John Woodgate wrote:
"The problem is that people say "output impedance" when they mean "load
impedance".

Quite right. I`ll use "source" and "load".

Current through a load depends on the voltage. Ratio of volts to amps is
the impedance. A source with the same resistance and offsetting
reactance to the load enjoys a Goldilocks relationship with its load.
The source`s volts and amps perfectly match the demands of the load.
It`s just right. There`s no surplus of either volts or amps when source
and load are connected. Its a match. Only a matched source and load
deliver all the power available in a source.

If we have too much resistance in our load, it doesn`t take as much
power as it could.

If we have too little resistance in our load, too much power is lost in
our source.

The perfect match of equal source and load resistances, with the
reactance neutralized, is the only condition permitting maximum power
transfer.

Somme amateurs want all the power they can get from their transmitters.

Best regards, Richard Harrison, KB5WZI