[BC] German Radio Spying 1938

[Mark Croom]

I would expect it is likely an audio device since the 455 khz IF in an AM radio would take a fairly large antenna to pick up at much of a distance. Maybe I am all wet on this since I am also presuming the IF frequencies of the radios would be the same as I have known during my lifetime (and my parents were toddlers during WWII).
I would love to know more about this as well if someone can point us to an authoritative source.
Mark
MN