How to amplify and analyze EM signal?

[daslolo]

I'd like to study EM fields. I bought a cheap AM radio with no noise filter and by the sound of the AM radio speaker I can tell what machine is nearby.
For example one of my LCD monitor makes a high pitch whine, the other LCD monitor makes a lower sound, the computer another one. How does an AM radio pick up on that and why is the sound audible (the frequency of an LCD signal must be in the Mhz, no?)
So I connect the radio earphone jack to the oscillo and get very little voltage, why is the voltage of the earphone jack very low, the speaker I'd think would have a higher voltage to move that large membrane, no?
I'd like to make an amplifier like what's inside the radio so I can hook up the output to an analog pin of the M5Stack. I don't know where to start.
Is there a simple tuto on how to do that?
What's the best way to analyze EM signal to recognize what is what? Is there an equivalent to voice recognition? And how to make one?
Thanks.

[fourtytwo42]

You could try one of the USBradio dongles, I have seen software that gives a waterfall display indicating frequency and amplitude, very usefull for investigating suspected EMI sources though calibration is a problem.

[daslolo]

Good idea, I'm trying this https://www.amazon.com/gp/product/B009U7WZCA/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

[fourtytwo42]

Looks OK, I wish you luck with Amazon, they ripped me off so I closed my account!