I think you'll need a video booster amp, since just the ohmic losses in 50 meters of coax in a 75 ohm system can eat up your nominal 1 volt peak to peak output.
Also be prepared for earthing current problems if your PC and the far away TV monitor are on different powerlines. Even inside a single building, I've seen power current in the framing that could produce over a volt differential. And the currrent flow in in the coax shield was over ten amps.
Fav quote - "Experience is whatcha don't get 'till ya don't need it no more."
System - Athlon 1.4GHz, Win98, Hauppauge PVR250 receiver and compressor.
Software -Magix Movie Edit Pro 10, Nero 6 + NeroVision Express, Moho 4.61, PSP 8.1, Bryce, Quicktime 6.52 pro, Goldwave 5, DVD-Lab.
Cameras - Panasonic GS9, Canon ES8400V, Canon EOS D20 and Canon A70