[Elecraft] Re: magnetic fields and phase noise?

[Bruce Bowman]

Hi Earl-

Here's a wild guess to throw in the mix. Since you have tried shielding 
and separation to eliminate or minimize the presumed radiated noise 
path, I'm beginning to wonder if the noise source is conducted via the 
power lines vs. radiated.

To validate the premise, perhaps you could conduct the same (different 
room) test, but instead of running just the coax over to the K2, try 
also running a large extension cord from the same outlet you would 
normally use in your shack. If the noise is indeed radiated, then you 
ought to see the same improved results; but if the noise is conducted, 
then I would expect similar results as if the K2 & Alpha were still 
co-located.

Just a thought.

Bruce, NM5B

----- Original Message ----- 
From: "Earl W Cunningham" <k6se at juno.com>
To: <g4bjm at hotmail.com>; <dbarker at visioncomm.net>; 
<elecraft at mailman.qth.net>
Sent: Saturday, March 19, 2005 9:27 AM
Subject: [Elecraft] Re: magnetic fields and phase noise?


> Fraser, G4BJM wrote:
>
> "Interesting Earl, the non exhaustive tests I've done indicate that it 
> is
> not due to magnetic fields."
> ----------
> When I first told Elecraft about this problem, they sent me the new
> shield for the KPA100, which didn't help.  Then they sent a mod kit 
> that
> had to do with reducing spurious RF, which didn't help.
>
> Then I eliminated the KPA100 as being the culprit by removing it (and
> installing the original cover).  Driving the amp (with only the 10 
> watts
> available) resulted in the same problem.  Clean when barefoot (as is 
> the
> KPA100).
>
> Then I manually keyed the amp (instead of using the KPA-100's key 
> output)
> -- no change in problem.
>
> Then I brought my K2/100 over to a friend's QTH and tried it with his 
> amp
> -- same problem.  Separation from his amp was 6 feet.  His amp is an
> Alpha 99, mine is an Alpha 76CA (both have hypersil HV transformers).
>
> Then, at my home QTH, I set up the K2/100 in an adjacent room and ran 
> a
> coax from it to the amp in the ham shack -- no trace of the problem.
>
> All tests were done on CW, monitoring the transmitted signal on 
> another
> receiver (FT-1000MP) using narrow (250 Hz) bandwidth.  The problem 
> sounds
> like noise on the sidebands of the transmitted CW signal extending out 
> at
> least +/-5 kHz from center freq.  There's no reason to believe that 
> this
> problem does not also exist on SSB.
> ==========
>
> "But if indeed that is the case, there must be a relatively easy, if
> perhaps not elegant, way of significantly improving this."
> ----------
> It has been suggested that mu-metal shielding might alleviate the
> problem.  I'm considering making mu-metal bottom and side covers for 
> my
> K2.
>
> Another ham (W4FMS) told me he had the same problem with his K2/100 
> and
> Alpha 87A amp.  He found that placing an aluminum cookie sheet between
> the K2 and amp with only 3 feet of separation resolved the problem.
>
> All things point in the direction of a K2 problem that is not phase
> noise.
>
> 73, de Earl, K6SE
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