Fwd: Re: K2 Problem

[Don Wilhelm]

Sorry folks,  I did not copy my reply to Lenny to the reflector.
I will likely follow up with him by private email as he works through
the problem, but I thought some might be interested in what I initially
had to say.

73,
Don W3FPR

-------- Forwarded Message --------
Subject: Re: K2 Problem
Date: Sat, 17 Oct 2020 13:11:23 -0400
From: Don Wilhelm <[hidden email]>
Reply-To: [hidden email]
To: w2bvh <[hidden email]>

Lenny,

In my experience with over 1000 K2 repairs, I have never seen anything
like that.  But I would look first at the PLL/VCO area, and possibility
the BFO.

If you have a good monitor receiver, scan the signal at TP3 (near 12,000
to 12,100 kHz) to see if the problem is present there.
Next would be the VFO at TP1 - the frequency will be determined by the
band you are on - consult the VCO Table chart on the schematic Key page
in the manual.

If all is well above, check the BFO at TP3 - you will have to set the
menu CAL FCTR to get a signal there.

If all those are clean, then the problem has to be some sort of strange
coupling somewhere in the transmit chain (or a failing component)

If it is in the VFO, add the VFO ALC change, if it is in the BFO, then
add the K2BFOMDKT.

73,
Don W3FPR

On 10/16/2020 9:31 PM, w2bvh wrote:

> 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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