Satellite radio transmission has promised to revolutionize radio, a technology that has seen little change since the introduction of FM bandwidths almost 40 years ago. Although there are two companies with a license from the Federal Communications Commission to broadcast digital radio, XM Satellite Radio is the only digital satellite radio service currently available in the U.S. XM employs cutting-edge technology to ensure maximum coverage and signal clarity. XM hopes that its high quality signal and public interest benefits will appeal to consumers, paving the way for the success of American satellite radio.
Introduction
On December 12, 1901, the Italian inventor Guglielmo Marconi sent a message across the Atlantic Ocean by means of electromagnetic waves, giving rise to a technology called "radio". By 1920, the first radio station (KDKA) began broadcasting from Pittsburgh, and by the 1930s, the radio console was in many American homes. Marconi's means of communication using analog radio waves survives even today. About 40 years ago, frequency modulated transmission was introduced and has seen little technological change. Now, at the turn of a new century, satellite radio is poised to become the third major broadcast medium and transform the radio industry.
Satellite Radio - How It Works
Broadcast Studios
The first element needed in the satellite radio infrastructure is broadcast studios, used to send signals to satellites. XM consists of a state of the art broadcast center in Washington, D.C. - the largest and most advanced of its kind in the world. Its sole purpose is to support the on-air talent and programmers with the technical facilities to produce radio quality desirable to the public. Housed in a century-old former printing loft, the center takes advantage of massively reinforced construction - which once supported multi-ton press machinery - to create acoustically isolated broadcast rooms. Digital satellite radio has such a wide dynamic range (90 dB - compared to FM radio's 40-50 dB) that even soft background noise can be detected (Huber 392). Background noise propagates through air as waves (as might occur with nearby auto, or jet traffic) and through solids as vibrations (such as rumbles of underground subways through building foundations). In order to reduce such extraneous noises, special construction techniques are required.
Thick Walls and Floating Floors
In order to preserve the integrity of the broadcast signal, studios should be constructed so that they are isolated from unwanted acoustical noise. Therefore, steps must taken to reduce the intensity of unwanted sounds that may leak into the studio environment. The reduction in the sound pressure level (SPL), i.e. loudness, of a sound as it passes through an acoustic barrier of physical mass is called the transmission loss (TL) of a sound. A heavier acoustic barrier yields a higher transmission loss. In a studio, the primary goal is to increase the transmission loss through a wall at most frequencies. This is accomplished by building a wall that is as massive as possible (in terms of both cubic and square density) and that is highly damped (meaning well supported by its reinforcement structures and not susceptible to vibration). Also, for many recording and broadcasting facilities, the isolation of floor-borne noises is an important consideration. For example, a building that is on a busy street and whose concrete floor rests directly on ground foundation may experience severe low-frequency rumble due to passing motorists. Thus, some form of isolation from floor-borne sound is essential. One of the most common ways to isolate floor-related noise is to construct a "floating" floor, which is a floor that is structurally decoupled (to a certain degree) from its sub-floor foundation. In this approach, either discrete isolation mounts or continuous rubberized floormat coverings are used as an underlayment over the existing floor foundation. This underlayment is then covered by another concrete floor.
Multimedia
Principles of Satellite Radio
Dr. Dan Goebel of USC Electrical Engineering explains the principles of this recently unveiled technology View
