A diode detector is used to detect an amplitude modulated wave of `60%` modulation by using a condense of capacity `250` picofarad in parallel with a load resistance `100` kilo ohm find the maximum modulated which could be 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.