Keying transmitter causes USB devices to fail

Discussion in 'Computers, Hardware, and Operating Systems' started by WB4WOJ, Oct 1, 2020.

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  1. WB4WOJ

    WB4WOJ XML Subscriber QRZ Page

    Thanks for all the advice and problem has been solved but it took a number of steps.

    I purchased from Amazon the following 20201005_145225.jpg 20201005_183133.jpg
    1) 85x55x20mm ferrite core (large core)
    2) 58x35x15mm ferrite core (2 to a pack)
    3) USB 2.0 Hi-Speed A/B Cable with Ferrite Chokes (M/M) 6-ft
    4) USB Isolation USB Digital Isolation
    5) A box of assorted ferrite Snap-On cores

    First I tested with the radio and PC not connected by anything other then the common power cord. I found that the following caused my PC USB and HDMI (to second screen) to fail:
    1) 80M just running the tuner
    2) 40M cw with 80 watts
    3) 20m cw with just 10 watts
    4) 10m cw with 80 watts

    So obviously I have a ground loop RF issue.

    With the radio and PC still not attached by any connectors:
    Step 1) I applied the snap-on cores to every cable going into the radio and PC. This only helped a little but not much.
    Step 2) I wrapped the incoming RG8X as many times as I could around the large 85mm core. This stopped the problem for 80 and 40 meters but not 20 and 10.
    Step 3) I added the 58mm core to the incoming RG8X right after the larger core and wrapped this as many times as I could. This stopped the problem for 20 and 10 meters.

    Yea ! Now able to run radio and PC at same time. BUT still not connected radio to PC.
    So next steps:
    Step 4) Attached the radio's USB to the PC's USB using the shielded USB cable with ferrite cores. Now problem is back but not nearly as bad and would be usable but not what I want.
    Step 5) I added the USB isolator and this was the final piece of the puzzle that now makes my radio and PC work together using HRD to control the radio and WSJT-X without any issues!!

    If anyone wants to know the exact products I got from Amazon please email me. I just picked them out when shopping on line and I am sure there are many similar products that will do just as well.

    NK2U, KA0HCP, WR2E and 1 other person like this.
  2. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    I'm just now reading this thread. Good job being persistent and getting a solution to the problem!

    Did I understand you to say that the dipole is for 40m but you use it on 80, 20 and 10? If so, that could be the root cause of the trouble.

    On those other bands the dipole is being used at an even harmonic and will have a very high feedpoint impedance. There will be lots of common mode current trying to find a path back to the radio. This would explain why 40m was not much of a problem but the other bands were, and also the large mounts of choking needed to start reducing the problem symptoms.

    It would also explain why the USB isolator was needed - because it blocks the path on the USB shield bringing RF common mode current coupling to the AC power wires in the house back to the radio.

    For these and other reasons, such as very high stress in the tuner, it's usually a really bad idea to drive a dipole on even harmonics of its half wave frequency.
    WB4WOJ likes this.
  3. WB4WOJ

    WB4WOJ XML Subscriber QRZ Page

    I suspect that my problem is the reflected RF but being in a condo (duplex) with very limited antenna placement options (only because I am the HOA prez was I able to get what I have accomplished) this is probably as good as I can get until move to a place with some land. The antenna is a purchased (DX40SH) shortened dipole (only 33 feet long) because that is all the room I had to string the antenna, but it is published to be good for 40, 20,17, 15, 10 and 6, (with traps) but I find that for me it only works on 40 without a tuner. But seems to be working well for me on 40 and 20 now. So at least I am able to do some hamming again :) 20201001_123455_HDR - Copy.jpg
    N0TZU likes this.
  4. AI3V

    AI3V Ham Member QRZ Page

    I am glad you were able to tame the issue, and a great write-up of the typical cut-and-try (poke and hope :)) that is required.

  5. WB4WOJ

    WB4WOJ XML Subscriber QRZ Page

    Thanks :) I know this is not the best antenna and feedline situation but given my constraints I am happy with the results. I have made contacts from Japan to Florida and almost got a EU contact the other day with transmitter at only 50 watts. I will probably tweak it in the spring or maybe see about adding a stealth vertical in the tree but this is good for the coming winter months. 73.

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