[TowerTalk] ? Yagi Interaction on 15m: KT34XA and XM240

[Al Williams]

Try checking the rigs vswr accuracy at 5w & 100w with resistive dummy loads
of say 25 and 100 ohms.

k7puc


----- Original Message -----
From: "Todd Dravland" <wd0t@sd.cybernex.net>
To: "Dave Hachadorian" <k6ll@juno.com>
Cc: <towertalk@contesting.com>
Sent: Thursday, October 26, 2000 9:07 AM
Subject: Re: [TowerTalk] ? Yagi Interaction on 15m: KT34XA and XM240


> Dave Hachadorian wrote:
> >
> > On Thu, 26 Oct 2000 10:24:59 -0400 "Jeff Maass" <jmaass@columbus.rr.com>
> > writes:
> > > What are the signs of interaction between tribanders and 40
> > > meter yagis?
> > >
> > > I recently installed a KT34XA at 69' and an XM240 at 79' (~10 feet
> > > separation). I'm seeing differences between the measurements
> > > made with my MFJ-259 and a transmitter (90W and 1000W) with
> > > wattmeter. You can see the measurements at:
> > >
> > > http://www.zing.com/album/?id=4293852949&p=4282913117&idx=69
> > >
> > > Is it possible that the interactions are not measurable with the
> > > low-power
> > > signal of the MFJ-259, but clearly evident when running more power
> > > for the measurement?
> >
> > I can't think of any mechanism which would make swr power-dependent,
> > other than balun saturation, which shouldn't be happening, especially
> > at the 90 watt level. Are you measuring swr at exactly the same point,
> > such as through any antenna switches or other accessories?
> >
> > Normally, I would suspect that the low power analyzer was being thrown
> > off by a local BC transmitter, but in your case, the analyzer shows
> > the lowest swr, and it looks like the KLM double minimum curve.
> >
> > Here's a good interaction check to make:
> > While transmitting 90 watts into the XA on 15 meters, disconnect the
> > 40 meter feedline, and intermittently short its center pin to the
> > shield. Also, intermittently ground and unground the 40 meter shield.
> > Observe if the 15 meter swr changes. If it does, you have
> > chosen an unlucky length of feedline for the 40, which is making
> > the 40 meter driven element resonant on 15. Change the length of
> > the 40 meter feedline to solve the problem.
> >
> > Dave Hachadorian, K6LL
> > Yuma, AZ
> > K6LL@juno.com
> >
> > --
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>
> I have noticed on my TS940s wattmeter/ vswr that when running 5 watts
> the vswr is typically lower than with 100 watts.. what I am getting at
> is that I don't believe my feedlines are ideally decoupled from the
> antenna, due to either not good enough balun isolation or perhaps the 50
> ft. horizontal run of feedline to the shack.  In any case, have seen
> VSWR change with increasing power.
>
> 73, God Bless!
> todd,WD0T
>
> --
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>


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