[ARC5] Zero Beat Question

[Fuqua, Bill L]

   I located a book I have written by R.R. Ramsey on Experimental Radio.
Very old book around 1929.
  I read a comment in the preface that was confusing at first and then I realized what
it was about. 
  It was in regards to frequency mixing and beat notes. Mind you, many formed their
opinions back in the spark era where a crystal receiver was coupled to another tuned
circuit connected to a buzzer. The RF from the second tuned circuit and buzzer produced
a beat note with the incoming signal. In fact Marconi had a patent on a balanced detector
using a second tuned circuit and buzzer. 
  Quantum Mechanics had just been given birth by Max Plank around 1900 and some 
physics thought the beat note was due to having two tuned circuits which, I am guessing here,
was like having two energy states and the audio beat note was produced by state (frequency) change
from the higher frequency tuned circuit to the lower one. 
  However, engineers disproved this but many physicist still believed this for some time. They were
completely stuck to a quantum mechanics explanation.
  I am hoping that I can find some other reference to this in earlier books. 

73
Bill wa4lav