[RFI] USB qrm - what to do?

[David Harmon]

I use Logitech wireless keyboard and trackball.....no cables....no problems.


73

David Harmon
K6XYZ
Sperry, OK


-----Original Message-----
From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of Pete Smith N4ZR
Sent: Monday, March 13, 2017 6:32 AM
To: RFI List <rfi at contesting.com>
Subject: [RFI] USB qrm - what to do?

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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