Some people really do have money to throw out the window…
The converter is super expensive and will cost you a **bleep**load of electricity on the long run but also it won’t allow you to connect your UPC box to receive the whole set of channels, replay, etc.
I’m not sure if I get all the aspects of what you’re trying to achieve here but it seems to me the easiest and cheapest solution would simply be to pull a coax in the very same tube as your cat 7 cable… why don’t you do that????
If really you cannot for any obscur reason you can also replace you cat7 with a BKS solution.