[Elecraft] K3 Microphone Hum

[Bill Breeden]

I noticed an AC hum in the monitor audio in my headphones while calling 
with one of the W1AW portables.  While wondering if the hum was really 
in my transmit audio, the W1AW Operator came back to me and reported the 
hum.  I use a Heil Proset K2/K3 via the front panel microphone connector 
through a Kenwood style (red band) Heil pigtail.  After completing the 
QSO I switched to Test mode and I could still hear the hum when I 
transmitted.  Thinking I had a poor connection, I disconnected and 
reconnected both ends of the pigtail, but the hum persisted.  While 
doing that I noticed there was no hum if I activated the push to talk 
with microphone unplugged from the pigtail.  That had me baffled for a 
few moments until I remembered that the Proset K2/K3 requires bias 
voltage from the K3.  At that point I used the "2" button in the "MIC 
SEL" menu to turn the bias off and on a few times and the hum was 
disappeared.  I haven't researched the details of the bias switching 
arrangement in the K3 but it appears that mine needed some exercise to 
clear a bad connection.  I thought I would pass this on to the rest of 
the group in case someone else encounters this issue.

73,

Bill - NA5DX