Larry Dighera wrote in message . ..
Frankly, I didn't know that radio direction finding was employed for
aviation use before the '20s. I'd sure like to know more about this
subject.

Not ADF, of course, but DF existed from the early 1910s, and was
shortly thereafter installed on some naval vessels.

Apparently by 1914 DF was being tested on winged aircraft. The
British looped a wire from the cockpit out along the top wings, and
back via the lower wings... thus creating a loop antenna on each side
of a biplane. This allowed the pilot to easily home into his base's
radio station. ("Most Probable Position, a History of Air
Navigation")

By the end of WW-I, DF equipment was well along, and the SE950 model
in the eBay ad was designed and built in early 1918 in only two weeks
after it was requested. See:

http://earlyradiohistory.us/1963hw23.htm

The first aircraft to cross the Atlantic (the "NC-4" in 1919) used a
SE950 to figure out it was off course, after its compass jumped its
gimbal on takeoff.

Cheers, Kev