About RG, actually it is not needed since in the JFET gate the current can be also zero and only a voltage is required to make the gate voltage lower than source. In this case the voltage is indeed the mere microphone capsule (C) since it has a fixed Q (Q=Vc*C) and then a range of possible values of Vc. If it used a BJT instead of a JFET, then RG is needed since a current should be sent in the gate.
About RL, maybe it is not present. I only know that datasheets say a value for RL, then I have 2 options:
1) RL is inside the JFET and you must put a value of external bias resistor equal to RL, in order to have pin1-pin2 = Vbias/2. This can work fine, but the voltage between drain and source must be really small and negligible. In this way, the operating dc voltage is almost pin-pin2 = Vbias/2, and by connecting to pin1 and pin2 two decoupling capacitors I can extract the ac components, which are the really small variations of the drain-source voltage. This ac voltage must go to an amplifier since very small.
2)RL is not a physical resistor but a value given to put an external bias resistor equal to that in order to let the JFET working in the expected and corrent operating point. Then, from pin1-pin2 directly the drain-source voltage can be seen and the output is taken from there.
Actually, I think the more realistic is option 1) but can anyone confirm that?
I would really appreciate your help, please...
Thank you,
N.