[RFI] USB qrm - what to do?

[Jim Brown]

On Mon,3/13/2017 9:19 AM, Gary Smith via RFI wrote:
> How is your station grounded?  Trusting the old "attach it to the 
> water pipe, that'll be fine"? Sounds like ground looping to me.

There is no such thing as a "ground loop."

>
> Most ground looping problems, to me this is what your describing, can 
> be cured by going back to the basics. That is, a 6 or 8 foot ground 
> rod driven into the dirt (ground) nearest your shack. If you can't 
> find or don't want to spend the bux for 1.5 wide copper strapping, 
> take a old piece of coax, marry the center conductor to the shield, 
> then rung it into the shack. Hook each piece of equipment to the coax, 
> (don't series them) see if that doens' help reduce the noise level.  
> Sounds as if you have lots of little antennas looking for any signal 
> of any kind, and, finding quite a few.

WRONG!  The earth is not a sump into which noise is poured. The ONLY 
reason for a connection to Mother Earth is LIGHTNING protection. Those 
recommending proper chassis-to-chassis bonding of everything in the 
shack, and from there to all other grounds in the house, are on the 
right track. Also, those recommending multi-turn ferrite chokes on 
interconnecting cables. And so is the recommendation to figure out WHICH 
device(s) are generating the noise.

I wrote a long tutorial for NCJ that ran in two parts last summer. It's 
on my website as a pdf. In it, I told how my neighbor, W6GJB, tracked 
some nasty noise in his shack down to USB speakers that were powered 
from the USB line. My guess is that they contained a DC-DC converter to 
run the amp that drove the speaker. In that tutorial, I list four 
specific ferrite parts, list a haf dozen vendors who sell them at good 
prices, and suggest number of turns for the ham bands where you're 
experiencing noise.

Some noise sources must simply be thrown away, like that noisy computer 
Chet encountered, and W6GJB's powered computer speakers. And switch-mode 
power supply wall warts.  Study the tutorial.

k9yc.com/publish.htm

73, Jim K9YC