RG-6, the sixth page, was wildly successful. Since each RG number is just a page in a book, it really doesn t mean anything. Actually, I lie. Here s a quick guide to RG numbers and what they mean. You can probably find exceptions to every one listed if you look hard enough.
Shielding is another area to explore.
Also study applications. Do not forget there are dozens, maybe even hundreds, of coaxial cable designs that don t fall under any RG or Mil spec. So 53.5 ohms would exhibit a fair amount of mismatch. As the military itself changed the original spec, it brought out different versions. And some of these could be considerably different from the original.