title_body: Is it possible to transmit a high-resolution image over an analogue signal?
upvoted_answer: Bandwidth is the main issue. An HD signal has about four times as many pixels as an ordinary TV picture, so you'd need most of the range of FPV frequencies just for one pilot. I think that would also require four times the transmission power to get the same range.
  Then the problem is that all the gear we use is based on old CCTV chips rather than having been developed specifically for FPV (which is one reason the channel allocations are such a mess). I guess no one built a CCTV system for just one HD camera - multiple cameras are important in CCTV, and lag isn't an issue, so they could use digital compression.
  So, I guess the cost to develop a custom system is the big issue, especially if it might have a limited market, or become obsolete in a few years as faster, cheaper processors allow digital systems to overtake it.