[TowerTalk] adjusting insulated wire dipole

[Pete Smith]

Something I came to relatively late in my ham life is the realization that 
you can adjust the resonance of antennas where you only have access to one 
end, just by lengthening or shortening that one end.  I have a K3LR-style 
lazy-vee dipole array for 40, and have adjusted all 4 dipoles at their 
bottom ends to bring their lowest SWR frequency up into the CW band, by 
folding the insulated wire back on itself.  The change in resonance seems 
to track nicely with what would be expected if I had cut off the extra 
length instead of folding it back.

73, Pete N4ZR

At 03:28 PM 11/30/2004, Jim Lux wrote:

>My practical experience with tuning a multiband dipole (where you have
>separate elements for 40,20, and 10) is that folding the elements (or
>wadding it up in a ball) is a great way to adjust it, because you can
>shorten easily, and then lengthen again when you decide that you
>overshortened.
>As for adding capacitive loading.. it might, but it's probably not hugely
>significant (you're basically increasing the effective diameter of the
>wire). I doubt that the capacitive loading is enough to shorten the antenna
>enough to make a difference in, for instance, the SWR bandwidth. You're
>probably talking about a foot or two out of 40-50 feet, which isn't a huge
>difference from the bandwidth/Q standpoint.
>
>In any case, you're adjusting it by trimming, not calculation, right? so any
>effects from the extra length just wind up changing the optimum tune point.
>I assume that you'll leave it folded up forever, once you've found the
>point?  Or are you planning on cutting off the extra?  If the latter, then,
>you do have a problem, because, while the overall antenna performance won't
>change much, the wire will change the resonant frequency.
>
>
>Jim, W6RMK.
>----- Original Message -----
>From: "Ken Kinyon" <w7ts at comcast.net>
>To: <TowerTalk at contesting.com>
>Sent: Tuesday, November 30, 2004 10:06 AM
>Subject: [TowerTalk] adjusting insulated wire dipole
>
>
> > I am building a trapped inverted vee from insulated wire.  I expect that
> > there will a lot of length adjustment to be done on each segment before I
>am
> > happy with the center frequencies.
> > My thought is to leave extra wire (still insulated)  folded back along the
> > length of the segment and clamp it.  I seems to me that this should act
>like
> > capacitive end loading on each segment and increase the electrical length.
> > Is this correct?  Is the amount enough to be significant?
> > Thanks,
> > Ken W7TS
> >
> > -------------------
> > Kenneth E.  Kinyon
> > 34 Princeton Circle
> > Longmont, CO 80503-2106
> > -----------------------
> > E-mail: W7TS at comcast.net
> > ------------------
> >
> >
> > _______________________________________________
> >
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>
>See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless 
>Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with 
>any questions and ask for Sherman, W2FLA.
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