On 2/18/2024 8:45 PM, Pete Smith N4ZR wrote:
I have about 8 USB cables in my station, two going directly to my
computer and 6 to a hub. I suspect some RFI because periodically-
every couple of hours - a couple of USB devices - keyboard, mouse,
Winkeyer - stop working. Stopping and re-starting N1MM does not cure
it - I have to restart Windows 10, and then it's OK again for a few
hours. There doesn't seem to be any correlation between the band in
use and the problem - in fact, sometimes when I come back to the
station after hours away, with N1MM left running, what was working has
now stopped, and a computer restart is required.
I'm wondering if it is feasible/useful/foolish, with several USB
cables going to a single physical location (back of computer, front of
computer, hub) to wind the cables that terminate nearby together on a
single big 31 core, or do I need one core per cable to be useful ?
One problem I can see with several cables through one core is that the
currents in the wires may be out of phase, rather that true common mode.
Imagine the two halves of a zip cord dipole meeting at the core, then
passing through it as a transmission line. The currents would just
cancel each other out, resulting in no flux in the core, so the core
would have no effect on this differential mode current. That current
might have a big effect on your USB device, though. Now, if each of
those wires went through a separate core, the currents would be attenuated.
One exception might be a bundle of cables from a common source, if that
source is very small compared to a wavelength.
73,
--
Scott K9MA
k9ma@sdellington.us
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