[Elecraft] K3 Hum on Audio...

[Jim Brown]

On 1/13/2012 10:30 AM, Phil Hystad wrote:
> I disconnected EVERYTHING.  Nothing on the back panel of the K3 at all except for a Li-nano-phosphate battery as my power source.

Was your antenna connected?  If so, where is the coax shield connected 
to ANYTHING -- the earth, other gear, at a tower, etc.?  These are all 
paths for AC leakage current, and your K3 can be in that path.

>    All AC off at the breaker panel for this room.  The only electrical equipment on was my K3 via the battery and my Macbook Pro laptop via its battery.
>
> Given those conditions, the hum was still there.
>
> Jim Brown suggested that I consider TXEQ to cut off the low frequencies,  I did max cut for all frequencies up to 400 Hz.  The hum did not start being attenuated until 400 Hz cut.  But, max cut on 400 Hz did not attenuate it completely.  I did not do higher frequencies.

Then what you have is BUZZ, NOT HUM. HUM would be affected ONLY by the 
60 Hz  frequency band.  The coupling mechanisms are entirely different. 
That's why it was my first question!

BUZZ is leakage current from the AC mains power, OR, as Ron suggested, a 
flaky shield connection of the mic.  BUZZ is almost never due to 
magnetic coupling, so magnetic shielding doesn't matter.  What DOES 
matter is ELECTRIC shielding, which is what the cable shield provides.  
And MAIN thing that matters is BONDING -- CHASSIS TO CHASSIS, and from 
the combination of those chassis to the station ground, AND to the power 
system ground.

Study   http://audiosystemsgroup.com/HamInterfacing.pdf

73, Jim Brown  K9YC