Re: varactor diode
FM can be generated by means of direct method or indirect method( form PM) ...
in the case of Direct method, circuit reactance will varied..since circuit reactance will determine frequency of output signal.....if reactance is varied w.t .r mesaage signal than output signal freq. will be varied.it is nothing but FM signal..
for varactor diode,under reverse bias its capacitance varies inversely...
Vα (1/√C)**n...n a constant dependinfg upon doping profile
if reverse bias varied inaccordance with message ,ouptut is an FM signal