K3/100 into DX-CC antenna (HI-SWR)

[Jay Krishna]

Hi all,
 
Just spent the day putting up a multi-band DX-CC (fan dipole, 80-10M) in an inverted V configuration. Unfortunately, I could not get the center mast extended beyond 20 feet, with one end up ~9 feet from ground, the other, ~5 feet from ground. I am seeing HI-SWR on all bands. Any suggestions on what might be the issue? I was able to get decent SWR with my old 20M monoband dipole, 30 feet up.
 
I have heard that the DX-CC is sensitive to height above ground, and am concerned that 20 feet might be too low. On the other hand, I was hoping it will at least tune well on 20 M at that height, if not all the bands...
 
Appreciate any ideas/suggestions. I don't have an ATU in my K3/100, and was hoping a multi-band fan-dipole like the DX-CC would work well without need for an ATU.
 
73,
 
Jay (KD6AMA)    
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[Jay Krishna]

Sorry for the multiple emails; on more careful checking, I found that the SWR is nice and low on 40, 15 and 10. High (3+) on 20 and 80, so I must have some mismatch on just 20 and 80.
 
Jay
 



From: [hidden email]
To: [hidden email]
Subject: K3/100 into DX-CC antenna (HI-SWR)
Date: Mon, 31 Dec 2012 18:34:20 -0800




Hi all,
 
Just spent the day putting up a multi-band DX-CC (fan dipole, 80-10M) in an inverted V configuration. Unfortunately, I could not get the center mast extended beyond 20 feet, with one end up ~9 feet from ground, the other, ~5 feet from ground. I am seeing HI-SWR on all bands. Any suggestions on what might be the issue? I was able to get decent SWR with my old 20M monoband dipole, 30 feet up.
 
I have heard that the DX-CC is sensitive to height above ground, and am concerned that 20 feet might be too low. On the other hand, I was hoping it will at least tune well on 20 M at that height, if not all the bands...
 
Appreciate any ideas/suggestions. I don't have an ATU in my K3/100, and was hoping a multi-band fan-dipole like the DX-CC would work well without need for an ATU.
 
73,
 
Jay (KD6AMA)
     
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[Rose]

Hi Jay !

I suggest that you need to use ... borrow? ... some sort of an antenna
analyzer such as an MFJ-259B and find the points on each band where
the antenna -is- resonant.  The resonant points on some bands will be
quite narrow (80M), but I'd think you can adjust the lengths of the dipoles
to make the antenna resonant on portions of the bands that are of interest.

I have one here that I use for a general purpose receiving antenna for my
K3's second receiver, so low SWR resonance isn't so important.

Bear in mind that like all "fan" dipoles, there is considerable interaction
between the elements and length adjustments on a given band will almost
certainly impact the other bands.  You're likely to "chase your tail" as
you try to make it satisfactory on all bands it's supposed to cover.

An antenna tuner will be almost mandatory.

73!

Ken - K0PP
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[alsopb]

Jay,

I had one of these in my attic for several months.

I had to tune each band by generally shortening the elements.

Start at 10M.  Find its resonant point via antenna analyzer or by
"sweeping" frequencies with your SWR meter.  You need to confirm that
the resonant point is too low before trimming.

If the frequency is only about 100 KHz too low, pull some wire from the
end insulator out and wrap it about the incomming wire to the insulator.
  Otherwise you have to cut it.

Proceed to the next higher frequency band and do the same.  Recheck the
lower band again.  There is some interaction.

When you are done, all bands should present a decent SWR.  I had to take
a lot of wire off the 40M section beyond the trap.

The difficulty with this is that if you move the antenna to another
location, it will need to be re-pruned.  The advantage is that you don't
need a tuner.   While you're at it, remove the spike suppression "pill".
  It is almost inevitable that it will get shorted sometime in the
future if your running any higher power level.

73 de Brian/K3KO


On 1/1/2013 03:49, Ron D'Eau Claire wrote:

> Yes. A horizontal, or semi-horizontal, antenna is sensitive to height above
> ground. You want to be about 1/2 wavelength up for optimum DX results. The
> way the radiation interacts with the earth provides additional gain - up to
> 6 dB - at those heights.
>
> Your "inverted V" configuration provides some vertical polarization that has
> a lower radiation angle, but it's not much.
>
> It will be effective for at least short skip down to about 1/4  wavelength
> above ground where the main lobe is straight up and will scatter off of the
> ionosphere. That's what many Hams today call a NVIS (Near Vertical Incidence
> System) antenna. At lower heights the main lobe continues to point straight
> up but with less and less strength as more of the RF is absorbed by the
> earth.
>
> What you've run into with the SWR is exactly why tuners are so popular. It's
> very difficult to get an antenna to show a low SWR, especially on several
> bands, without one.
>
> 73, Ron AC7AC
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Jay Krishna
> Sent: Monday, December 31, 2012 6:34 PM
> To: [hidden email]
> Subject: [Elecraft] K3/100 into DX-CC antenna (HI-SWR)
>
>
> Hi all,
>
> Just spent the day putting up a multi-band DX-CC (fan dipole, 80-10M) in an
> inverted V configuration. Unfortunately, I could not get the center mast
> extended beyond 20 feet, with one end up ~9 feet from ground, the other, ~5
> feet from ground. I am seeing HI-SWR on all bands. Any suggestions on what
> might be the issue? I was able to get decent SWR with my old 20M monoband
> dipole, 30 feet up.
>
> I have heard that the DX-CC is sensitive to height above ground, and am
> concerned that 20 feet might be too low. On the other hand, I was hoping it
> will at least tune well on 20 M at that height, if not all the bands...
>
> Appreciate any ideas/suggestions. I don't have an ATU in my K3/100, and was
> hoping a multi-band fan-dipole like the DX-CC would work well without need
> for an ATU.
>
> 73,
>
> Jay (KD6AMA)  

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