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07-29-2016, 09:21 AM   #1
April155
Junior Member

Join Date: Jul 2016
Posts: 4
Problem of building an AM radio need advice !

Hello, everyone in here. Very glad that i can post my questions here to get your help.
I have been following the tutorial below to build an AM radio, and when powered on I was picking up what id presume to be radio waves (what I'd describe as a mishmash of "whooshing" sporadic oscillations).
http://www.instructables.com/id/Simple-OP-Amp-radio/
Alright all I need for this project are the following:

x1 LM386 op amp IC chip (From http://www.kynix.com/Detail/1267823/...-4%2FNOPB.html)
x2 1000 microfarad capacitors (any capacitor works but it's louder with these)
x1 100 microfarad capacitor
x1 8 ohm speaker
x1 9 volt battery
x1 project board
some wire (I used about a foot and a half)

optional - a wire parabola (such as a mini fan cage, a colander, etc.)

This was great, but I wanted to single out a specific frequency and listen to a radio station. I did some research and figured out that I have to add a resonance circuit called an LC circuit to single out specific frequencies. I made one with a variable inductor I made with 47 coils in 10cm with square steel railroad spike of diameter 1.5 cm in the center and a capacitor like below. I experimented with 220 pF capacitors in parallel to make 220, 440, and 660 pF and tried using my variable inductor to tune into a station for each of them but it did not work.

(apologize for the poor drawing)
I chose that coil count using the following equation to tune into mid freq radio singles (535-1500 khz), I made sure it covered the lowest frequency and then I could shorten it to get the higher frequencies.:

At this point I was stumped, I heard that you had to put a diode in to single out high frequency singles so desperate, I inserted it between pin 3 and my LC circuit but it didn't help. I also made a home made variable capacitor but likewise I coundn't tune into a station. Most importantly I heard you had to ground the circuit so I attached a wire for the tuner circuit to my computer(which is ground) and it changed the tone slightly but still couldn't tune into a station.
I started to wonder whether there were any am stations in my area due to its falling popularity, but a quick test with my mother's car radio yielded handful of them.
I apologize if my troubleshooting may seem stupid but I'm a little new to this circuit building stuff. I Thank you for reading thus far, and I appreciate any assistance you guys may offer.
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