In reply to G3NYY:
As for SSTV, there is absolutely no need for an SSTV signal to occupy
more than 2.5 kHz bandwidth. It fits perfectly within a standard SSB
filter. I use it this way on the HF bands myself. NBFM (so-called)
is an inappropriate and wasteful vehicle for the transmission of SSTV.
All the nets that I know of in that part of the band, which is officially all-mode, use NBFM for the talkback, in fact the ratio of talk time to picture time is something like 10 to 1, and Hampal or Easypal are the dominant modes. At least some of the net participants have no other mode available, so willy-nilly, it has to be FM. The band plan specifies a maximum -6 dB bandwidth of 20 kHz implying 25 kHz channels for FM, but with such heavy use this would be antisocial and 12.5 kHz channels would seem to be good practice.
Whatever the past politics, 12.5 kHz is the bandplan.
When I started on 2m, there were no “channels” and none were
needed. All modes managed to co-exist happily within the 2 MHz
available on 2m. Channelisation was the product of a CB-like mentality
in the mid-1970s and it resulted in the waste of at least 50% of the
spectrum between 145 and 146 MHz.
Indeed, when I started on 70 cms and a few years later was let loose on 2 metres, it was the age of the geographical band plan and we were all crystal controlled except for a very few with VXOs and eventually a few mixer VFOs. Channelisation was not something that sat well with me, but it had nothing to do with CB and a lot to do with the availability of used cheaply available crystal controlled mobile radios, and later channelised rigs using more advanced technologies. Repeaters and FM channelisation was driven by the explosion in V/UHF mobile operation. I didn’t like it so I graduated to a Liner-2 on SSB, which if I remember correctly was based on rubber crystals, anyway! However, again if my memory isn’t faulty, it was SSB introduced the concept of the “calling channel” within the SSB enclave.
Since occupancy is so low, both on FM and SSB, I think the concept of wasted space is a little irrelevant. Quite possibly even repeaters have had their day, too! Without SOTA it would be possible to argue that V/UHF sees so little activity that the government would be justified in assigning the bands to uses that they would find more profitable!
Cassandra, shove over, luv!