[emeritus]

Here's an advert for "CO-AX" coaxial cable from the September 1943 "Wireless World". It is the only mention of co-axial cables in the issue, and "CO-AX" seems to be used as a brand name. An internet search revealed that the company was founded in 1942 and later acquired by Radiall. Interesting that the characteristic impedances of the two cables mentioned are 70Ω and 214Ω.

In the other contemporary literature I have from the late 1930's- early 1940's, coaxial transmission lines are constructed using copper tubes and spacers. According to a booklet "The Feeders and Aerials of the Marconi-EMI Televison System" that describes the design and construction of the original transmitter aerial at Alexander Palace, it was found that the original coaxial feeder ( Marconi's standard No. 0 feeder for short waves, 78Ω ) was not satisfactory as the discontinuities introduced by the spacers, and the boxes which provided right angle bends, gave rise to unacceptable reflections, and after much experimentation, a compromise of 8 supports to the wavelength was arrived at. Presumably no coaxial cable with uniform insulation that would have avoided the discontinuity problem was available at that date. The length of feeder required was about 20 wavelengths.