The mystery of the spy number stations has been a recurring theme in Media Network. Perhaps the most elaborate project to catalogue them was a 4 CD project set up in 1997.

I see it's still listed in Wikipedia. The edition of Media Network talked with the producer of the CD in the second half of the show. We also looked at how radio was seen in the dim distant past (Remember the TM Century Punk Country Campaign?) and Jim Cutler threw in a surprise T-shirt competition. Perfect proof that the nineties weren't boring, even though no-one had a smart phone.