Four Stage FM Transmitter

This FM transmitter circuit uses four radio frequency stages: a VHF oscillator built around transistor BF494 (T1), a preamplifier built round transistor BF200 (T2), a driver constructed round transistor 2N2219 (T3) and a power amplifier built around transistor 2N3866 (T4). A condenser microphone is connected at the enter of the oscillator.
Circuits diagram :

Four-Stage FM Transmitter Circuits Diagram

Working of the circuit is inconspicuous. When you discuss close to the microphone, frequency-modulated alerts are bought at the collector of oscillator transistor T1. The FM alerts are amplified via the VHF preamplifier and the pre-driver stage. You may additionally use transistor 2N5109 rather than 2N2219. The preamplifier is a tuned class-A RF amplifier and the using force is a class-C amplifier. Signals are ultimately fed to the class-C RF energy amplifier, which delivers RF power to a 50-ohm horizontal dipole or ground airplane antenna. Use a heat-sink with transistor 2N3866 for heat dissipation. Carefully adjust trimmer VC1 connected across L1 to generate frequency within 88-108 MHz. Also modify trimmers VC2 thru VC7 to get maximum output at most vary. 

Regulator IC 78C09 offers stable 9V provide to the oscillator, so edition in the provide voltage won't have an impact on the frequency generated. You can also use a 12V battery to energy the circuit.

Assemble the circuit on a general-purpose PCB. Install the antenna properly for maximum vary. Coils L1 via L5 are made with 20 SWG copper-enamelled wire wound over air-cores having 8mm diameter. They have 4, 6, 6, 5 and seven turns of wire, respectively.  

EFY note. This transmitter is meant handiest for educational functions. use of this transmitter with outdoor antenna is against the law in most sections of the arena. The author and EFY might no longer be chargeable for any misuse of this transmitter.

Author : Pradee G.  - Copyright : EFY