Hello, I'm looking at inductors and I've notice some look like resistors, some with ferrite cores or some with just coils of copper with air core. Does it matter which one you use like say for an oscillator? Or do they all do the same thing?

 

They all have different values of inductances.
Air core coils have very low inductances and are used in RF circuits.
Inductors looking like resistors are your typical inductors for general purpose use.
Ferrite beads are used for power supply filters to reject high frequencies.

 

So what would you recommend for an oscillator circuit?

 

Depends on your frequency.

 

Frequency I wish to achieve is 2 Mhz.

 

Next you have to show your circuit.

 

Here's the circuit

 

Sorry this pic is bigger

 

It's a Colpitts oscillator. RF chokes would be fine - you may need to adjust something (capacitors say) to obtain the 2Mhz.

C1=C2=6.2nF say

 

An important thing to remember is that inductors have parallel capacitance which is distributed between coils and or the package capacitance. This parallel capacitance will resonate with the inductor inductance to give you a, parallel, high impedance resonance. This frequency is called the SRF, self resonance frequency. If you want to have a desired inductance at a given frequency make sure you use a an inductor that has a much higher SRF than your use frequency. The parallel capacitance will force the effective inductance to increase in frequency to SRF then above that point it looks like capacitor. RF chokes are inductors used above their SRF and behave as low value capacitors.