The tests were to prove the the owner that the ship could broadcast (even without a decent aerial). He threatened to pull the plug when Lindau wanted another £50k for more balloons. It was a last ditch attempt to show we could attract listeners (proven by over 2,000 reception reports, those who bothered to send one DID help save the project).

I dont think Lindau chose the frequency - it seems to have been Paul Hodge. Certainly done in his day, and he signed the order for the transmitters. (I'm pretty sure most of this is in the book Radio Adventures of the MV Communicator)