Tom, K7ITM wrote:
"FWIW, the "aingle loop terminated in a diode" that provides both
magnetic and electric coupling at the same time" is not the only way to
make a directional coupler."

Agteed, but the Bird Electronic Corporation has been successful making
the plug-ins for their "Thruline Wattmeter" that way for about 50 years.

Best regards, Richard Harroison, KB5WZI