I stacked about 10 torroids directly below the feed point of my wire
vertical, but it didn't do a thing to choke the common mode currents. Seeing
I can't have a heavy coax coil balun directly under my elevated the feed
point (as the support mast is a flimsy aluminium pole on the roof!), I wound
the coax around a 3.5" dia 12" former at the point the feeder enters the
shack - Viola......it cured all my RFI problems. The former was the largest
dia container I found and stole from the XYL's kitchen!
I am certain that larger dia PVC pipe would be more effective.
One needs to improvise when you live in a place like Jamaica! No stores for
UNUNS, Baluns etc! In fact, I can hardly find 50 ohm coax here!
73,
Ron, 6Y5/4S7RO
----- Original Message -----
From: Pete Smith <n4zr@contesting.com>
To: <towertalk@contesting.com>
Sent: Friday, December 19, 2003 7:38 AM
Subject: Re: [TowerTalk] Vertical balun
> At 07:41 AM 12/19/03 +0100, SM2EKM wrote:
> >If there are RF currents on the braid of the
> >feedline you need to cut the braid, that is from
> >an RF point of view. That you do with forexample
> >ferrite beads, as you correctly point out below.
> >I would put them as close to the feedpoint as
> >possible, if that doesnt solve the problem I
> >would move them.
> >Why complicate things with unneeded stuff, keep
> >it correct and simple and it will pay of in the
> >long run.
>
>
> I think it was W8JI who pointed out that effective placement of bead
chokes
> on feedlines can be somewhat mysterious unless you can somehow sniff out
> the current on the shield, so Jim's advice strikes me as right on. It's
> also not unreasonable to think about putting more than one on a
feedline --
> for example one might put one right at the feedpoint, and one at the point
> where the coax enters the house. I would also check the towertalk and
> topband reflector archives for his very sound advice on what mix of
ferrite
> to use for this purpose, because he says the wrong ferrite in a
> transmitting application can generate a lot of heat with QRO power,
> possibly even destroying itself.
>
>
> 73, Pete N4ZR
> Happy Holidays
> Check out the World HF Contest Station Database at
> www.pvrc.org/wcsd/wcsdsearch.htm
>
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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