[Milsurplus] The old 2 MHz boat channels ?

[Mike Morrow]

Many here are familiar with the old marine radiotelegraph calling and distress frequency of 500 kHz, which up to 12 July 1999 was the most interesting frequency in the world.  All traffic on the MF radiotelegraph band, as well as that on HF radiotelegraph frequencies ceased between 15 to 18 minutes and between 45 to 48 minutes of each hour to allow all stations to monitor 500 kHz for A2 auto-alarm and SOS signals.

The MF radiotelephone calling and distress frequency 2182 kHz also had equivalent silent and monitoring periods in ITU regions 1 and 3 (but not ITU region 2...the Americas) between 00 to 03 and between 30 to 33 minutes of each hour.  Post WWII radio room clocks will always indicate the two 500 kHz A2 silent periods in red and often indicate the two 2182 kHz A3 silent periods in green.

FWIW, these now-surplus marine band AM radios ALL became obsolete on 1 January 1977.  It was USB transmission only after that.

Mike / KK5F