Index

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.

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.

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).

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.
 

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,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.
 

LNB (Low Noise Block)

(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.