Sometimes, they broadcast ZX Spectrum, sometimes it was MSX programs.
The Dutch NOS radio created BASICODE to transmit BASIC binaries over radio. It was used in several countries until the early 90s.
BASICODE could be understood by almost all computers at the time, including Exidy Sorcerer, Colour Genie, Commodore PET, VIC-20, C64, Amiga, Sinclair ZX81, ZX Spectrum, QL, Acorn Atom, Micro, Electron, Tandy TRS-80, MSX, Oric Atmos, Philips P2000T, Grundy NewBrain, Amstrad CPC, IBM PC, Apple II, Texas Instruments TI-99/4A & Mattel Aquarius.
It only used a minimal subset of BASIC command, all system-specific commands were replaced by GOSUB calls, for example GOSUB 100 to clear the screen. The program itself would then start at line 1000.