[Elecraft] XV-222 Oscillation during TX

[Stu2]

On 08/20/2011 02:29 PM, Mike & Becca Krzystyniak wrote:
>     Last night I was talking with a local on 222 SSB, and I noticed most of
> the lights on my XV-222 bar graph were staying on in TX, like it was in a
> peak-hold mode.  At the same time I noticed Hi-RFI alarm coming up on the K3
> display while transmitting.  A quick check and everything seemed tight, SWR
> was good, and no other rigs were on (at least in TX).  I did look at some of
> the reported RFI cases here on the reflector, but they seemed to be RFI into
> the XV-222 from other rigs.
The XV432 was giving me all kinds of trouble like your XV222, while 
preparing for the June VHF contest this year. It worked fine in the past 
with a solid state amp, but when I tried using a Henry 1KW amp, the XV 
oscillated and displayed similar symptoms as you describe. The XV has 
been modified as per the Elecraft site. I varied the coax lengths 
between the xv and amp, drilled holes to connect the top/bottom ground 
planes, double sanded the case, ensured the N connectors were tight, 
preset the amp loading using my TS2K as a driver, etc. All with varying 
success, but nothing permanent. Note, the xv never oscillated when I 
used a 50 ohm dummy load.

Our final solution (thanks to WA0DYJ) was to use a 50 ohm dummy load in 
parallel with the load using a T connector on the output. Luckily, there 
was still enough power to drive the amp. The combination worked well 
during the VHF contest.

BTW - we also use a XV222. It feeds a solid state amp and I think we 
have the right length of coax and load. I noticed we needed to be 
careful about routing the power and RF cables to ensure we don't 
introduce any RF back into the XV.

The Elecraft guys have been very responsive and helpful, but it seems we 
are fighting some sort of stray capacitance problem that may be inherent 
in the design/layout. So try the various methods mentioned. We didn't 
try the plexiglass cover.

Stu2
W7IY