[MRCA] Utility AM Modes

[mstangelo at comcast.net]

While in college in the 1970's I had a job repairing 2 & 4 MHz AM Marine Radios. Most of the work involved matching the output to the fiberglass whip mounted on the boat. The Marine band was transiting from the MF/HF AM bands to the VHF FM bands so I advised the boater to invest in an FM set instead of fiddling with the AM set but few took my advice. Crystalized FM sets weren't inexpensive back in the days.

The FCC mandated transiting the Marine band and I believe other HF utility services to other modes. Does anyone know what the date of the transition?

I believe the HF Marine bands also had to transition to SSB mode. Did the Aeronautical HF bands have to transition form AM to SSB at that time? Were any other services affected?

Finally, the Marine SSB channels back then were spaced at 3.1kHz. Why was this odd channel spacing chosen? Eventually the Marine SSB channels transitioned to the present 3kHz spacing.

Mike N2MS