XV-222 Oscillation during TX

[Mike & Becca Krzystyniak]

   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.

   So, I popped it on my spectrum analyzer and, while transmitting, there it
was, a strong osciilation at about 300 MHz.  Now, with 222 present it swamps
the oscillation so when you're sending CW, the oscillation is present
between the character spaces, and on the watt meter all you see is around
15-20 watts output. Or like FSK with a 78 MHz shift.

   Next I popped off the XV-22 top cover and of course the problem was gone.
I suspected that there was coupling from the PA output into the top cover
and back into an earlier stage causing this instability.  In fact, I can
hold the cover in my hands, and covering just half of the XVTR PA and it
starts oscillating.  Has anyone seen their XV-222 unit oscillate during TX
(sans an applied 222 signal)?  

   Oh, yea, everything has been sanded and grounded per the instructions and
as suggested by Wayne in the RFI emails.

   Has anyone seen this on their unit?  Is there a tech note or app note out
there on this?    

   Thanks in advance.

73  Mike K9MK/5   Haslet TX.


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[Myron Cherry]

Mike, I've had the very same problems with both my 222 and 432 transverters just as you.  With the top of the enclosure in place, it goes into oscillation.  With the top removed, problem solved.  I don't have the problem with my 144 transverter.  Also, I have found that I can't stack anything metallic on top of either the 222 or 432 transverters with the top of the enclosure removed or oscillation becomes a problem again.  I have replaced both top covers with plexiglass purchased from Lowes.  Easy to cut on the bandsaw.  All problems are now solved and it also looks cool. :-) 73....Myron....K4YA
 > From: [hidden email]

> To: [hidden email]
> Date: Sat, 20 Aug 2011 13:29:16 -0500
> Subject: [Elecraft] XV-222 Oscillation during TX
>
>    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.
>
>    So, I popped it on my spectrum analyzer and, while transmitting, there it
> was, a strong osciilation at about 300 MHz.  Now, with 222 present it swamps
> the oscillation so when you're sending CW, the oscillation is present
> between the character spaces, and on the watt meter all you see is around
> 15-20 watts output. Or like FSK with a 78 MHz shift.
>
>    Next I popped off the XV-22 top cover and of course the problem was gone.
> I suspected that there was coupling from the PA output into the top cover
> and back into an earlier stage causing this instability.  In fact, I can
> hold the cover in my hands, and covering just half of the XVTR PA and it
> starts oscillating.  Has anyone seen their XV-222 unit oscillate during TX
> (sans an applied 222 signal)?  
>
>    Oh, yea, everything has been sanded and grounded per the instructions and
> as suggested by Wayne in the RFI emails.
>
>    Has anyone seen this on their unit?  Is there a tech note or app note out
> there on this?    
>
>    Thanks in advance.
>
> 73  Mike K9MK/5   Haslet TX.
>
>
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>
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> Please help support this email list: http://www.qsl.net/donate.html

     
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[Stu2-3]

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
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