A diode detector is used to detect and amplitude modulated wave of `60%` modulation by using a condenser of capacity 250 pF in parallel with a load resistance `100 kOmega`. Find the maximum modulated frequency which could be detected by it

Options

A. 10.62 MHz
B. 10.62 kHz
C. 5.31 MHz
D. 5.31 kHz

Answer

B

Explanation

`tau = RC = 100 xx 10^(3) xx250 xx10^(-12)sec`
`=2.5 xx10^(2) xx10^(-12)sec =2.5 xx10^(-5)sec`
The higher frequency which can be detected with tolerable distortion is
`f=(1)/(2pim_(a)RC)=(1)/(2pi xx0.6xx2.5xx10^(-5))Hz`
`=(100xx10^(4))/(25xx1.2pi)Hz =(4)/(1.2 pi)xx10^(-4)Hz=10.61 KHz`
This condition that rate of decay of capactor voltage must be equal or less then the rate of decay modulated signal voltage for proper detection fo modulated signal.