Chuck W. wrote:
"I`m wondering what is the best practice for connecting two tranceivers
to a single transmission line / antenna,----?"

A "circulator" is the device to route the right energy to the right
destination among multiple input/output devices. It is composed of line
segments in multiples of 1/4-wavelength of transmission line or
waveguide. I made one of 600-ohm open-wire line to parallel two 50-KW
shortwave broadcast transmitters to one antenna and a dummy load in case
of upset. Both transmitters were excited from the same oscillator. It
worked well and there was no upset. I didn`t need the dummy load. The
circulator is sometimes called a "rat-race". In any case, I swear that
they work.

Microwave repeaters are often equipped with waveguide ferrite isolators
which allow energy to pass through in one direction with almost no loss
but which absorb rf power in the opposite direction. These make clever
use of "Faraday" rotation of the plane of polarization as the microwaves
travel through a ferrite slab lying in a magnetic field. These ferrite
sections allow the transmitter energy to reach the antenna but not reach
the associated receiver input of the repeater, so it won`t be
overloaded, desensesitized, or accept power which would be better spent
in reaching the next repeater.

With ferrite isolators, energy can be routed almost at will. I am still
embarrased when I recall dropping an isolator in Motorola`s Chicago
plant 45 years ago. The ferrite shattered like glass. They cost several
hundred dollars each at the time. The Motorolans graciously said to
think nothing of it, it happens all the time. Well I don`t drop valuable
stuf every day. If I did , no one would let me in! , unless I was going
to spend a few millions, which we did.

I think you can probably use a "rat-race".

Best regards, Richard Harrison, KB5WZI