Make your own FM radio

Engr Sabir Hussain

Radio is a well known source of media and it plays a vital role to keep people updated through news, entertainment and informative programs. In this regard, it is worth mentioning to know that a modern radio station is equipped with high quality sound equipment and noise free voice transmission that oblige people to listen their favorite programs on radio. The International Telecommunication Union (ITU) has allocated the (300KHz-3MHz) as medium wave in which AM radio broadcast frequencies exist, accommodating around 120 channels. Similarly, 3MHz-30MHz is called short waves in which a portion is dedicated for FM radio broadcast.

The message data (human voice or recording) is low frequency signals and cannot be transmitted to longer distances as it is distorted due to interference offered from surroundings, therefore, a career frequency which is a high frequency and can travel long distances prerequisite to accomplish the broadcast. The old radio station was based on amplitude modulation (AM) which still exists in some areas around the globe, uses amplitude modulation to transmit signal. The amplitude of career wave is varied in proportion according to the message signal. It is usually used to cover longer distances as the signal is strong enough to travel long distances, however, can easily be interfered by noises and weather conditions.

In addition, it has low voice fidelity. The frequency range for AM radio broadcast is 550KHz to 1720KHz. On the other hand, frequency modulation (FM) invented by an American engineer, Edwin Armstrong in 1933, varies frequency of career wave as that of message signal. It covers small areas as compared to AM but its signal is strong enough to resist most of the interruptions except very large objects like high buildings and hill sides. The FM radio broadcast frequency range is 87MHz to 108MHz.

For a simple FM radio station, the obligatory equipment is mic, audio cables, audio mixer, modulator, a transmitter and frequency bandwidth. Mic or microphones are a type of transducer - a device which converts energy from one form to another. Microphones convert acoustical energy (sound waves) into electrical energy (the audio signal). Audio cables carry this audio signal in the form of electrical signals. A sound mixer is a device which takes two or more audio signals, mixes them together and provides one or more output signals, as well as combining signals and mixers allow you to adjust levels, enhance sound with equalization, effects, monitor feeds and record various mixes, etc. Mixers are frequently described by the number of channels they have.

For example, a “12-channel mixer” has 12 input channels, i.e., you can plug in 12 separate input sources. Next is a modulator which modulates the incoming data signal and feed it to transmitter. The transmitter itself generates a radio frequency alternating current which is applied to the antenna. When excited by this alternating current, the antenna radiates radio waves and the message signal broadcasts in the space. This signal is received by the receiving antennas and the signal is demodulated to extract the original voice signal and feed to speakers for the listeners. The frequency allocation is monitored by the respective frequency allocation boards (FAB) which allot and monitor frequencies to avoid interferences of different broadcasters to maintain quality of service. However, acquiring license is mandatory from the respective monitoring boards before broadcast.

The audio cables come in different types and specification depending upon the selection of the equipment and their ports. The most popular is the external line return (XLR) cable which has a good resistance against interference. Its shield consists of three cables inside, positive, negative and neutral. The signal flows through positive cable while the inverted copy of the same signal passes though negative cable and the neutral is always ground. On the other side of the cable, the inverted signal is converted back and matched to the positive cable which resultantly cancels all noises if any.

The cheapest radio station is Web Radio which needs only mic, a computer, broadcasting software, and a good internet connection. Almost all computers come with built-in audio input/output and USB ports, however, broadcasting software is mandatory which pushes the audio from the computer to online web radio. Also, it has the features of media management, gains, and mixing capabilities to allow web broadcast.

The writer is a satellite engineer by profession. He did B.Sc Electrical Engineering (Telecom) from the COMSATS University, Lahore Campus and M.Phil in Space Science from the University of Panjab, Lahore. He can be contacted at:

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