About 15 years ago, I bought an HF antenna at an ungodly price with a huge coil, about five feet long and six inches in diameter, from these
people. They no longer sell them, but it was advertised as being left over from a batch ordered for the Virginia Class submarines. It lacks only a whip, which could be maybe twelve feet high. The notion was that if submarines depended on this antenna for long-range HF communication, then it must be pretty reliable. It's sat ever since I bought it, and it's one of those projects I've scheduled for retirement.