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Re: Topband: My Shunt Fed Tower

To: Bob Garrett <>
Subject: Re: Topband: My Shunt Fed Tower
From: Guy Olinger K2AV <>
Date: Sun, 29 Jan 2017 21:57:29 -0500
List-post: <">>
Anything you add to a tower tuned up as a primary 160 radiator can mess up
160. Just depends.

To decouple the vee's from tower/160,

1) the coax shield needs to be grounded to the tower at the vee feedpoint
just before the balun.

2) the coax shield needs to be grounded to the tower at the tower base.

3) the vee wire elements need to be isolated from the tower with a balun
that has good and stiff blocking **AT 160 METERS**.  A commercial version
of the needed blocking, for comparison and design, or outright purchase is
Balun Designs 1116d. Various hardware configurations are available.

They have links to a graph of the blocking curve on this page.

The above steps will keep the vees from looking like 160 antennas parallel
to the tower.

You are not the first one to discover that low/mid-band dipoles and vees
are de-tuning 160 radiators, or changing their patterns.

Good luck  :>)

73, Guy K2AV.

disclaimer: no commercial association with Balun Designs.

On Sun, Jan 29, 2017 at 9:23 PM, Bob Garrett <> wrote:

> Greetings Listers,
> I'm looking to this group for some input on my shunt fed tower loaded down
> with antennas HI.
> I have 85 feet of Rohn 25G with three sets of broken up guy wires that was
> installed in 1999.  Probably 200 to 300 short radials that have been put in
> since 1988 for the previous tower and added to over the years, all bonded
> to
> the base of the tower.
> On top, from bottom up I have - Optibeam 9-5 9 EL yagi, 5 EL M2 6 meter
> yagi
> and at 100 feet, an Optibeam 30 - 40 rotary dipole.  All cables run inside
> the tower and are grounded at the base.  I use an omega match made up of
> two
> vacuum variables.
> Now, this season, I wanted to have a few more options for contesting.  I
> installed a 3 foot metal support from KF7P and put up a 80 meter inverted
> VEE at 70 feet and a 60 meter inverted vee at 60 feet using the same
> arrangement.  I did have to adjust the omega match after adding the two
> additional antennas.
> Regarding the shunt, I use a piece of RG8X with the attachment point at
> about 48 feet and a spacing of 24 inches, a 1KPF variable in series and a
> probably 400PF cap for the omega match.  No problem getting a perfect
> match.
> Over the years, this arrangement prior to adding the two inverted vee
> antennas this year performed very well.  Now I know about TB conditions so,
> I am not making sweeping statements but, seems like I just don't get
> through
> those pileups as quickly as before.
> My questions - Is there any fact to the statement that an 80 meter antenna
> on a 160 meter shunt fed tower will degrade the performance?  Is it just
> one
> happy amount of loading?  Anything else I should be considering?  The
> problem is I live on a small lot and only have so many options to cover all
> bands.  Any input appreciated.  73, Bob K3UL
> _________________
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