phaedrus wrote:
I seem to recall that ladder/open-wire feeders are relatively high
impedance ~500 ohms. Is it possible to construct 50 ohm open wire
feeder and if so, what would the spacing be?

Thanks!

Possible, perhaps, but not practical. Assuming air insulation, the
spacing between the wires would have to be just under 9% of the wire
diameter, and this spacing would have to be maintained very closely to
keep the impedance constant. I might still have some 72 ohm twinlead in
my junk box, which consisted of wires embedded in molded polyethylene.

With your interest in transmission lines, you'd benefit a great deal
from getting a copy of the _ARRL Antenna Book_.

Roy Lewallen, W7EL