# Antenna coupling via capacitor 2

I would like to clarify following detail I still not understand so far on the explanation what's the proper purpose of the coupling capacitor C1 in following receiver circuit is (found in http://makearadio.com/misc-stuff/regennotes.php ) but there are no explanations what finally the job of this coupling capacitor is): The answers I got to my original question on this problem I asked a week ago, suggest in unison that this coupling capacitor C1 has an important effect on the Q factor of the L1-C2-tank, which in responsible for selection of desired frequency.

Since the goal of this L1-C2-tank is to be selective, it's Q should be relatively big, and seemingly (at least as far as I understood the answers in the linked discussion) the Q of the L1-C2-tank depends on this coupling capacitor C1.

I not understand it. Why the tank's Q depends on coupling capacitor? If we separate the L1-C2-tank from the rest of this circuit then it's just a parallel LC-circuit:

(note that the LC-tank in the first picture above there is no resistance R explicitely depicted, that's just for sake of brevity, a real coil has always a small resistant component R, which we should take into account if we want to calculate the Q of this LC-tank.

Now comes the point which confuses me: For a parallel LC-tank seemingly there is a closed formula for Q (see eg https://en.wikipedia.org/wiki/Q_factor#RLC_circuits). And the problem is that it seemingly not(!) depends on the coupling capacitor C1, instead only on L1 (+ it's resistant conponent R menstioned before) and C2? So inly on component which belong to the LC-tank, not external components like the cap C1.

Problem: So in summary we deal with two statements:

(I) (based on answers from original question ) "The Q factor of the L1-C2-tank depends explicitely on capacitor C1 as well"

(II) (based on the linked formula from wikipedia) "The Q of this LC-tank depends only on C2, L1, R

Well, obviously these two statements contradict to each other. What is the problem here and how to resolve it? Did I quote one of them in wrong way?