[Elecraft] K3 Line In hum

[Jack Smith]

Of course if one does not wish to perform surgery on the K3, it would  
be possible to set up a 3-dimensional Helmholtz coil around the K3 fed 
with 50 or 60 Hz line voltage and adjust the X, Y and Z Helmholtz drive 
(level and phase) to null the ambient field at the offending transformer(s).

Jack


Jim Brown wrote:
> On Tue, 07 Jul 2009 13:13:57 -0400, Jack Smith wrote:
>
>   
>> Another alternative is to replace the transformers with shielded 
>> versions, assuming space on the PCB is available and a shielded 
>> transformer with the same electrical specifications and footprint 
>>     
> is 
>   
>> available.
>>     
>
> Or simply eliminate the transformers. They are totally un-necessary 
> if you do the simple chassis bonding shown in my Ham Interfacing 
> tutorial. 
>
> http://audiosystemsgroup.com/HamInterfacing.pdf  
>
> More stuff, in words, in  
>
> http://audiosystemsgroup.com/RFI-Ham.pdf  
>
> See the chapter on Solving Problems In The Shack. 
>
> Another thing to try before digging into the rig. If Elecraft has 
> followed my recommendation and made TXEQ work on the LineIn, you can 
> Use TXEQ with maximum cut on the two lower frequency bands. This is 
> good engineering practice to maximize communications audio quality 
> anyway, and it should suppress 50/60 Hz by about 20 dB (15dB for the 
> lowest filter, plus a few more dB from the skirt of the next highest 
> filter). 
>
> This problem with magnetic field susceptibility is well known. My 
> neighbor, K6XX (who as it happens also works part time as an 
> engineer for Elecraft) has so much magnetic coupling to his K3 from 
> a big power supply that it regenerated to 500W when he tried using 
> the LineIn for RTTY.   
>
> 73,
>
> Jim Brown K9YC
>
>
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