[RFI] USB qrm - what to do?

[Steve]

Do common, run-of-the-mill USB cables have shields? The USB page on 
wikipedia says a shield for the data pair is part of the USB 
specification. Just wondering if cheaper cables omit the shield?

I see on various web sites that some USB cables are advertised as having 
a shield, it seems that web pages for most cables do reference a shield. 
So if you want a cable with a shield, do you need to look for those 
cables that specifically state that they have a shield?

One more question: If a USB cable has a shield, to what is the shield 
connected? Perhaps the USB connector's outer metal shell? On both ends 
of the cable?

Steve, K8JQ

On 3/13/2017 10:27 AM, Matthew King - KK4CPS wrote:
> 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
>> spotting RTTY activity worldwide.
>> For spots, please use your favorite
>> "retail" DX cluster.
>>
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