Now, as the project requires, I fiddled the caps into a binary addition
series (1pF, 2pF, 4pF, ... , 1024pF) using a capacitance bridge with a
1kHz
oscillator. I was careful to measure the caps in situ so as to take into
account any stray capacitance on the circuit board. However, the tuner
doesn't appear to be matching as expected (its an L-match). Does anyone
have any views on using this dielectric? Is it possible that it has a
frequency-dependent dielectric constant so that the cap values as measured
at 1kHz are different at HF?

Any comments/help etc gratefully received!
==========================
Have you tried to make capacitors from pieces of double sided fibreglass PCB
material ? Or even better the thin teflon material used for microwave
frequencies (expensive stuff). Because the dielectric material is thicker
,you might need a larger area to arrive at the wanted capacitance.

If you own or can borrow a MFJ 259B analyser ,you can measure the
capacitance at the operating frequency instead of at 1000 Hz.


Frank GM0CSZ / KN6WH