[RFI] USB qrm - what to do?

[Gary Smith]

How is your station grounded?  Trusting the old "attach it to the water 
pipe, that'll be fine"? Sounds like ground looping to me.

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.

Gary...wa6fgi


On 3/13/2017 7:48 AM, Robert Nobis wrote:
> Pete,
>
> Besides using quality shielded USB cables, make sure that your computer is also separately grounded to your common station ground with a one inch ground strap. In other words don’t rely on the ground pin of the AC power line.
>
> 73,
>
>
> Bob Nobis
> n7rjn at nobis.net
>
>
>> On Mar 13, 2017, at 04:31, Pete Smith N4ZR <n4zr at comcast.net> wrote:
>>
>> My shack computer has 6 different USB devices attached.  When I disconnect all but the keyboard, it cuts the background noise level on 160M by a whopping 25 dB, from S9+18 down to S8 (as monitored by HDSDR and my QS1R, calibrated by an Elecraft XG3).
>>
>> What is to be done?  It doesn't seemvery feasible to wind each usb cable on a small type 31 toroid and get enough attenuation .  Available snap-ons all seem to roll off dramatically below 25 MHz. Can a common mode filter be built using discrete components that will have decent attenuation at 160 M? Or, maybe, is such a filter available commercially?  I have Googled and reviewed K9YC's tutorial but found nothing directly apposite.
>>
>> Thanks for any ideas!
>>
>>
>> -- 
>>
>> 73, Pete N4ZR
>> Check out the Reverse Beacon Network
>> at <http://reversebeacon.net>, now
>> spotting RTTY activity worldwide.
>> For spots, please use your favorite
>> "retail" DX cluster.
>>
>> _______________________________________________
>> RFI mailing list
>> RFI at contesting.com
>> http://lists.contesting.com/mailman/listinfo/rfi
>>
> _______________________________________________
> RFI mailing list
> RFI at contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi