[RFI] USB qrm - what to do?

[Matthew King - KK4CPS]

Pete - I had similar problems until I purchased shielded USB cables with
the small ferrites already molded in. The ones I have are silver and look
braided under a clear insulation. They are noticeably thicker than a
regular cable.

Those these don't LOOK the same as mine, I'd trust the Tripp-Lite brand to
be properly shielded, I do believe.

*https://www.amazon.com/Tripp-Lite-Hi-Speed-Ferrite-U023-006/dp/B003MQ29B2
<https://www.amazon.com/Tripp-Lite-Hi-Speed-Ferrite-U023-006/dp/B003MQ29B2>*

This is more what mine look like - I don't know that it's necessary to be
able to "see" the shielding or not! *:-)*


*http://www.ebay.com/itm/1-5M-USB2-0-A-Male-to-B-Male-M-M-Extension-Shield-Cable-Blue-for-Printer-Scanner-/321535280583?hash=item4adcff05c7:g:n2oAAOSw~AVYuMEa
<http://www.ebay.com/itm/1-5M-USB2-0-A-Male-to-B-Male-M-M-Extension-Shield-Cable-Blue-for-Printer-Scanner-/321535280583?hash=item4adcff05c7:g:n2oAAOSw~AVYuMEa>*

Anyhow, maybe that'll help ya out.

Be good!

73

Matt
AK4MK

On Mon, Mar 13, 2017 at 7:31 AM, 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
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>
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