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Why can't I receive radio waves using LM386?

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Posted on January 15, 2017 at 17:56:38
soda156
Audiophile

Posts: 2
Joined: January 15, 2017

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 details of the IC :

 

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RE: Why can't I receive radio waves using LM386?, posted on January 15, 2017 at 20:00:28
hifipaul
Audiophile

Posts: 671
Location: NY
Joined: December 22, 2008

I think you need a circuit to demodulate the signal from the carrier. I think the lm-386 is just an audio gain device.

 

RE: Why can't I receive radio waves using LM386?, posted on January 15, 2017 at 20:38:22
Eli Duttman
Audiophile

Posts: 9416
Location: Monroe Township, NJ
Joined: March 31, 2000
Contributor
  Since:
January 5, 2000
He's got a demodulating diode in the circuit. He probably needs a 0.01 μF. cap. to ground, at the diode's O/P.

What I want to know is why this thread is on a TUBE "board".

Eli D.

 

It's almost a crude crystal radio but the tuning portion is connected wrong...., posted on January 15, 2017 at 21:38:42
Steve O
Audiophile

Posts: 6661
Location: SE MI
Joined: September 6, 2001
...since it's shown as a parallel-resonant circuit, the diode should be connected to the junction of the antenna, (variable?) cap and inductor. The bottom of the parallel cap and inductor should be tied to a good earth ground as should the signal (-) input of the 386. A 500-1000pf at diode output to ground would improve sound quality such that it is and probably make the 386 happier too.

Did not examine 386 circuit for correctness but doesn't strike me as optimum load for tuned circuit. High impedance is better.

Why in Tube DIY? Expectation of superior knowledge! ;-)

 

RE: It's almost a crude crystal radio but the tuning portion is connected wrong...., posted on January 16, 2017 at 00:08:12
Eli Duttman
Audiophile

Posts: 9416
Location: Monroe Township, NJ
Joined: March 31, 2000
Contributor
  Since:
January 5, 2000
Right you are about the diode attaching to the antenna. I missed that. Also, the place the diode is currently attached to should be grounded.

From my quick look at the LM386 data sheet, it does use low I/P impedance BJTs. Perhaps a simple JFET source follower between the diode and IC is needed. When I was a youngster, we used tapped tuning coils to connect to the diode and (ultimately) the BJT AF amp.

With a genuine long wire antenna and earth ground, a lightning arrestor is ESSENTIAL. That device can be made from a non-resistor spark plug.

Another tweak for the external antenna/earth ground setup is to connect them to a separate winding on the same form as the tuning coil. That winding has quite a fewer turns. Presto/chango step up transformer.

Eli D.

 

RE: It's almost a crude crystal radio but the tuning portion is connected wrong...., posted on February 10, 2017 at 20:03:18
Jim Doyle
Audiophile

Posts: 1146
Location: Medford, MA
Joined: July 8, 2001
You can protect this with a GDT - which are about $4 in qty 1 from Mouser.
These guys are mini versions of the OB2 OA2 glow regulators.... They conduct around 90V or so, so your FET needs to have a gate breakdown voltage above that....

Another longwire protection device is a simple neon lamp....

-- Jim

 

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