As wigwam says 75 ohm is the impedance of the cable, which is the standard for Freeview, Sky and Virgin. When testing with DC (multimeter) with ether end of the coax connected it will always read a direct short but that does not mean there is a short at RF frequencies. I wonder how many folk this has caught out? The other problem useing a multimeter is if there’s some dampness or water in the air space of the dialectic ora rusty piece of wire from the braid is slightly touching the inner core or there in a minute gap between them it maynot be shown on a DC meter but it will fook with RF frequencies. Like I said previous there’s specialality test equipment for pro installers.
Given you have said the coax runs down the gutter I’d be getting WF100 or PF100 due to it having a solid HD foam that won’t suffer from water ingress as a air spaced honeycomb dialectic would. There is alot of inferior cable around, so stick to Webro or Triax if you can.