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
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