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 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 the transmission of audio information using electromagnetic waves. The radio frequency spectrum lies in the range of 3 Hz to 300 GHz. The broadcast transmission is carried out using an entity known as radio stations. Broadcasting means one-to-many, and hence the signal transmitted by a radio station is received by multiple radio receivers.

In earlier days, radio was developed as a separate electronic device with support for both FM and AM radio receptions. Nowadays, radio has become part of almost every mobile device such as phones, tablets, etc.

Image Courtesy : wikimedia

Figure-1 depicts the electromagnetic spectrum with the radio frequency (RF) spectrum highlighted. It also depicts the use of AM and FM modulation for the transmission of audio information. The full forms of FM and AM are Frequency Modulation and Amplitude Modulation, respectively. They are both forms of analog modulation.

In FM modulation, the frequency part of the radio carrier signal is varied as per analog baseband information (here, audio). In AM modulation, the amplitude part of the radio carrier signal is varied as per analog audio.

What is Regular Radio Broadcasting?

It refers to the traditional method of transmitting audio content over radio waves to reach a broad audience. As mentioned, it’s a one-to-many mode of transmission to relay radio content to a wide geographical area. 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 that 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 the radio station’s coverage area.
• It uses both AM and FM for radio signal modulation before transmission.
• Stations broadcast specific content at pre-determined times, known as scheduled programming.
• Stations can broadcast live content and pre-recorded content, or a mix of both.
• Radio broadcasting includes both local and national relaying stations, which can cover specific areas and large geographical areas, respectively.
• Radio stations can be either public (government-funded) or private (commercially operated).
• It can cover a wide area, which depends on the transmit power and height of the 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 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
• A broadcasting tower to raise the antenna to an optimal height for wide coverage.

FM radio receivers are required to receive and demodulate FM radio signals to listen to desired stations or programs.

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

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 systems are easy to integrate with other wireless standards such as Wi-Fi, Bluetooth, etc.
• Maximum output power is about 15 nWatt.
• The broadcast range is about 5 meters.

Figure-2 depicts typical components for FM radio in a mobile phone. As shown, it consists of an FM transmitter, FM receiver, antenna (either external or internal), and 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 information. 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, and 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 a 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 a step size of 10KHz. This gives AM frequency channels 540, 550 to 1700. Please note that 530KHz is not used for AM radio broadcasting and is reserved for a 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, the picture carrier is VSB-FC modulated, the color subcarrier is QAM modulated, and the 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 content. They provide wireless connectivity using radio waves to diverse audiences around the world.