Assuming 75 ohm feed line as you said it is CATV. It is useable but it is a hassle. You have to get an exact multiple of a half wavelength of the frequency you are using it on, and you have to factor in the velocity factor of the coax.
Any error in this calculation will be multiplied by the fact that the the length of the feed line will include many half wavelength sections at 2m frequencies. There is also a margin of error on the feed line velocity factor rating itself, although likely not much, but again, not much over many half wavelengths adds up.
You could build a feed line transformer to convert to 75 ohms by using quarter length 50 and 75 ohm feel line segments and and eliminate the need for half wavelength multiple lengths, but then you might also have to convert it back.
This is done in the order of any length 50 ohm feed line, 1/12 wavelength 75 ohm feed line, 1/12 wavelength 50 ohm feed line, any length of 75 ohm feed line. You could in theory ignore the first 50 ohm segment and run the 75 ohm feed line directly from a radio, but in practice several feet of the 50 ohm feed line before the first 75 ohm feed line segment works better. As above don't forget the velocity factor in your calculations.
It is possible that you might not have to convert it back depending on the properties of the antenna, and its matching network if it has one. Some antennas actually prefer the 75 ohm feed impedance (such as a center fed dipole), and antenna matching networks (think Maco style but many others as well) will match to a wide range of input impedances, and are thus more forgiving.
I suppose you could put an antenna tuner between the 50 ohm input and 75 ohm feed line sections as well, you will need a 75 ohm dummy load at the end of the 75 ohm coax to tune the tuner properly.
Any way you do it it could be an interesting project to post about what and how you did it.
Mind you, if it is 50 ohm feed line after all you can ignore my post completely.
The DB
Edit for error correction in one of my numbers.
