I would like to implement a circuit that will electronically control the resonance frequency of an LC-network by providing an additional, electronically adjustable capacitance. The nominal resonance frequency of the network is 1.5kHz and I would like to decrease this frequency even down to 50Hz. So I guess a Varactor is not very suitable.

Does anyone have any idea?

Actually I have thought of perhaps using the topology of a capacitance mutliplier or the negative impedance network (both implemented with BJTs or MOSFETs), but (1) I am not sure if I can indeed control the equivalent capacitance by controlling the biasing of the transistors and (2) I have not seen anywhere in the net any detailed analysis on the implementation of such circuits.

Thus, any help on this direction would be really helpful!

Nikos