The early transmitter for radio broadcasting is so big and bulky that they do occupy numerous spaces. The circuitries are mainly designed with valves, which are big in sizes.
With the advent of semiconductor materials such as transistors electronic equipment are now becoming miniaturized such that small transmitters are now becoming handy and compact.
In line with this we choose to design a complete radio broadcasting equipment tat is compact and existence of semiconductor materials.
The system units are of two categories namely: audio console for the processing and mixing of musicals is basically a condenser microphone.
The transmitter unit is where the center frequency is provided. All these were designed to be in compact and small manner. This project is aimed at serving a community using a small and compact radio broadcasting equipment with a power watt of 1 watt a community of 1 kilometer in radius should be covered comfortable and the audio production very clear unlike the common noisy FM microphone project.
This our project work is all about design and construction of a complete radio broadcasting equipment that is compact and miniaturized. It is capable of delivering a power output of 1 watt and assumed to cover a distance of 400 meters ie 200 meters radius depending on obstructions.
The transmitted signal is frequency modulated stays constant and its frequency varies according to the amplitude variations of the audio signal. When the input signals amplitude increases (ie during the positive half cycle) the frequency of the carrier increases too, on the other hand when the input signal decreases in amplitude (negative half-cycle or no signal) the carrier frequency decreases accordingly.
The output frequency of the transmitter is adjustable from 88 to 108 MHZ, which is the FM band that is used for radio broadcasting. The circuit as we have already mentioned consist of four stages. Three RF stages and one audio preamplifier for the modulation. The first RF stage is an oscillator is controlled by LC network L-C, C is there to ensure that the circuit continues oscillating and C adjusts the coupling between the oscillator and the next RF stage which is an amplifier. This is built around TR2 which operates in clas c and is tuned by means of L and C. the last RF stage is also an amplifier built around TR3 which operates in class c the input of which is tuned by means of c and l. From the output of this last stage which is tuned by means of l-c is taken then the output signal which through the tune circuit l-c goes to the aerial.
The circuit of the preamplifier is very simple and is built around TR4. The input sensitivity of the stage is adjustable in order to make it possible to use the transmitter wit different input signals and depends upon the setting of VRI. As it is the transmitter can be modulated directly with a piezoelectric microphone, a small cassette recorder etc. it is of course possible to use an audio mixer in the input for more professional results which we did
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