[Lowfer] Magic Circle Transmitter?

[KD7JYK DM09]

: I have numerous "Magic Circle" transmitters of various sizes.  The
operating
: frequencies are:
:
: 150, 181, 213, 244 and 276 KC, labeled as 2, 3, 4, 5 and 6.
:
: They also have modulation codes:
:
: K, L, R, T, X and Y
:
: Which equates to:
:
: 15, 17, 19, 20, 22 and 25 CPS
:
: The one in my hand is labeled channel "2.5", which is Channel 2 (150 KC),
5
: = X or 22 CPS.
:
: The devices transmits 22 pulses per second on 150 KHz.
:
: Now then, what are thay and what were they used for???
:
: Kurt