I bought a 1972 surfing movie on DVD called:

Five Summer Stories. In it is a scene where they put a wireless microphone on a surfer. A very famous surfer named Corkey Carroll. Footage is from 1970. Then they film him talking while on the beach and surfing, also. From what I have been able to figure out is, that the mic might of transmitted on 37Mhz...

https://i.postimg.cc/YqMHQzxZ/5-SS-Corky-Carroll-Mic.jpg (https://postimages.org/)

https://i.postimg.cc/jjNg8GxX/20230219-172649.jpg (https://postimg.cc/B8SBb71L)

https://i.postimg.cc/mDBwmk6L/20230219-172744.jpg (https://postimg.cc/TyNgwd6F)

Hidden microphone....Hidden like a sore thumb.

I wonder what the mike picked up when they pulled all that tape off !