[jrblasde]

The components arrived today, which was far faster than I expected. I’ve tried prototyping both the coupled inductors and the individual conductors. I believe I’ll have to adjust the capacitance to get things just right, because I seem to have no range of adjustment at 9.1 MHz. I seemed to have better luck with the individual inductors than I did with the coupled inductors, but the resonant frequency was 3.5 MHz. I noticed that I seemed to have roughly a 200 kHz bandwidth (perfect for FM), because the output signal began attenuating whenever I adjusted the signal generator up or down by even 0.1 MHz. I also happened to notice that the output had some variation as I adjusted the secondary capacitance, but not as I adjusted the primary capacitance. This could be some external capacitance (possibly from my oscilloscope) interfering with the total capacitance of the circuit.

I also find that the inductors need to be very close to each other for best results. If the gap gets bigger than about an eighth of an inch then the output signal is attenuated severely.

I’ve attached several photos showing the reduction of amplitude of the output voltage as frequency increases from 3.5 MHz up to 9.1 MHz. By that point I had to adjust the volts per division of my channel 2 input.

I was testing this circuit in unloaded conditions, meaning that I did not have it integrated into the IF circuitry of the actual radio. 

At this point, I have two thoughts on why the resonant frequency was lower than expected.
1) My oscilloscope may be introducing some series capacitance. Recall that capacitance is additive when in parallel.
2) The inductance might be too high. A value of 22 µH is quite small, but it may still be high enough to start choking any signals higher than about 3.5 MHz.