Radio Broadcasting Basics
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 support of FM as well as AM radio reception. Now-a-days radio has become part of each and every mobile device such as phones, tablets etc.
Due to this radio broadcasting has evolved and new advances are happening in this arena.
The figure-1 (taken from wikimedia commons) shows electromagnetic spectrum with radio frequency spectrum. 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. Refer modulation basics and types and AM vs FM vs PM modulation types.
Mobile FM Radio Broadcasting
• 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 ara 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
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.
FM Radio Frequency Channels
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.
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