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How satellite TV works
4/8/2019

Satellite television onboard boats is one of those technologies that used to be only for owners with deep pockets. Today with lower costs for both equipment and programming, and with systems that are small enough to be fitted aboard boats down to 30 feet or so, boaters of all stripes can take their favorite TV entertainment, sports and news programs with them pretty much anywhere they cruise.

While pulling in content is as easy as touching the screen there’s a lot that goes on behind the scenes. Here’s a primer that will get you started down the road to understanding how that magic happens.

By John Barry

Satellite TV has become widespread on yachts.  In the commercial world, some unions require Sat TV for the crew as part of the contract, making it a mission-critical system.  In the US, we use two different providers, DIRECTV and DISH Network.  These two competitors use different methods to send Sat TV to our boats.  Satellite TV is broadcast in the Ku- and the Ka-band---Ku-band broadcasts at about 13 GHz and Ka-band broadcasts at about 26 GHz. DIRECTV is the only satellite service provider in the US that utilizes Ka-band, and at the time of this writing it broadcasts all of its high-definition content using the Ka-band frequencies.
 
The satellites used for television are in geosynchronous orbit around the earth.  This means that they are located above the equator and appear to be motionless, staying at the same longitude.  We name these satellites based on their location; sat DTV101 is at 101 degrees longitude at the equator (0 degrees latitude) and 22,000 miles up.  Since the satellite stays still and our boats move around, we use "stabilized” antennas, often called "in-motion” antennas in the marketplace.  These dish antennas use gyros and motors to keep the dish aimed right at the satellite.  There are some great apps for finding satellites in the sky, like SatBeams.com. 

Direction matters

Satellites are very directional.  Their "footprint” is the area of the planet where the satellite can be received.  DIRECTV has a footprint that covers the US, as does DISH Network.  The actual footprint of the satellite extends offshore some distance but eventually dies.  The area where you can expect reception to be acceptable is determined by where the satellite is aimed.  When you get near the edge of the coverage territory shown by the satellite footprint, the signal becomes weak and unusable.  Use of a larger, higher-gain antenna dish means a larger coverage area.

Satellite reception can be a confusing thing.  The dish has to see the satellite for it to work, so there are conditions where Sat TV does not work, like under a bridge or in a canyon.  We need a view of the sky and we also need to see toward the equator (typically south from these parts).  

To see the spacecraft 22,000 miles above the equator, we must look up.  The angle that we look up is called the "elevation angle” or the "look angle.” This elevation angle is based on latitude or how far north (or south) of the equator our dish is located.  Since our boats move around quite a bit, the elevation angle changes.  In far north latitudes, the elevation angle is very low on the horizon, and this presents problems requiring larger dishes.  In southern latitudes, the elevation angle is very high or straight up, requiring more complex three-axis dishes. In the lower 48 states, satellite reception is possible with fairly small dishes, 2 feet or less.
 
A satellite is actually a radio which receives and transmits signals originating from the satellite TV providers.  These highly specialized radios contain patch transponders, which send the satellite signals for various channels.  When we test satellite TV installations by using "Check Signal Strengths” in the satellite receiver menu, we see the strengths of the signals received from each of the transponders.  There are even- and odd-numbered transponders.

The elliptical shape of the sat antenna dish focuses the RF energy coming from the satellite on to the LNB---or Low Noise Block converter.  The LNB has two jobs. First it is an amplifier to boost the very weak signal from the satellite to a usable level.  This is the Low Noise Amplifier part of the LNB.  The other job that the LNB does is to convert the RF signal from Ku- or Ka-band frequencies down to a lower frequency.  This gives us a frequency that will work through normal coax cables.  This is the Block Converter part of the LNB.  

Miminize coax runs

Satellite TV installations on boats vary greatly.  When determining what is best for a given boat, you must first determine where the antenna will go, how many satellite receivers you need, and where the boat owners are cruising.  Try to locate the equipment for minimal coax lengths.  Often it is best to locate the receivers at a central location and use RF (radio frequency) remote controls.  It may be better to repeat the video from one TV to another TV instead of having a dedicated satellite receiver.  Using just two satellite receivers simplifies the installation considerably.  Distributing the video signal though the boat can be done over Ethernet or wirelessly, saving substantial wiring.
 
Satellite TV on boats can be a distraction to safety.  Sat TV should never be located at the helm as this could cause accidents. Satellite reception operates at very high frequencies and all the normal rules apply.  Antenna placement matters—satellite antennas need a view of the sky.  Keep your coaxial cables as short as possible.  Don’t kink or crush the coax.  Terminate the coax properly.  As usual, the coax is the culprit most of the time when it comes to weak signals, intermittent operation, etc. Robust quad-shield coaxial cable should be used.  For long runs, ditch the RG6 and use RG11, low-loss, fat coax.  Follow the rules and your satellite installation will last for years.
 
 
Getting geeky
 
For anyone who wants to wander a bit deeper into the technical swamp, here’s a short introduction about power considerations and multi-switches. The info won’t turn you into a competent installer but it will give you a taste of some of the complexity involved in setting up a system properly.
 
The LNB is an active device.  Once the signal is received by the LNB, amplified and block converted, the signal goes to a satellite receiver.  The sat receiver supplies 21VDC to the LNB through the coaxial cable and this is why we need a good shield connection for power as well as shielding.  The LNB outputs 13 and 18 VDC levels with RF superimposed in a composite signal containing the even and odd channels from the transponders.  This allows the receiver to detect all of the channels that are present in the signal from the LNB. As long as we use just two receivers, connection can be quite simple.  For three or more receivers, we use a multi-switch.
 
Standard multi-switches are easy to install. We just hook up the 13 volt line to Sat A and the 18 volt line to Sat B, and we hook the receivers to the Sat Out jacks on the multi-switch.  The multi-switch sends even or odd channels to the receivers on demand.  If you are missing half the channels, chances are you are missing one of these voltages or there is a bad multi-switch or LNB.
 
Another type of multi-switch is a Swim Switch (SWM), or Single Wire Multi Switch.  These highly specialized multi-switches modulate specific channels to each port on demand.  SWM installations require compatible receivers and power insertion, so care must be taken to ensure proper hook-up prior to power on.  Refer to manufacturer/service provider instructions for latest on SWM technologies.  We will look more closely at multi-switch in a later article.
 
About the blogger

John Barry owns and operates Technical Marine Support Inc. in Pleasant Prairie, WI. He is a Certified Marine Electronics Technician and has an ABYC (American Boat & Yacht Council) electrical certification. John also instructs Marine Electronics Installer and NMEA 2000 training courses.
 
 

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