LM386 cannot operate at RF. Hence what you will hear from the LM386 is AF. It acts as its own low pass filter.

C6 is also a low pass filter to remove the RF and leave the audio.

Really I didn't know a low pass filter can turn high frequency to the audio frequency?!!!
Maybe my oscilloscope is wrong it shows the same frequency in the output

 

The filter doesn't turn one frequency into another.
Rectified AM includes both the RF and the AF.
The low pass filtering removes the high frequency signals (in this case the RF frequency) to leave the audio frequencies unaffected.

 

Hello,

An AM detector can be seen as an envelope detector.
See this wiki page for more info:
https://en.wikipedia.org/wiki/Envelope_detector

Bertus

 

LM386 cannot operate at RF. Hence what you will hear from the LM386 is AF. It acts as its own low pass filter.

The filter doesn't turn one frequency into another.
Rectified AM includes both the RF and the AF.
The low pass filtering removes the high frequency signals (in this case the RF frequency) to leave the audio frequencies unaffected.

Then how some people used LM386 for amplifying FM?
even after FM demodulating frequency is the same so it can't work at this frequency.
then how it can turn it to the sound frequency?

 

Then how some people used LM386 for amplifying FM?

They use LM386 to amplify the audio demodulated from a frequency modulated RF signal.

 

They use LM386 to amplify the audio demodulated from a frequency modulated RF signal.

As u can see here FM demodulator can't turn input FM frequency to the audio frqecuency,
but it can be detected like AM in the output that's why I said LM386 can't work at FM frequency.

 

As u can see here FM demodulator can't turn input FM frequency to the audio frqecuency,

What you are thinking of as an FM demodulator isn't a demodulator - it only converts the FM into AM. Then the diode demodulates the AM.

 

What you are thinking of as an FM demodulator isn't a demodulator - it only converts the FM into AM. Then the diode demodulates the AM.

I don't know maybe circuit is wrong, can u show me an FM demodulator output

 

I don't know maybe circuit is wrong, can u show me an FM demodulator output

Look in Google for Ratio Detector and Foster-Seeley Discriminator which are common FM demodulators.
Your simple FM slope detectors still have the amplitude fluctuations such as snap, crackle and pop of AM radio.

 

If I can turn FM to the AM and demodulate it with a diode then I made an FM demodulator.
If you put a diode front of LC for demodulating AM only you can cut half of the wave then you didn't turn carrier frequency to the audio frequency.
Then how you can hear audio?

 

If the LC is tuned to the centre frequency of an AM broadcast then you have an AM receiver. This is the standard circuit of a crystal set.

If the LC is tuned to the side of an FM broadcast then you have a FM receiver using a slope detector.

Neither will make a good radio receiver.

 

Hello,

On the internet archive there are books and articles from the ARRL (american) and RSGB (british) available:
https://archive.org/search.php?query=electronics arrl&and[]=loans__status__status:"NULL"&and[]=mediatype:"texts"
https://archive.org/search.php?query=electronics rsgb&and[]=mediatype:"texts"

Those will have a lot of info for you.

Bertus