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A 4 Kilometer Range 100MHz FM Transmitter Circuit

A 4 Kilometer Range 100MHz FM Transmitter Circuit
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1). Here is the Specification of the Transmitter:


  1. No. of stage: 4
  2. Frequency of operation: About 100MHz
  3. Antenna type: Folded 300 ohms dipole.
  4. Range obtained in free space: Up to 4km with dipole antenna 30 feet above ground level. More range with yagi antenna.


This was made to give it a little directional bias, and indeed, it transmitted very directionally, boosting its range to several kilometers in free space.

Our intention, as a small startup company, to sell this as a finished kit, or do-it-yourself kit. In those days, people were tending to copy any transmitter design and claim as their own. So, we made a tricky decision. In the PCB, I changed the dimension of the three coils so that they mimic something like our company name ‘RCL’.  See the PCB design below:




For the sake of this particular transmitter, consider the special design of coil now just mearly a coil; and does in no way represent any company or company name.

This actual design was made using a very early version of ‘Protel‘, called ‘Protel 99SE’. I designed this on a 486 desktop having just 4MB RAM and a 256KB video RAM. Today when I see this, I find myself that, to create brilliant things, we may always not need the latest gadgets and software.

Because, this first design, and all subsequent improvement of this version (that I designed on the same computer using same software), was best-seller for our company back then.

So after selling many thousand units of this transmitter across the globe, the design has been retired and I decided to offer this for free to the internet community and posted that to ‘Tripod’.



2). Circuit Diagram and Brief Description

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