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Author Topic: All USB Ports are not created equal  (Read 1634 times)

Offline jFarley

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All USB Ports are not created equal
« on: September 08, 2015, 1720 UTC »
at least on a laptop...

I learned an important lesson today, and maybe it might be of use or interest to others.

Today I installed the remotely tuned NDB loop outdoors, and began testing.  Tuning the loop requires communicating with the loop server SBC via a long network cable.  Here I use a CAT5 cable for the long haul, with a pair of USB to CAT5 adapters (and vice versa) at each end, one at the computer and one at the loop.  I anticipated some possible noise issues, but nothing like what I encountered.  The noise floor was about 20dB higher than what I would like to see, and I had intermittent communication problems which I had not noted when testing in the basement.  The communication link would unexpectedly lockup for no apparent reason, and the controller program on the PC would hang and become non-responsive.

I added the obligatory 5 pounds of ferrite to the system without much luck.

The fix was rather simple, and almost embarrassing to say.  For this first test, I plugged the USB adapter into the most convenient port, which was the USB port right next to the laptop power adapter socket.  It turns out that this USB port is just full of noise from the laptop switching power supply which was being communicated to the loop.  It is also likely that the switcher noise was causing the local USB to CAT5 adapter to misbehave.

Moving the adapter to another USB port solved the problem, almost in entirety.  There is still some spurious junk being picked up by the loop, but we will work on that in the future.

Bottom line is: choose your USB ports with care, and test them all for best noise performance.  While you may not have a USB connected antenna, it is possible that a noisy port may be corrupting a sensitive outboard device such as a USB sound card or SDR.

« Last Edit: September 08, 2015, 1730 UTC by jFarley »
Joe Farley, Near Chicago
SDR-IQ / R8 / R7
Remote Resonant Loops for HF and LF / ALA 1530
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Offline BDM

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Re: All USB Ports are not created equal
« Reply #1 on: September 08, 2015, 1927 UTC »
Very true. Just to add to this, most of my computer work involves full size PCs (I build my own). I've found long ago using the remote USB ports vs the motherboard ports can also show issues with noise due the jumper cables/circuits used inside PC tower (due to poor quality non-shielded internal jumper cables or poor connections). Especially if you transmit from the same location with three & four digit watt outputs ;)
Radios -- Perseus SDR // Icom IC-7410 // Tecsun PL-660 // Panasonic RF-5000A --Antennas-- Pixel Pro 1B loop - 82' fan-dipole at 40' - tuned MW/BCB 40" loop and 100' receive only dipole
-Brian--North of Detroit--MI-
1710/KHz the MW Pirate Clear Channel (not so much anymore "sigh")