Is SSB with pilot tone superior to SSB without
Good question. SSB without carrier is more power efficient, since the carrier "wastes" a great deal of the overall
power of the signal, but does not convey any voice information. ACSB (which includes one side band with carrier), was up and coming in the early 80's as requiring less bandwidth, and being power efficient. The carrier/pilot tone helps the radio tune the signal without having to fiddle with a fine tuning knob, since being off frequency slightly in SSB changes the pitch of the audio.
My recent reading on the related topic of why AM radio was used (for radio station broadcasting) was cost. Double side band SSB with carrier, which is regular am, was used, even thought it was not terribly efficient, because at the time, it made
for more affordable receivers.
With regard to military aircraft there is another reason to favor AM. Again, from my readings the doppler effect
can be significan if aircraft are closing each other at speed. On an FM signal, since it is frequency modulated
changes in frequency would make undesirable noise on the signal.
There were (and perhaps a few linger)/are a few 220 mhz commercial ACSB systems out there. I recall reading about a wide area system somewhere
up the east coast. A small utility near me lists a 220mhz trunked system on the FCC listings, but I believe they are filing to go with a more modern digital mode. My reading indicates that there were cost/performance issues with these systems. The allowed power levels were not very high. The channels, I believe used on these systems were close together in frequency. This required using more costly and "lossy" filtering systems, which further sucks up the already limited power. Net results was a system that was challenging to provide good coverage with. For example when you have a repeater its nicer to have the user transmit 5mhz or more away from the repeater output, then say .25 mhz away. The former is easier to filter then the latter.
