[RFI] USB qrm - what to do?

[Dave Hachadorian]

Page 10 of K9YC's Noise Suppression Manual suggest 7 turns on a 
0431177081 Snap-on for 80/160.  I think 7 turns will fit in 
there.  I've got an HDMI cable with 5 turns, and it looks like I 
could jam two more turns in there.  How about trying a USB Hub, 
with one of those chokes between the hub and the computer?


Dave Hachadorian, K6LL
Yuma, Arizona


-----Original Message----- 
From: Pete Smith N4ZR
Sent: Monday, March 13, 2017 4:31 AM
To: RFI List
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
Check out the Reverse Beacon Network
at <http://reversebeacon.net>, now
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