Topband: Changes To My Shunt Fed Tower

[DL2OBO]

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 at contesting.com [mailto:topband-bounces at contesting.com]
Im Auftrag von Mike & Coreen Smith
Gesendet: Montag, 12. Dezember 2011 16:30
An: topband at 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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