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@nobis.net
> On Mar 13, 2017, at 04:31, Pete Smith N4ZR <n4zr@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.
>
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