Over the last few months, I have been been pretty uninterested in amateur radio because I literally could not hear and stations due to S7+ RF interference on bands below 20m and made me think that I had fallen victim to nearby solar systems from neighbours.
On a whim, I decided to go RFI hunting around the house and it was quite an eye opener.
Using a Sangean ATS909 Receiver that I have had for at least 20 years and is a somewhat prized possession in my radio equipment as being a reasonable, portable wide-band receiver capable of SSB along with AM and FM, I started wandering around the home.
Listening on around 3.5Mhz AM, it soon became apparent that nearly every “wall wart” power supply, that are typically switch-mode, were generating impressive amounts of RFI. The biggest puzzle though was the incredible amount of RFI around the radio equipment itself – an area that almost exclusively runs on DC with a quality power supply.
The classic “turn it off and on and see what happens” procedure was applied, and a culprit was quickly found:
This was a cheap USB-C charger purchased on Amazon (Searching Amazon for “USB-C PD Charger 40 Watt” will show you similar variants). I had put this charger in to power a wireless access point that is used for network connectivity to the equipment on the radio desk after finding the long ethernet run was creating other problems for me.
The USB charger has found a new home in the bin. Unsurprisingly, my FT1200 HF radio’s noise issues on low bands has disappeared and I can now hear more stations again. I might even pick up a microphone one day..
It won’t be possible to get rid of all RFI in the house – switching to a LW frequency and walking past the NBN equipment in the house is a whole magnitude worse than the USB charger, but I can at least start looking into replacing some of these noisy power supplies with good old fashioned linear power supplies.