Speaking of shielded cables I wanted to share something I have
encountered on more then one occasion when I worked in the aerospace
industry.
We had an issue with a product during some specialized radiated tests.
Tasked with the investigation I found that the item was using shielded
USB cables, as expected, the only problem was the maker of the cables (a
large company that starts with an L and ends with a com) was not
terminating the cable shield in any way. What was more disturbing to me
was that I had to explain to two of their engineers that the shield had
to be properly terminated to do any good. Just because it has a shield
or braid around the conductors means absolutely nothing.
So, just because a cable says "shielded" do not assume it is properly
terminated on both ends.
Gedas, W8BYA
Gallery at http://w8bya.com
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 2/28/2019 5:12 PM, Jim Brown wrote:
On 2/28/2019 11:34 AM, N4ZR wrote:
I want to try to manage RFI in my shack, among other things, by
bonding all chassis together, including my shack computer, but the
question has come up - where can I find chassis ground on a PC
without serial or parallel ports? Is there a design standard, such as
connecting the power supply chassis to ground buses on the
motherboard, that makes this easy or does it have to be figured out
PC by PC?
Bonding should always be to the shielding enclosure (chassis) if there
is one, and this is the required connection point for the Green wire.
DB-connectors are sometimes bonded, so consider the VGA connector (if
there is one). To make that connection to my laptops, I solder a short
bonding conductor to a lug small enough to fit under the retaining
screw for the DB connector, with a single Power Pole on the other end.
If your PC only has USB ports, try making the connection to the shell
of one of them by sacrificing a USB cable like one of these.
https://www.amazon.com/Cable-Matters-USB-Black-Feet/dp/B00C7RXR72
USB is carried on twisted pairs, and cheap cables are often
unshielded. If you're experiencing RFI, using shielded cables might
help.
73, Jim K9YC
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