HDTV over coax

[Philosofy]

OK, so Comcast can send several HD signals to me over coax, how come I can't do a home network and distribute HD signals from my DVR over a coax cable?

[sonnik]

I don't think there's a consumer level device that outputs HD over coax.

Your HD DVRs and similiar devices put a lot of hardware on the task of decoding HD into colors and sounds you can see and hear. It's a complex process. Even at it's cheapest - it's still pretty costly hardware wise.

Over-the-air and cable use slighty different mechanisms, but they essentially rely on the concept of sending modulated data over a medium. The process of taking this data, and modulating it into an analog signal requires a good amount of hardware also. Any device like an old vcr, game system, or TiVo that tells you to tune your TV to channel 3 or 4 is actually doing an analog modulation, which is pretty easy in the grand scheme of things. Do a Google search for "HD Modulation." Technically, it's doable - but no one has apparently seen a reason to make it economical.

For the time being, your cheaper alternative would be storing the HD content on a hard drive and distributing it over a high-speed home network via something like VLC or MPlayer. I've done this. It's not ideal, some concessions have to be made (network capacity), but it works.

[stevel]

There are also devices (baluns) that let you send component video signals at HDTV quality over Cat5E wire (not using networking). This can be an inexpensive way of distributing a signal.