TopBand: Shunt-fed tower probs - saga continues.

[Ron Stone]

I had a LOT of very helpful replies on this, and please forgive me if I
do not reply individually to all who gave me some excellent ideas. 

A partial solution has been found, primarily due to the advice given to
me by G3SED and others about connecting a strap from top to bottom of
the rotator casing. I also connected a strap from the top of the tower
to the stub mast, in case the head bearing was not providing a good RF
path. 

I also disconnected the feeder to my 40m yagi about 10ft below the tower
top (there is relay there) and it was not in circuit at the weekend. 

Those changes had a significant effect on the tuning of the Omega
capacitors so must have had something to do with the prob. I used the
tower for several hours during the contest and noted no drift in the
SWR. 

The issue now (thanks to N2IC/0 and others for raising it) is the balun
on the 40m beam. Is it doing it's job and choking RF? - unfortunately
topband RF in this case - and heating up causing the tuning drift ?.
We'll find out by reconnecting the feeder in the next week or so. 

Then if it is a prob, I wont want to take the beam down if I can avoid
it, so perhaps the fertile brains of the reflector subscribers can
suggest a less painful solution than more January tower work (relays ?)

I'll keep reflector readers informed. 

Bill W4ZV - apologies if this is a bit wide of the topband context for
the reflector but I've had at least 20 replies on this subject and it
seems pretty topband-centred to me !

73
Ron Stone
Vine Antenna Products - for World-Class RF Communications
Telephone +44(0)1691 831111
Mobile          0585 785659
Facsimile +44(0)1691 831386
Mail - The Vine
       Llandrinio
       Powys SY22 6SH
       Wales, UK

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