I had a great uncle who said a 'flip-flop' was an old slang word for a radio. Has anyone else ever heard this?

I don’t believe my great uncle was right on this one because I never heard it anywhere else and never found any other reference to this. But I have found a few references associating the word(s) flip-flop WITH the word radio. Probably as the name of a broadcast corporation or seller of radios.

My great uncle was born in 1919 and fought during WWII and spoke Danish and Frisian though I’m sure he meant American English slang.