Hello? I have a GMC 320 I purchased to monitor potential radiation emitting from a project I am working on that uses high frequency pulsed DC current and elec magnetic fields. The circuit that I am using calls for an earth ground on the negative side of the circuit. The issue I am having is that when I have the meter powered by the 2 prong usb supply when I operate the device I am working on I get extremely high counts from the meter. If I remove the 2 prong usb wall power supply and power the meter by the batteries I do not have this issue. Could anyone possible help me to figure out what is going on?
Whatever type of machine this is - unless you are somewhere along the setup use 50 kilo-Volt there is not even a remote chance of creating radioactivity which any Geiger counter could detect!
When you do see counts in your Geiger counter, it is because of electric disturbances. The GMC counter are NOT immune to electric noise! But the numbers are utterly meaningless.
Much like avoiding distractions to improve your score in Friday Night Funkin, ensuring a clean power source might help. Try using a different USB supply or an isolated power method to minimize noise. Have you considered shielding the meter or checking grounding connections? https://fridaynightfunkingame.io/
The meter I think you want is the GQ EMF (Electrico-Magnetic Field) meter. That shows a broad spectrum of emissions from microwave to radio waves. Different meter completely and one that everyone should consider if they have a microwave. You likely won't be watching your food and beverages heat up once you take a few readings in the vicinity of one.
Sounds like a ground feedback loop. Also sounds like the 2 prong usb power supply is being used for powering both your 320 and your project which is where the loop probably exists. Breaking that ground loop would solve your problem as you found out by using your GMC-320 battery. You could also use another wall outlet with another usb charger for the other device. Is your project involved with ionizing radiation or non-ionizing radiation?