Plugged each of my usb devices into the computer separately, and
discovered that most of the RFI is coming from the cable to my Seagate
USB hard drive. It is a USB 3.0 device fed off a USB 2.0 port, I then
wound 5 turns of the cable - all that would fit - on a Type 31 big
snap-on, and all but 1-2 dB of the RFI disappeared, roughly a 10 dB
improvement from this device alone.
Next step is to wind 10 or more turns on a USB extension cable as Dave
suggested and see if it reduces further.
On the audio display of HDSDR I can see pretty distinct hum lines at
multiples of 120 HZ. I intend to bring everything I can to a common
ground bus and see if that helps, then go sniffing for other hum genrators.
Thanks everyone for your suggestions!
--
73, Pete N4ZR
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