Have a Look at my AM reciever

Thread Starter

Never Give Up

Joined Apr 25, 2007
2
Hi everyone,

How is it goin' with u guys? I hope u r having great time

Actually this is the first time I write in this fourm. I would like to have ur opinions about my project which is all about designing an Am reciever. I searched the Internet and I found this circuit:



I don't know wheter is it going to work or not?
Also, do we have to have an amplifier or r we goin' to hear the AM station clearly?

Thnx for taking the trouble of reading my thread. I hope that I can get benefit from ur experince.

Ur litTle BroTHer
Never Give Up
 

thingmaker3

Joined May 16, 2005
5,084
The circuit pictured is an oscillator. A superheterodyne reciever does make use of an oscillator, but an oscillator alone will not recieve AM broadcasts.

An amplifier is not actually required to hear AM radio broadcasts. Crystal recievers can produce sound in an ear-piece without amplification. My very first electronics project, three decades ago, was a germanium diode reciever. It was a fun project.
 

Thread Starter

Never Give Up

Joined Apr 25, 2007
2
thnx a lot thingmaker3 for ur quick response.

however, can u suggest a complete circuit for an AM reciever that I can implement easily? since I'm gonna buy the elements myself.

I'll appriciate it.

Ur litTle BroTHer:
Never Give Up
 

Ron H

Joined Apr 14, 2005
7,014
The circuit pictured is an oscillator. A superheterodyne reciever does make use of an oscillator, but an oscillator alone will not recieve AM broadcasts.

An amplifier is not actually required to hear AM radio broadcasts. Crystal recievers can produce sound in an ear-piece without amplification. My very first electronics project, three decades ago, was a germanium diode reciever. It was a fun project.
I don't think that's an oscillator. Add an antenna to the tank circuit (I would couple it in with a series 10pF cap), and the first two stages comprise a tuned RF amplifier. The last stage is a detector/audio amplifier. It is indeed an AM radio, and would work with high-impedance headphones. Otherwise, it needs and audio amplifier to drive a speaker.
I ran some sims on it. It works better if you add about 3.3nF from the output to GND. I would also increase the interstage coupling cap to 2.2uF.
The bias levels are very dependent on transistor beta. The stibility would be improved with a better biasing scheme.
 

Ron H

Joined Apr 14, 2005
7,014
Is that third amp running Class B? Hmmm.... yes it is. So the headphones and output cap form a low-pass filter?
Well, for normal low-level signals it's running class A, but the base-emitter junction is nonlinear, so it acts as a detector. The capacitor that I suggested helps get rid of the carrier, and is probably unnecessary unless the output goes to another amplifier, in which case the carrier could overload it.
 
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