TopBand: Shunt-fed tower - HELP !!!

[Ron Stone]

Greetings chaps.

I got some excellent reports yesterday from the East coast on my
repaired shunt fed tower. But every now and then the amp would trip out. 
Never done that on the dipole at 120ft (which is 2 s-units down on the
vert).

Also something very odd was happening. If I sent a string of dots, the
reflected power would creep up (and sometimes the "resonant frequency"
would creep up too) to the point where it would go up to amp cut-off
point in about ten minutes.

 I changed the feeder.
 I changed the jump leads from amp to power meter in the shack.
 I changed the shunt-wire, from all the way up the 105 ft tower spaced 1   
   foot, to the ON4UN 5ft out - 30 ft up version. (had to change to an 
   Omega match to match it.)
 I changed all the capacitors in the matching unit and checked for signs
 of burning. Nothing. The capacitors I am now using for the Omega are 
 0.125" between plates. Pretty meaty. 
 I checked the earthing of my radial system to the tower. Nothing bad
 there.
 I tested the amp with the dipole for a long time. no probs.
 I checked all the other cables in the installation (rotor - feedline 
 for the 40m beam) nothing wrong.  

I have just tomorrow to fix it. After all day today and half of
yesterday I'm clean out of ideas. Anyone got any suggestions on a fix
please. 

It's driving me round the bend !!!

73 and good luck in the contest. You may or may not hear me on !
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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