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TUCoPS :: Hardware Hacks :: simplefm.txt

A simple FM transmitter





                         A simple FM transmitter

      .---------------------*------*----------------*-----*------.  _____
      |                     |      |            C6  |     |      |   \|/ Ant.
      |                     |      |           15pF_|_  L1@      |    |
      |                     |      |               -.-    @----- | ---'
      |                 12k|~| 15k|~|               |     @      |
      |                    |_|    |_|               |     |      |
      |                     |      |                *-----*      |
      |                     |      |                |     |      |
      |                     |      |             c _|     |      |
      |                     |      |             _/       |      |
      |               ___   | +    |           |/        _|_5pF  |
      |           .--|___|--*--||--*------*----| ECG123A -.-     |
      o +9V       |330k  c _| 1uf  |      |  b |\_        |     _|_.01uF
      |           |      _/        |  .01 |       \_      |     -.-
Mic |~~~|     +   |    |/          |     _|_     e  |     |      |
    |   |-o-||----*----| ECG123A   |     -.-        *-----'      |
    |___|   1uf   | b  |\_    4.7k|~|     |         |            |
      |           |       \_      |_|     |        |~|47ohm      |
      o -9V      _|_     e  |      |      |        |_|           |
      |      .001-.-        |      |      |         |            |
      |        uF |         |      |      |         |            |
      |           |         |      |      |         |            |
      `-----------*---------*------*------*---------*------------'

Notes: L1 is air-wound, 4 turns, #20 enameled wire, 6mm diameter,
       5mm long, center tapped.  The antenna comes off the center tap.

       The antenna is 18 inches long - any wire of that length will do.

       You can tune the circuit by changing C6 or L1.  Try using a
       variable (tuning) capacitor in parallel with C6.  These values
       should place the signal in the FM broadcast band.

       The mic is an electret type.

       Output range should be a few hundred yards.

       The ECG123A transistors can be substituted with 2N706.



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