Topband: Changes To My Shunt Fed Tower

[Herb Schoenbohm]

Bob,  To avoid the trips up and down the tower in the winter merely add 
an Omega cap from the shunt to ground,  You can start with a bread 
slicer and replace with a fixed mica later when yu find what you need.
IMHO I would replace, when you can, the shunt wire with a three or four 
wire cage feed as this will broaden out your B/W response significantly. 
If you don't want to try an Omega match then i recommend a CLC network 
rather than a straight series Cap.


Herb, KV4FZ


On 12/11/2011 1:21 PM, Bob Garrett wrote:
> 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
>
>
> _______________________________________________
>