Line at 40Hz

Hi everyone,

I’m new to using the Rapberry Shake and was wondering if someone can explain what the line I often see at 40Hz is? Ive seen it on other people’s shakes too and can’t find an answer on Google.




An excellent question. Here’s an example from mine but for HDF (infrasound) rather than EHZ (vertical geophone channel) - excuse the signal breakups**.

I guess the question becomes is it real or is the Shake generating it?

Given my 40Hz signal stops after a period of time and isn’t always there I’d say it probably is a genuine signal. Often though I see other different frequency straight line signals on the EHZ channel (or HDF channel) so wouldn’t go so far as to say there is anything special about 40Hz. As for what it could be my guess is it’s something human made for example a generator, extractor fan, compressor, etc. Is yours permanent, does it vary with the time of day, temperature, weather conditions for example wind, etc?

This page mentions “The pressure transducer used by the RBOOM and RS&BOOM is sensitive to RF at some frequencies” Raspberry Boom (RBOOM/ RS&BOOM) Infrasound Monitors and goes on to describe other sources though mainly for infrasound. I moved to an external WiFi dongle on a USB extension cable rather than use the built in WiFi in an attempt to eliminate any possible RF interference & improve WiFi signal until such time as I can plumb in Ethernet to prevent **signal dropout.

Please do keep us informed if you are able to determine the source as I have a number of signatures like this that equally pique my interest.


Hello Gregor,

That’s a very interesting observation that could spark a nice “hunt” around your house (or neighbourhood) to find the cause of that signal @ 40Hz.

I have something similar, together with other constant lines at different frequencies, all related to the computers I turn on and off in my house and, during the Summer, to my indoor electric fan.

Try to turn off/on some appliances/devices and see if the line disappears. Or, check your daily/weekly records and see if there are specific times where the line is not present, or when it suddenly appears/disappears out of nothing. This could give you a clue about what is generating it.


Thanks folks for your replies,

I thought this would have had a simple explaination that more experienced users would have answered in a sentence. It now makes sense that something is making it and after looking at the data from my Shake it’s not happening all the time so eliminates things like aquarium pumps that are on 24x7. This is going to be an interesting hunt as it appears when we’re asleep so it’s not anyone in the house turning something on causing it.

I’m going to record the start and end times to see if I can figure out what it coincides with. I stay in the countryside with no close neighbours so it’s maybe not from other houses. I have other sensors around the place plus a weather station so I can see if the times match any events on them too. There’s also an oil refinery not too far away so maybe something coming from there?

Thanks for your help and I’ll let you know if I figure it out.



I’ve also recorded signals on my RS3D at around 40hz. You can see my posting a while ago. Mine are even more unusual, and consist of two frequencies, one around 41hz, the other about 43hz. They are co-incident and last exactly 5 minutes. They don’t occur at regular intervals but are frequent. They are stronger in the Horizontal axis than in the Z Axis. This is in Southern Ohio, and I’ve never been able to link them to any local activity.


This is interesting. I’ve just figured out how to display greater than the default time window in the app and here’s how the spectrogram looks over nine hours. It’s actually at 39Hz and seems to appear at regular intervals.


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I also have a mysterious line at approx 36Hz that shows on my wired 4D but not the wired Boom directly adjacent to it. I think it’s related to my spa’s mains power. I’m wondering if it’s RF/induction from the spa’s power supply, heater or power cabling rather than vibration from the PSU transformer. Even when it’s asleep and not heating or pumping it still emits it. The staircase pattern is the spa doing it’s pumped cleaning cycle. My next step in the process of elimination is to kill the power to the spa and see if the line disappears.