[TowerTalk] <LONG> New Info: Yagi Interaction on 15m: KT34XA and XM240

[Jeff Maass]

Thanks to all the folks who made suggestions on resolving my
15 meter questions!

I ran curves with the feedline of the Cushcraft XM240 shorted and
unshorted at the shack. Shorting the 2 element 40 yagi feedline
made small but noticeable changes in the SWR of the KT34XA on
15 meters. The separation of the two antennas is about 10 feet,
and they are pointed in the same direction (not offset by 90 degrees).
The15 meter curves with the XM240 shorted were not significantly
different. Interaction was not my problem.

For the second time with this installation, Dave Hachadorian, K6LL,
gave me the key suggestion that has me feeling better tonight!

Dave asked "Are you measuring swr at exactly the same point,
such as through any antenna switches or other accessories?"

I wasn't. But I did today.

Attaching the MFJ-259 to the same point as the transceiver
and retesting gave curves comparable to those by the transmitter/
wattmeter technique. Using a second W4 wattmeter gave curves
closer to the MFJ259 measurements and the SWR display on the
FT1000MP. My confidence in the MFJ-259 was restored today.

The SWR curves at the point the feedline entered the shack were
very good. The curves at the transmitter were not.

So, I started the process of eliminating from the signal path the
two wattmeters, the amplifier, the RCS8V remote switch, the
(bypassed) N4XM XMatch antenna tuner, and each of the
interconnecting cables.

I suspected the Ameritron RCS8V remote antenna switch that I
use in the shack to select antennas, but removing it made no
difference at all.

To make a medium-length story shorter, the problem was the
XMatch tuner. Although it was in "Direct" (that is, bypassed),
it raised the minimum measured SWR at the low end of 15m
(using either measure) from around 1.2:1 to 1.5:1 or 1.6:1!

The story is told in the curves shown at:
http://www.zing.com/album/?id=4293852949&p=4282615550&idx=72

(Click on the graph to see it full sized) The bottom three curves are
with the XMatch completely removed from the signal path, and the
top five curves are with the XMatch in the signal path, but set to
"direct" (bypassed internally). Adjusting the tuner controls while
bypassed did not affect the SWR measurement at all, so it wasn't
coupling to the internal components.

I'm going to do some more checking to see if the XMatch has a
similar effect on the other bands when bypassed, but for now I
think my 15 meter questions are answered! I also intend to open
the tuner and see if there's any obvious explanation for this behavior.

Thanks again to the eight guys who provided suggestions throughout
the day! It was a busy but productive day for me!

73,
Jeff Maass       jmaass@columbus.rr.com     Located near Columbus Ohio
         USPSA # L-1192       NROI/CRO    Amateur Radio K8ND
    Maass' IPSC Resources Page:  http://home.columbus.rr.com/jmaass


----- Original Message -----
From: "Jeff Maass" <jmaass@columbus.rr.com>
To: "towertalk Mail List" <towertalk@contesting.com>
Sent: Thursday, October 26, 2000 10:24 AM
Subject: [TowerTalk] ? Yagi Interaction on 15m: KT34XA and XM240


> 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?
>
> Jeff Maass       jmaass@columbus.rr.com     Located near Columbus Ohio
>          USPSA # L-1192       NROI/CRO    Amateur Radio K8ND
>     Maass' IPSC Resources Page:  http://home.columbus.rr.com/jmaass
>



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