Tuning Range of the circuit that utilizes two varactor diodes with L = 15 mH and capacitance varies

Determine the tuning range of the following circuit that utilizes two varactor diodes with L = 15 mH and whose capacitance varies from 10 to 70 pF .

Options:

a. 318 kHz to 1 MHz
b. 418 kHz to 1 MHz
c. 594 kHz to 1.83MHz
d. 694 kHz to 1.83 MHz

Correct Answer: d. 694 kHz to 1.83 MHz

Explanation:

As per the circuit configuration,

C_{T ( min)} = 10 /2 = 5 pF & C_{T ( max)} = 70 /2 = 35 pF

f_{r (max)} = 1 / 2π (√LC )

= 1 / 2π ( √15 x 10^-3 x 5 x 10 ^-12)

= 1.83 MHz

f_{r (min)} = 1 / 2π (√LC )

= 1 / 2π (√15 x 10^-3 x 35 x 10^-12)

= 694 kHz