I'm doing a project at work which involves driving coils at high frequency (~20 MHz), but we would like to be able to go even higher in frequency without getting into resonance in the coil (we want to be below the resonance frequency) but still have as many turns as possible.
The resonance frequency is due to the LC interaction, so we want to minimize the capacitance (inter-winding capacitance is now a few pF) in the system driving and measuring the coils.
We have a few trim-potentiometers connected to and from the coils (voltage division), and I was wondering what order of magnitude the capacitance from a multi-turn cermet potentiometer could be?
This is not listed in any datasheets and it would also be tricky to measure a capacitance of only ~1 pF in parallel with the resistance of the pot (~100 ohm)
It'll be typical of size. Supposedly, the smaller SMT ones are good for a few GHz (i.e., capacitance / inductance / transmission line equivalent impedance not very different from the rated resistance and electrical length).
Tim
This is not listed in any datasheets and it would also be tricky to measure a capacitance of only ~1 pF in parallel with the resistance of the pot (~100 ohm)
For what it's worth, if it'll have an effect on your circuit it should be measurable simply by the nature of the effect it will have. Build something similar to the circuit in which you plan to use it, and try it out.
it would also be tricky to measure a capacitance of only ~1 pF in parallel with the resistance of the pot (~100 ohm)
If so, does it matter to your circuit?