Dear RFI Expert:
The background noise levels in my shack on the lower HF bands are pretty bad (e.g. S9+ on 160m and 80m). I’ve listened on several rigs and it’s the same, a general white noise across that part of the spectrum and worse during the day. Effectively, it rules out daytime chasing on 80m for me except for the strongest of activator signals.
So, I had assumed it was general atmospheric noise caused by D-layer absorption, lightening strikes and other natural sources. I haven’t done 80m portable for several years [I’ve even cannibalized my homemade 80m dipole to make a ‘high’ bands linked dipole] but Mark @M0NOM informs me that he gets little or no noise on 80m when portable in the countryside. So, maybe it’s not all atmospheric noise.
I don’t think it’s coming via the mains electricity cable to the shack [a small outbuilding a few metres from the house] as the noise is about the same if I use a LiPo for the receiver [and switch all mains appliances off including lights]. I haven’t yet tried moving the rig and antenna feeder out into the garden and away from any mains cables.
There are mains (3-phase?) electricity cables running up the street on telegraph poles but they are 15m from the shack [and much further from most of the antenna wire] and about 8m up which I thought was too far away to be a problem.
Could my choice of antenna be a factor?: a horizontal long wire, inverted-L configuration (22m horizontal at 8m average height, 4m slope to ground and 9:1 UnUn, short earth wire to earth stake, 10m coax to radio/ATU).
So, any ideas where the noise could be coming from?