Rating of FM
  Transmitter

Coverage

Cost of bare
transmitter

27 Km.
48 Km.
75 Km.
100 Km

sets can interpret.

Critical factors
affecting FM
transmission

Harmonic Distortion:
   Electronic circuits generate harmonic waves. Suppose a frequency consists of a fundamental 1000 Hz waveform equal to the input voltage ‘v’. Then we also get a second harmonic wave of 2000 Hzthat may be ‘0.2v’ in amplitude and a third harmonic of 3000 Hz having perhaps ‘0.1v’ amplitude. They deform the fundamental wave. Greater

 
oven. We eliminate through sinks the heat dissipated by system-elements. Heat-sinks are cooled by an air blower.

Frequency Drift:
   As the electronic equipment ages, there is a slight drift in the operational frequency. It is less than 500 Hz per year in well-designed products.

How an FM
transmitter
operates
Stages of Main system:
   Audio Amplifier adjusts level of input signals from left and right channels to
   

 
required intensity. Stereo Coder converts the left and the right channel signals into ‘L+R’ and ‘L-R’ elements. It multiplexes them with a synchronising pilot-signal of 19 KHz. It can also combine signals of traffic radio, radio data system, or Subsidiary Communications Authorisation channels. Modulator superimposes the signal on Carrier Frequency. Synthesiser can set transmitter’s Rated Frequency in steps of 10 KHz over the entire range. It synchronises the signal with Reference Frequency.

  
   Audio Amplifier, Stereo Coder, Modulator and Synthesiser together make up the Exciter portion of an FM transmitter. A standby Exciter takes over if the operating one fails.  Power Amplifier intakes a weak signal. Several push-pull amplifiers progressively magnify it about 500 times. They generate the final signal at the rated output power in on Carrier 88 to 108 MHz range. The Power Amplifier does not break down if a critical component fails. It absorbs any unbalance produced in the system and continues working at reduced

  the number and amplitude of such frequencies, more serious is the harmonic distortion.

Inter-modulation
Distortion:
   Harmonics also interact among themselves. Low harmonic frequencies modulate high ones. Such inter-modulation distortion emits irritating sounds. Hence we equip each sub-system with a filter circuit to nip harmonics in the bud.

Frequency Deviation:
   A crystal generates the Rated Frequency of an FM transmitter. Change in temperature deviates it. Radio receivers miss the new signals as they are trying to sense signals of the Rated Frequency only. We can maintain the crystal at constant temperature by placing it in a self-regulated

FM Transmitter of
2x5 KW rating with combining rack

intensity. Amplified signal exposes any harmonics that survive till the last stage. Harmonic Filter suppresses them. Antenna converts electrical energy of the signal into magnetic energy and propagates it through space.

Supporting systems and their functions
  
   Switch-on Control Unit triggers each sub-system in its logical order. It can adjust output power of the transmitter. It switches overto standby Exciter if the   to standby Exciter if the operating one fails.
   FM Monitoring Demodulator controls the carrier wave as per International Radio Consultative Committee rules. It is adjustable from 88 to 108 MHz. Directional cou-