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Chapter 1 - Basics of Satellite Internet Communication

 
 

If you’re reading this page, know that you are in good company. All satellite installers were new to satellite technology at some point in time. This program is aimed at giving you a foundation of satellite installation technology so that you may be confident in your installation at any location. For those that are somewhat knowledgeable in satellite communication technology, this online training program is likely to help to fill in some gaps.

What is Satellite Communication?
This is a broad question, but in general terms, Satellite communication, (sometimes referred to as satellite Internet) is the ability to transmit and receive data from a relatively small satellite dish on Earth and communicate with an orbiting Geostationary satellite 22,300 miles above Earth's Equator. In turn, the orbiting satellite transmits (and receives) its information to a single location called the Network Operations Center or NOC (pronounced "knock"). The NOC itself is connected to the Internet (or private network), so all communication made to the Internet must flow through the NOC.


This is a simple diagram on the left shows how data moves through the a satellite network.

Data communication via satellite is not much different than someone using a land based data provider, at least from the end-users standpoint. The key to remember is that once the satellite system is configured by the installer, the service acts nearly identically as any other data service and may be configured as such.



What is a Geostationary Satellite?
There is a location in space where you can place a satellite in orbit so that from the ground, the satellite appears stationary. What is happening is that the satellite is actually orbiting the Earth at the same speed the Earth is rotating. The satellite makes a complete orbit around the Earth in 24 hours, or exactly one day. Geostationary satellites are only located at 22,300 miles directly above the Earth's equator and nowhere else.


A Satellite's Longitude
All Geostationary satellites have a name like "G-18" or "AMC-4". These satellites will also have a longitudinal position - 117w or 101w (the "w" stands for "west" or western hemisphere). All satellite longitudes will be either East or West, though all installations in the western hemisphere will use Western Longitude satellites.. You can refer to a satellite either by its longitude or by its name. 

Longitudinal lines travel from pole to pole vertically along the Earth.  There are 360 degrees of longitude readings for Earth (360 degrees is a full circle).  If one knows the longitude of a satellite, one knows where the satellite is located in the sky because all Geostationary satellites are always located above the equator (or zero latitude).


AMC-4 has a position of 101 degrees Longitude.  If you were to follow Longitude 101 north from the Equator, you would run through the middle of Texas, up through the middle of North Dakota.

Satellite Latency
It takes time for a satellite signal to be sent from your dish to the orbiting satellite back down to Earth… The speed of light is 186,000 miles per second and the orbiting satellite is 22,300 miles above earth. Calculated out, satellite latency is roughly ½ of a second, which is not a lot of time, but a few applications such as VPN (Virtual Private Network) don’t like this time delay. It is important to know if Satellite Latency will affect the way you will use the Internet.

A Misconception About Satellite Latency

A common misconception is that latency has an effect on transfer rate. This is not true. A one Megabyte file will transfer just as quick over a 1000Kbps satellite connection as it does over a 1000Kbps terrestrial connection. It just takes the satellite connection less than a second for the file to begin transferring.

Polarization
You will hear this term often in the satellite Internet world. It refers to a trick that is used by the satellite industry to effectively double the transmission potential of satellites by transmitting on Vertical and Horizontal planes or "Polarities".

Using differing polarities allows service providers to re-use the same frequency by simply transmitting a vertical wave or a horizontal wave.


To capture the signal is the job of the "Wave-Guide", which is a portion of the satellite dish electronics. The wave guide has vertical and horizontal openings that create a "polarity" filter for the incoming (or transmitting) signal. Below, the Wave Guide can be seen among the radio assembly of the satellite dish.




Note that the physical rectangular dimensions of the waveguides openings determine the polarity of the incoming or outgoing signal. Note that a vertical rectangular channel of the Receive Feed is receiving HORIZONTAL waves (which is counter intuitive). This is the same for the transmit feed who's horizontal rectangular opening will transmit VERTICAL waves.

As always, refer to your installation documentation for the correct polarization of the equipment. For this demonstration and this course, we will be working with AMC4 - 101W which receives Horizontal and transmits Vertical.

Cross Polarization - Adjusting the Dish Polarity
Knowing that a satellite in orbit transmits on a vertical or horizontal polarity, then it should come as no surprise that you will need to rotate (or SKEW) the radio assembly so that you be aligning the dish electronics to be perfectly in line with the orbiting satellite signals. We will get in more detail on this process in a different chapter dealing with the actual dish installation.

For now, just take a look at this picture and understand that rotating/skewing the radio assembly is the process of aligning the dish with the orbiting satellite horizontal and vertical polarities. This process is known as "Cross Polarization".



Rotating or "Skewing" the radio assembly to align to the orbiting satellite

Timing / Ranging
In order for a 2-way dish to communicate properly with the satellite in orbit, the signal that transmits from the dish must be precisely timed to be received by the Satellite. If the transmission is received a fraction of a second late or early, communication will not exist. A transmission from Texas arrives at the satellite faster than a dish located in Canada because Texas is physically closer to the satellite. This process of timing a satellite is sometimes called "ranging" because you are defining the range between the satellite dish and the satellite. Ranging needs to be extremely precise by using a handheld GPS device to give you your current installation location.

Satellite Footprint
The footprint of a satellite shows the location that a satellite dish may be located to communicate with the satellite. Below is the footprint for AMC-4 for North America



EIRP - Effective Isotropic Radiated Power In the above footprint, the numbers in red represent the EIRP regions on the planet. The number itself is a representation of Decibels "dBW" or power level of the EIRP (in reference to one watt. The higher the dBW, the greater the signal strength. If you have a region with a low EIRP dBW level, you may have to use a larger satellite dish in order to receive the signal.

Dish Size is important
Below is an example of a footprint that shows the minimum size of satellite dish required for connectivity in certain regions in North America.


The KU Band
Satellite communications are radio transmission in the KU Band of the electromagnetic spectrum. The KU Band is the same band that police officers use for their radar detectors.

KU Band satellite dishes transmit between a frequency of 14000 to 14500 MHz.
They receive a frequency range between 11700 to 12750 MHz.

Other common Satellite bands are C-Band and KA-Band.

Transponders (or Frequencies)
Satellites use TRANSPONDERS to communicate with the Earth. A Transponder picks up on a small slice of the KU Frequency Band. The Satellite has "Receive" transponders and "Transmit" transponders. When you make a request to the Satellite for a web page, you transmit to a receive transponder on the Satellite. The Satellite then sends it down to Earth with a "Transmit" transponder. In fact the satellite can be thought of as a giant "repeater" in space.

Below is a picture of the 24 transponders (or frequencies) of AMC 4 for the uplink (up to the satellite) and downlink (down from the satellite).




Note that the frequencies of AMC 4 are somewhat rectangular looking, and in the center of the rectangle is the "center frequency" of that transponder. This term Center Frequency is used during your installation.

On a spectrum analyzer, the frequencies look like this:


A spectrum analyzer is helpful in fine tuning the aiming of your satellite dish. In this program, we will show you how to use the Birdog satellite pointing utility which is easier to operate than a spectrum analyzer. We will cover that in the hardware installation section of this program.

 
     
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