first principals of radio transmission are to homebrew by a doorbell (the interruptor provides a signal what is useful for short distance as TX) ,,
and a detector radio simply made by a wire as antenna, a coil with C and germanium diode, following a high impedance headphone for listening.
the lowest stage of radio is the detector.
the next a detector with audio amplification,
the next a Regen or Super Regen radio, with Tube, oder Fet,
the next a Regen with pre amplification stage,
the next a superhet (this are the most of all home radios)
the master is a double / triple conversion superhet (the big ear)
Coils are to wind self by hand.
There is some low expensive test equipment required, at best a HF signal generator with a trustful scale.
greetings
Martin