[Elecraft] K2 VCO Shielding mod

[Ron D'Eau Claire]

I was one of the guys who, six years ago, found himself suddenly afflicted
by a bad-sounding signal from my newly-built K2. It was maddening because
every time I buttoned up the rig it would hum. When I pulled the cover off
to investigate, the hum went away. After going through that several times,
it occurred to me that when I "buttoned it up" I also put it back on its
perch atop my small linear power supply! It didn't help that in commercial
service we commonly mounted transceivers atop their power supplies for fixed
station use to avoid taking up unnecessary desk space. I had never seen a
problem with the magnetic field getting into the commercial transceiver.
Then again, those were 800 and 900 MHz FM transceivers with receivers that
suppressed any amplitude modulation. 

My power supply has long since been banished from the operating desk, but
since that hum is something that one cannot hear unless one checks the
signal with an oscilloscope or monitors it on a suitably well shielded
monitor receiver it seemed a good idea to take the precaution of installing
the mod. (The signal on a normal receiver often sounds bad simply because
very low level modulation inaudible a short distance away may come roaring
through, even with the receiver's antenna terminals shorted!) 

The mod doesn't make the K2 "bullet-proof" in terms of avoiding hum on the
signal if the rig is immersed in a magnetic field, but it sure helps! 

Ron AC7AC