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Re: A Simple Radio Circuit




Hi
Without the diode, the earphone sees the AM frequency and tries
( and probaly fails) to move with these oscilations. With the diode in
place, the earphone only sees the positive half of the cycle and with a
small amount of resistance and capactiance in the earphone this half
recified AM is averaged or smoothed into the modulation envelope without
the radio frequency. It is a little like how 60 Hz AC is smoothed in a
power supply that has just diodes and capacitors ( and maybe a transformer)
into DC. The voltage in the power supply will track the long term trends
of the input voltage ( usually on or off) but one gets rid of the 60Hz
part as best one can.


Thanks
Roger Haar U of AZ Physics



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On Mon, 27 May 1996, Tom K. McCarthy wrote:

In a simple radio circuit, there is a diode that links the signal to the
piezeoelectric crystal, the ear phone. Could someone please let me know
why this is required Also, is it true that people have supposedly heard
radio stations through their fillings and, again, how might this be
achieved? Thanks for the info.

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Tom McCarthy Email:mcca6300@spacelink.msfc.nasa.gov