How does the low pass butterworth filter of 5 poles and cutoff frequency of 2Khz work

[silverstar_28]

Hi, can pls explain how does the low pass butterworth filter of 5 poles and cutoff freq of 2Khz works after demodulation.. with a message freq of 100hz and carrier freq of 2khz..


Thanks,

 

[IanP]

dsbsc demodulation

The bandwidth of a DSBSC signal is twice that of the highest modulating frequency. So, for a single tone message of 100Hz, the DSBSC bandwidth is 200Hz. But the bandwidth of the envelope is many times this ..
So the lowpass filter will need to have a bandwidth wide enough to pass at least the first few odd harmonics of the 100Hz signal; say a passband extending to at least 1 kHz should be enough ..
2kHz seems to be to high as it will overlap the F(carrier)-F(message) product ..
Regards,
IanP