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Topic: radio on accident. (Read 2468 times) previous topic - next topic

andytt11

So i think i made a radio of some kind. I was trying to make a wav player and im picking up a sports broadcast.

keeper63


So i think i made a radio of some kind. I was trying to make a wav player and im picking up a sports broadcast.


Likely it's some kind of AM broadcast; you likely did create a radio circuit of some kind on accident, but given how easy it is to build a crystal set from rudimentary junk (they don't call them POW radios for nothing) - it's more amazing when you -don't- create a radio.

In fact, some people are actually able to pick up radio in the fillings of their teeth (depends on age of filling, how loose it is, bone conduction, how close they are to the transmitter, and a whole host of other unpredictable factors).
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andytt11

It a local AM high-school broadcast. What is the easiest method for stopping it. I understand some form of resistor would reduce it on the input side,but all I have hooked up now is VCC and ground along with a speaker. I have the http://dx.com/en/p/lm386-chip-20-gain-audio-amplifier-module-blue-222010#.UvUC63cSCRM style.

keeper63

I'm not an RF expert by any means, so I am not sure what the best solution would be.

Likely, the interference is coming thru via the board itself; you might try putting the entire board inside a metal box (and maybe connecting the ground wire of the board to the metal box as well - so that the box becomes "ground". Attach the board in some manner to the box so that it doesn't come into contact with the box and short the board out (seeing that there aren't any mounting holes on that board, double sided tape might be the easiest option for mounting).

You might also try looping the input (and/or the output) wires (and maybe the wires for the power) through a ferrite ring or similar.

One or more of those together might be able to stop it. Perhaps someone on here more knowledgeable on the subject might chime in with other potential solutions...
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Grumpy_Mike

The way to stop this is to place a small ceramic capacitor across the input as close to the chip as you can get. Anything between 100pF and 1nF should do it.

keeper63


The way to stop this is to place a small ceramic capacitor across the input as close to the chip as you can get. Anything between 100pF and 1nF should do it.


It looks like there's already something there on the PCB (C2 or C11 is my guess); then again, who really knows on a board like this (not to mention how finicky the LM386 is for a design).
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andytt11

it was a cheap board. I couldn't beat the price but you do get what you pay for. I will try to use a ring but like i said i have nothing on the input line.

keeper63


it was a cheap board. I couldn't beat the price but you do get what you pay for. I will try to use a ring but like i said i have nothing on the input line.


From what I have read, the LM386 is really picky in circuit layout - in some cases, it can be almost impossible to prototype an amplifier using it with a solderless breadboard, depending on the breadboard used and a whole host of other issues.

Some tutorials go so far as to say to prototype on a regular PCB, keep all leads as short and close as possible to the IC, and have everything else on the PCB be a ground-fill plane as much as possible.

Other times, you can just slap something together with it, and it just works. Like I said - it's picky.
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