[Elecraft] K3 Hum on Audio...

[Guy Olinger K2AV]

Hi Jim,

For a price and/or sufficient work and enough expertise, it might be
possible to shield anything.  There is that mu-metal stuff. But mostly
that level of induction from something pulling that much current into
microphone level devices is a really really hard cure, hence
"uncurable" in quotes. For equipment that is sold at ham-affordable
prices, and where most people do not have the problem, and it is a
layout choice, the level of shielding would seem a good commercial
choice by manufacturers.

Again, if one considers all these issues when one is CHOOSING one's
station layout, you really do not have to kick all those dogs and put
yourself in the position in the first place.

I WOULD expect YOU to be able to cobble something to make it work in
spite of a station layout that kicks the dogs.  :>)   But for the rest
of us for which that is endless experimenting and not necessarily
knowing WHICH detail of the fix we messed up when we tried it, not
kicking the dogs at all, when we don't have to, is a very profitable
direction.

73, Guy

On Fri, Feb 3, 2012 at 11:27 PM, Jim Brown <jim at audiosystemsgroup.com> wrote:
> On 2/3/2012 12:43 PM, Guy Olinger K2AV wrote:
>> This is an endemic "uncurable" problem.
>
> Maybe not.  One mechanism I suspect, based on the symptom that it
> happens with the Line Input turned up, is magnetic coupling into the
> unshielded audio transformer on the Line Input. That coupling is nearly
> always pure 60 Hz, without harmonics, and is a well known problem.. In
> data modes, the Line Input is rolled off sharply at some frequency like
> 200 Hz or so, which knocks the hum down by something like 18dB.. I
> recommend doing that for SSB too, because the lower octaves carry no
> intelligibility but can waste a lot of TX power.
>
> The separation that matters this this case is the generator of the
> magnetic field, usually the power transformer for a big power amp, but
> it can also be caused by wiring errors in the power wiring in a home. It
> can help a lot to rotate the amp to put its field at right angles to the
> magnetic receiver (the audio transformer in the K3), and also to move it
> further away from the K3.
>
> As to RFI with lines running past a computer -- I had that issue in
> Chicago, where I used a long wire antenna on 80 and 160, and it locked
> up the serial connection.  The culprit there was the K2 serial cable,
> which used PARALLEL wires inside a shield. I replaced it with TWISTED
> PAIRS without a shield, with one pair for each circuit used between the
> computer and the rig, with the return for each pair going to the chassis
> on each end, and the problem went away.  With the original cable, it
> locked up at 12 watts. With the twisted pair, I could run full power
> from my Titan 425.
>
> 73, Jim K9YC
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