Fringe physics: Trying to understand WTF the A field is in electrodynamics, and how I can measure it for a price I can afford. Specifically, I want to communicate through a wall of rock or sea water at VHF frequencies, with high bandwidth. I just upgraded my subscription with ChatGPT to try to grok all of the physics involved. It decided that since this could be used to covertly exfiltrate data, it wasn't something that could be discussed. ;(

Recently a friend acquired a Collins KW-1 transmitter, serial number 1. I helped him get it working again after a long period of disuse by it's previous owner. You wouldn't believe how often it turns out that wires and bolts don't actually conduct electricity.

Maybe I can help with one or two conceptual things. In classic E&M a field describes the potential (or force, if you prefer) a test charge would experience at that point. Note that the general case is impossible to visualize, as you're associating 6 numbers (3 for E 3 for B) with every point in space, so we normally think of simple setups and slice them up. Accelerated charges make waves in the field which are WAY more complex than people think. The way you model matter is dependent on the frequency of light. For visible light you normally think of it (especially metal) as a crystalline lattice of some characteristic length, electrons that can jump discrete energy levels, with molecules forming some sort of dipole that has more degrees-of-freedom (wobbling, twisting). I don't know about VHF, but the wavelengths are huge, like kms, and therefore way too low energy to cause electron shell jumps, so you'll probably model matter according to some very general characteristic like permittivity and conductivity. For seawater (which is a good conductor) subs use ELF, which is 100s of kms in air and can only communicate at bits/s. It's a fascinating topic, and very niche. Good luck!

Electrodynamics is taught to literally millions of people in Physics or engineering degrees across the world. It is the furtherest from fringe as it could be.

I would recommend following along the MIT OCW course or similar, doing the exercises. Use AI to help you follow the course and ask questions about things not clear to you.