Radio Receivers -- 1942 Training Film -- Crystal Sets to Superhets

This 17 minute film provides a good but simplified description of the state of the art at the start of World War II. 

--  The description of how a signal gets to the input coil of a receiver is quite good.  Imagine if that coil had no good ground, and no counterpoise.  We see the importance of the counterpoise in this video: https://soldersmoke.blogspot.com/2023/03/an-antenna-for-high-school-direct.html

-- I like the repeated demonstration of the reality of envelope detection.  Too often people have bought into the idea that envelope detection is not real, and that some form of mixing using the carrier in lieu of the local oscillator is what is really happening.  That is just not true.  Envelope detection as described in this film is real. 

-- The description of mixing is very simplistic.  They describe the generation of the difference product, but not the sum.  But hey, the film is only 17 minutes long!  It takes a lot longer than that to fully describe mixing (ask me how I know!).  

-- At the very end, there is a shout-out to the BC-348.  FB.