Further to Peters experience, I have used the same method:-
ie lightly couple a sig gen into the coil (I use a single turn of wire )
resonate to the required freq. and find the 3db points with an oscilloscope
again lightly coupled.I get very similar results with all my loading coils
Q=150 to 200 only.I have also tried the same technique with small inductors
for filters and here find it very difficult to measure anything above 250.
One point with the large inductoras is that nearby objects reduce the Q
considerably I try to keep the coil at least one diameter from all objects
including the bench or table.
Like Peter I have been dissapointed with the figures I obtain especially
when I have seen figures like 600 mentioned.
There was a technique of measurment in an article in QEX Sept/Oct 2001 The
Art of Making and Measuring LF coils by IW2ACD and IK2WAQ which claims Qs up
to 600 and they use a measuring technique which series resonates the coil
and drives it from a very low impedance source through a transformer.I have
yet to try the technique but can recomend the article.
There is another article in the same QEX which deals with the Q of coils in
a mathematical way. 73s Laurie.
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