[Elecraft] ATU Flashover

[Darwin, Keith]

When you switch from CW to SSB are you also changing frequencies from
the CW subband to the SSB subband?  If so, repeat your test on the same
frequency.
 
My simple world view makes this one easy to solve.  Stay on CW :-)
 
- Keith N1AS -
- K3 711 -

________________________________

From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of G4MKP
Sent: Friday, October 17, 2008 10:47 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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