[AMRadio] Strange (bassackwards) Oscillator

[JAMES HANLON]

Charlie,
 
I'm a little confused about your description of the oscillator frequency change as a function of the coil slug and the trimmer capacitor changes.  Maybe if you started over in your explaination it would make more sense to me.
 
If the oscillator frequency goes up when you move the slug into the coil, then the inductance of the coil must be decreasing as the slug moves inward.  AsI think you know, moving a brass (conductive) slug into a coil will lower its inductance.  So if the slug is conductive, then this part of your observation makes sense.  
 
How is the "trimmer capacitor" connected in the circuit?  If it is in parallel with the coil, I would expect the resonant frequency to go up when the capacitor is opened.  If it's in series with the coil I would also expect the resonant frequency to go up when the capacitor is opened.  But I understood your message to say that the oscillator frequency went DOWN when the capacitor was opened, and that doesn't make sense.
 
I would usually expect to adjust the inductance of the oscillator coil at the low frequency end of the tuning range for proper calibration, and to adjust the parallel capacitance across the coil at the high end of the tuning range for proper calibration.  Is that what is going on?
 
Jim, W8KGI