Satellite radio introduced a new way to broadcast and receive commercial radio. Traditional radio towers still broadcast local stations, but digital radio beams data from satellites in an entirely new way of transmitting information. One of the first major digital radio providers, XM Radio, was named to highlight that difference. When XM Radio merged with another digital provider, Sirius, the company became SiriusXM, still highlighting the difference between digital and standard broadcasting.
Types of Radio Broadcasts
The earliest form of commercial radio broadcast used variations in the strength, or amplitude, of the radio wave to transmit sound. This form of broadcast, using amplitude modulation, or AM, bands was efficient but had limitations. Later, another form of broadcast which broadcast waves of a consistent amplitude but variable frequency was developed. Frequency modulation, or FM, radio was more powerful and clearer than AM but still limited in how far it could be transmitted before the signal became garbled. Digital, or satellite radio doesn't use traditional modulation of waves, but rather transmits a data stream from orbiting satellites special radio equipment then translates. Because it is unmodulated, digital radio is sometimes called XM -- or No Modulation -- radio, and that name was taken by one of the major digital broadcasting companies.
In AM radio broadcasts, the amplitude of the combined audio frequency and radio frequency waves varies to match the audio signal. Because the strength of the waves is so inconsistent, it becomes particularly vulnerable to interference from electrical energy. Household electronics, car engines, lightning and static electricity can cause disruption that the listener hears as static.
In FM radio broadcasts, the frequency of repetition of the broadcast radio waves changes to reproduce the audio signal. FM radio does not have as much distortion from electrical energy or other interference as AM radio, but is still limited by the strength of the broadcast signal and the sensitivity of the receiver.
Satellite Radio (No Modulation)
Digital radio broadcasts from satellites as a digital signal that is unscrambled by a chip in the radio receiver. Subscribers pay a monthly fee to have access to digital radio channels, similar to how satellite television is marketed. As of April 2013, different subscription levels offer access to between several dozen and more than 100 channels
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