There are some good guesses here and I think an ?A? for effort is due. LOL ?.. I guess I?m really showing my age with this one, ?. I didn?t think I am that old?.
So, ?. The survey says???. That was the ground plane for the old AM ship to shore radio.
Up until about 1972 all marine ship to shore radios were AM radios, transmitting in the AM frequency range. That system had a very limited number of channels in (only about 10 as I remember), USCG calling and distress had two of the frequencies ?2182? and ?2678? kHz. This AM marine radio frequency band had a couple of practical shortcomings, the first one being the limited number of frequencies available, another being major radio traffic congestion, to the point that the system was becoming almost useless (even the calling and distress channels were so clogged with traffic that boats in distress couldn?t contact the Coast Guard). This congestion was due to three factors. 1) The very limited number of channels (as mentioned), 2) AM radio broadcast signals are not ?line of sight?, the radio waves will bend and follow the curvature of the earth, which allows for longer transmission distances (adding to the congestion), and 3) there was no transmission power limit as there is with the 25 watts today. -- Our family boat growing up had a 150 watt AM ship to shore radio and on any decent day we could contact the Atlantic City (NJ) Coast Guard from where we boated in the Sandy Hook (NJ) area, that is a distance of just about 100 miles (unheard of with today?s VHF). With so few frequencies, long transmission ranges, and a lot of transmission power available the system was all but useless (unless you had a lot of power and could simply over-ride everyone else when you needed to). Those AM ship to shore radios required a sizable ground plane in order to function, this would have been left over from that time.
About 1970 the FCC proposed and introduced the current VHF system as a direct solution to the problems above. 1) lots of channels available, 2) VHF which is ?line of sight? only ? to eliminate long distance transmission clutter, 3) power limited to 25 watts, to again reduce the long distance transmission clutter. (As everyone knows, there is no ground plane needed for these radios).
There was a two or three year change over period (ending about 1974), at the end of which it was no longer legal to use the old AM ship to shore radios.
Just some useless trivia for those who might be interested.
I will say that spending some of my young years with the old system, and having 150 watts available certainly re-enforced proper and polite radio use. Knowing that whenever you key up the mike you pretty much stomp out everyone else within a 25 mile radius REALLY makes you think twice; and makes you keep it short, to the point and polite.
