Voice Transmitter via Frequency Modulation

Figure 1 

The circuit is designed to establish a voice transmitter by means of frequency modulation band.

• Modulation – can be defined as the modification of one signal, called carrier, by another, called the modulating signal.,
• Transmitter – an electronic device that can produce or amplify a carrier wave signal, modulates it with a significant signal, and radiates the resulting signal from an antenna which are being utilized in television, telecommunications, and radio
• Frequency Modulation (FM) – transmits its signal or information over a carrier wave by changing its frequency but it can also be taken into account as a special case of phase modulation where the carrier phase modulation is the time integral of the FM modulating
  signal
  The diagram utilizes two BC548 transistors, more importantly descent results although not as good as RF transistors which provide high performance at wide bandwidth. It also utilizes electret condenser microphone because of its high quality recording. The inductor used contains 7 turns per quarter inch with a tuning slug that is used to tune the transmitter. The antenna to be used is a few inch of wire but longer lengths might reduce the amplitude of its oscillation and make the circuit useful. The circuit may be constructed in a bread board with an organized connection. Also, the circuit should be enclosed in a housing to avoid body capacitance.

FM is commonly used at VHF radio frequencies for high fidelity broadcasts of music and speech. It is also used at intermediate frequencies by all analog VCR systems, including VHS, to record both the luminance and the chrominance portions of the video signal. It can also be used at audio frequencies to synthesize sound.

Source:www.zen22142.zen.co.uk/Circuits/rf/2bjttx.htm