What you are describing sounds like the frequency division multiplexing
systems I used to maintain for the Navy.  Instead of loading a single
amplitude on the designated frequency it was an actual communications
channel.  This system was a hold-over from the early 70's (I served in the
90's) and it took up a full sized rack to fit all 25 or so modules in
because it used entirely analog components.  It was always in need of tuning
and all of us techs were happy when it was replaced with newer digital
modems.  Of course, it did work reasonably well despite everything.

If you want to try and implement a new version of this I would recommend
spending a lot of time getting the frequency management digitally controlled
and use digital filtering for each receiver unit.  This would make it much
easier to control and maintain without all the drift the analog approach
inherently adds.  Maybe using a digital pot to run a vcxo?  I know the Navy
has a lot of its technical documents online and they would be a good source
for this.  You will have to search for it because I dont remember where I
have seen them.

This may not be too many answers but it may point you in the right direction
at least.  Having said all this I tend to use rs-485 systems myself.

Regards,
Andy

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