[RFI] USB qrm - what to do?

[Parker Dinkins]

Shielding is part of the specification for USB cable.

Parker W5ADD


> On Mar 13, 2017, at 15:45, Barry Merrill <w5gn at mxg.com> wrote:
> 
> K9YC states:
> 
> Shielded cable rarely solves RFI problems, partly because
> to do anything useful cable shielding must continuous with equipment
> shielding, and lots of
> equipment to which you would like to connect it is unshielded!
> 
> My question:  does it matter whether the USB cable is shielded when run thru
> a toroid?
> 
> Barry, W5GN
> 
> -----Original Message-----
> From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of Matthew King -
> KK4CPS
> Sent: Monday, March 13, 2017 9:28 AM
> To: Pete Smith N4ZR <n4zr at comcast.net>
> Cc: RFI List <rfi at contesting.com>
> Subject: Re: [RFI] USB qrm - what to do?
> 
> 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-C
> able-Blue-for-Printer-Scanner-/321535280583?hash=item4adcff05c7:g:n2oAAOSw~A
> VYuMEa
> <http://www.ebay.com/itm/1-5M-USB2-0-A-Male-to-B-Male-M-M-Extension-Shield-C
> able-Blue-for-Printer-Scanner-/321535280583?hash=item4adcff05c7:g:n2oAAOSw~A
> VYuMEa>*
> 
> 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
>> spotting RTTY activity worldwide.
>> For spots, please use your favorite
>> "retail" DX cluster.
>>