USB Interference Fun on HF

On Thursday, 4/18/19, we acquired a shelf to use in our ham shack/office/workshop room. On Friday I organized and set it up to use as a radio bench and computer workstation. Once all the gear was in place and power was run, I turned on a few items to make sure everything would work together. I noticed that on 10 and 11 meters I had a new background noise that was really loud and irritating.

On Saturday (4/20/19) at the RSOC I mentioned this to Kent, KL5T, and after the obligatory MFJ jokes, got to thinking about what items we added to our station recently. We recently acquired a laser printer, a 32” TV to use as a monitor and a label printer.

When I got home and started investigating the noise, I remembered that when I plugged everything in, all the new items were on a separate power strip. With the CB radio turned on and the noise blanker turned off and the squelch turned off, so all the noise was coming through, I turned off the power strip in question. The noise instantly stopped. That narrowed the search down to 6 plugs, 2 of which were there before we moved everything around.

I turned it back on and unplugged one at a time the two existing plugs and the noise continued. Then I unplugged the laser printer and the label printer. Again, no change. Next was the TV with the same results. This left a lonely USB cord going to my charging iPhone….. I unplugged it and the noise stopped completely. I plugged everything else back in and the noise stayed quiet, confirming the USB cable was the culprit.

I tried plugging the offending USB cable info my iPad with the same noisy results. I then unwound it from where I had it and the noise was still there, but very much improved, and only slightly above the regular background noise. I replaced it with a different brand/type of cord and the result was similar to unwinding the other cord. I then unplugged it from the power strip’s USB plug and used the small cube USB power supply Apple provides. The results were the same as switching the cord and unwinding the original cord. Slightly above normal background noise, but not nearly as loud and irritating.  It seems that when I plug the phone in to other outlets around the house away from the shack, there is no interference detected.

I also checked the other bands that my Icom 718 can operate on and/or receive. I found the interference on the following bands: 40/30/17/15/12/11/10 meters. On 160, 80 and 20 meters, I couldn’t tell the difference between when the phone was plugged in and when it wasn’t. My antenna currently plugged into the radio is very noisy and the background noise and interference blended together.

The cord that was noisy is a flat, rubbery feeling USB to Lightning cable I got at the GCI store. The brand is Ventev. The other test cord was an Apple Certified 6’ cable I’ve had for years (model number APLLIG24TVL-F) from Walmart.

Check out the photos below to see the differences I saw when trying to solve this problem.

73,

John Lime III – KL4OF

The layout

 

Flat offending USB cable plugged into power strip USB charging port

 

Plugged in Apple USB wall wart

 

Cord wrapped about frame of book shelves…..induction?

 

With phone plugged in … S8 noise

 

Phone unplugged … noise gone

 

Phone plugged in … S3 noise

 

Phone unplugged … noise gone