[TowerTalk] RE: Question

[Tyler Stewart]

I would suspect that the problem with the XM240 could have been solved by
simply uninsulating the reflector.  That is the only substantial electrical
difference between the 402CD and the XM240.  That fix should be as simple as
putting a short jumper at the center of the reflector to the boom

----- Original Message -----
From: "Guy Olinger, K2AV" <k2av@contesting.com>
To: "William F. Beyer Jr." <n2wb@arrl.net>; <towertalk@contesting.com>
Sent: Sunday, October 08, 2000 5:45 PM
Subject: Re: [TowerTalk] RE: Question


>
> 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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> FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
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