Does anyone know if there exists an electrical/electronic standard for high definition video on a single wire, like composite TV which integrates luma, chroma and sync? I'm still interested in this long distance high bandwidth project, and maybe transmitting analog HD is the answer. 720p would be good, 1080p would be fantastic. And a way to convert between component and composite would need to be figured out by me, but I figure a very fast DSP or even FPGA ought to be the solution.
Composite cables have a very poor quality factor associated with their construction. The RCA connectors can create a lot of reflection and the soldering jobs on the wires are not always great. Also, many composite cables aren't shield causing noise and unintentional radiation to be an issue.
At the lower bandwidths used by analog TV these issues weren't really a huge issue. However, be definition, HD has to use more bandwidth. At the higher bandwidth situations a poor cable can really eat your lunch. This is one reason why no one has ever put high def on a composite cable.
Now if you are looking to use something other then composite, but just want it to be 1 wire, then you can use any serial communication method you wish that is able to handle the bandwidth over the distance you wish. By "1 wire" I am going to assume you mean 2wires in a single line (1 signal, 1 ground), if this isn't the case you are going to have a horrible time with noise when you have no reference point or way of shielding.
Yes, it's called SDI: http://en.wikipedia.org/wiki/Serial_digital_interface
With one coax cable you can transmit 720p or 1080i, with two coax cables you can do 1080p.
cable television (at least in the US, not sure in other places) uses QAM-256 encoding for transmitting digital channels, including HD, over a single coax cable. Thats for a compressed digital stream however.
I don't know of anything for analog HD other than 3 wire component signaling. I doubt you'll find much other than that for HD, its almost exclusively transmitted around in a compressed digital format (MPEG2).
Ok, until today I believed it was impossible to carry a HD signal over a composite cable, however that is not entirely true. I have a 1920 x 1080i HDMI signal, which is converted to HD-SDI signal to carry over a long distance (50m) to a monitor. At the monitor end I used a HD-SDI to Component converter to drive the component input of the monitor in HD.
Unfortunately the Monitor developed a fault and it was replaced (By a non -technical person) with a Monitor that only had a composite input (and HDMI). Using the same HD-SDI to component converter I just connected the Y signal to the composite input (In theory shouldn't work, and the picture should be black & white if it did work). However I got full colour and full resolution - The Monitor reports 1920 x 1080 @ 50hz (I am in the UK hence 50Hz). I understand composite video perfectly, and this hsould not work for 1000 reasons - but it does. The composite cable is only 16" long.
There is no down or cross conversion - so bemused at how it works.