Schematic for the Micro FM transmitter

Posted on Feb 5, 2014

Tetsuo Kogawa`s circuit is pretty well documented, but not in conventional schematic form. I decided to enter it into LTSpice to see what it could make of it, and decided to go ahead and put the schematic online here, with perhaps a few comments: I`ve set this up more or less as I built the circuit: in my circuit C1 is a small air variable cap tha

Schematic for the Micro FM transmitter
Click here to download the full size of the above Circuit.

t goes up to about 18pF, so I`ve set it to 12pF here. I use a 9V supply, so that`s what I put in for V2. I changed the power supply bypass cap to be 0. 1uF instead of 0. 01uF, since I have a bag of 0. 1uF ones, and it doesn`t seem to affect the circuit. The L1 value of 0. 08uH was determined by plugging numbers into the formula for an air wound solenoid coil: it`s probably only very roughly what the inductance actually is. Instead of the 2SC2001, I went ahead and put in the 2n3904 that I used. V1 is supposed to model the audio input, supplying a 1000 Hz, 1V amplitide sine wave to the modulation input. The output should be tapped from the emitter of Q1. I`m going to experiment with the circuit a bit more: I`m particularly interested in jigging this up so I can figure out what the deviation is likely to be, and how it can be controlled, and how the biassing might change with a 6V supply.

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