This is only a preview of the December 2002 issue of Silicon Chip. You can view 25 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
Items relevant to "The Micromitter Stereo FM Transmitter":
Items relevant to "A Windows-Based EPROM Programmer; Pt.2":
Items relevant to "Build The Decision Maker":
Articles in this series:
Items relevant to "SuperCharger For NiCd & NiMH Batteries; Pt.2":
Articles in this series:
Items relevant to "Simple VHF FM/AM Radio":
Purchase a printed copy of this issue for $10.00. |
It has been quite a few years since we have described an up-to-date,
free-to-air home satellite TV system. In fact the last time we covered
the subject was in May 1995 and that article sparked a huge amount of
interest. But times (and satellite TV) have changed in the last few years.
With the right gear, you too can watch
INTERNATIONAL
SATELLITE TV
Part 1: by Garry Cratt*
www.siliconchip.com.au
December 2002 7
S
ince 1995, more satellites have been launched, more
free-to-air channels have become available and prices
have dropped, hence our revitalised interest in the
subject. And all this in the face of Pay TV which continues
to have mixed success in Australia.
One of the significant technological improvements that
has had a major affect on home satellite systems is the
introduction of MPEG broadcasting. This is a form of digital compression that allows a huge improvement in the
efficient use of the satellite spectrum.
As more channels can now be transmitted within a
fixed bandwidth, the operating cost to broadcasters has
decreased, making international satellite broadcasts an
economical alternative to shortwave broadcasting.
More powerful satellites now cover larger populated
areas of the Earth than ever before, translating into a huge
audience for broadcasters.
The good news isn’t restricted to broadcasters. Consumers benefit from the mass production of digital satellite
receivers, capable of producing high quality video and
audio signals, at similar cost to an analog receiver a few
years ago.
Depending upon your (earthly!) location, there are between eight and twelve satellites visible from Australia.
These satellites carry around 200 channels of international
programming.
While many of these are broadcast in the language of
the country of origin (which is a great source for learning
a language), there are enough English
language channels to provide a great
source of international news, documentaries and general entertainment.
to illuminate specific populated parts of the world with
strong signals.
For example, Pay-TV services use the Ku-band because
they can target areas more effectively and efficiently.
In Australia, most Pay-TV operators can provide adequate
signals, with some margin for rain fade, using only 65cm
dishes.
However, these signals are concentrated along the east
coast and areas outside this “footprint” require a much
larger dish for adequate reception.
Rain attenuation is more severe at these frequencies, so
higher power must be used to overcome this problem. But
the main advantage of Ku-band remains the size of the
required dish.
Incidentally, the term “Ku” is used to identify a certain
section of the overall band. The “Ku” band goes from 10.715.4GHz, the “K” band stretches from 15.4-27.5GHz, while
the “Ka” band goes from 27.5-50GHz.
What is of main interest to us here are those free-to-air
international signals on the C band.
How it works
Most enthusiasts are familiar with the principle of geostationary satellites.
But if you’re not, basically the satellite is placed about
37,000km above the equator and appears to travel at the
same speed and direction as the point directly “below” it
on Earth.
C-band and Ku-band
There are two frequency bands utilised by satellite operators, “C” band
and “Ku” band. Both are in the super
high frequency (SHF) region of the
electromagnetic spectrum (SHF goes
from 3 to 30GHz, with wavelengths
between 10cm and 1cm)
By international convention, C-band
signals are transmitted in the 3.44.2GHz area. Unfortunately there are
also some terrestrial services that operate in this region, so satellite signals
do not rule exclusively here.
As the amount of power able to be
transmitted by a satellite is limited by
the available spacecraft power supply,
efficient use must be made of this limited resource.
C-band signals are used for coverage
of wide landmass areas because they
are less affected by rain attenuation.
Because they are intended for wide
area coverage, the average signal level
is far less than the spot beams used to
cover smaller, populated areas.
Ku-band signals are transmitted
(at least for our part of the world) in
the 12.25-12.75GHz region and are
generally used by satellite operators
8 Silicon Chip
A 2.3m C-band mesh dish mounted in a suburban backyard. Note the heavyduty steel mounting pipe: this is set in concrete another 1.5m into the ground to
prevent the dish moving in high winds. The mesh construction also assists this.
www.siliconchip.com.au
Of course, the satellite travels very
much faster through space than the
point on Earth moves. But the important point is that it moves at a speed
which keeps it in the same relative
position as that point on the ground.
The Earth’s gravity constantly tries
to pull the satellite out of orbit but at
roughly 37,000km the centripetal force
of the moving satellite exactly balances
the pull of the earth’s gravity. So the
satellite neither falls to Earth nor spins
out into space.
Therefore, the satellite appears to
be in a fixed position. In practice, it’s
not quite that simple – regular “adjustment” firings of the satellite’s rocket
motors are required to keep it in geostationary orbit. When the limited amount
of rocket fuel on board eventually runs
out, the satellite will fall and probably
burn up on re-entry.
This fixed position simplifies things
significantly, because a fixed dish can
now be used as there is no need to move
the dish to follow, or “track” a moving By way of contrast, a 3m C-band solid dish in a commercial installation. This
satellite. This is quite different to LEO required a crane to lift it into position and very extensive anchoring to the flat
satellites (low earth orbiting) such as roof. Windage can be a real problem with solid dishes, especially up high.
those used by GPS and weather satellite
services.
panels. This reflector is mounted on a support ring, which
The only reason to change the position of the dish is to in turn sits on top of a mounting post.
lock onto the signal from another satellite.
Commercial dishes are often one piece spun aluminium
Satellites can be launched from a number of sites around construction, making transport and mounting a far more
the world, using multi-stage launchers to propel the satel- difficult proposition.
lite to the final orbit. By contrast, the USA’s Space Shuttle
Due to the mesh construction, the reflector is semi transcan take the satellite to an altitude of 200 Km, where an parent, and hence not nearly as instrusive as a solid dish.
“apogee” kick motor boosts the satellite into the final orbit. That’s important when it comes to satisfying neighbours
There are now commercial launch sites in Russia, China, and local councils.
India, Japan, USA, French Guiana and from the Boeing
“Sea Launch” platform in the Atlantic Ocean. A consor- Size does matter!
tium is also reported to be currently trying to put together
The dish shape is a parabola. The unbelievably tiny
a commercial site in Australia using the now-largely- signals which arrive at the dish’s surface bounce off it and,
disused Woomera research centre in South Australia.
because of the parabolic shape, concentrate at the dish’s
focal point.
What you need
The lower the signal levels, the larger the dish required.
Basically an international satellite TV reception system It’s not so much that C-band signals require a large dish
comprises a dish of suitable size, an LNB (low noise block because they are longer wavelength (even though that is
down converter), a feedhorn, a digital satellite receiver and true!), it’s because they are invariably much lower in level
connecting cables. In some cases, a multi-system video than Ku-band signals.
standards converter may be required.
The further away from the satellite you are (ie, the higher
The simplest implementation is a system designed to your latitude), the less signal you will receive . Again, the
look at one satellite. The dish is simply pointed in the larger the dish you will need.
right direction and a single coaxial cable runs inside to
The same applies to satellites located further around
the satellite receiver and TV set.
the equator from your location. Satellites located on your
A more comprehensive (and complex) system is one longitude will require a certain sized dish, while satellites
that has been fitted with a motor, allowing access to all on distant longitudes will require larger dishes.
visible satellites.
Ultimately, where the satellite is located below the hoThis system relies on a particular type of dish mount rizon from your location, no dish, not even a monster the
called a “polar” mount. This achieves polar tracking of the size of the Parkes radio telescope, will be able to receive
geostationary arc using only one motor.
signals from that satellite because there is a little barrier
The most obvious component of the system is the dish. called the Earth in the way.
Typically, for domestic use, the reflector is constructed from
Therefore, when you hear people talking about watchexpanded aluminium mesh, supplied as four pre-assembled ing programs from domestic USA or European satellites,
www.siliconchip.com.au
December 2002 9
A C-band Low Noise Block Downconverter/Filter (LNBF)
together with its associated feed horn. These devices are
made to very tight tolerances due to the extremely high
frequencies involved.
they are talking through their hats (or should that be
through their Earth?).
Undoubtedly, what they are watching is a USA or European program received by a much closer earth station
and re-transmitted on one of the satellites you can see
from Australia!
It can be shown mathematically that at best (ie, an unobstructed path) you cannot view a satellite more than 81°
from your longitude. As Sydney, for example, is at 151°E,
that limits you to satellites located from 70°E to 128°W.
To adequately capture C-band signals at latitudes between, say, Brisbane and Melbourne, a dish of around 2.3m
minimum diameter is required. Further south, you might
need a 3m dish, or even larger. Further north, you might
get away with 1.5m or so. Again, these sizes assume your
satellite is reasonably close to your longitude.
So why do TV stations and satellite earth stations have
such enormous (10m+) dishes? They are there to capture
every last femtovolt of signal to ensure rock-solid reception,
good enough for commercial applications. And they may
also be looking at satellites close to the horizon.
of signal anyway). And it must be able to convert a whole
“block” of frequencies to lower frequencies which (a) are
within the range of the receiver and (b) won’t be as severely
attenuated by the length of coaxial cable between it and
the receiver.
(There will always be some attenuation of the signal
along the coax and the higher the frequency, the greater
the attenuation).
Remember that the incoming signal is within the frequency band of 3.4-4.2GHz, so we need to convert the signal
to a more manageable frequency to run down a piece of
coax, if we are to have any hope of getting the signal to
the receiver!
The LNBF has an internal local oscillator at 5150MHz,
and this mixes with the incoming signal to produce a block
of intermediate frequencies (IF) from 950-1450MHz. That’s
a far more manageable range!
For maximum spectrum efficiency, most satellites transmit signals of both polarities (horizontal and vertical), so
the LNB has two probes (one for each polarity) that can be
remotely selected by the satellite receiver.
By convention, cables used in satellite TV are 75 ohm
and it is important that a good quality cable is used to
connect the LNBF to the receiver. For best results RG-6/U
quad shield coax is recommended. The quad shielding
ensures that any adjacent RF field (generated by 2-way
radio, mobile and cordless phones, etc) does not interfere
with the satellite IF signal being fed down the cable.
The dynamic range of most satellite receivers allows
signals to be received anywhere between –20dBm and
–50dBm, so some cable attenuation can be tolerated. Typically RG6, the coax most used for satellite receivers, has
25dB attenuation per 33m (100ft) at 1000MHz, so this is
a about the maximum length we can use without amplification. The use of a 20dB line amplifier can extend this
considerably.
Coming indoors
The only indoors component for the system (apart from
the bit of coax that enters the building!) is the satellite
receiver. The receiver takes the IF input and processes
this digital stream to produce composite video and audio
signals.
The digital receiver connects like any other audio/video
Feedhorn and LNBF
Mounted at the focal point of the dish, supported by
three or four arms, is an assembly called the feedhorn and
LNBF (low noise block downconverter/filter).
The feedhorn “looks” at the reflector surface, and collects
the signal reflected from the surface of the dish, concentrating the signal into a piece of waveguide to which the
LNBF is connected.
The parts of the LNBFs name are significant. It must
have very low electrical noise (so it doesn’t introduce any
significant noise of its own to what is a very tiny amount
10 Silicon Chip
A typical digital receiver for C-band TV. MPEG-2 digital
DVB compliant, his one retails for around $495 and has
4000 channel capability.
www.siliconchip.com.au
Receiving Pay-TV and
other encrypted services
This map of Asiasat II’s (100.5°E) “footprint” gives a good
idea of the size of dish required for various areas. Note that
the footprints are not circular – combinations of satellite
transmitters and antennas are used to achieve the best
footprint over populated areas.
component in a home entertainment system: composite
video and/or SVHS video output, stereo line audio outputs,
and RF (generally UHF) modulated output. Most receivers
have at least two sets of A/V outputs for routing to VCR,
TV, etc.
OK, so now that we have all these components in place,
just what is there to see ?
There are really two reasons why free to air satellite TV
signals exist. Either they are an extension of international
shortwave broadcasting, or they are “fortuitous”.
Over the last few years, satellite TV has taken over from
the more traditional shortwave broadcasting. For example,
the BBC no longer transmits on shortwave but they do
produce a satellite TV channel, BBC World.
Other examples of government-operated satellite channels include Deutsche Welle (Germany), Worldnet (USA),
NHK (Japan) and our own ABC Asia to name a few. These
are deliberately set up to promote the culture, lifestyle and
customs of the country of origin. These signals are of great
interest to tourists, expatriates living overseas, schools,
universities, and hotels. Such broadcasters normally produce a satellite “TV Guide” which can be accessed through
their internet web sie.
The second type of free-to-air satellite TV signals encountered, are those that are “fortuitous” – another word
for lucky! Many of these are not specifically intended for
public consumption (for example, a broadcaster’s link
between one country and another) but suitably equipped
satellite enthusiasts can view these signals. Every now and
then you can see a real gem – like a movie transfer.
All such signals are subject to copyright which is designed to prevent commercial use being made from these
signals.
SC
* Garry Cratt is Technical Director of Av-comm Pty Ltd,
suppliers of satellite TV equipment and peripherals.
While this article has concentrated on C-band, free-toair services which can be received and viewed by anyone
with a suitable dish and receiver, there has been a lot of
discussion over whether it is possible to receive Ku-band
signals, such as those from Pay-TV service providers,
and whether having your own dish and receiver is legal.
Of course, technically speaking Ku-band signals can
be received with suitable equipment, otherwise satellite
Pay-TV wouldn’t be possible.
But it’s not quite as simple as pointing your dish in the
right direction and tuning in. Nor, apparently, is it now legal.
For a start, Pay-TV services are encrypted (with the
exception of one channel – TV Shopping Network). So
they have to be decrypted before you can watch them
(that’s one of the things the Pay-TV set-top-box does!).
Second, Pay-TV providers don’t take kindly to people
watching their service for free. That’s why the set-topbox is provided with a smart card, a digital “key” which
unlocks the box.
This key is periodically changed by a signal from the
satellite which turns the box off if you haven’t paid your
bill or it is unauthorised. All you’ll see on your TV set is
a message such as “unknown service” or “this channel
is encrypted”.
There are a number of ways the service providers
do this but the most usual is to periodically change the
“country code” (or coco) after a message from the satellite
tells the decoder that it is about to be changed. If the coco
being transmitted and the coco stored on the card don’t
match, your signal disappears. So stolen set-top-boxes
and cards only work for a short time. (That’s one reason
that there isn’t a huge market in stolen boxes).
Finally, there is now legislation designed to stop you
receiving Pay-TV signals without paying for them, even if
you work out how to decrypt the signals yourself. Owning,
buying and selling satellite dishes and receivers is not
illegal but trading in the smart cards designed to make
those receivers decrypt signals definitely is.
And even if you are particularly clever and are able to
program your own smart card, since March 2002 there
has been legislation to prevent you obtaining the benefit
of a received Pay-TV satellite signal unless it is with the
authorisation of the provider – ie, you’ve paid for it!
Unless you pay for it, don’t hold your breath for authorisation! (In fact, it’s rarely, if ever, given – they come and
install their own equipment even if you have your own.)
And finally, a tale: in the US, service providers have
been known to broadcast “stings” – offers so good they’re
impossible to resist. But they are also specifically coded
so that legitimate viewers don’t even see them. When
people respond to these amazingly good offers, they
know they’ve caught themselves some pirates!
Aaaaarrrrrr, me hearties . . .
NEXT MONTH: Putting together your own satellite TV system
(including a special system discount offer – exclusive to SILICON CHIP readers).
www.siliconchip.com.au
OVERLEAF: Currently available
C-band digital f-t-a services
December 2002 11
C-BAND FREE-TO-AIR DIGITAL CHANNEL LIST
FREQ
USER
SR
FEC
Video
Polarity
PAL
PAL
PAL
PAL
Vertical
Vertical
Horizontal
Vertical
5.150 LO
5.700 LO
Origin
1445 MHz
1354 MHz
1302 MHz
1174 MHz
1995 MHz
1904 MHz
1852 MHz
1724 MHz
China
India
Hong Kong
Thailand
(symbol (forward error
rate)
correction)
APSTAR 2R<at>76.5° E
3705
3796
3848
3976
Channel News Asia
DD NE
TVB8
I Cable
6111
2500
13280
5000
3/4
3/4
3/4
3/4
THAICOM 3 <at>78.5° E
3424
3448
3551
3600
3666
3671
Korean Central TV
3366
2/3
NTSC
Horizontal
1726 MHz
2276 MHz
N Korea
TV Cambodia
6312
1/2
NTSC
Horizontal
1702 MHz
2252 MHz
Cambodia
TRT
13330
3/4
PAL
Horizontal
1599 MHz
2149 MHz
Turkey
Thai TV 5
26667
3/4
PAL
Horizontal
1500 MHz
2100 MHz
Thailand
VTV 4
Vietnam
ATN Bangla India
ETC Punjabi
CMM Music
Test pattern India
MR TV
4442
2/3
PAL
Horizontal
1484 MHz
2034 MHz
Burma
MR TV
13330
3/4
NTSC
Horizontal
1479 MHz
2029 MHz
Cambodia
INSAT 2E<at> 83° E
3683
3831
3911
4005
Asianet
DD1 National
DD2 Metro
ETV bouquet
4340
4998
4998
27000
3/4
3/4
3/4
3/4
PAL
PAL
PAL
PAL
Vertical
Vertical
Vertical
Vertical
1467 MHz
1319 MHz
1239 MHz
1145 MHz
2017 MHz
1869 MHz
1789 MHz
1695 MHz
China
India
India
India
ASIASAT 2 <at> 100.5° E
3660
Saudi TV 1
27500
3/4
PAL
Vertical
1490 MHz
2039 MHz
Saudi
Muslim TV Saudi
Kuwait Space Channel
Kuwait
Jame-Jam Network Iran
IRIB 3 Saudi
3705
Satlink adhoc
5632
3/4
PAL
Vertical
1445 MHz
1995 MHz
Europe
3706
Henan TV China
4418
3/4
PAL
Horizontal
1444 MHz
1994 MHz
China
3714
Satlink adhoc
5632
3/4
PAL
Vertical
1436 MHz
1986 MHz
Europe
3717
Quinghai TV
4418
3/4
PAL
Horizontal
1433 MHz
1983 MHz
China
3720
Fujian TV China
4418
3/4
PAL
Horizontal
1430 MHz
1980 MHz
China
3727
Jiangxi TV China
4418
3/4
PAL
Horizontal
1423 MHz
1973 MHz
China
3734
Liaoning TV China
4418
3/4
PAL
Horizontal
1416 MHz
1966 MHz
China
3799
APTN news feeds
5632
3/4
PAL
Horizontal
1351 MHz
1901 MHz
Europe
3806
GX TV
4418
3/4
PAL
Vertical
1344 MHz
1894 MHz
China
3813
Shaanxi TV China
4418
3/4
PAL
Vertical
1337 MHz
1887 MHz
China
3820
AH TV
4418
3/4
PAL
Vertical
1330 MHz
1880 MHz
China
3827
Jiangsu TV
8410
3/4
PAL
Horizontal
1323 MHz
1873 MHz
Mongolia
3827
JSTV
4418
3/4
PAL
Vertical
1323 MHz
1873 MHz
China
3830
Northern Mongolia TV2
8410
3/4
PAL
Horizontal
1320 MHz
1870 MHz
Mongolia
3834
Hei Long Jiang TV
4418
3/4
PAL
Vertical
1316 MHz
1866 MHz
China
3840
Guangdong TV
4418
3/4
PAL
Horizontal
1310 MHz
1860 MHz
China
3847
Hunan TV China
4418
3/4
PAL
Horizontal
1303 MHz
1853 MHz
China
3854
Hubei TV China
4418
3/4
PAL
Horizontal
1296 MHz
1846 MHz
China
3872
Jilin Satellite Channel
4418
3/4
PAL
Vertical
1278 MHz
1828 MHz
China
3880
Worldnet USA
20400
3/4
PAL
Horizontal
1270 MHz
1820 MHz
USA
4000
Deutsche Welle
28125
3/4
PAL
Horizontal
1150 MHz
1700 MHz
Germany
RAI Italy
TV5 France
TVe1 Spain
RTPi Portugal
4020
Dubai Sports
27500
3/4
PAL
Vertical
1130 MHz
1680 MHz
UAE
Dubai Business
Dubai EDTV
Europe
12 Silicon Chip
www.siliconchip.com.au
ASIASAT 3 <at>° 105.5° E
3700
3714
3742
3755
3760
3820
3900
4000
4095
4129
Bharathi TV
27500
3/4
PAL
Vertical
1450 MHz
2000 MHz
India
Kaveri TV India
MS TV
5868
3/4
PAL
Horizontal
1436 MHz
1986 MHz
China
SABe
3300
3/4
PAL
Vertical
1408 MHz
1958 MHz
India
Arirang TV
4418
7/8
PAL
Vertical
1395 MHz
1945 MHz
Korea
Now TV
26000 7/8
PAL
Horizontal 1290 MHz
1940 MHz
USA
Bloomberg Asia
Splash TV
S/S Music
Speedcast TV
27500 3/4
PAL
Vertical
1330 MHz
1880 MHz
China
Indus TV
27900 7/8
PAL
Vertical
1250 MHz
1800 MHz
India
Phoenix I
26850 7/8
NTSC
Horizontal 1150 MHz
1700 MHz
China
Xing Kong
Phoenix C
Channel V
Sun TV
5555
3/4
PAL
Horizontal
1055 MHz
1605 MHz
China
CCTV 3,4,9
13240 3/4
PAL
Horizontal 1021 MHz
1571 MHz
China
PALAPA C2 <at> 113° E
3473
4000
4080
4184
RCTI
Channel News Asia
Swara TV
Quick TV
Anteve
Global TV
Metro TV
TPI digital
8000
26085
28125
3/4
3/4
3/4
PAL
PAL
PAL
Horizontal
Horizontal
Horizontal
1677 MHz
1150 MHz
1070 MHz
2227 MHz
1700 MHz
1620 MHz
Indonesia
Taiwan
Indonesia
6700
3/4
PAL
Vertical
966 MHz
1516 MHz
Indonesia
PAS-8 <at> 166° E
3740
3852
3829
3880
3900
3940
4020
4060
4180
MTV China
27500
3/4
PAL
Horizontal
1410 MHz
1960 MHz
China
Tzu Chi TV
28000
5/6
NTSC
Horizontal
1298 MHz
1848 MHz
Taiwan
Hai Hua Satellite TV
Taiwan
29 radio services
Power TV Taiwan
CCTV 4,3,9
13240
3/4
PAL
Horizontal
1321 MHz
1871 MHz
China
Lakbay TV
28694
3/4
PAL
Vertical
1270 MHz
1820 MHz
Philippines
CNBC
27500
3/4
PAL
Horizontal
1250 MHz
1800 MHz
USA
EWTN
27690
7/8
NTSC
Horizontal
1210 MHz
1760 MHz
USA
Fox News feed
USA
BBC UK
ESPN
26470
3/4
NTSC
Horizontal
1130 MHz
1680 MHz
USA++
NHK World
26470
3/4
NTSC
Horizontal
1090 MHz
1640 MHz
Japan
Channel J Japan
NIME TV Japan
ABC Asia
27500
3/4
PAL
Horizontal
970 MHz
1520 MHz
Australia
Radio Australia
PAS-2<at> 169° E
3743
3771
3837
BBC World (Singapore)
21800
3/4
NTSC
Vertical
1407 MHz
1957 MHz
UK
YTN Korea
11574
3/4
NTSC
Horizontal
1382 MHz
1932 MHz
Korea
RAI Australia
13331
3/4
PAL
Vertical
1372 MHz
1922 MHz
Italy
RAI Radio Italy
3903
CBS/ Adhoc feeds
30800
3/4
NTSC
Horizontal
1249 MHz
1797 MHz
USA
Bloomberg TV USA
BloombergRadio
ABC Asia
Radio Australia
3992
Fox MUX
26470
7/8
NTSC
Vertical
1158 MHz
1708 MHz
USA
3940
Napa feeds
7498
2/3
PAL
Vertical
1210 MHz
1760 MHz
3942
Napa feeds
6620
2/3
NTSC
Horizontal
1208 MHz
1758 MHz
4026
TVBSUSA
22000
3/4
NTSC
Vertical
1124 MHz
1674 MHz
Taiwan
INTELSAT 701 <at> 180°E
3769
3886
TBN
Worldnet
20000
25000
7/8
3/4
PAL
PAL
RHCP
RHCP
1381MHz
1264MHz
1931MHz
1814MHz
USA
USA
+ = audio only * = 0900-1800UTC $ = 1800-0900UTC LAST UPDATE: 6/9/02
www.siliconchip.com.au
December 2002 13
|