MC2833 FM RF Transmitter

A very simple FM transmitter circuit can be constructed using this schematic diagram based on MC2833, designed for cordless telephone and FM communication equipment. It includes a microphone amplifier, voltage controlled oscillator and two auxiliary transistors.

This FM transmitter circuit , based on the MC2833 IC has an low drain current ( ICC =2.9mA typically ) and supports a wide range operating voltage ,from 2.8 to 9 volts .

Other features of this MC2833 FM transmitter circuit are : – 30 dBm power output to 60 MHz using direct RF output ,+10 dBm power output attainable using on–chip transistor amplifiers .
Crystal X1 connected at pin 16 and pin 1 ( trough a 5.1uH coil ) is fundamental mode, calibrated for parallel resonance with a 32 pF load.

The final output frequency is generated by frequency multiplication within the MC2833 IC. The RF output buffer (Pin 14) and Q2 transistor are used as a frequency tripler and doubler, respectively, in the 76 and 144 MHz transmitters.

The Q1 output transistor is a linear amplifier in the 49.7 MHz and 76 MHz transmitters, and a frequency doubler in the 144 MHz transmitter.
All coils used are 7 mm shielded inductors, CoilCraft series M1175A, M1282A–M1289A, M1312A or equivalent.

Power output is 9 + 10 dBm for 50 MHz and 76 MHz transmitters, and 9 + 5.0 dBm for the 144 MHz transmitter at VCC = 8.0 V. Power output drops with lower VCC.
Other transmitter frequency can be set , by modify the components value ai is shown in this table .

This FM transmitter circuit need to be powered from a 9 volts DC power supply ( for full performance) .