Just thought I'd let you know what the problem turned out to be Bill...
I had started with a new 205BA which I'd had in storage...
I converted to a 205CA... but I missed something important...
The center 1 1/4" tubing is the same on both antennas EXCEPT for D1 where it
was increased from 21 to 37"...
I missed this during assembly, and D1 is 16" short. I substituted this into
the YO taper schedule, and the YO predicts the antennas performance
exactly... resonant at 13.85, F/B about 16db instead of 20+ and a lost of
about 1/3 db gain. Funny that shortening the director lowers the resonant
point! Not what I would have expected...
As soon as the weather improves (very windy), I will correct this error. But
it's not so urgent, as the gain is not compromised very much...
Thanks for your interest.
----- Original Message -----
From: "Mel Martin" <ve2dc@rac.ca>
To: "Bill Cotter" <n4alg@qx.net>
Sent: Monday, November 03, 2003 13:08
Subject: Re: hygain 205ca swr question
> Funny... my experience exactly...
>
> I think it's working well... hard to tell with the bands last night and
this
> morning...
>
> My swr is approximately
> 13.8 1.2
> 13.9 1.1
> 14.0 1.3
> 14.1 1.7
> 14.2 1.9
> 14.3 2.2
>
> yet the pattern seems very good, with F/B falling off rapidly at about
> 13.85... as predicted
>
> I used YO for the 3 antennas... and the 105/155 were pretty much exactly
as
> predicted.
>
> I "optimized" but didn't move the elements to preserve the wind/weight
> balance...
>
> But YO had predicted min SWR at 14.175, and I'm not even close!!! I'm also
> using a choke balun. Any thoughts as to what is amiss?
>
> A quick run through with the modeling program indicates that the shorting
> strap won't resolve it... I have to shorten the DE considerably.
>
> BTW, tilting is difficult because of other antennas and guy-wires... so
I'll
> probably have to lower it eventually.
>
> I think I might just use the recommended Hy-gain settings... they are not
> that different from my optimized design...
>
>
> ----- Original Message -----
> From: "Bill Cotter" <n4alg@qx.net>
> To: "Mel Martin" <ve2dc@rac.ca>
> Sent: Monday, November 03, 2003 12:47
> Subject: hygain 205ca swr question
>
>
> > Mel,
> >
> > I have a highly modified 205CA (converted to optimized 4ele20m on
> > 36ft boom for 100mph), and had the same experiences you described.
> > This antenna retains the HG-205 beta match on the driven element
> > with the BN-4000 balun. On the ground, it matched fine (pointed
> > up). At 85ft it was resonant at 13.800, hi! Had to tilt the antenna
> > several times to adjust the beta shorting strap to make it resonant
> > at 14.050mHz.
> >
> > Using a computer, YO to generate the electrical data, and YS to
> > generate the mechanical stuff - the antenna plays incredibly well.
> > I will be moving it to the backyard tower (Rohn-45 at the 120ft
> > level) and hope to see some even better performance.
> >
> > Unless you are driven to get it on the mark, as I was, using a
> > tuner to get the match right will suffice. The relationship of the
> > elements will keep the performance where it belongs.
> >
> > 73 bill n4alg
> >
> >
> > At 11:49 AM 11/3/2003, you wrote:
> > >I sure wish it was that easy! no... it won't work... not even a
> > >meaningful
> > >reading is possible that close to the ground.
> > >
> > >Pointing it in the air, reflector down, will tell you if you are
> > >in the
> > >ballpark, but you can't "tune" the antenna that way.
> > >
> > >I just put up a 205CA yesterday 150' in the air on a guyed tower...
> > >
> > >damn thing is resonant at 13.8 ????
> > >
> > >A 105 and 155 we also put up are right on the money... I'm not
> > >sure where I
> > >went wrong with the 205...
> > >
> > >It works great, good pattern, just SWR too high... so I think I'll
> > >"fix" it
> > >when the WX improves next Spring...
> > >
> > >But in retrospect I wish I had done the "point in the air"
> > >thing... might
> > >have spotted a problem.
> > >
> > >BTW, I like EL34's also...
> > >
> > > > I just put together my 205ca today and put it up on sawhorses in my
> > >backyard.
> > >Is this still too close to the ground to get an accurate reading?
> > >
> > >_______________________________________________
> > >
> > >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.
> > >
> > >_______________________________________________
> > >TowerTalk mailing list
> > >TowerTalk@contesting.com
> > >http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
> > ----------------------------------------------------------
> > Bill Cotter, N4ALG E-mail: n4alg@qx.net
> > 173 Carolyn Lane Home: (859) 887-5563
> > Nicholasville, KY 40356-9340 Work: (859) 323-6474
> >
> > ARRL ARCI #9878 QRPl #1646 QCWA #29393 FISTS #4535
> > ----------------------------------------------------------
> >
>
_______________________________________________
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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