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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