Category Archives: AzTrax TV Antenna

Satellite TV – AzTrax™ TV Antenna

Minor editorial revisions: 1/30/2016;
Content and editorial updates: 2/17/2017

Aboard Sanctuary, we like to anchor, and do so often.  We depend upon, and frequently use, our satellite TV service while at anchor.  Like most boats and all trawlers, Sanctuary will “swing,” (horse, veer) at anchor under the influence of winds and currents.  She swings through an arc up to about 120° to 140° when winds are 20 mph or greater.  Satellite tracking units must be leveled so the rotation axis of the antenna remains perpendicular to the plane of the water’s surface.  Otherwise, the angle of the antenna with respect to the geostationary satellite will change slightly as the boat swings; particularly so in reversing tidal currents.  Any lack of level can result in signal dropout or even in complete signal loss.

We subscribe to a DirecTV™ satellite service.  We want to be able to view a choice of series entertainment programs and a choice of news channels.  We are not concerned with sports or movie packages.  Direct TV™ has several different satellites in geosynchronous orbit above the earth’s equator.

Factors affecting the choice of satellite TV service include:

  • mounted as it is in water, a boat is an inherently unstable platform that must deal with waves and wakes,
  • an HDTV dish is larger and heavier than a non-HDTV dish, and
  • aiming an HDTV dish is more demanding than aiming a non-HDTV dish.

apparent_satellite_locationBecause of these considerations, we subscribe to the non-HDTV satellite service.   That service is a digital TV signal which gives perfectly satisfactory picture quality in our relatively small space.  With respect to North America, the Dish™ and DirecTV™ satellites are in geostationary orbit in the southwest sky.  Our service is provided by the DirecTV™ satellite located above the equator at -101º West Longitude.  From anywhere in North America, that satellite appears to be located south of Texas.  The antenna dish, of course, needs to point to the satellite within 2° ~ 5° of both elevation and azimuth.  We have found that antenna aiming is less critical when the antenna is located farther south in latitude.  Farther north, dish elevation needs to be adjusted somewhat more frequently.   When cruising the Mid-Atlantic between Florida and New York City – dish elevation needs to be adjusted about every 100 miles of latitude.  The elevation angle changes more slowly the farther south we are.  Along the gulf coast, the elevation angle doesn’t change at all.

aztrax1

Motorized tracking unit, controller and IR remote control.

Sanctuary and crew installed an AzTrax™ satellite TV tracking antenna in October, 2004.  This unit is manufactured by Marine Satellite Systems (MSS).  The MSS website is located here: http://www.mssat.com/.

Functionally the AzTrax™ antenna tracking unit is very similar to the Follow-Me-TV® (now Track-It TV®) unit, and in the same price class.  These units contain a fluxgate compass and stepper motor that automatically maintains the selected azimuth setting.

We chose the AzTrax™ unit over the Follow-Me-TV® unit because we thought it had several design advantages.  The unit is small, light and well built.  All exterior wiring is permanent and sealed against rain, spray water intrusion and corrosive environmental contaminants.  The design of the reversing mechanism seemed more resistant to future failure.  The unit comes with a plastic, oval dish reflector designed by MSS, which is somewhat smaller than the

Average signal strength of MARINE-SAT compared to standard 18

Average signal strength of MARINE-SAT compared to standard 18″ and 24″ antennas as a function of angular ofset

round metal dishes and has a metalized UHF-reflective coating.  The MSS web site advertises their dish’s response curve as broader than the standard 18″ round form DirecTV™ dish.  The LNB that comes with the AzTrax™ is a dual output LNB device which supports the two separate tuners in our DirecTV™ DVR.  The very important antenna leveling system is easy to use and mechanically secure.

We usually mount our AzTrax™ unit on an aft rail.  A viable alternative location is on the flybridge.  When we relocate the antenna, we have position and leveling details to manage:

  • Aboard Sanctuary, our water tanks are asymmetrically positioned in the hull.  As we add and draw off our water stores, the trim of the boat changes slightly.
  • When the net influence of wind and currents is from the southwest, Sanctuary will lie in the water with the bow pointed towards the satellite.  Lying thus, with the antenna mounted on an aft rail, our wooden mast and boom, and our canvas flybridge enclosure, lie in the path of the signal as it travels from the satellite to the dish.  These “obstructions” cast a signal “shadow” across the face of the dish as the boat swings at anchor, resulting in intermittent signal dropout.
  • In marinas, clusters of nearby sailboat masts and rigging can occasionally have a similar “signal shadowing” affect.
  • If our flybridge enclosure is wet with dew or rain, received signal strength will often be diminished.
  • As we travel north or south through hundreds of miles of latitude, there is a 25° or more change in the apparent elevation of the satellite above the horizon.

All of these factors mean that that we occasionally need to adjust the elevation angle of the dish, relocate the tracking unit and/or adjust the leveling of the unit.  The AzTrax™ unit mounts to any available rail.  It uses a mount made for a Magma® Barbecue Grille.  The design of the Magma® rail clamp makes it very easy to relocate and level the AzTrax™.  Furthermore, the antenna’s base platform has a built-in bubble level which further facilitates accurate and fast re-leveling.

From Florida through the Chesapeake Bay, we typically experience signal strengths in the high 80s to 90%.  In the 70s on the Hudson River and in the NYS Canal System.  In Canada above 45°N latitude, we rarely saw better than 70% signal strength.  On our DirecTV™ system, we have found 50% ~ 55% signal strength gives us watchable TV.  The farther north we are, the aim of the dish becomes increasingly more important and more sensitive.  It is also less forgiving in the sense that the small mechanical adjustments to change 5° of elevation are incrementally smaller the farther north the antenna is located.  That said, though, we’ve had few problems getting perfectly watchable signal strengths anywhere along the Great Loop cruise, in the Abacos, or as far up the New England Coast as Acadia National Park at Penobscot Bay in Maine.  Our DVR has built in signal strength “meters,” which make it fairly easy to adjust the antenna’s azimuth settings for peak signal strength.

Our experience has been that the fluxgate compasses built into azimuth tracking units are affected by the inherent and non-uniform magnetic profile of the boat.  Because of the non-uniformity of the boat’s magnetic field, the azimuth heading setting when the boat is lying to a westerly heading may be several degrees different than when the boat is lying on an easterly heading.  The physical mounting location of the unit on the boat also affects the azimuth heading setting.  We got used to this quickly.

The fluxgate compass is also affected – sometimes dramatically so – by large nearby off-boat metal masses located within the nearby dock infrastructure.  Steel bulkheads, concrete bulkheads containing re-bar, metal safety ladders and railings, and lock walls can all have a significant effect on the operation of the fluxgate compass because these metal masses distort the local magnetic field.  The affect of nearby metal masses is to cause the satellite to appear to be at an abnormal azimuth in the sky.  Once we recognized what was happening, we learned to simply expand the range of azimuth when sweeping the antenna to find and maximize the satellite signal.  We’ve seen azimuths as much as 100°M away from the reported heading of the compass.  For example, the “normal” satellite heading aboard Sanctuary in the Baltimore area of Maryland is about 238°M, but on the metal-containing sea wall on Ego Alley in Annapolis, we found the signal at 294°M.  We saw a great deal of this kind of magnetic disturbance along sea walls on the NYS Canal System and other high, metal-containing, side-tie locations along the Great Loop.

We do experience signal drop out when cloud cover is very dense, as in heavy rain and thunderstorm weather.  However, the antenna is quite forgiving when we experience small boat wakes at anchor, with very little annoying dropout.

We live aboard full time.  We have had our AzTrax™ for over 13 years now, with no problems.  Well, yes, one small problem.  At about the 3 year mark, the remote control for the control box died.  We simply programmed the DirecTV™ remote control to talk to the AzTrax™ control box, and life went on.  We are very happy with the AzTrax™ system, and we recommend it to those with a personal tolerance for making the small mechanical adjustments described herein for elevation and leveling.

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