[TowerTalk] Vertical balun

[Tom Champlin]

The recent discussion of ground radials has been a big help for me. There is just one other thing that bothers me. Most hams would probably either run buried PVC to put the feed line in, which would of necessity be parallel with the nearest buried radials. Even if everything was above ground, my question would be the same. Assuming it would be desirable to use some kind of balun on the coax before or at the vertical feed point, possibly a W1JR toroid type, or some ferrite beads. The object being to keep RF from running back to the shack on the coax braid.
So, would one want to place this balun past the radial field but before the feed line gets close to the house or right at the antenna, or does it matter? 

Tom W0HH