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A 4 Kilometer Range 100MHz FM Transmitter Circuit

A 4 Kilometer Range 100MHz FM Transmitter Circuit

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Many electronics enthusiast love transmitters. It is very hard to imagine that a hobbyist in his lifetime has never tried to build a transmitter. Remember your childhood when you were fascinated about building a small, one transistor based medium-wave transmitter. And how thrilling it was to hear the voice or song played back to your neighbour’s radio set few hundred feet away.

When I was a school-going student, this ‘transmitter’ bug bite me and I tried my best to build a medium wave transmitter using just a single transistor, and the MW antenna coil with the ferrite rod, as the oscillator part, and just a stick antenna to radiate the signal. It was giving very good sound, but the transistor was getting too hot despite using a heat sink.

So, what I did, is very funny. I put few droplets of water on the transistor and it kept evaporating. And I kept putting drops after drops to keep running the transmitter and tried to mimic a local radio station.

To my amazement, one of my neighbour picked up the signal. And it was a ‘Joy’ moment for me in my life – it felt like one of the biggest achievement in my life. And indeed it is. I still remember it vividly.

Then comes the FM transmitter era. To broadcast to more and more of my neighbours, I started hunting for many long range FM transmitter circuit. And as time passes on, I built myself several. One of such circuit is still on Tripod website. Internet was at its infancy stage back then, Google, Facebook etc. were not popular. And free sites like ‘Tripod’ allowed common internet users to build a free page. (And they all were non-existent when I built that medium-wave transmitter).



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That was around 1998 when I already have built several FM transmitters. Just two years before this website was born. Yes, this website, Electronics Infoline, you are in right now, is 15 years old at the time of this writing in 2015.

Today on 29th June, 2017, we celebrate 17 years birthday of Electronics Infoline.

At that early time, our company ‘Radio Communication Lab’ was new. So, I myself developed a transmitter circuit for my company and put the complete details on ‘Tripod’ webpage.

In this article you learn about:

 

  1. Specification of the Transmitter

  2. Circuit Diagram and Brief Description

  3. Design of BALUN

  4. PCB Design Details

  5. Parts List

  6. Conclusion

 

This is a long range fm transmitter circuit. This transmitter uses four transistors and a BALUN transformer (Balanced to Unbalanced Transformer) to use with a dipole antenna, instead of commonly used Ground Plane antenna. Exactly like old days television receiver set that used a yagi antenna, a booster, and a flat feeder cable. See the circuit in the next page. This transmitter will really work if you construct it carefully and follow all the information honestly.

 

 

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1). Specification of the Transmitter

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