[TowerTalk] RE: Question

[Guy Olinger, K2AV]

15 feet might not be enough...

The problems with 40m/tribander interaction consist almost entirely of
the 40 meter antenna messing up the 15 meter section of the tribander.
Whose tribander or which tribander doesn't even matter, the 40 meter
antenna is the problem. Modeling shows that even when the SWR
disturbance is improved by separation, that significant pattern
distortion remains on 15m (not gain, f/b and f/s).

This occurs because the ENTIRE 40 meter antenna (including the boom) can
have miscellaneous resonances, particularly on 15 meters.

Two 40 meter 2 el yagis without this problem are the older Cushcraft
402CD (NOT the XM240), and the F12 240N. The XM240, in addition to some
excellent strength modifications, changed the metal to metal
connections, and introduced 15 meter interactions not found on the
402CD.

A local contester was not able to solve interaction between an X9 and an
XM240 up 15 feet, even turning the XM240 90 degrees (remember, the boom
is a conductor, and the elements can act as end loading). He finally
sold the XM240 and is using a single element 40 parallel to the X9 boom.
X9 is working fine.

Part of the equation for you may be how much SWR trouble you can
tolerate on 15 m. If you have automatic antenna tuning, you may not even
care. If you have one of the non-automatic 8877 linears, they respond to
SWR swings with grid current increases which can trip out the amp. If
you run high power in contests, going up and down the band, this might
be intolerable.

Wanted to make sure you knew.

- - . . .   . . . - -     .   . . .     - - .   . - . .

73, Guy
k2av@contesting.com
Apex, NC, USA



----- Original Message -----
From: William F. Beyer Jr. <n2wb@arrl.net>
To: <towertalk@contesting.com>
Sent: Saturday, October 07, 2000 10:14 PM
Subject: [TowerTalk] RE: Question


>
>
> Is 14 to 15 ft. spacing OK with a Force 12 C-19XR and
> A C.C. XM-240.
>
> 55 and 70 FT.
>
> With the C-19 on top.
>
> Any interaction problems?
> --
>
> 73 & see you in the pileups!
> William/N2WB
>
>
>
>
> --
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>
>


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