DIY RF Condenser Mics

[rogs]

If there was no resonance, I wouldn't be getting hundreds of millivolts RF at the gate.

The amplitude of the RF at the gate can be quite large - even without considering any resonance.
It will depend on the difference in value betwen the capsule capacitance and C4..... In other words, the amount of 'bridge' imbalance.
It is the change in amplitude level at the gate that determines the signal output, not the level of RF present.