Eureka! Source of Major RFI Identified

I have been intrigued by these two bands of signals on upper and lower ends of 20 m band ever since I started monitoring the waterfall display on FT-710. You may note that it is at least 5,9+10dB. Yesterday I posted a picture on Twitter and Greg, SP3RNZ was quick with a reply “Definitely switching circuit noises Jon”. I have noted similar noise bands on other amateur bands as well, though at varying regions. So thought of checking out the source today morning. Initially I switched off the phone chargers and laptop chargers as suggested, but there was no change in the RFI bands on the waterfall display. I did not switch off the UPS powering my WiFi modem as that would take me offline for some time.

Next I switched off the power supply to the UPS so that it will start working as stand alone on battery backup, without losing my WiFi internet connection. With each switching on and off, there was change in the pattern on the waterfall display! So the UPS has something to do with this RFI in my radio.

Finally I had to switch off the UPS itself, taking me offline for a few minutes. As suggested by SP3RNZ, that was indeed the culprit. The bands of RFI seen on the monitor disappeared, only to reapper as soon as the UPS was switched back on. As the last check, I removed the AC adaptor of the WiFi internet modem from the UPS output, to confirm that it was not the culprit. Finally I have found the source of this RFI in my radio, though I am unable to do anything about it other than avoiding those regions of the band. If I switch off the UPS, other users of the WiFi internet at home will be after me! That is why I had to delay this test for early morning hours when there are no other users.