the
> 12m and 10m driven elements with lengths from the switch box
> that make them
> appear open when on the other band. Helping to minimize interaction?
>
> 4. I want to add a 30m folded loop to the driven element
> and a 40m
> folded dipole to the reflector element using short spreader
> extensions along
> the lines of EI7BA, see http://www.iol.ie/~bravo/Cubical%20Quad.htm.
> Wondering about the impact of the 30m loop on 10m and the 40m
> folded dipole
> on 15m?
>
>
>
> Grateful for any input.
>
> Martin, HS0ZED
>
>
>
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