The simple answer to that is to buy a security DVR to handle the camera feed and providing a digital output... Analog camera converting to a digital signal by itself probably isn't a good path... Pick a different camera or another solution.
Not sure if this will help you or not...I was considering this before I switched from analog to ip cams to get the signal from the cam to my TV.
Yes, these are good for analog only but to convert the cameras analog video to HDMI is quite complex - especially if color video is needed. The analog NTSC video would need to be decoded to RGB, digitized, deinterlaced, scaled, and then formatted to HDMI. Quite possible to do and there probably are some boxes that do it but my guess is we are looking at several hundred dollars to start.
i'm not super familiar with the details of security camera output, but maybe one of these, plus one of these? the 70ft part would be up to you. there are any number of types of cable combined with various adapters/"baluns" that would work.