The transmissions from NOS in The Netherlands could be received here in Denmark, and I actually succeeded in downloading several programs based on the BASICODE 2 standard. At that time (eighties), people had all sorts of home computers, but this way we could actually run the same programs, whether you had a BBC computer, a ZX81 or one of the many other brands.
The way it worked was that the programs used a common (primitive) BASIC dialect, and where there was a difference, a subroutine was added with a high line number.
E.g. instead of clear screen you would just write GOSUB 100.
There's a user manual here:
https://archive.org/details/BASICODE2Manual/page/n7/mode/2up
Here is an example of the sound that was heard on the radio for approximately 2 to 3 minutes that was broadcasted on the Dutch radio.
https://on.soundcloud.com/QAUa2Kkgef1gDxDQ6
To my ear it sounds like AFSK, kind of like the Bell 202 scheme. Here's the first passable search result I found with a clean recording: https://www.youtube.com/watch?v=-PXxSHGrF-8
