Satellite and Internet Radio

Satellite radio signals come from over 22,000 miles out in space. Although former XM Satellite Radio’s transponders (two Boeing HS702 satellites) were set aloft in a geostationary orbit, Sirius Satellite Radio’s birds (three SS/L-1300 satellites) rotate in an elliptical pattern ensuring that each satellite spends around 16 hours over the United States. Offering CD-quality digital radio, these satellite radio signals are beamed to nearly 10 million receiving dishes located in cars and homes. Satellite radio uses the S-band (2.3GHz) for its digital audio radio service (DARS). Both services keep a satellite ready for launch in the event one of their satellites malfunctions. Program origination from ground stations are uplinked to the satellites and then relayed to terrestrial end users (subscribers). Receivers unscramble the incoming signals, which offer over 100 channels each. In addition, the signals contain encoded data for display on receivers allowing listeners to see what is being broadcast (artist, song, etc.). Ground repeaters are employed when needed to strengthen incoming satellite signals. An international satellite radio service called WorldSpace utilizes the L-band to provide digital audio to Africa and Asia. According to former XM Satellite’s chief programmer, Lee Abrams, the operation’s technical department consists of four key areas: studios, hardware development, satellites and repeaters, and IT.

Since the 1990s, radio has been available over the Internet. There are two types of Internet radio stations: those generated by broadcast stations and those that are Web-only in origin. In the case of the first category, stations typically simulcast their broadcast signals over the Web. The second category of Internet station is typically more eclectic in its programming offerings, because the formatting constraints prevalent in broadcast radio do not exist in the independent, cyber-only outlets. Unlike traditional terrestrial stations, whose reach and operating parameters are limited, there are no geographical limitations in Internet radio. With Web access, anyone anywhere can enjoy the medium. A Web station emanating from Dayton, Ohio, may be heard in Bangkok, Thailand, and tens of thousands of broadcasts are available. Unlike terrestrial and satellite radio, Internet radio has the capability of providing a full range of visual data, such as photos, text, and links. Interactivity also adds further cache to the 

medium’s appeal, which has been battling copyright issues concerning the use of music through the decade. The process of distributing an Internet radio signal is not complex. Internet radio operations possess an encoding computer, which converts the audio in a stream. The audio is then sent to a server and it routes the audio data over the Internet to the computer plug-in of the end-user/listener.

The difference between the two bands. Courtesy Brian Belanger, Radio and Television Museum.

Radio has been undergoing a metamorphosis as analog signal processing is being supplanted by digital processing. The reason for the transformation is simple: the demand for better and more evolved sound is at an all-time high. Broadcast stations must convert to digital, or they will not be competitive with audio alternatives, such as MP3 players, satellite radio, and mobile music services.

The full conversion to digital broadcasting is being planned and is likely to be completely realized within a few years. At the 1992 World Administrative Radio Conference (WARC), conducted by the International Telecommunications Union (ITU) in Spain, the FCC proposed use of the S-band 

Although some things remain to be resolved, in-band on-channel (IBOC) digital radio, as created by iBiquity, has been given the go-ahead. This is something the NAB has long supported as a way of maintaining a station’s brand identity as established by its frequency numbers. Although the present system of analog broadcasting essentially replicates sound waves (with inherent shortcomings), digital converts sound waves into a bit-stream of 1’s and 0’s for processing into a low bandwidth. 

In digital, sound waves are assigned numeric values and become coded pulses. Simply put, in digital, sounds are quantified. This allows a more accurate representation of audio signals. Unlike analog, which is limited in what it can reproduce, digital provides greater frequency response and dynamic range. Thus, more audio information is conveyed to the listener, who hears more. Another positive feature from the broadcast operator’s perspective is the fact that digital signals do not require as much power as do analog signals.

Obviously, the transition to digital requires the manufacture of new receivers, and several companies now offer such products. Part of their appeal, according to telecommunications professor Ernest Hakanen, is the fact that they “will allow for much more faithfulness of signal reproduction. High-definition (HD) receivers are designed to use reflected signals as alternative sources of information when the primary signal deteriorates. Using receivers that correct the fading and interference problems associated with AM and FM broadcasts, DAB signals that include specific information that can ‘tell’ the receiver how to compensate for information lost between transmitter and receiver can be received.”

Eventually, the existing analog system of AM and FM broadcasting will be passé. It is not likely, however, that the conversion to digital will occur overnight. Some predict that analog broadcasting will be around for a few more years and that, even when digital is the preeminent broadcasting system, analog AM and FM stations will still be out there – that is, until the FCC no longer perceives them as providing a viable service. In any event, the switch to digital is mandated, and so digital is inevitable. Analog broadcasting will go the way of the turntable.

Radio engineer Aaron Reed expresses his views on the issues that will confront the full implementation of digital radio. “Dealing with the political boondoggle and the necessary paradigm shift in how ‘radio’ will be done after its implementation (from the technical changes necessary to augment the programming delivery to the altering of the way people think of radio as a mostly one-way medium) will prove a major challenge to any engineer. Couple that with station managers demanding they be digital because ‘the other guy is’ but then balking at the hefty price and you can see the problems. It won’t be easy, and inevitably many stations will try to do it on the cheap and fail because DAB is not something that can be done incrementally. Just saying your station is digital is not going to get the listeners. Something far more radical in the programming services that stations offer will be required. The potential is there. Whether engineers and their moneymen are willing to do it is the big question.”