..

I wonder ... if the pipe were sufficiently large, it would tend to
broadband
the antenna. I know of this effect at UHF. How about 10m???

I'm looking forward to this. g



Yes it does, solves some of the problem you have with the all coax type of
sleeve antenna. stuff some pieces of styrofoam inside the pipe to center the
coax. Wind a choke in you coax and it is a pretty decent antenna. Consider
this, make the sleve out of 2 inch conduit, at the middle of the antenna put
a cap on the pipe with a hole drilled to accept a mount for a whip, RS and
truck stops sell these. Bottom end screws into a 2inch PVC pullbox, other
side of the pullbox screws on another piece of pipe used as a mast. There
should be enough room in the pullbox for the choke.