Anybody know anything about the internal configuration
of these?

I bought one on behalf of my friend yesterday at Wimborne
to replace the 5/8ths one (not a colinear - misunderstanding)
that had been badly manufactured (q.v.)

On this Diamond, it gives an SWR of 1.01:1 and yet a DC test
shows no continuity between the centre of the coax and the
vertical radiator - the outer of the coax shows a dead short
to the monopole.

How are these things wired internally? - Mystified