trond wrote on Oct 21st, 2006, 12:57am:>>How about changing some values to see the delta freq.?
I did, but could only change them by a little since I have only 2.7nH till 10nH 0805 components laying around. When increasing the inductance I would have anticipated a further decrease of the already too low frequency, but it remained at around 50MHz. Leads me to believe the inductors might not work right. Hmmm.....
So how about just shorting across the 0805 indcutor placements ? As changing L makes no effect and the L value is already next to nothing at 50 MHz..., I would guess that shorting would also make no impact (expect a modest increase if f)... Then we are sure our ocsillation isn't hartley obeying 1/(2*pi*sqrt(LC)).
In any case if you are measuring the frequency ok (best method would be Active high impedance probe into a spectrum analyser). An analog scope a couple of octaves outside its bandwidth doesn;t represent something you can trust... so if you got it working correctly, you might not see it!!
trond wrote on Oct 21st, 2006, 12:57am:How big would you chose the Cf capacitor? Literature never tells you that as it's always being ignored. If I play around with it Cf will increase f when it is very small, the bigger Cf gets the less it influences f.
Cf should be large (but not add much parasitic), i'd go for >100pF.
Are you using a large value and good quality for your supply decoupling C as well ? remeber that forms the return path for your resonant circuit... especially if your power supply is crummy.
Are you using a good pcb, suitable for RF ? have you looked at extracting what parasitics the PCB gives you ?
anyway best of luck with it...