[Elecraft] ATU Flashover

[Mike Fatchett W0MU]

Are you running your K3 tuner into the amp?  If so, shouldn't' the amp be
giving the radio a nice match to start with?  Are you running a tuner after
the amp as well?   If you are running the K3 tuner, turn it off.
 
Is this on the exact same frequency or are you switching between the cw and
ssb portions.  What freq is the antenna tuned for?

  _____  

From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of G4MKP
Sent: Friday, October 17, 2008 8:47 AM
To: elecraft at mailman.qth.net
Subject: [Elecraft] ATU Flashover



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

 

 

 

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