Andy,
Just from those readings, I'd have to say the antenna seems to be
operating normally/correctly. Shaking things while doing that
continuity test is usually a fairly good idea, intermittents, although
shaking the antenna isn't going to be very easy, sort of.
Not making both connections at the antenna terminal, only the
center pin, and changing the antenna's characteristics is normal.
Sort of going from a "tuned"/resonant antenna to a random length wire
kind of thing. (Receivers just aren't as 'picky' as transmitters,
have different requirements. Not a very good way of putting it, but
you get the idea?)
Don't give up, I'm interested in what happens.
- 'Doc