Richard Fry wrote:
The total average power available at the hybrid output for both of these
conditions is twice that of a single tx without the hybrid.

Does the quote from Born and Wolf support this?

Yes, there is obviously no interference between the
two transmitters if the powers simply add together.
You have doubled the current capability without
doubling the voltage capability - that's not
interference.

For interference to occur, both the E-fields and
the H-fields must be superposed at the same time
such that both fields increase or decrease by the
same percentage. So how do we double the voltage
and double the current in the 50 ohm transmission
line to the antenna?

Put a transformer on the output of each transmitter.
Wire the secondaries in series. We have doubled the
voltage output. Now drive the 50 ohm load with that
doubled voltage and see what happens. This is equivalent
to constructive interference. Hope you are running
the transmitters at half power. :-)
--
73, Cecil http://www.w5dxp.com