Fiber Optic, and
Internet (IP) Transmission
In this module we will cover a variety of point-to-point video and audio transmission approaches.
Although it's being slowly replaced by fiber optics, especially for transporting TV signals over significant distances, coaxial cable is still the medium of choice for simple video connections and for many CATV (Community Antenna Television) systems.
On the right of this photo you can see a standard coax connector, and to the left a cutaway view of the single copper wire inside.
Note that a white insulator surrounds the central copper wire and that this is surrounded by metal foil. Around this there is electrical shielding consisting of layers of braided wire and, finally, a rubberized coating.
Today, instead of the coax (two-conductor) video cable shown above, triax, or three-conductor video cable, is sometimes used to meet extra video needs. A cutaway version of triax is shown on the left.
Two other types of coax-based connectors are shown below. On the left is a professional BNC video connector and on the right we see the popular RCA connectors, used in both audio and video.
Although coaxial cable has been used for decades to conduct TV signals, it has a number of shortcomings.
The medium that has many advantages over coaxial cable is fiber optics (also called optical fiber or OF).
The medium of transmission is light. Light waves have an extremely high frequency and travel at 186,000-miles (300,000Km) per second.
A single OF cable can theoretically carry trillions of bits of information every second.
The thickness of an optical fiber is only slightly larger than a human hair. The photo on the left shows a light conducting OF strand going through the eye of a needle.
The tiny, flexible glass or plastic fiber is coated, both for protection and to enhance its characteristics as a reflective lightwave guide.
Fiber optic cables normally carry numerous OF strands within a single enclosure.
Compared to a coaxial cable, optical fiber has ten advantages:
As cable and telephone companies continue to move toward optical fiber, eventually home-to-TV-studio video transmissions may become as simple as hooking up video equipment to the OF cable in your home.
In much the same way that a flashlight projects a beam of light from one point to another, microwaves can be transmitted along a straight, unobstructed line from a transmitter to a receiver.
In the process the microwave beam can carry audio and video information.
Microwaves were originally only used for coast-to-coast network television and for studio-to-transmitter links.
However, as remote broadcasts became more popular, TV stations saw an advantage in having field production trucks equipped with microwave dishes so that news stories, athletic events, parades, civic meetings, etc., could be covered live.
Small, "short hop," solid-state microwave transmitters and receivers, such as the one shown on the left above, can be mounted on lightweight tripods to relay TV signals from the field to a nearby TV production van.
The van then sends the signal to one of the city's relay points -- generally on top of a tower or tall building -- and the signal is then sent to the studio or production center. Note photo on the right above.
Microwave signals must have
a straight, line-of-sight path. Solid obstructions, or even heavy rain,
sleet, or snow, can degrade or completely obliterate the signal.
Vans, Boats, Airplanes and Motorcycles
Although normal microwave signals go in a straight line, it's possible to use an omnidirectional (nondirectional) microwave transmitter to send audio and video signals over a sizeable receiving area.
With this approach signals can then be sent to a TV studio from helicopters, moving cars, boats, and, as shown below, motorcycles.
A complete "very mobile mobile unit" is shown on the left.
A cameraperson sits on the back of this especially equipped (and necessarily quiet) Honda motorcycle with an image stabilized video camera.
While the motorcycle is moving scenes can be transmitted live to the studio or recorded.
When possible, the motorcycle can be parked and the camera set up on a tripod.
Not only can this unit get to news scenes that remote vans can't, but it can get to them faster and in terms of fuel costs much cheaper.
TV Production Vans
The photo on the left below shows an extendable microwave mast on top of a mobile van. The microwave signal can be aimed at a receiving dish at the a local station, or the signal can be beamed to a relay receiver to be retransmitted one or more times until it reaches its final destination.
of a remote production van is pictured on the right above. The van is
a mini-production facility with camera control units, audio and video
recording equipment, a satellite receiver, and video editing equipment.
From the large commercial satellite services we now turn to point-to-point satellite applications used in electronic newsgathering.
News agencies use satellite phone links to send audio and video from remote locations -- generally from third-world countries where standard satellite services are not readily available.
Although satellite phone links were originally intended only for voice transmissions, it was found that a highly compressed video signal could also be sent on a standard audio channel or on a higher quality broadband channel.
Because of the highly competitive nature of TV news, this technology has seen rapid improvement.
Even though the technical quality of satellite phone links still leaves much to be desired, a satellite phone system is small enough to be put in the overhead bin of an airplane. Plus, it can be set up quickly in the field. This is not the case with --
In the late '80s portable, freestanding satellite uplinks referred to as flyaway units were introduced for electronic newsgathering (ENG) work. Note photo on the right.
These units can be disassembled and transported to the scene of a news story in packing cases.
Flyaway units are used in remote regions, including offshore
areas and third-world countries. Flyaway units provide full quality video
and audio signals.
Internet (Wi-Fi, TCP / IP)
Transmission of News Stories
Once a program segment is on a tape, disk, or in a solid-state memory card, it can be sent through a FireWire or USB connection to its destination via a high-speed Internet connection.
Cybercafés or wireless Wi-Fi "hot spots," now as common as McDonalds and now in tens-of- thousands of locations around the world, can serve as transmission points.
In TV news, stories can be saved on a USB thumb drives and can then be uploaded to an Internet site for downloading by the station for editing and use on the air.
A complete, news segment can be stored in the device shown here.
Videos from cell phone cameras are now regularly sent to both social networks and news sites. After being checked and verified, some of these videos end up on TV newscasts.
Today, anyone with a cell
phone camera is a potential news reporter. It's often a matter of just
being at the right place at the right time and, of course, knowing what
you are doing.
TCP / IP
With the increased speed and reliability of Internet service (both wired and Wi-Fi) has come the ability to transmit live or recorded TV programming with what it called IP or Internet Protocol.
Technically, Internet Protocol (IP) and Transmission Control Protocol (TCP) are different transmission approaches.
However, TCP and IP are so commonly used together that IP represents the common designation for video and audio sent via the Internet.
This includes most TV stations that
their programming both over-the-air and through the Internet.
Devices such as Teradeck's Cube, shown on the right, can be mounted on a video camera. The basic "cube" is not much bigger than a pack of cigarettes and can transmit a high-definition camera signal via 4G Wi-Fi to a station's control room to be recorded or put directly on the air.
approach is far less expensive than the satellite, fiber optic, or microwave
approaches discussed earlier.
Satellites hovering about 36,000-kilometers (22,300-miles) above the earth relay most television programming to world viewers.
Each satellite or "bird" is composed of a number of transponders, or independent receive-transmit units.
Geosynchronous satellites rotate at the same speed as the earth and end up being stationary in relation to the earth's surface. This obviously simplifies the job of keeping them within the range of both the uplink and downlink dishes on the earth.
The reflector dish of a ground station uplink is shaped like a parabola, which is similar to the reflector of a powerful searchlight, the kind that can send a sharp beam of light into the night sky.
Signals reflected from the center element (note photo above) will hit the dish and then be sent upward on their 36,000-kilometer (22,300-mile) path to the satellite.
As illustrated on the left below, once the signal is received, it's amplified, the frequency changed, and then it is sent back to the earth.
The footprint (coverage area) of the returning signal covers many thousands of square kilometers or miles of the earth's surface.
Within the footprint area, receiving dishes work in reverse of the uplink ground stations. The signal from the satellite is collected in a dish and directed toward the receiving element, as shown on the right above. This signal is then amplified thousands of times and fed to a TV receiver.
Satellite Distribution of Programming
Networks and TV production facilities routinely distribute their programming via satellite. This is how TV productions originating in the Los Angeles-Hollywood area are sent to the East Coast for network distribution.
Once they arrive on the East Coast they are recorded, scheduled into the network lineup, commercials are added, and then the programs are beamed back up to satellites for distribution by TV stations throughout North America.
When the network-to-affiliate link is not being used to relay regular programming, it's used to send news stories, program promotion segments, and other broadcast-related segments to affiliated stations.
Cable (CATV) companies also receive most of their programming from satellites. This includes both TV and audio services.
There are two classifications of satellites used in television:
C-band was the first satellite frequency range to be widely used in broadcasting. Until the advent of paid satellite-to-home services such as DISH and Direct TV, many people had large C-band dishes in their yards.
Although dish size is not a major issue with permanently mounted installations, C-band dishes impose limitations for SNG trucks. (Satellite newsgathering trucks or SNG trucks are vans that have been especially outfitted to uplink ENG stories to a satellite.)
Compared to Ku-band, C-band is more reliable under adverse conditions -- primarily in heavy rain and sleet. At the same time, C-band frequencies are more congested and more vulnerable to interference.
Because of the higher frequencies (shorter wavelinks) involved, Ku-band dishes can be about one-third the size of C-band dishes.
Because Ku-band also has fewer technical restrictions, it means that users can quickly set up satellite links and start transmitting. This is an important advantage in electronic newsgathering.
Although many satellite services such as DISH and Direct TV are scrambled, subscription-based services, there are several hundred free TV services available on C and Ku bands that are available free to anyone with the proper receiving equipment. These include:
C-band satellites typically carry 24 TV channels and have names such as Galaxy 9, Satcom C3 and Morelos 2. For example, the Florida Sunshine Network is on Satcom C1, Channel 24.
C-band and Ku-band satellite assignments occasionally change without notice. Several newsstand publications are available which represent a type of "TV Guide" for home satellite viewing.
Although most satellite TV programming is in English, Spanish or French, satellite programming is also available in dozens of other languages.
A single C-band or Ku-band satellite channel is capable of carrying both a TV signal and one or more separate audio channels. Taking advantage of this fact are more than 100 free audio services, most in stereo and many without commercials.
For people living in rural areas out of the range of local TV and CATV services, a satellite receiver may be the only way they can get TV programming.
Originally, these were all C-band and Ku-band services. However, most people now subscribe to digital satellite-to-home services, such as the DISH Network and Direct-TV, which use their own satellites and frequencies.
In the photo on the right the dishes are aimed at two different satellites.
These services have a capacity of more than 50 simultaneous digital TV channels -- many of them in HDTV.
Once subscription fees are paid, the unique identifying number in your satellite receiver is uplinked along with the satellite TV signal. When your home satellite receiver receives this identifying number it unlocks the signal so it can be displayed on your TV set.
In late 2001, satellite radio was launched in the United States. More information on this can be found here.
In the next module we'll take up a totally different aspect of the cybercourse: legal issues.
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