[RFI] USB qrm - what to do?

[Robert Nobis]

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
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