Introduction: Welcome to the world of tracking satellite systems!!!
There is much more to the world of satellite TV than fixed little
dishes that look at only one satellite. It takes a little more
effort to install a tracking satellite system. However, with
a good understanding of the equipment options and if the adjustments
on the tracking/tuning page are performed
in the correct order, you will have a dish that tracks perfectly
and a bigger window to the world. You should have an unwarped
satellite dish, and a perfectly vertical mounting pole, it will
make things easier. This site deals with prime focus (or
center focus) satellite dishes, meaning incoming signals
are directed to a point.at the center of the dish. It is impossible
to cover every detail in a site such as this, otherwise the pages
would never load!! Some details, such as using UV resistant tie
wraps to tidy your cabling is common sense.
And for pole installation, covered in detail on a companion page,
is ground poles in concrete
and mounts on concrete pads
as well as a brief discussion on wind
loading. For an azel
mount, i.e. not a polar tracking mount, proceed directly to the
azel mount setting notes.
NOTE: Azel mounts are used when you have no intention of moving
the dish to another satellite as in the case of a system feeding
video into a hotel or apartment complex or other similar cable
distribution system; if this is the case, then use an azel mount
as they are more stable than polar mounts.
Other good information on companion pages is a nice, detailed
section on noise which includes discussion on signal loss due
to rain fade and free
space travel, earth thermal
noise and terrestrial interference
(TI) and Shortcut
to Tracking/Tuning Section.
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GENERAL OVERVIEW: Television
satellite signals originate from 
a
single 'uplink' facility and are transmitted to a communications
satellite orbiting 22,300 miles above the earth's equator. These
type orbiting communications satellites are considered to be
'parked' in orbit; though in reality they travel from west to
east but appear stationary to an observer on 
Earth
because their speed is the exact speed of the Earth's rotation
thus they are termed geostationary satellites. The overwhelmingly
common receive frequency of satellite transmissions, for video
purposes, are either in the C-band (frequency range from 3.7
to 4.2 gigahertz) or in the Ku-band (10.7 to 11.7 Ghz and 11.7
to 12.75 Ghz). New generation satellites are being built with
Ka-band capability (22Ghz) and a very few, older specialty satellites
are in the lower frequency S-band. After receiving the signals
from earth, the satellite amplifies the signals then rebroadcasts
them, or 'downlinks', back to
earth in a predetermined beam pattern commonly called
a 'footprint'. The calibration of the footprint is in EIRP (effective
irradiated power) and its units are in dBw (decibel watts).
The downlinked signal from the satellites, upon reaching the
earth, is very weak not only because of the great distance the
signal has traveled but also because of the 'spreading' effect
of the signal from a point source at the satellite to a regional
image at its footprint. To begin the process to receive this
signal, in effect, a satellite dish is a passive amplifier in
that it 'collects' the weak signals from space, thus the bigger
the dish the greater the signal amplication which is why a larger
dish is required to receive satellite signals that are weak into
your receiving location. A satellite dish 
collects
these weak signals and focuses (reflects) the energy to a central
spot known as the focal point or focus. All satellite dishes
are designed according to a family of mathematical formulae known
as parabolas (dish design
formula). All incoming signals to a parabolic reflector are
'bounced' to the same point - this point is known as the focus
(or focal) point of the dish. Ideally, all incoming signals from
the orbiting satellite are reflected to the focal point. If the
dish is properly installed and has no major surface irregularities,
the reflected incoming energy will be tightly concentrated at
the focus, therefore maximizing dish gain. Note that an offset
dish is simply a section of the total parabola.
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CHOOSING A DISH:The obvious
statement is that the bigger the dish the more signal it can
gather and the weaker satellite signals it can pull in. So your
first consideration in choosing a dish is to make a list of satellites
you are interested in receiving and look at their footprints
then calculate, using a link budget program, the size dish required
to receive them. If you are interested in a DBS (direct broadcast
system) satellite and only have interest in receiving the programming
from that satellite only then purchase and install the recommended
system from your local satellite store. If you have interest
in receiving multiple satellites then be sure to get a C and
Ku-band compatible dish. If you are buying a used mesh satellite
dish, be sure it has the smaller diameter perforations or a significant
portion of Ku signals will pass through the dish. Do not waste
your time buying a fiberglass dish as that is early technology
and will be guaranted to have C-band only mesh embedded within.
If you have consideration to purchase a solid metal dish, or
one piece mesh dish, stand aside from it and sight across it
to be sure it is not warped - if so, do not purchase it regardless
of the price. In buying a new dish, a solid dish will not necessarily
have a greater efficiency rating than a mesh dish; look at the
dish specs and see its efficiency rating which is the percent
of signal that hits the dish is actually reflected into the feed
- the greater the efficiency rating, the more gain the dish will
have. In considering a buttonhook feed support or leg feed support
dish, today's feeds and LNBs are so compact and lightweight (as
compared to the equipment from the early days of the industry)
that a buttonhook will provide sufficient support. On the other
hand, a feed supported by legs will always be more stable in
winds. In another consideration of mesh vs.solid dish, at wind
velocity of about 50mph the two offer the same resistance to
wind forces; a mesh dish is easier for the actuator to 'push'
around though on smaller diameter dishes (less than 2.5m) today's
actuators handle a solid dish with minimal problems. For more
technical information on choosing a dish, go to the side
lobe discussion page. To look at the dish size required for
your site, if your know your EIRP, go to the EIRP/dish
size charts page. To make a complete link budget which includes
your LNB rating, dish efficiency parameters, latitude and longitude,
slant angle, bandwidth and rain factors in the equation (program),
go to this link, Swedish
Microwave Link Budget program; (this is a real easy program
to use and an example output of its
TV screen display is seen here).
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The next consideration in dish selection is the F/D ratio
of the dish. In general, the less the F/D, the
deeper the dish, the lower the gain and the greater the rejection
of unwanted signal.
Thus the choice
of satellite dish can assist in rejecting terrestrial interference
in that the deeper the dish the more narrow will be its acceptance
of satellite signals and the less chance unwanted signals will
enter the feed assembly. A dish is considered deep with F/D ratios
of 0.25 to 0.32 and is considered shallow with F/D ratios of
0.33 to 0.45. So choose a high gain, shallow dish if you have
no fears of TI entering your system. Remember that the more shallow
the dish the closer to the dish the scalars
are set on the feed.
One thing to remember, the deeper the dish and the larger
the dish, the narrower is the central reception beam pattern
(see side lobe discussion
page); the implications of this is that the effect on installation
is that the narrower a main beam then the more difficult it is
to focus on the satellite while tuning a dish. This is not appreciably
noticeable under strong footprints or sizes under 3.0m, but is
noticable when tracking Ku satellites and when using a larger
dish. A larger dish, for instance a 4.0m diameter dish, has a
much more narrower main beam pattern than a 3.0m dish and you
have to be more 'dead on' the satellite when tracking them so
your elevation/declination/north-south adjustments are more critical.
If you use a 5.0m dish it is real easy to loose a satellite while
making mount adjustments (due to the narrow receive beam pattern)
so choose the highest gain, shallowest dish when possible.
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FEEDHORN: (For
assembly instructions.) At the focal point, the received
satellite signals are gathered by, i.e. pass into, an apparatus
called the 'feed', or feedhorn. The feedhorn is located exactly
where the mathematics of the parabola, used in the dish design
(dish design formula),
determine the focal point to be located. The feedhorn is designed
to accept incoming satellite signal 
while
rejecting unwanted signal (such as signals bounced from nearby
walls into the dish or signals from nearby telephone and/or television
towers that might enter the dish) and it is designed to select
signal polarity and to efficiently direct the gathered signal
towards (into) the LNB (low noise, block downconverter, amplifier).
Feedhorns have a scalar plate, composed of concentric rings,
which surround the feed throat. Scalar rings are designed to
accept desired signals and assist in rejecting undesired frequencies
- notice the difference in scalars on a C-band feed and that
of a Ku-band feed. The position of the scalar around the feed
throat determines the feedhorn's field of view and, to some extent,
its acceptance or rejection of unwanted signal (scalar
settings for deep and shallow dish). The proper scalar location
is determined by dish design mathematics and is the F/D
setting. Inside the feed throat is a polarity probe which
is the acual antenna that receives signals from a satellite.
The feed throat and probe are designed for efficient reception
of specific microwave frequencies and is why they should never
be tampered with; they are designed to pass (channel) frequencies
to the LNB with minimal signal loss or distortion.
A single LNB feedhorn is called a polarotor and if you have
a C-band system only then you are using a C-band polarotor and
if you have a Ku-band system only 
then
you are using a 
Ku-band polarotor. A small motor is mounted
atop the polarotor
that moves the polarity probe, inside the throat of the feed,
and this motor is called the 'servo motor' or 'servo' for short.
Satellite signals are transmitted at two polarities and, on command
from the satellite receiver, the servo moves the probe so as
to accept one polarity and reject the other.
Satellites use a dual polarization transmission system to
allow more efficient use of their equipment, this
is termed frequency reuse (for
further discussion on frequency reuse). Some satellite 
manufacturer's design their satellites to transmit
signals in a linear format and some in a circular format and
some satellites, such as the Soviet Gorizont satellites, are
designed to be linear in one band (C-band) and circular in the
other. In a linear format, signal polarization is either horizontal
or vertical. In a circular format, signal polarization is either
right hand or left hand circular polarization, abbreviated to
RHCP/LHCP. To receive circular polarized signals, a circular
feed is required - this is often called an 'international feed'.
To 
further understand, for example, in other words,
channels 1 and 2 on earth could be transponder 1-horizontal (or
RHCP) and transponder 1-vertical (LHCP) in space on the satellite.
It is the role of the probe inside the feed (whether linear feed
or international feed) to pass one polarity and reject the other;
this action by the feed is transparant to the user as it is automatically
controlled by the receiver. To pass a polarity, the probe within
the fee throat moves to be in line with the desired incoming
signal polarization thereby being in-phase with the desired polarization
and out of phase with the opposite polarization. The physical
act of the probe to be out of phase with the undesired polarization
has the effect of disrupting the coherency of that polarization
therefore prohibiting it to pass into the LNB. When you change
channels, while watching TV, the feedhorn's servo motor rotates
the probe, which swings back and forth while switching between
the polarized signals (horizontal/vertical channels or RHCP/LHCP
channels as appropriate). The act of using one main signal transmission
to host two polarizations within that signal is termed 'frequency
reuse' and is a technique to double a satellite's channel capacity
without adding additional transponders. It is common to use the
term 'polarity' when referring to signal polarizations though
polarization is the correct term.
When both polarities of signal are desired to be received at
the same time (as in the case for a 
distribution system as used for
a motel or apartment complex or to allow each TV in your home
to independently receive all satellite channels) two LNBs are
installed on the feed, one for each polarity, and this style
feed is called a dual feed, not a dual band feed as band typically
refers to either C or Ku signals and a dual feed receives only
one band. A dual feed can be for any frequency band; a dual feedhorn
does not have a servo motor. 
Note on a dual
feed the LNBs are at right angles (orthogonal)
to each other; technically, a dual feed is called an 'orthomode
feedhorn'. Another popular type feed is one that accepts multiple
frequencies, usually C-band and Ku-band signals, this style feed
is called a corotor and is a dual
band feedhorn (sample receiver
wiring for corotor system). A corotor will have a servo motor
to control which incoming signal polarity is passed on to the
LNB and it uses both a C-band and a Ku-band LNB. The style feed
combining the dual C-band and single Ku-band LNBs (three in total,
the Ku uses a servo) is called a 'dual C corotor' (sample
receiver wiring for dual C, single Ku system); and a dual
C/dual Ku (four LNBs total) is called a 'bullseye' feed. When
a feed is designed to receive circular polarity it is called
an international polarotor, international corotor, etc.
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LNB: (For
assembly instructions.) Attached to the feed is the LNB (low
noise amplifier block downconverer); you will see a probe (post)
inside the LNB throat and this probes receives the mechanically
vibrating microwaves and converts it into electrical energy to
be passed the LNB circuitry then on through the cable to the
satellite receiver. Additional to accepting the signal from the
feed, the function of the LNB is to both immediately amplify
the weak satellite signals from space (received by the dish and
passed through the feedhorn probe as gigahertz - a billion cycles
per second) and to convert them to an intermediate 
frequency
(megahertz - a million cycles per second) that can be used to
travel efficiently thru the coaxial cable attached to the LNB
at one end and to the satellite receiver at the other end. Summarizing,
satellite frequencies are in the gigahertz (GHz) range and the
LNB downconverter output is in the megahertz (MHz) range (the
industry standard is to downconvert to the 950-1450MHz range
though proprietary systems will use a different downconvert range);
inside the satellite receiver, the signal is again downconverted
and this time to the frequency range acceptable by your television.
Note the downconverted frequencies are in a range, i.e. block,
thus the term 'block downconverter'. With a block downconverter,
for a twenty-four channel satellite, i.e. twelve transponders,
for example, the output of the downconverter contains the information
for either the twelve horizontal or the twelve vertical (or RHCP/LHCP)
transponders depending on which polarity is being accepted by
the feedhorn. Because all twelve channels (in this example of
a twelve tranponder satellite) are being carried into the house
at one time it is possible to connect multiple satellite receivers
to the same satellite dish each with the capability to tune a
different channel (a dual feed is
used to bring both banks of transponder polarities into the house
at the same time when multiple receivers are desired). Block
downconversion allows independent channel selection from multiple
TV's (each fitted with its own satellite receiver) though, of
course, they have to watch the same satellite at the same time.
The LNB coaxial cable
is typically a 75ohm, RG-6 coaxial cable though for longer travel
distances, over several hundred feet, a larger size cable, RG-11,
is used because frequencies will attenuate (loose strength) over
distance and the object is to deliver a strong signal to the
receiver.
LNBs are rated in noise temperature - the lower the number
the better. Noise temperature is a value that indicates the unavoidable,
inherent level of background atomic (molecular) motion in an
object and this inherent noise (called ambient noise) is in the
microwave frequency range. The lower the noise figure, the less
ambient noise an LNB injects into the received signal; the lower
noise rating of an LNB, the weaker signals it can effectively
process. For C-band satellite signals, 
the
noise figure is in degrees kelvin; a value of 25 or lower is
today's industry standard. For Ku-band signals, the noise figure
is in dB; a value of 1.0 or lower is today's industry standard
with 0.7s being very commonly available.. An important fact to
remember, natural molecular motion within all matter generates
random noise and this random noise 'infiltrates' communication
signals so that a received signal must be strong enough to override
(rise above) the noise floor created by natural molecular motion.
Therefore, the lower noise figure an LNB is rated the weaker
satellite signals it can process and thusly the smaller diameter
satellite dish it can accomodate. Modern LNB design and circuit
technology advancements have lowered the noise figure values
of today's LNBs considerably from the early days of the industry
so by applying the lowest rated LNB to your system, the better
signal processing you will receive and the smaller dish you will
need.
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