ByTheWay, un-plasticised PVC has ideal dielectric properties for HF and
below. I once wound similar coils on two formers, one of UPVC and one of
stout cardboard, and measured the Q (at ~3MHz IIRC). The UPVC was much
better, with a good value.
Any takers?

A factory renovation has resulted in some 315mm dia. UPVC pipe, with 6mm
wall thickness, being thrown out. If anyone wants some for a coil former,
let me know quickly, before the skip goes. Will saw to length, you will

have

to pay post or collect.

Julian G3TFR, Stockport.