ALL Marker Beacons transmit on a frequency of 75 MHz.

The Carrier Wave is Amplitude Modulated with an audible identifying signal which varies:

OUTER - 400 Hz O _ _ 2 x Dashes per second

MIDDLE - 1300 Hz C _ . _ . Alternating series of Dashes and Dots keyed at a rate of 2 x Dashes and 6 x Dots per second

INNER - 3000 Hz I . . 6 x Dots per second