QRM & Power Line Adaptors

So last night (11/5 – 12/5) Turned into a bit of a QRM mission. Not exactly sure how, but found myself really getting trying to find the source of a specific hum, as I am gradually reducingt the amount of interference/QRM I am picking up. I started with taking my little AM radio (D-328) around the house buzzing very present. What I wanted to rule out was the utilitys nearby and the garage. Being 1AM and wandering around with a pocket radio should make for amusing footage on the overnight security video from the garage today 🙂 Anyhow, I could pick none up.

I returned home,sure enough the ‘buzz’ was back. So as it was quiet in the house (trust me, we are 24/7 shop here!) i started going thru the fuse box, its an older one, but still thankfully a trip/RCD (?) type box where I can easily flip the circuits. Sadly the circuits are not labelled, which I find quite unprofessional, apart from the ‘light’ fuse. I started flipping fuses and on the 5th one the buzzing on the radio stopped, as did all the mains power to my study and I think the front part of the house.

I set about unplugging everything in my study with the mains back on, hum still there. So I started to research/googling hum between 50 and 500Khz – it seemed so precise, I figured it must be some form of ‘man made’ interferance.

Here is a video of what it sounds like :-

So you can hear it all the way up from 50kHz to a very loud abrupt end at 500kHz. I set about googling as to what that could be, and sure enough found th GM4FVM page on ‘power line adaptors’. I’ve been very careful to remove and limit the use of ethernet in the house now, so suprised that this had caught me out. I immediatly removed the BT Ethernet over Power adaptors I had. This is the result

A longer video with manual AM tuning and a ‘sweep’ of USB

If you are patient enough to have watched the whole video, i congratulate you 🙂 But you can hear the big difference between what a power line adaptor can do to HF/RF in a shack, i.e. completely destroy all but the strongest signals.

This morning I tried out WSPR, the results on receive and transmit speak for themselves :-

wspr map is somewhat busier…

So now its time for work but I think i have taken another big step in reducing QRM in my shack

Next Steps – reduce this hum MORE and MORE

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