A question for the RF boys:
I've been making 50 MHz LC oscillators using some 150 nH 1008-sized surface-mount inductors. These are ceramic-core types, not ferrite.
They work fine, but Qs are low, in the 30 range. Coilcraft has "surface mount" parts with Q above 100, but they are either bare springs or springs glued into a plastic case...
and
(We have used this Coilcraft "maxi" inductor in the past, and found that the plastic cold-flows over time and slowly changes L. So we bake them for a day or so to relieve stresses. Coilcraft claims they don't cold flow!)
My concerns are...
For the highest Q parts, the bare springs, does L change as the FR4 board changes dims with temperature? I suspect Coilcraft doesn't test them soldered to a board... they apparently use some HP q-meter fixture.
What's the effect of a PCB ground plane on L and Q? Ditto.
Are these things significantly microphonic?
Any experience or suggestions for stable, repeatable TC [1], high Q inductors, preferable surface mount?
John
[1] so we can pad them with NTC caps and kill most of the temperature drift. Actually getting NTC caps is a whole nother story.