Hey guys, we just a practical to do in college and the whole class is completely confused as the lecturer would not/could not help us.
We had to demodulate an FM signal which was modulated by a DC signal using a Phased Locked Loop (PLL). The idea here was to increase the amplitude of the DC signal which would deviate the modulated signal from 20kHz up to the point where the output of the PLL would stop following the FM signal. Whats bothering me is, according to my lecturer, the PLL only starts following the FM signal at +-8kHz from 20kHz. I.e. starts around 28kHz and 12 kHz these values are supposed to be the point at which the PLL starts to LOCK. The lock then breaks at just over 10kHz on either side of 20kHz.
Whats confusing me is firstly, why must the PLL only lock at the above values? It makes more sense to me for the PLL to follow as much as it can.
Also, my telecomms board, my PLL was following EXACTLY right from 20kHz.
This is apparently wrong and i have no idea on how to rectify it???
We had to demodulate an FM signal which was modulated by a DC signal using a Phased Locked Loop (PLL). The idea here was to increase the amplitude of the DC signal which would deviate the modulated signal from 20kHz up to the point where the output of the PLL would stop following the FM signal. Whats bothering me is, according to my lecturer, the PLL only starts following the FM signal at +-8kHz from 20kHz. I.e. starts around 28kHz and 12 kHz these values are supposed to be the point at which the PLL starts to LOCK. The lock then breaks at just over 10kHz on either side of 20kHz.
Whats confusing me is firstly, why must the PLL only lock at the above values? It makes more sense to me for the PLL to follow as much as it can.
Also, my telecomms board, my PLL was following EXACTLY right from 20kHz.
This is apparently wrong and i have no idea on how to rectify it???