Hi Barry,
It's always best to use high quality cables with a good shield when they
are available, but as noted, they only solve problems when the connector
on the equipment they're plugged into is properly bonded. Shielding
prevents DIFFERENTIAL radiation from the cable (the signal inside the
cable). The toroid works on COMMON mode radiation (the signal outside
the cable).
73, Jim K9YC
On Mon,3/13/2017 1:45 PM, Barry Merrill 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@contesting.com] On Behalf Of Matthew King -
KK4CPS
Sent: Monday, March 13, 2017 9:28 AM
To: Pete Smith N4ZR <n4zr@comcast.net>
Cc: RFI List <rfi@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@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
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