[Elecraft] ATU Flashover

[G4MKP]

Problem on 80m SSB.

 

I am experiencing what I can best describe as ATU Flashover on 80m SSB. 

 

Background - I have a K3 and Challenger 3 linear amplifier. Headgear is the
Heil Proset plus. I can tune up the rig and amp to well in excess of 500W
without any problem. CW can be operated at full power without any problems.
However, when I modulate the radio using SSB on 80m at anything above approx
275W, the SWR goes from 1:1 to infinity and I can hear the ATU flashing
over. It also occurs when modulating the radio using AFSK for RTTY
operation. Opening the ATU reveals arcing between the capacitor plates. The
problem does not occur on any other band.

 

Grounding - all equipment is individually wired to a central rf earth point
which is connected to a buried copper earth rod. I have a further 4 copper
rods connected to the previously mentioned rod that are spread over a few
feet.

 

Antenna - 80m inverted L with six radials spread over about 45 degrees.

 

I don't have another rig at present to substitute.

 

Any idea what's going on please?

 

Cheers,

 

Terry

G4MKP

 

 

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.qth.net/pipermail/elecraft/attachments/20081017/c5c15160/attachment.htm