Help Needed with Sound Interference

[richardhoeg]

Please see the attached image which shows the frequency noise present a touch above 3, 6 and 9 kHz in my BirdNET-Pi at my small Northwoods cabin. I have tried many different microphones, ferrite beads, and shielded cables. Nothing seems to work, and the Pi is plugged into a grounded circuit. The exact same equipment including my microphone works on newer electrical systems w/o noise interference. My cabin was built in 1958. Thanks in advance.

[gitmatt19]

If you plug the pi into a USB power bank at the cabin does it do the same thing ?
If it does then you probably have dirty power at the cabin and might need a power filter, a UPS might work depending on the model.
If it still has noise while on the USB power bank you could try moving away from the cabin and see if it stops. If it does your cabin is transmitting and I'm not sure how to stop than other than run power out to the pi away from the cabin.

[richardhoeg]

Sound is clean when hooked up to a USB power bank by itself. Given the age of the cabin I suspect "dirty power". Thanks for the response

[stevedee]

I suspect you have a regular mains voltage to 5Volts switching power supply (as most of us do).
Given that the 3kHz (& harmonics) is not there when on a PowerBank, and you don't have a 50 or 60Hz mains hum problem (so your earthing is good), I wonder if you might solve your problem by trying a linear DC power supply.

[richardhoeg]

Thanks! This sounds like a good idea. I need to to do some research and learn some more about linear DC power supplies. Thank you once again.

[richardhoeg]

After doing additional research, this sounds like it is worth a try. I have ordered a DC power supply and will give it a test within the next two weeks. Once again, given the noise harmonics I was hearing this sounds very promising. Thank you!!!

[stevedee]

If you are running a Pi 4 you probably need a 5V 3A linear supply fed from a suitable mains transformer, unless the supply you have found has its own, built in transformer.
The linear power supplies I've seen on Amazon don't come with a transformer. This is where it gets tricky; if you supply too high an AC drive, the DC regulator may overheat.