Regular and FM Radio Broadcasting Basics

As we know traditional regular and FM radio broadcasting are forms of terrestrial radio transmission that deliver audio content to a wide audience. Regular broadcasting uses both AM and FM modulation schemes while FM broadcasting uses Frequency Modulation radio. Both the systems utilize radio towers, but their designs and coverage characteristics differ due to their operating frequency ranges and signal propagation paths.

The term radio broadcasting refers to transmission of audio informations using electromagnetic waves. The radio frequency spectrum lies from 3 Hz to 300 GHz range.

The broadcast transmission is carried out using entity known as radio stations. The broadcast means one to many and hence the signal transmitted by radio station is received by multiple radio receivers. Earlier days radio was developed as separate electronic device with the support of FM as well as AM radio receptions. Now-a-days radio has become part of each and every mobile device such as phones, tablets etc.

Radio Broadcast Transmission
Image Courtesy : wikimedia

The figure-1 depicts electromagnetic spectrum with radio frequency (RF) spectrum part. It also depicts use of AM and FM modulation for transmission of audio informations.

The full forms of FM is Frequency Modulation and AM is Amplitude Modulation. They both are form of analog modulation type. In FM modulation, frequency part of radio carrier signal is varied as per analog baseband informations (here audio). In AM modulation, amplitude part of radio carrier signal is varied as per analog audio.

What is Regular Radio Broadcasting

It refers to traditional method of transmitting audio content over radio waves to reach broad audience. As mentioned it is one to many mode of transmission to relay radio contents to wide geographical area. The listeners tune in using radio receivers to listen to the radio broadcasts. It is also known as terrestrial radio. The key characteristics of regular radio broadcasting are as follows.
• It uses radio stations which transmit audio content over the air using radio waves. These radio waves travel through the Earth's atmosphere and are received by radio receivers within radio station's coverage area.
• It uses both AM and FM for radio signal modulation before transmission.
• Stations broadcast specific contents at pre-determined times, known as scheduled programming.
• Stations can broadcast live contents and pre-recorded contents or mix of both.
• Radio broadcasting include both local and national relaying stations which can cover specific area and large geographical areas respectively.
• Radio stations can be either public (government funded) or private (commercially operated).
• It can cover wide area which depends on transmit power and height of tower.
• Radio receivers are relatively simple and inexpensive and are commonly found in homes, cars, smartphones and other portable devices.

What is FM Radio Broadcasting

This broadcasting type uses frequency modulation to transmit audio content over radio waves. It offers higher sound quality and it is popular for music and high fidelity audio relay or broadcasting. The FM radio broadcasting system consists of an audio source, an audio processor to optimize audio quality, a transmitter that converts the audio signal to a high-frequency carrier wave, an antenna to radiate the signal, a transmission line to connect the transmitter to the antenna, and a broadcasting tower to raise the antenna to an optimal height for wide coverage. The FM radio receivers are required to receive and demodulate FM radio signal to listen desired stations or programs.

• FM Radio Broadcasting utilizes frequency band 88 to 108 MHz.
• The carrier frequencies are separated by 200 KHz.
• The peak frequency deviation is fixed at 75KHz.
• Intermediate frequency fIF in case of FM is 10.7 MHz.
• Polarization is horizontal.

The other benefits of FM radio broadcasting are as follows:
• The system is energy efficient
• The system is connection free
• It is ubiquitous
• It is cheap
• FM radio system is easy to integrate with other wireless standards such as wifi, bluetooth etc.
• Maximum output power is about 15 nWatt
• The broadcast range is about 5 meters

Mobile FM radio

The figure-2 depicts typical components for FM radio in the mobile phone. As shown it consists of FM transmitter, FM receiver, antenna(either external or internal), codec chip.

Radio Broadcasting Frequencies

The frequencies are categorized into two bands viz. AM (Amplitude Modulation) and FM (Frequency Modulation). They are allocated region wise across different parts of the world. The radio channels are used to carry either data or control signal informations. The FM radio frequency channels are numbered from 200 to 300. They are mapped with values from 87.9 MHz to 107.9 MHz. All the channels are 200KHz wide. Hence FM channel 201 is located at 88.1MHz, FM channel 202 is located at 88.3MHz (200KHz from channel 201). The last FM channel 300 is located at 107.9MHz frequency.

Below the radio frequency bands in the EM spectrum, TV channels 5 and 6 are allocated. The TV frequency band is from 82 to 88 MHz. Above the radio frequency bands, aeronautical frequencies are allocated with frequency range from 108 to 136 MHz band in the EM spectrum.

In the US, AM frequency bands are allocated from 540KHz to 1700 KHz with the step size of 10KHz. This gives AM frequency channels 540, 550 to 1700. Pls. note 530KHz is not used for AM radio broadcasting and it is reserved for specific purpose.

In some other regions AM radio broadcasting frequencies are allocated with 9kHz BW. This gives AM radio channels such as 531kHz, 540kHz, 549kHz and so on. In the case of TV signal broadcasting, picture carrier is VSB-FC modulated, colour subcarrier is QAM modulated and sound is FM modulated.

Conclusion: Despite the rise of digital media and streaming services, regular and FM radio broadcasting continue to play an essential role in providing real time audio contents. They provide wireless connectivity using radio waves with diverse audiences around the world.

Similar posts on radio

RF and Wireless Terminologies