When looking fore example at Trendspotting 64 graph, I see those cycles....

Hi Peter,

That looks perfectly normal. It's not interference or anything like that, it's just the nature of background counting. The fluctuations are common in all background counters I have seen and will most likely be a combination of actual background radiation, cosmic rays/muons etc. Interference would show more of a pattern, as would UV light interfering with a glass tube. Nothing to worry about. I have just looked at 5 different stations on the stations page and they all look similar. It does appear to form some kind of cycle, but not sure why, and does seem somewhat arbitrary in it's timing.

What I find particularly interesting is a similar pattern is seen on two of Juzzie's stations - southofhobart and southofhobart1. The reason I checked these is they are a slightly different setup where air is pulled through a filter trapping any radioactive particles and the particles are left on the filter for the radiation to be counted. My thoughts were that if the filter had sufficient radioactive material on them, they would act as a sort of capacitor/storage and the readings would be much smoother. Alas, they are not and show a similar arbitrary pattern as others. It is possible the filters haven't caught any radioactive particles so is acting just like every other counter. I'm going to have to build something like Juzzie's air filter counter. I think it would be useful in a Radon area.