[AMRadio] Numbers Stations - NPRs slant

SBJohnston at aol.com SBJohnston at aol.com
Sat Nov 13 12:26:14 EST 2004

acohen at texas.net writes:

> I also had a friend who discovered that old pay telephones used to use 
> the sound of the falling coins striking a bell to determine whether the 
> money was properly deposited in the phone.  

Payphones later used frequency-shifted DTMF tones to signal the deposit of 
each coin.  I changed the crystal in an accoustic speed dialer to make that set 
of tones... worked quite well until they rigged the phones to mute the mic 
until money was deposited.  And now it is all done as digital signaling out of 
the voice-frequency range.  

Steve WD8DAS

sbjohnston at aol.com
Radio is your best entertainment value.  

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