Sunday, December 20, 2015

Great AM radio.





Did you know you could build an intercom with homemade power. AM (amplitude modulated) radio makes it very easy to do.  To do am radios you need and audio source such as a microphone. We could transmit that signal but it might be hard to demodulate and the transmission signals would not be standardized so to speak. So you mix the audio signal with  a transmission signal.


So that signal gets transmitted over the airwaves. So so good. What to we do to turn that signal back into something we can use? If we receive the signal as is the speaker will not play it as the signal cancels it self out.


So we must divide the wave in half or demodulate it so to speak to make it useful. So we will use a rectifier or diode to do just that. The the signal becomes:

Now the signal looks much more like the audio signal we first used to send in the beginning. More has to be done, but that is the gist of the conversion.



Circuits:

Transmitters:


Receivers:

Add a .002 pf capacitor across the antenna ground connection for better signal.

Receiver with tank circuit for tuning.

WWII Vintage radio,
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Fm? under construction.





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