The best way to handle the problem is to assume the new antenna made an
impact on the match. The first step would be to measure the actual
resistance and if it is not 50 ohms, reset the tap for 50 ohms. Then
measure the J again and you can easily calculate the amount of C
required to cancel the J. Anything else is just guessing.
On 12/12/11 11:38 AM, DL2OBO wrote:
> AFAIK all Optibeam elements are always isolated from the boom. So there
> shouldn't be any additional toploading from them (elements), just the
> loading from the boom should be considered
>
> 73 Tom
>
>
> DL2OBO (T88DL)
> Carsten-Thomas Dauer ( Tom )
> c/o Hotel Hellers Krug
> Altendorfer Str. 19
> D-37603 Holzminden
>
> www.dl2obo.com Ham-Radio
> www.hotel-hellers-krug.de my hotel / rent-a-shack
> www.carstendauer.de photografy
>
> -----Ursprüngliche Nachricht-----
> Von: topband-bounces@contesting.com [mailto:topband-bounces@contesting.com]
> Im Auftrag von Mike& Coreen Smith
> Gesendet: Montag, 12. Dezember 2011 16:30
> An: topband@contesting.com
> Betreff: Re: Topband: Changes To My Shunt Fed Tower
>
> Hi Bob,
>
> If I recall (correctly).<and you should double check> The D40 is completely
> isolated from the mast, so it would be nearly invisible to your 160m
> RF...given all the other loading you have going on there.
> I don't know a thing about the Optibeam...is it also isolated or grounded?
> I am guessing grounded, as you now have a change.
> If that IS the case, you'll need more capacitance to counteract the loading
> you've added. As to the amount, I could only hazard a guess. If you've
> maxxed out your 1000pF air variable, you can add some random length of
> RG-214 or other coax in parallel and start hacking off a foot at a time, and
>
> then tweak with the cap as neccessary.
> It's cheap and saves climbing ! I forget at the moment how many pF RG-214
> or other similar dielectric coax is, but maybe 10-15pF per foot springs to
> mind. Try adding 10 or 15' on and see what you can do with your cap.
>
> My brain is still numb from ARRL-10 CW this weekend...I keep hearing "T E S
> T, V E 9 A A" in my ears , hi !
>
> DIT dit,
>
> MIke
>
> ----- Original Message -----
> From: Bob Garrett
> To: 'Jim F.' ; 'top Band'
> Sent: Sunday, December 11, 2011 1:21 PM
> Subject: Topband: Changes To My Shunt Fed Tower
>
>
> Hello Topbanders,
>
> It is getting cold in the Northeast and as I get older, I dislike the cold
> even more.
>
> In April of this year, I replaced my Cush craft D40 40 meter rotable
> dipole
> with an OptiBeam OB-4030 dipole for 30 and 40 meters right at the top of
> the
> mast. The overall length of the antenna is about ten feet longer and I am
> assuming that it has added some additional capacitance to my 100 foot
> shunt
> fed tower with a Cush craft X7, A3WS, 5 EL M2 6 meter yagi and the new
> OptiBeam dipole.
>
> My match on the tower went from 1.0 x 1. To 1.9 x 1 after I installed the
> new antenna. In terms of loss, this isn't a huge change but my amplifier
> doesn't like the change. Before I spend a lot of time running back and
> forth to the tower making random changes, any thoughts as to what I can do
> to improve the match. I'm currently using one series capacitor 1000PF for
> the matching network. I have attempted to adjust this capacitor but it
> looks like the 1.9 x 1 is the low point. Perhaps some thoughts - increase
> or decrease the spacing of the shunt wire? Move the connection up or down
> on the tower?
>
> Before I get to crazy, just wanted to look to the base of knowledge on
> this
> reflector for your input.
>
> 73 and tnx in advance.
>
> Bob K3UL
>
>
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
>
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