Rebecca Eureka i seem to recall was the full name, with not many stations eqipped to provide a service. They were flagged in the red book as 'D4' or 'C6' sort of pairing to dial up.
i also seem to recall it never worked, or unlocked if you flew a wide circuit. The associated read out is the dial to the right of it, calibrated up to 20 nm it seems, with the needle at the bottom to chase for homing - now that never worked!
...makes you fond of tacan.
wets