Satellites, Technology of
SATELLITES, TECHNOLOGY OF
As with radio or television itself, it is not necessary to understand thoroughly the electronics and physics of satellites in order to understand how they work. Operating a satellite system is a bit more complicated than turning on a television and changing the channel, but the concepts are not difficult to grasp.
Satellites are Earth-orbiting spacecraft that are used to relay radio frequency signals. They are normally powered by batteries and/or solar cells. Satellites operate on various frequency bands, and they carry voice, data, fax, audio, and video information. The focus of this entry will be on television news uses of satellites, so it will be more concerned with audio and video than with other types of transmissions.
All satellite transmissions (i.e., feeds) begin with an uplink, which is the Earth-based transmission station that sends a signal to the satellite. The word "uplink" is also used as a verb; to uplink is to send a signal to a satellite. Two of the most common frequency bands that are used for audio and video transmissions that originate in the United States are Ku-band and C-band. C-band is the part of the electromagnetic spectrum between 3.7 and 4.2 gigahertz, and the range for Ku-band is 11.7 to 12.7 gigahertz. Ku-band is the more portable of the two, but it is not as powerful as C-band. Because C-band is very powerful and because some frequencies in the range are also used for other types of transmissions, each C-band transmission that originates in the United States requires clearance from the Federal Communications Commission (FCC).
The dishes that are used for C-band transmissions are so large it takes tractor-trailer rigs to get them into place. Ku-band satellite dishes are small enough to fit on the roofs of medium-size trucks, and transmissions on those frequencies do not require prior clearance. Hence, the portability and speed that are afforded by Ku-band transmissions make it the choice for most news uses. However, because Ku-band signals can be affected by adverse weather, C-band transmissions are commonly used for lengthy, planned events, such as sports contests or political conventions.
Hardware and "Windows"
In order to make a satellite feed, a television or radio station needs hardware and satellite time. The hardware includes the uplink. Uplinks can either be fixed or portable. Fixed satellite uplinks are those that would be mounted on the roofs of television stations or elsewhere. Portable uplinks (PUPS) would be mounted on the roofs of large vans or medium-size trucks, and it is those types of uplinks that are used to send signals from remote sites. The technology has become sophisticated and small enough that all of the necessary hardware for a satellite transmission can fit into a case that is the size of a large suitcase. These fly-away packs allow news crews to access sites to which they could not drive even a medium-size satellite truck.
Most satellite trucks include the following elements:
- controls to raise and position the dish,
- monitors to check that signals are meeting technical requirements and are going to the desired satellite and transponder,
- a complete communication package, including land-line phones, cell phones, and a way to communicate via audio subcarrier on the satellite in places that have no regular or cell phone service,
- a means to access electrical power and a generator for use in remote locations,
- videotape playback units, and
- inputs for one or more live cameras.
Many trucks also come equipped with redundant transmission systems, which means they contain two of every component that is needed to send a signal. Some also include editing equipment for on-site compilation of stories.
Some large-market television stations or networks might own one or more uplinks, but most do not own satellites; instead, they lease space. A coordinator merely calls one of the many providers of satellite time and books a window. The "window" is the time that is reserved by that news operation for that particular satellite feed. Windows are set up in military-style time (meaning, for example, that they are scheduled for "18:10" instead of "6:10 p.m."), and they can be booked in intervals that can last for as little as five minutes. Satellite feeds run the allotted time and no more. Should a station book a window from 18:10 to 18:15, someone in the news operation must ensure that the feed ends by 18:15 because the computer that times the window will "pull the plug" at 18:15.00, even if the reporter who is live on the scene needs only a few more seconds to finish the story.
Once the window is purchased and "opens" (at 18:10 in the above example), an uplink operator directs the signal to a specific transponder on a satellite. Most communication satellites carry a minimum of twenty-four transponders, which are the specific parts of the satellite that accept the signal, process it, and direct it back to Earth. Some satellites carry as many as seventy-two transponders, thirty-six C-band and thirty-six Ku-band. Each transponder operates on a specified frequency, and all communication satellites are in the same relative orbit at all times, so by merely consulting a chart of satellite positions and "dialing in" the signal, the uplink operator can locate the desired satellite. This does require some precision. Because there are more than two hundred communication satellites in geostationary orbit above the Equator, they are so close to each other as to be positioned only two degrees apart. (If satellites are aimed at different landmasses or operate on different frequency bands, they can be even closer than two degrees apart.) If a satellite suddenly stopped in its orbit for some unexplained reason, there would be a space pile-up of major proportions. The International Telecommunications Union (ITU) and the FCC help maintain order in the satellite industry by assigning orbital slots to spacecraft. Because of the closeness of one satellite to another, technicians must be careful not to "light up" the wrong satellite. However, once the proper satellite has been identified, it is merely a matter of punching in the frequency of the particular transponder on which the news or programming operation has booked time and then sending the signal.
Communication satellites are always in the same relative orbit because they are programmed to match the speed of Earth's rotation. This puts them in geosynchronous (or geostationary) orbit. What this means is that the satellite appears to be stationary relative to a given point on Earth. In the early days of satellite communication, before the use of geosynchronous orbit, Earth-based transmission units had to track the satellite as it passed overhead, and because of that, the satellite was available to accept signals only a few minutes out of each hour. Modern satellites, until they fall out of geostationary orbit, are available around the clock and never change their relative locations.
The transponder accepts the signal, processes it, and sends it back to Earth on a different frequency. Many satellite dishes are equipped both to send and receive, so the dish on top of a building or atop a satellite newsgathering (SNG) truck is capable of sending a signal on one frequency and receiving the return signal on a different frequency. If two different dishes were required, it would be a much more costly and difficult process to do satellite feeds. Although the signal from the uplink to the satellite is very directed, the signal that comes back to Earth from the satellite covers a wide area that is referred to as the "footprint." Any receiver (downlink) that is within the footprint can receive the downlink signal if the receiver is tuned to the correct frequency. As with the term "uplink," "downlink" can refer to the hardware or the process.
Any given satellite can have a footprint that covers land area that is equivalent to the size of the continental United States. Beyond that, Earth's curvature becomes a problem. So, for example, in order to broadcast portions of the 2000 Summer Olympics live back to the United States from Sydney, Australia, NBC had to use satellite "hops." This entails sending the signal up to a satellite, back to a downlink, back up to another satellite, and so on until the signal reaches the intended receiving point on the other side of the globe.
Often, a satellite feed actually involves two feeds: the distribution feed and the backhaul. The backhaul is the feed that goes to the distribution point for refeed. For example, a news feed service brings in a number of stories from various sources and compiles those stories to be sent out as part of a regularly scheduled feed. Another example is sports. A game might be beamed back to a central point for insertion of commercials, graphics, or other material before it is beamed back out for distribution. Therefore, a game telecast might occupy two transponders for hours. The same is true of coverage of political conventions and the like.
Because of the large area that is covered by the footprint, stations are able to share audio and/or video with each other quickly and efficiently. In the "dark ages" of television news, if several stations in various markets requested a story from a sister station in another city, it would involve reshooting film for each of the requesting stations and putting it on a bus or driving it to the other city. Even when video came into use, stations had to make a copy of the story for each of their requesting partners and ship the tapes somehow. With satellite technology, however, the originating station merely sends its version of the story via satellite to all of the requesting stations at once. To take advantage of the technology, groups of stations have banded together to share video from market to market. These cooperatives are called consortia.
All geostationary communication satellites are positioned 22,300 miles above the Equator. It is at this precise distance that a satellite can maintain an orbit that perfectly matches the period of rotation of the earth: twenty-four hours. Although satellites are so far out in space, they are not necessarily directly overhead, and a line-of-sight is required between the uplink and the satellite. For example, if a particular satellite is low on the eastern horizon and the satellite truck is positioned on the west side of a high-rise building, it will be impossible to hit the satellite with the signal, and the news operation will have to move the truck or use a different satellite.
It takes about half a second for a signal to hit the satellite and bounce back to Earth. Because of that delay, a reporter can be caught off-guard and be confused if he or she starts hearing what was just said as he or she is trying to say something different. It is necessary for a reporter on a remote site to hear any questions that a news anchor might ask, so to deal with the problem of voice delay, an audio operator feeds "mix-minus" into the earpiece of the reporter. Mix-minus is the audio mix that is going out from the station to the viewers, minus the reporter's own voice. The station's program audio is fed to the reporter on-scene through an interruptible fold back (IFB) system. This is the same system through which a producer in the control room communicates with the news anchors in the studio.
At times, a reporter will be doing a story live and will do the same live report for sister stations in rapid succession. However, if the story is big enough to be the top story on a number of stations in a state or region, the personnel at station B will not want to postpone airing the story for the three to five minutes that it might take station A to complete its report. In these instances, news managers will arrange for the story to appear simultaneously on the reporter's station and on other stations within a consortium. These are referred to as "hit-time" or "hard-start" live shots. Each station in the consortium must arrange to "hit the window" at a precise time. At each station, an anchor will say something like "John Smith joins us from the scene." Since the reporter can hear only his or her own station's anchor, timing is critical, because the reporter will start talking as soon as the anchor tosses to him or her. Therefore, a hard-start live shot with a hit time of 6:01:00 means exactly that. Each station must be ready to have the reporter start talking at exactly 6:01:00.
In most cases, the reporter would have fed the taped portion of the report via satellite earlier, and each station will have a copy. When the reporter reaches a predetermined roll cue (i.e., the final few words that will be said before the tape is to begin), each station will play its copy of the tape. When the tape reaches its conclusion, each station will switch back to the reporter live on the scene. He or she will then wrap up the story and end it with a generic line such as "and now back to you in the studio." All stations that are using the hit-time live report can move on to other stories, and the anchors at the reporter's own station can continue to talk to him or her if the newscast producer has decided to have the anchors do so. By doing shared live shots this way, all the stations that are within the consortium have the advantage of having a reporter live on the scene, even though, except for one station, it was someone else's reporter and equipment that generated the story.
It is no exaggeration to say that satellite technology has changed many things about television and radio news. In fact, the technology has changed the very definition of local news. No longer does a local newscast on television or radio contain only stories that occurred within a half-hour drive of the station; it can include anything of interest to the local audience, from anywhere in the nation or the world. Whereas it once took a crew of technicians the better part of a day to set up a live television remote, now one person can set up a satellite truck and be sending pictures to any number of stations within about fifteen minutes of having arrived on the scene. This has led to concerns that technology now drives journalism, particularly in television news. It has also led to calls for news managers to use the technology to advance stories rather than as an end in itself.
See also:Cable Television, Programming of; Cable Television, System Technology of; Digital Communication; Radio Broadcasting, Technology of; Satellites, Communication; Satellites, History of; Telecommunications, Wireless; Telephone Industry, Technology of; Television Broadcasting, Programming and; Television Broadcasting, Technology of.
Cremer, Charles; Keirstead, Phillip; and Yoakam, Richard. (1996). ENG: Television News. New York: McGraw-Hill.
McAvoy, Kim. (1998). "Net Expands to Fill News Hole." Broadcasting & Cable 128(33):24-28.
C. A. Tuggle