[Elecraft] K3 Ground Loop Issues using Ameritron ARB-704

[Jim Brown]

On Thu, 4 Jun 2009 19:43:30 -0400, Joe Subich, W4TV wrote:

>Unfortunately, the AL-82 and SB-200 both create a pseudo-neutral 
>by placing high voltage bypass capacitors from each line to the 
>chassis/ground.  Unless the chassis is properly grounded to the 
>station common point ground along with every other piece of 
>equipment in the shack, the noise (hum) s still going to appear 
>in common mode on the shields/cases. 

Actually, nearly ALL equipment powered from the AC line has 
capacitance between phase and ground, thanks both to stray 
capacitance in the power transformer and bypass capacitors that 
are part of line filters. This capacitance couples leakage current 
to the green wire (the equipment ground). The return path for this 
current is to the power system ground via the breaker panel, so 
there will be IR drop in the green wire. Because the coupling is 
capacitive, most of this current consists of the harmonics of 60 
Hz, and is what we commonly call "ground buzz."  

As Joe and Paul have noted, some older power amps improperly 
connect 120V fans between one side of 120V and the green wire. In 
addition to the IR drop issues, there this current generates a 60 
Hz hum field that can magnetically couple into the rig and/or 
interconnect wiring. This field tends to be pure 60 Hz, so is 
heard as HUM, not buzz. 

For a more detailed analysis of both mechanisms, see 

http://audiosystemsgroup.com/RFI-Ham.pdf  and 

http://HamInterfacing.pdf 

Another source of HUM is the magnetic field produced by the 
transformers in big power supplies. The unshielded audio 
transformers used in the K3 make it susceptible to strong magnetic 
fields. The above tutorials show how to reliably interconnect ham 
gear, computers, and other audio gear without transformers.  

73,

Jim Brown K9YC