K2 Problem

[w2bvh]

I've got a problem with my K2 and would like some advice. S/N is around
1500, and I built it in mid 1999. No problems with it since.

The problem started with a complaint from a nearby (8 miles away) ham.
He was seeing regularly spaced spurs across his passband when I
transmitted FT8 (with a XV50 - 6 Meter transverter). I double checked
his complaint with a friend who is around 35 miles away. He saw the same
thing but the offending signal (of course) were much weaker.

I did a LOT of debugging of the system, assuming ground loop(s) were
causing the problem. I actually found and fixed some problems with
ground, but there are still spurs.

Recently I decided to stop focusing on ground and just simplify my
setup, which is quite complex (2 IF rigs, 7 transverters and multiple
power amps). Box by box, I disconnected things until I was left with
just the K2, a straight key and a dummy load. The spurs are still there.
Even the transverter is not connected. And to make sure that grounding
is not an issue, I powered the K2 for awhile off a battery. Probably
more interesting, the spurs are there even when the K2 is set for CW!

With the K2 set to CW and 28.100 MHz, the significant spurs are (with
respect to the carrier):

+558Hz -39.2 dB

+296Hz -36.7 dB

+178Hz -25.6 dB

-178Hz -25.5 dB

-306Hz -39.0 dB

-558Hz -40.0 dB

I also ran the K2 set for SSB  with a 2-tone generator into the mic port
and the IMD looks fine .. around -29.5 dB). But those same spurs are
present on either side of both tones. (I  didn't take actual
measurements but by eyeball it  looks like the same pattern as with CW).
I have no doubt these levels are strong enough to cause mischief on FT8.

The measurements were done with an HP8566, in good working condition,
and I trust it.

I can't imagine this is "normal" for the K2.

I left some phonemail at Elecraft asking for a callback a few days ago
so I could discuss this, and I'm sure I'll hear back from them some time
soon. (In this age of pandemics, I have no doubt they're overwhelmed).

But in the interim, is there anyone who's a real expert on the K2 who
would know a) how abnormal is this? b) what might be the cause?  I don't
think I'll  fixing  this myself unless some expert says something to the
effect of "Oh yeah, I saw that a few times, its usually caused by X".
Hopefully that's what will happen and I'll just fix "X".

Thanks in advance for any help.

73 & stay safe,

--Lenny W2BVH

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