For the Birds:
Everyday Satellites
War, for all its
destructiveness, can have some positive outcome as well. The Second World War, for
instance, saw an astonishing outpouring of technological innovation. The reasons for
developing some things may not have been particularly noble at the time, but few would
deny that our world has been fundamentally changed by computers and rockets and nuclear
energy, all of which owe their origins to that conflict.
One of the most notable forms of electronics in the second
half of our century -- television -- was in fact developed before the war. John Logie
Baird demonstrated a workable system as early as 1926, and there were experimental
stations on the air in London and New York in the year before the war.
The BBC broadcast a limited amount of regular programming,
but one account of the American station suggests that if you owned a TV set in New York
and wanted to demonstrate it to your friends, you called up the station and whatever
technician happened to be nearby would step in front of the camera.
The coming of war put an end to these inaugural efforts,
partly for reasons of security, at least in London. Unlike AM radio, which typically uses
transmitters placed well away from the cities they serve, television works best with the
antenna right in the middle, and it was felt that this was too easy a beacon for enemy
aircraft.
More importantly, the Allies would need to use all their
electronics and cathode-ray tube manufacturing capability to produce devices specifically
required for the war, notably radar. In its original form, radar played an enormous part
during the war, and continues to be vital for aviation, shipping and defence. But without
one offshoot of radar, its hard to imagine that postwar television could have developed in
the way that it did.
Prior to the relaunch of television in the United States in
1947, the primary mass medium was AM radio, and in North America that meant network radio.
For the first time in history, millions of people could experience the same entertainment
at the same moment.
That was revolutionary, but this network was hooked
together in a very low-tech way: by phone lines. Programs were sent from one side of the
continent to the other by copper wires, but while the system was subject to noise and
various sorts of losses, the radio medium itself had a narrow enough bandwidth that it
didn't matter very much.
Television was very different. While it is possible to move
TV signals about by wire -- cable companies are based on that -- it's not a very practical
technology for long distances. Television requires enormous bandwidth: 6 megahertz for a
broadcast signal, and this doesn't travel very well.
Yet it was inevitable that the broadcasting companies would
want to repeat in the new medium the pattern established for network radio, so there was a
requirement for a new, wide bandwidth communications medium. An adaptation of radar
provided the answer.
The secret of radar was the development of transmitting
tubes that could produce extremely high-frequency output. As with all sorts of radiating
energy, the higher the frequency, the shorter the wavelength, and radar used what we now
call microwaves.
One principal attribute of microwaves is that they are
extremely directional: it's possible to create a beam that widens hardly at all over many
miles. Radar works by sending out such a beam and using a receiver to detect its return if
it bounces off anything. The length of time between the transmission and the reception
indicates how far away the reflecting object is.
If instead of sending a signal out more or less randomly to
see if it bounces, you were to aim it at a distant receiving antenna, it could be
modulated with information that could be decoded at the other end. And because of the high
frequencies involved, an enormous amount of material can be carried on a single channel.
Where once you needed a wire for each phone call from one place to another, with microwave
thousands of calls could be carried on a single communications channel. Or several TV
signals.
And because there's so little dispersal of energy by
spreading of the beam, very little power is required. An ordinary radio transmitter might
put out 10,000 watts of power or more omnidirectionally in order for there to be a
fraction of a watt at your receiver's antenna. If it could focus its whole output on your
antenna, it would only have to produce that fraction of a watt.
After the war, the conversion to a microwave network saw
the building of thousands of relay towers, stretching the network to all parts of the
continent. The aim was to accommodate the expanding telecommunications market and to
facilitate military communications during the Cold War. But television was a beneficiary
as well: microwave links made network TV possible.
But there was one serious drawback to terrestrial
microwave: there was a limit to how far apart you could place the relays. At one point,
the curvature of the earth will interfere and block the signal. The higher the towers, the
farther apart they can be positioned, but the practical distance is typically 30 to 50
miles. That means a huge number of relays are needed to provide coverage to the whole of
North America. Because of the efficient nature of the system, however, if you could place
one tower right in the middle, high enough that it could "see" both coasts, that
one would be all that was necessary.
When the system was being built, a 200-mile-high mast was
not a practical solution. But then in 1957 came that little beeping grapefruit called
Sputnik, the first man-made satellite. For those who weren't around then, the
disappointment in the West that this landmark event -- and several other space firsts --
were accomplished by the Soviets was the impetus needed to push the U.S. space program
into high gear.
The most visible parts of that had to do with manned
missions, but the real revolution was in communications. The satellite became a part of
popular culture so fast that one even had a top-40 song named after in in 1962 --
"Telstar" -- only five years after Sputnik.
The first satellites were used for international
communications. One problem with terrestrial microwave was that it stopped at the
seashore; there was no route by which you could get from North America to Europe in
30-to-50-mile hops, so transatlantic (and transpacific) telephone connections had to be
made either by undersea cable or shortwave radio, neither a very satisfactory medium.
And international television was impossible. Canadians and
Americans alike marvelled in 1953 that we could see Queen Elizabeth's coronation the same
day it occurred. But that was only possible by filming the British coverage, flying the
film across the Atlantic, and popping it into a telecine projector in eastern Canada, from
which it was fed to the rest of the continent. Less than a decade later, it could have
been carried live.
The initial satellite systems were expensive and difficult
to operate. They orbited only a few hundred miles above the earth, and so were out of view
of earth stations for a part of every orbit. For a continuous signal, multiple satellites
were used, and pivoting dishes tracked them across the sky. Only the major
telecommunications carriers could operate them.
Even so, they revolutionized how information was moved
around the world. Microwaves were ideal for this because the narrowness of the beam let
the uplinks hit the satellites with precision, and the need for very little transmitter
power in the birds themselves meant they could operate from relatively modest solar panels
on board.
By the 1970s, geostationary satellites had come into use.
These orbit some 22,300 miles above the equator, in the direction of the earth's rotation.
Because of the speed they must travel at that distance, they remain above a single spot on
earth, and can be fed and received by static dishes.
Satellites are a natural for Canada, with its widely-spaced
population centres and sparsely populated north, and Canada was the first country to build
a domestic synchronous satellite. Anik I was launched in 1972, and joined by Anik II the
next year. Each had twelve channels (or transponders, as they're sometimes called), each
of which could carry one television channel or 960 telephone calls.
The Anik satellites were used by outfits like the Canadian
Broadcasting Corporation and the phone companies to ferry their signals about the country
from one Telesat installation to another. In fact, the signal blanketed Canada and much of
the U.S., and anyone with a dish could have picked up the signal.
It wasn't until several years later that people started to
do that, and that was a result of the launch of the first of the American domestic
satellites. Prior to that, television in the States had been restricted to the big
networks except in a few cities large enough to have an independent station or two;
special cable-TV programming was unknown.
But the satellites made elaborate ground networks
unnecessary. A program provider simply had to rent transponder space and beam a signal to
the satellite; each cable company could receive it by its own dish for distribution to
customers.
It didn't take long for people to discover this was going
on and to set up their own dishes to pick up both the cable services and to watch
"wild feeds" -- the networks sending program elements from one part of the
network to another, prior to broadcast. Dishes were (and are) especially popular in rural
areas poorly served by cable and off-air TV.
Dish ownership was an expensive matter at first. The
satellites operated in what is known as C-band, which uses the same frequencies as
terrestrial microwave networks. Partly to avoid interfering with the land systems, and
partly to keep the power panels to manageable size, the satellites put out very little
power, typically a few watts divided among twelve or twenty-four channels. For that
reason, the receiving dishes (called TVRO, for TV-receive only) had to be large. Ten feet
was not unusual.
But, as always happens, prices did come down, and C-band
dishes remain popular, even in the face of competition from the newer direct-to-home (DTH)
services. The program providers long ago began to scramble their signals so that dish
owners couldn't watch them without payment, but there are numerous companies that offer
packages that let you decode the signals for a fee, as you would for cable.
From the beginning, there were predictions that eventually
a new service would be launched using satellites operating in a different band. That would
reduce the interference risk and let the satellites operate a higher power levels. That,
in turn, would allow the use of much smaller dishes.
After more than a decade of such speculation, the first DTH
service was inaugurated in the U.S. in 1994. DSS (Digital Satellite System) was launched
by Thomson Electronics' RCA division, in partnership with program packager DirecTV..
The system uses a pair of specially-built satellites in
geostationary orbit, with enough output power that 18-inch dishes can be used. DirecTV is
a division of Hughes Electronics, a sister company of the firm that built the satellites
(and, incidentally, that built those original Aniks). One thing that made the system
possible for the first time was the development of high-quality digital video compression,
which allows a great deal of material to be transmitted in relatively little bandwidth;
the C-band systems are totally analog.
The official introduction of DTH into Canada was less
smooth, coming something like two years after it was supposed to happen. As a result, an
enormous number of "gray market" dishes receiving U.S. services have been
installed, although their legal status is a little vague.
There are two Canadian services available (and one that's
come and gone). Both offer packages of Canadian and American channels similar to those
available on the larger cable systems (they're not allowed to carry anything not approved
for Canadian cable systems anyway), although we're miles from the proverbial 500-channel
universe.
I'm old enough to remember going to some lengths at home in
Toronto to pull in the two lone channels from Buffalo, New York, so all this seems a bit
unreal to me. Still, I'm not about to question all this technological evolution; I'm
content to put my feet up and enjoy the digital pictures and sound from the sky. But first
I think I'll hit the kitchen and nuke up some popcorn.
That's another thing we owe to radar.
Satellite Glossary
The proliferation of communications satellites has spawned
its own distinctive vocabulary. Here are some of the more common terms:
Anik I: The world's first domestic geostationary
satellite, launched by Canada in 1972.
Bird: Informal name for satellite.
C-band: The original range of frequencies used by
communications satellites. Same as for terrestrial microwave systems, so power had to be
limited to avoid interference.
Digital video compression: The technique of
discarding redundant picture information in satellite (and other) signals, to fit more
programs into a limited amount of bandwidth. More accurately called data reduction.
Dish: The parabolic reflector that concentrates the
weak radio signal from a satellite so that the LNB can deliver it to a receiver with
sufficient strength.
DSS: Digital satellite system. The largest DTH
system in the United States, developed by Thomson Electronics' RCA division and Hughes
Electronics. Very popular as a "gray market" product in Canada.
DTH: Direct-to-home. Satellite signals intended to
be received directly by consumers, rather than being delivered by cable companies or local
TV stations. Require much smaller dishes, and use digital techniques to maximize the
number of programs available, and to ensure high picture quality.
Earth station: An installation on the ground that
sends signals to satellites overhead.
ExpressVu and Star Choice : Canada's official DTH
services, which went on the air in 1997. The first is owned by Ma Bell, the second
controlled by cable giant Shaw Communications.
500-channel universe: The much-ballyhooed future of
television. So far, nobody gets more than about a quarter of that.
Geostationary: Also "geosynchronous." A
satellite whose orbit around the Earth is set so that it remains above a single spot on
the ground, and appears from Earth to be motionless. Can be used with fixed dishes, rather
than tracking antennas.
Gray market: Generally, selling in one country the
products of another by other than the official means of distribution. With satellite TV,
it refers to the popularity among Canadians of U.S. satellite services not officially
available in Canada.
Ku band: The range of frequencies used in the new
DTH satellite systems. Because it is not used for terrestrial communications, the
satellites can have more power, which means smaller receiving dishes on the ground.
LNB: Low-noise block converter. The point at which a
satellite dish focuses its signal. The LNB boosts it to the point where a receiver can
deal with it.
Microwaves: Very high frequency radio waves that can
carry large amounts of information very efficiently. Used both for satellites and on the
ground.
Orbit: The path of a satellite as it circles the
Earth. Early satellites were only a few hundred miles up, but most communications
satellites today are geostationary, sitting 22,300 miles above the equator.
Satellite: Anything that moves around the Earth (or
other planet) in a stable orbit. The Moon is one, but the term usually refers to man-made
objects.
Scramble: The practice of encoding satellite TV
signals so that dish owners can only receive them by paying a fee.
Sputnik: The first man-made satellite, launched by
the Soviet Union in 1957.
Terrestrial microwave: A communications system using
high-frequency transmitters and receivers on towers placed 30 to 50 miles apart.
Tracking: Older satellites moved across the sky,
requiring antennas that could follow -- or track -- their motion. Practical only for
telecommunications utilities.
Transponder: The circuitry in a satellite that
receives a signal from the ground at one frequency and relays it back to Earth at another.
Most satellites have 12 or 24.
TVRO: Television receive-only. Industry jargon for
satellite dishes used by consumers to pick up TV signals.
Uplinks: Terrestrial transmitter/dish combinations
that relay communications information to satellites. Located at Earth stations.
Wild feeds: Internal TV network signals intended to
be integrated into programs later, but available to owners of large dishes, for some of
whom they provide popular glimpses behind the scenes.
...Ian G. Masters
ian@mastersonaudio.com
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