I've got a length of RG213u that wants to exit the house and then turn upwards
> to a roofmounted antenna.
>
> For practical reasons, I suspect it should, instead, turn downwards (driploop)
> before heading up. Regardless, I can't exit the wall parallel to the soil
> and then "suddenly" take a sharp bend (up, down or sideways) -- minimum bend
> radius is ~4.5".
>
> So, the bend has to start *inside* the wall.
>
> What are best practices, in this regard?
Dunno about best, but masonry drills can cut ugly slots if you're not too worried about unusual stresses on your tools.
Drill straight through (or maybe with a 15 degree down-slope) then on the outside drill another hole from bend-radius below the exit wound upwards to intersect with the original hole. then chain-drill and chisel out the rest of the delta
If the blocks are hollow you may be able just make 2 holes and then fish the wire round the corner - if you can see through the wall the top hole doesn't need to go all the way though
If the cable needs to be covered cover the slot with a surface box and/or fill what can't be covered with with caulk or mortar (use backing rod) bring a curved or flexable conduit out the bottom of the box.
And, is it best to route the cable "exposed" vs. hiding it in interior walls?
Will it need maintenance or protection?
Mount the lightning arrester *there*, above the loop?
Lightning is black magic, I'm not bold enough to state an opinion.