How to get a TV channel to stream as IP camera
I think I can see what you are asking, and Ken seems to have missed a big part of the question.

So assuming you are saying that the camera you want to watch is being broadcast as a TV channel that is connected to via an aerial (or equiv).  Then as you have said, you will need something to capture that with. That's going to depend a little on the hardware you are using with the capture device. But I am capturing local TV channels on a xbox usb tuner through a Ubuntu box.  But there are loads of low cost devices out there.

I am then using a bit of software called TVHeadEnd to grab that and spit it out as an IP stream. That can be watched on loads of devices. Of course if you want to watch this outside you home network, you are going to have to open ports on your router, and likely use something like DDNS (no-ip is a good provider for this) to find your router.  Just make sure what ever device you get to capture the broadcast and stream it, is compatible with the software you use to broadcast the stream.  Research before you purchase is recommended.

Lastly I think you will probably get away with running all this on something like a rasberry pi, depending on if you have to transcode the stream (which you would use FFMPEG to do, over an above most internal transcoders, but that's a whole different story).

There may be much simpler solutions out there, with everything just built in, perhaps a HDHomeRun, but I have not used one, worth a looks to see if it fits your need, it may remove the need for a PC all together. 

Without more details this is all the info I can offer at the mo. I hope it's enough to get you started.