[TowerTalk] Is my 5 el 10 detuning my 4 el 40? ?

[AA6DX]

I concur ... it is not the 10M causing that problem, for sure!  73 --- Mark
../ AA6DX
----- Original Message ----- 
From: "Michael Tope" <W4EF at dellroy.com>
To: "Scott R." <w4pa at yahoo.com>; <towertalk at contesting.com>
Sent: Monday, July 07, 2003 1:12 PM
Subject: Re: [TowerTalk] Is my 5 el 10 detuning my 4 el 40? ?


> Scott,
>
> A couple of questions:
>
> 1) Where are you measuring the impedance - at the
> feedpoint or through a length of coax?
>
> 2) If through a length of coax, how long and what type?
>
> 3) Did you cross over the conductors of the parallel metal
> strip feedline on the 40 meter dual driven element to get
> the 180 deg phase shift?
>
> 4) Are you sure the metal strips that form the parallel
> feedline on the 40 meter dual driven element aren't
> shorted together?
>
> If you are measuring thru a feedline, my guess is
> that you have a short somewhere on the parallel
> strip transmission line. The periodic variation of the
> impedance would be consistent with a short circuit
> being rotated in phase around the smith chart by
> a ~200' long feedline. The 5:1 (versus infinite)
> VSWR would be due to the finite loss of the
> transmission line (~1.7dB one-way loss). If the
> short is far enough from the balun (~1/4 wave),
> it will get reflected back to the balun as an
> open. This would explain why you might get good
> VSWR on 15 meters (the driven elements of the
> 40M4 are resonant here) where the distance
> between the driven elements on the 40M4 is
> probably getting close to a 1/4 wave on 15
> meters. You can check for this by disconnecting
> the metal strip feeders from the balun so you
> are only using 1 driven element. If there is a short
> on the other end of the metal strip line, you should
> see a dip in VSWR at around 7 MHz when you
> disconnect it from the feedpoint.
>
> I doubt the 10 meter antenna is having much
> affect.
>
> 73 de Mike, W4EF.....................
>
> ----- Original Message -----
> From: "Scott R." <w4pa at yahoo.com>
> To: <towertalk at contesting.com>
> Sent: Monday, July 07, 2003 12:32 PM
> Subject: [TowerTalk] Is my 5 el 10 detuning my 4 el 40? ?
>
>
> > Put your heads together and help K4JNY and myself come up with a
> > solution to this problem:
> >
> > KLM 4 el 40m beam at 120 feet, 5 el 10 meter beam on a 28' boom at 125
> > feet on the same mast.   45G tower guyed with Phillystran.
> >
> > The KLM antenna is (was) new in box and was built with all WØUN mods
> > and all DX Engineering hardware.   It's in the air, and exhibiting some
> > weird behavior.
> >
> > According to our MFJ 259B antenna analyzer, the SWR is about 5:1 from
> > 1.8 to 20 MHz.  At 20 MHz, SWR slowly drops to flat, remains flat to
> > about 22 MHz, then rises back up to where it was.
> >
> Are you talking about the 40 meter antenna or the 15
>
>
> >
> Every 800 kHz to 1 MHz of spectrum, we can see the antenna impedance
> > dip from about 400 ohms down to about 12 ohms and then rise back again.
> >   SWR does not vary when this happens - indicates the same value of
> > about 5:1, until the dip at 20 to 22 MHz.   We tried the same procedure
> > with an HF radio and got the same results.
> >
> > The antenna does have some pattern, we can tell by rotating it and
> > listening to stations on 40 in different locations.
> >
> > What we have tried so far:  Swapped out the 4:1 balun with a different
> > 4:1, then a 1:1 just for the heck of it.  No change was noted.  Nothing
> > appears to be disconnected or shorted and we were very meticulous when
> > assembling the antenna to not miss anything, use Penetrox on all
> > connections and NyLok hardware, etc.  Different feedlines were tried -
> > all act the same.
> >
> > The only thing we can think of is that the 10 meter beam is severely
> > detuning/interacting with the 4 el 40.   We tried shorting the 10 meter
> > coax out to see if it had any effect on the 40m - no effect (which
> > makes us wonder if it is, in fact, this.)
> >
> > What we plan to try next:
> > Rotating the 10m beam 90 degrees off the 40m beam.
> > If that doesn't work, pull the 10m beam down off the tower.
> >
> > Are we crazy?  Or is there something we haven't thought of?    We've
> > been puzzling this over for the past two days and have decided we just
> > "don't get it".  Any help?
ask for Sherman, W2FLA.
>