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Re: [TowerTalk] Antenna interaction tests

To: "K4SAV" <RadioIR@charter.net>, <towertalk@contesting.com>
Subject: Re: [TowerTalk] Antenna interaction tests
From: "Tom McAlee" <tom@klient.com>
Date: Sun, 15 May 2005 11:41:58 -0400
List-post: <mailto:towertalk@contesting.com>
Jerry - I'd really recommend option #4, the 10ft mast.

I have a 4 element SteppIR at 82 feet.  It is 10 feet below an OptiBeam 
OB2-40.  While I haven't done any fancy testing, it seems to work very well, 
especially on 17m (the OB2-40 has a special tuning stub designed to minimize 
interaction with other HF beams, perhaps that makes a difference).

I would not want mine turned 90 degrees away from each other.  40-50mph wind 
that lasts for 3 or 4 days in a row is not all that uncommon here.  During 
periods of high wind I like to keep them rotated such that the booms are 
broadside to the wind.

That is per the manufacturers instructions on the OB2-40 for obvious 
reasons; it's square 18' boom is less prone to bending than its 49' 
telescoped-tubing elements.

On the SteppIR, I don't know what they recommend.  The 32' boom is still 
shorter than the 36' elements.  And, when the boom is broadside to the wind 
there is very little movement but when the elements are broadside to the 
wind they turn into half-circle shaped things.  It might not be a big deal 
for gusts of wind, but I would be concerned for times when it went on for 
days.

With both antennas pointed the same direction there is very little movement 
anywhere.

It's something else to consider anyway.

73,
Tom, NI1N

----- Original Message ----- 
From: "K4SAV" <RadioIR@charter.net>
To: <towertalk@contesting.com>
Sent: Sunday, May 15, 2005 9:41 AM
Subject: Re: [TowerTalk] Antenna interaction tests


> The consensus for placing a 4 element SteppIR and an XM240 five feet
> apart is that this is much too close. Although it is true that the
> SteppIR can be retuned to lower the SWR because of interaction, you
> probably wont be able to recover the loss in gain or F/B.
>
> Thanks to Joe, K4IK for modeling this configuration and modeling some
> possible solutions.  Modeling shows with 5 ft seperation, on 17 meters
> the SteppIR loses 3 dB gain and most of its front to back.
>
> Possible solutions:
>
> 1.  Turn the antennas 90 degrees to each other
>
> 2.  Place antennas 5 ft apart and disconnect the feedline (center and
> shield) from the XM240 with a relay located at the feed point.  (Loses
> 1dB gain, 6 dB F/B on 17M, and loses 0.5 dB gain, no F/B loss, on 15M)
>
> 3.  Place antennas 5 ft apart and use an odd multiple of 1/4 wavelength
> on 17 meters feedline, to the XM240 and short line when using the
> SteppIR. (Loses 1 dB gain, 6dB F/B on 17M, and loses 1 dB gain, no F/B
> loss on 15M)
>
> 4.  Buy a new mast which will allow 10 ft seperation. (Another month
> wait for delivery and >$500 expense) This solution in combination with
> using the "odd multiple of 1/4 wavelength on 17 meters feedline to the
> XM240" loses only about 0.2 dB gain and 0.5 dB F/B, - insignificant.
>
> Thanks to all who replied
> Jerry K4SAV
>
> _______________________________________________
>
> 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.
>
> _______________________________________________
> TowerTalk mailing list
> 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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