Hi, why my signal is not demodulated well?

 

Hi halima,
Please post your LTSpice asc file.
E

 

Hi, here is my asc file

 

You are generating a double-sideband suppressed carrier signal, (DSB-SC) which cannot be demodulated with an envelope detector.
And an FM signal (your file title) also cannot be demodulated with an envelope detector.
(An envelope detector is not the same as a slope detector).

I modified your circuit to generate an AM signal by adding a DC bias to the modulating signal (attached).
I increased the difference between the modulation and carrier frequencies to make it easier to demodulate, and added a second-order filter to better remove the carrier frequency.
Also added a DC bias to the diode input to reduce the diode generated distortion.

It would appear you need to study the difference between AM signals, AM suppressed-carrier signals, and FM signals, and the different ways they need to be demodulated.

 

See

 

Your 1N4148 silicon diode has a 0.65V forward voltage. An old AM crystal radio used a 1N34 germanium diode that has a forward voltage of only 0.2V.
The BAS70 diode is Schottky with a forward voltage of 0.2V to 0.3V (at the very low current of your circuit).