Telephone Button FM Transmitter Circuit

Telephone FM Button Transmitter Circuit

The "Original" - Button Telephone Transmitter

FM Telephone button transmitter circuit - Down View
FM Telephone button transmitter circuit - Backside
FM Telephone button transmitter circuit - Side View
FM Telephone button transmitter circuit - Original

I Remember this device well. I built it back around 1984, some 33 years ago. Back then we only had telephones with the carbon button that you could get to by unscrewing the mouthpiece. I was looking for some wire in an old cardboard box a few months ago and found it laying in the bottom. Boy, did it ever bring back a lot of memories.

I was contracted for a job in Nashville, Tennessee and needed to "AH" do a telephone booth. Back then you could unscrew the headsets until the telephone company started gluing them shut a few years later since a lot of people would steal the buttons.

Anyway to make a long story short, I came up with it. It transmitted about a block in the band slightly above 108 Mhz. I opened the button up, dumped the carbon out of it, and modified it using a Heil micro HC-4 Element microphone, a single transistor, couple of resistors and caps. I left the tank circuit exposed so I could squeeze or expand the coil to cater my frequency. It had a 1 inch antenna wrapped around the element.

From there, I used an epoxy resin to encase it's components. A couple hours later I sanded it smooth. It worked great and did what it was engineered to do. When I went back to Georgia I loaned it out to a few enforcement officials and several south Georgia Sheriffs. It was a fantastic device during the days of those old phones. I believe it was in the middle 80,s when they started showing up in the illegal markets imported from some outfit out of the Netherlands somewhere in Amsterdam if I remember. Enjoy a look at the "Original" 1st one. John

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