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Re: 70cm antenna SWR problem solved?



Thank you Domenico,
I've actually studied all those links before. I would build a CP antenna as 
Howard, G6LVB has done except that I have nothing with which to measure the 
velocity factor of  the cable in the phasing harness. When it was working 
the 70cm linearly polarized did a pretty good job though. At least with the 
LEO's. Unfortunately I have no experience with HEO's.
73,
Michael, W4HIJ
----- Original Message ----- 
From: "i8cvs" <domenico.i8cvs@tin.it>
To: "Michael Tondee" <mat_62@netcommander.com>; "amsat-bb" 
<amsat-bb@amsat.org>
Sent: Thursday, June 05, 2008 8:46 PM
Subject: Re: [amsat-bb] 70cm antenna SWR problem solved?


> ----- Original Message -----
> From: "Michael Tondee" <mat_62@netcommander.com>
> To: "amsat-bb" <amsat-bb@amsat.org>
> Sent: Friday, June 06, 2008 1:30 AM
> Subject: [amsat-bb] 70cm antenna SWR problem solved?
>
>> After several unsuccessful attempts at solving my 70cm antenna problem
> while it was still on the mast, I resolved today to just go ahead and get 
> it
> down off there. Not that big a deal to do really and besides I've been
> thinking of rebuilding the whole shootin match anyway.
>> I was able to use my 2 meter SWR meter after a fashion once I got the
> antenna inside. I could see fluctuations in the amount of power the 
> antenna
> was taking as I tried various things. The problem lies in the area of the
> matching and feedpoint of the driven element. Again those of you familiar
> with the WA5VJB " cheap yagi" concept will know that the driven element is
> bent back upon itself forming a U shaped section on one side. Those less
> familiar with the design  might not understand this but there's something
> going on right there. Either with the spacing between the legs of the U or
> the braid and center conductor being too close together at that point 
> where
> they are soldered. Changing the spacing of the U legs didn't seem to help
> but spreading the center conductor and shield out from each other right
> where they  are connected to the DE made a marked difference. I suspect 
> it's
> because at this point they are very close to the "matching area" of the
> antenna. Hope that makes se!
>>  nse.
>> At any rate I have decided to rebuild both my 70cm and 2 meter antenna. I
> will keep 11 elements on 70cm but I'm going from 4 to 6 elements on 2
> meters. The other change will be to replace the boom material. I used PVC
> pipe before and the antennas have developed a bit of a sag along their
> booms. I will be using wooden booms coated with spar varnish this go 
> around
> and possibly add reinforcement if any sag appears evident. BTW, both of
> these are linearly polarized as I don't have an SWR analyzer to figure out
> velocity factor on cable while making phasing harnesses. Maybe someday!
>> Thanks much for everyones help and 73,
>> Michael W4HIJ
>
> Hi Michael, W4HIJ
>
> Before to rebuild your WA5VJB cheap yagi antenna look here:
>
> http://www.qsl.net/ve3cvg/antennas/cheapyagis/index.html
>
> here
>
> http://webpages.charter.net/w7my/cheap%20yagis%20designuhf-sw.pdf
>
> and here:
>
> http://www.g6lvb.com/HomebrewArrow.htm
>
>
> 73" de
>
> i8CVS Domenico
>
>


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