Hi, I have the answer to how Coax is made, or rather grown. The Coax Plant (genus Heliaxius Vulgaris) is thought to be a distant relative of the Spaghetti Plant, first grown in this country in the London hothouses of Kew Gardens in about 1892, after being brought back from the wilds of Peru by the intrepid explorer and botanist Sir Hubert Andrews, RGS.
The native plant has never really responded well to man's intervention and despite the best efforts of the experts first at Kew and later round the world, the hardiest and fastest growing variety is the ubiquitous 50ohm. Some 75ohm strains exist, but whilst yield has been improved, quality has remained elusive.
Coax plants live for very long times, up to 70 odd years and in that time can produce up to 50km of top quality cable. Of course it would be impracticable to wait that long for such a length and early on growers soon learnt to graft plants together to produce runs of sufficient length with end to end consistency. Whilst this was merely regarded as a technical exercise for the growers, worthy of the odd prize or two at the local village hall fete, the true worth of all there efforts were not realised until WW2 when , for obvious reasons, anything to do with radio was of use.
Quite how the long strands of coax had been found to be useful for RF is not clear, though it is rumoured that early radio listeners, perhaps tired of plant growing and fascinated with the new hobby of radio, were using dried pieces in the 1920's. Until then no one had seemed to care that as the stems matured and ripened, the copper braid and core emerged fully formed. Then of course it was obvious, though entirely NOT understood and many burnt out their precious collections with bad mis matches if they were foolish enough to try putting RF power down them.
During the war Coax plant production was put under the Ministry Of Food, which despite the best interventions of the engineering establishment, was where it stayed until rationing ended in 1952. This inappropriate line of command probably explains why the Americans were the first to develop the most famous type of Coax plan of them all, Heliax Splendiferous, which concentrated the latent structure of the Vulgaris to produce the lowest loss cable of all time. A high proportion of Japanese emigrants might also explain why they were so successful at producing the solid type microwave cables, cropped from Bonsai'd plants! Modern technology has made many changes since the war and there are now more versions than ever. Simple botanicals, however, still applies and if you want 5 cm feeder it takes longer to grow and hence it's more expensive. Like a good malt whisky, good things take time and care and PLENTY of patience! However battery production has lead to the emergence of UR43 and UR67 as cheap, commonly used, good quality cable, which is just as well because some of the more esoteric varieties can cost upwards of 90 pounds per metre!
Commercial brands are a closely guarded secret, you will never see a field of Coax plants, that would be to out in the open. No, they spend their lives instead in closely monitored nurseries, where a vigil is kept on conditions to ensure consistent quality. However, all is not lost. You can buy a Coax plant from most Garden Centres, though it will probably be by order. Lets face it Coax plants are not the most attractive of things in the world. Indeed they are plain ugly. They went out of fashion by the turn of the century, only having brief respite from their fall on the death of Queen Victoria when the dried, black ribbons were 'a la mode'. Another bad point were the cables which snaked away from the plant pot. Many have snagged one of these tough stems and found themselves on the floor.
Sadly that is how Sir Hubert Andrews ended his days, supervising the removal of the 13 foot high monster from the Kew gardens, which he'd donated to them some 20 years earlier, as it had come to dominate the floor of the arboretum where it was kept.
So there you have it. Next time you trim the end off some RG213, you can wonder at the marvel of nature that gives us Coax as we know it. Take a close look and see if you can spot the tiny swirling pattern of the inner that was later to be spotted and developed into Heliax.