A common lightning protection technique used in many commercial radio
stations is simply to wind maybe 50 turn of the coax around a 6 or 8"
carpet tube or PVC pipe, then ground the shield on the coax as it
leaves the bottom of the coil. Often but not always we would put a
spark gap to ground at the top of our so called "lightning choke". A
similar technique was employed to protect the "sampling loop" coax
feeders. The only thing that we used transformer lightning isolation
for was the tower lighting circuits (our tower lighting transformers
were large guys of conventional core construction, but with the
secondary winding isolated by about about 2" of air spacing in all
directions).

Each of our 4 225-ft towers sat on an insulator to isolate them from
ground, with a spark 1/4-inch spacing spark gap with two massive 2"
balls connected to the ground system. The only problem that we ever had
with this setup was that in the summer, occasionaly a large insect
would venture into one of the spark gaps and be instantly carbonized by
the r.f. being transmitted -- triggering automatic shutdown of the
transmitter in the process. When this happened, one of the operating
engineers would have to divine which of the four towers was shorted,
then fly like lightning itself with a flat file in hand to the tower
and clear the problem (while hoping that no one would take it upon
themselves to reset the transmitter while he was making repairs)!

Ahh, the fun days (NOT)!

Harry C.