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Old 03-13-2017, 10:46 PM
   
Join Date: Nov 2016
Location: hongkong
Posts: 1
Default I can not receive radio waves using LM386?

I've made two different circuits to receive RF using LM386 but they doesn't work. I've changed the values of C2 and L1 to change the frequency. I've also changed the gain but nothing happens.

The problem is that I hear a sound of noise or buzz from the speaker. When I touch Pin 3 (The input) or the Antenna, The sound become higher but anyway no radio station is received.

I've made a radio transmitter using a transistor before so, I turned it on. The receiver circuit received the song Which is the input of the transmitter. It receives no matter the values of the C2 and L1 of the Tank circuit so, I removed the tank circuit and connected the antenna directly to pin 3 and It also works receive the song.

Why it doesn't receive any radio station although it receive the signals that are transmitted by the transmitter circuit that I've made ?

What can I do to receive radio stations ? ( I live in area Where I can receive good radio stations AM and FM from my cell phone and Radio device )

here is the datasheet of the IC :LM386 - NS/ - IC Chips - Kynix Semiconductor Hong Kong Limited.
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Old 03-13-2017, 11:18 PM
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Join Date: Jun 2006
Posts: 6,122
Default

An LM-386 is simply an audio amplifier and you probably have a parallel resonant circuit with fixed inductor and variable capacitor to select the resonant frequency and a diode to demodulate the AM carrier feeding the LM-386.

This type of radio is very simple and requires a strong local AM station and a long wire antenna to get a good signal for the diode to conduct and demodulate the AM modulation. Your home made transmitter is sitting right next to your LM-386 receiver and probably works because it has a very strong signal into the antenna.

Another thing about your receiver is the selectivity is very wide and a strong radio station like your home made transmitter can be received no matter where you tune your LM-386 radio. You could take out the big inductor and variable capacitor and probably still receive the strong signal from your home made transmitter.

Try attaching at least 30ft or 50ft of wire to your LM-386 receiver and make sure it goes outside in the clear of any buildings and hopefully it will receive some radio stations. Another thing to look at is the diode. When I built my first crystal diode receiver in the 1960s it used a germanium diode with a low forward voltage drop. This is needed for the very small signals it needs to rectify. I forgot the part number but it was probably a 1N34 or 1N60 type.

If you use a silicon diode it will need a very strong signal to work. A schottky diode can also work but I don't know any appropriate part numbers to use.

If none of that works you might look into adding an RF preamplifier stage to the receiver.
prcguy

Quote:
Originally Posted by minini View Post
I've made two different circuits to receive RF using LM386 but they doesn't work. I've changed the values of C2 and L1 to change the frequency. I've also changed the gain but nothing happens.

The problem is that I hear a sound of noise or buzz from the speaker. When I touch Pin 3 (The input) or the Antenna, The sound become higher but anyway no radio station is received.

I've made a radio transmitter using a transistor before so, I turned it on. The receiver circuit received the song Which is the input of the transmitter. It receives no matter the values of the C2 and L1 of the Tank circuit so, I removed the tank circuit and connected the antenna directly to pin 3 and It also works receive the song.

Why it doesn't receive any radio station although it receive the signals that are transmitted by the transmitter circuit that I've made ?

What can I do to receive radio stations ? ( I live in area Where I can receive good radio stations AM and FM from my cell phone and Radio device )

here is the datasheet of the IC :LM386 - NS/ - IC Chips - Kynix Semiconductor Hong Kong Limited.

Last edited by prcguy; 03-13-2017 at 11:27 PM..
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