RF noise between a transceiver and computer

As noted in the instructions for setting up the TS-590SG to use digital modes on a Mac Mini, there is an increase in RF noise when the USB cable is connected between the Kenwood and the Mac Mini, through the SignaLink USB, and with a DB-9 serial cable to a USB to Serial adapter. I also tried connecting the serial cable to a Lenovo desktop - and even though the desktop was off, there was still an increase in noise. This leads me to think it is the cable itself that is coupling the noise to the Kenwood. Here are three possibilities of mitigating the interference:

  1. Use a shielded cable, ensuring the shield has continuity between connectors; and
  2. Ensure both the transceiver and the computer have a common ground.
  3. Use a laptop that isn't connected to the power lines.

The first alternative ensures the transmission of the interference from the computer to the transceiver. The second didn't work. The third....worked.

I was able to test the third alternative with a recent MacBook Pro. There was minimal additional interference (if at all) and I was able to install the USB drivers, download fldigi and WSJT-X, and get on the air. When the charger is connected, it will show a frequency dependent increase of an RF noise level of S2.

Conclusion: Use a laptop for digital modes to minimize or almost eliminate RF interference.