1. FEATURE Basic Knowledge
Polar Mount Antennas
Motorised Antennas for
Satellite Reception
Adolf Oberhuber
If you consult the relevant literature you will find that In general, if a satellite antenna is to
be rotated with a motor you would need
no or – at most – insufficient background information two motors – one for the rotating move-
is available about how this type of motorised polar ment (azimuth) to the selected satel-
mounted antennas actually works. The same is true for lite and the other one for adjusting the
dish to account for the differing heights
the required formulas and their derivation. The following above the ground (elevation). Mounting
illustrations are meant to provide answers to all questions the rotation axis in parallel to the rota-
in association with a polar mount. This also includes, tions axis of the earth, i.e. in a pole-to-
pole direction, alleviates this problem so
inter alia, various size determinations for positions as well that only one motor is required. How-
as calculations for the satellite orbit based on a specific ever, this can only be achieved with a
example. Altogether this report is a collection of data and more complicated and extremely precise
installation and alignment of the rotation
calculations which, the author believes, have hitherto been axis.
scattered across an endless number of publications and
accounts. For the sake of completeness and reference, Dealing with the installation of satel-
lite receptions systems – both in theory
technical terms and their origin will be explained in a and practice – requires gaining an
separate addendum at the end. understanding of sizes and proportions
relating to different sizes. As even the
Without exception, all calculations has unrestricted access to all transmis- relevant sizes and their derivations are
and remarks are for the northern hemi- sions of all satellites at any time. Natu- hard to come by, the following will estab-
sphere. If you live south of the equator rally, if several LNBs are attached to a lish all relevant data.
you need to interpret them accordingly, single antenna they cannot all be in the
such as antenna alignment to the north precise focus of the parabolic dish, which Before performing any calculations it
instead of the south, inclination of the means that they are slightly out of focus. is paramount to recall the interdepend-
rotation axis towards the south instead However, reception is only possible if the encies between the earth and satellites.
of north and so on. For all calculations satellites are rather close to each other This may also provide a welcome oppor-
you merely need a standard 10-digit and if the antenna has a certain (larger) tunity to correct some common miscon-
electronic calculator capable of per- diameter. ceptions.
forming trigonometric operations. If you
intend to receive several satellites at 3. Polar mount antennas: The earth
once you may choose one of the follow- For single users interested in maxing Due to its rotation the diameter of the
ing set-ups: out their reception possibilities a polar earth at the equator is larger than the
mounted motorised antenna is an inter- distance between the north pole and the
1. Several antennas: esting solution. As the name implies, the south pole, which means the earth does
Usually, such a set-up is only chosen for axis around which the antenna rotates is not have an exact spherical shape. How-
commercial applications as it requires a mounted in a pole-to-pole direction, i.e. ever, the differences associated with this
lot of space and also is more costly than in parallel to the axis of the earth. Such fact can be neglected for our calcula-
other solutions. a set-up does not restrict the number tions, so that we accept the established
of receivable satellites, provided they median radius of the earth of 6,731 km
2. A single antenna with two or more can be ‘seen’ from the location of the as given.
LNBs: antenna. It is no big deal to receive 15 to
This design is intended for multi-user 20 satellites without exceedingly elabo- Historically and depending on the
layouts that have to make sure each user rate equipment. purpose, positions and directions are
140 TELE-satellite International — The World‘s Largest Digital TV Trade Magazine — 06-07-08/2012 — www.TELE-satellite.com

2. defined using varying systems. Unless When installing a polar mount antenna 4. Even the sunspot activity may dis-
exact definitions rule out any ambigui- the most important parameter – apart tort the earth’s magnetic field.
ties, one sometimes needs almost inves- from the exact positioning of the mast
tigative skills to find out without doubt pointing north from its horizontal instal- 5. The glass protecting the magnetic
what is actually mean when reading lation – is the precise determination of needle may become electrostatically
about a position. the southerly direction at the location. In charged and then causes massive meas-
most cases a compass will be used to find urement errors if one is not cautious
The equator can be established as the the exact south. However, the results are enough. Plastic coverings are particu-
zero-point for the geographic latitude. frequently inaccurate and problematic larly problematic in this regard.
Towards the north the range extends in principle, as the following sources of
to 90 degrees north, or +90 degrees, error clearly demonstrate: If all these issues are taken care of a
towards the south it is 90 degrees south compass may actually deliver quite sat-
or -90 degrees to the pole(s). 1. The magnetic north pole as indicated isfying results. Still, the most reliable
by the magnetic needle of a compass is determination of the southerly direction
As regards the geographic longitude not the same as the geographic north is by locating a satellite that is as close
an artificial zero-point had to be deter- pole and shifts from year to year. This as possible in the exact south when seen
mined. The meridian crossing the Green- is also the reason way nautical charts – from the given location of the antenna.
wich observatory near London with its which have to show the exact geographic As a rule of thumb, satellites are mostly
line from the north pole to the south north – have to be redrawn almost every spread with a 3-degree spacing, which
pole has been accepted as zero meridian year and are sold with revised informa- makes this method very accurate.
since 1884. From this meridian, the circle tion in certain intervals. To give you an Generally however, you will first have
is divided into 360 degrees towards the understanding of the deviation look at to find out the exact position given in
East. This system is derived from astron- the following comparison for a specific geographic longitude and latitude of
omy which also employs a left system point in time: the location of the antenna. If you need
(seen from the north pole) for projec- help obtaining these parameters please
tions from the earth’s surface into space. The magnetic north pole was situated approach your local TV installer, check
This way the position of celestial bodies north of Canada at the Internet or look at special maps. If
such as satellites in a geostationary orbit - approx. 100 degrees western longi- you know somebody owning a handheld
can be precisely defined. tude and GPS device this would also be a conven-
- approx. 75 degrees northern lati- ient way of finding out where exactly
tude you are.
- and that was approx. 1,500 km away
from the geographic north pole. The ‘bad habit’ of giving the deviation
of satellites from a southern direction
The magnetic south pole was approx. towards the east or the west (azimuth)
2,500 km away from the geographic by stating the compass course is gain-
south pole and was situated at ing ground. This requires that we have
- approx. 140 degrees eastern longi- to take into account that a compass has
tude and its zero point in the north, which means
- approx. 65 degrees southern lati- that south is at 180 degrees. The com-
tude. pass rose is divided into 360 degrees
and constitutes a right system:
The further north we move, the larger
Fig. 1 features four points with their the deviation caused by a compass 0 north, 90 east 180 south 270 west.
positions, which are listed in the table becomes (depending on the geographic
below with their used designations. longitude, however). If we assume that a satellite is posi-
tioned three degrees east of the south-
In Europe the relative designations are 2. Below the surface conditions may ern direction, it has a compass reading
predominant, based on the zero meridian exist that influence the magnetic field. of 177 degrees. It would be easier to
towards west or east. While this is the simply state 3 degrees east, or azimuth
most complex and longest designation 3. Objects made of metal (such as +3 degrees (east).
it is one that leaves no room for misin- metal roofs, railings, concrete rein-
terpretation. As satellites are positioned forcements etc.) may be located close There are cases when older march-
near the equator, it is not necessary to to where the compass is used. Theses ing compasses are being used to deter-
also give the latitude as it is always zero objects may severely interfere with the mined the exact south. These also have
degrees. magnetic field. their zero point in the north, but the full
Absolute Relative Relative, in use
circle is divided into 64 segments (with
P1 20/30 degrees +20/+30 degrees 20 degrees eastern longitude/30 degrees northern latitude one segment equalling 5.625 degrees)
P2 320/30 degrees -40/+30 degrees 40 degrees western longitude /30 degrees northern latitude
and it is a left system:
P3 335/-30 degrees -25/-30 degrees 25 degrees western longitude /30 degrees southern latitude
P4 15/-20 degrees +15/-20 degrees 15 degrees eastern longitude /20 degrees southern latitude
Sat. Astra 19,2 degrees +19,2 degrees 19,2 degrees east 0 north, 16 west, 32 south, 48 east.
Sat. Hispasat 330 degrees -30 degrees 30 degrees west
142 TELE-satellite International — The World‘s Largest Digital TV Trade Magazine — 06-07-08/2012 — www.TELE-satellite.com

3. The satellites Polar mount antennas M = centre of the earth you connect your receiver to your PC you
R = radius of the earth (6,371 km) will end with a fully-fledged information
Satellites have to remain in their posi- If we were able to install a motor-
P = location of the antenna centre that leaves nothing to be desired.
tion relative to the surface of the earth ised antenna on the north pole or at the
φ = northern latitude of P Language barriers can easily be over- P`S = 42,16 – 6,371.cosφ
so that transmissions from them can be centre of the earth it would be possible
S1 = southern direction come with the help of images and the ε = µ −φ
used commercially – they have to be to receive signals from all geo-stationary
S1 and S2 are satellites (fictitious) Internet as well as TELE-satellite maga- This means the elevation ε towards the
positioned geo-stationary so that a fixed satellites – at least in theory. However,
MS1 = MS2 = radius of the satellites’ zine are valuable sources of information south is:
antenna can receive signals. Therefore, this would not be realistic even on the
orbit ( 42,160 km) for satellite enthusiasts.
satellites have to meet the following con- north pole as all satellites are below the
PS1 = PS2` = radius of the motorised
ditions: horizon and therefore cannot be received.
From this it follows that the reception
dish Elevation towards Fig.7
1. The have to rotate above the equa- range of an antenna that is directed the south (Note that the radii of the earth and
the satellite’s orbit are shortened in the Angle δ is defined as declination
If a spectator stands at location P
tor. towards the south and aligned towards One of the determining factors for the (deviation).
and ‘looks’ in the direction of the satel- calculations.)
2. The have to move in the same direc- the east or west is largest at the equa- successful installation of a polar mount
lites, what he sees appears to be similar
tion as the earth. tor and gradually decreases the more we antenna is the mast which needs to be
to Fig. 4a. A satellite that is positioned Figure 6 shows the angle by which the
3. The have to be positioned at a dis- move north. At a northern and southern inclined as precisely towards the north
in the exact south appears higher and rotation axis for the antenna has to be
tance from the earth that allows them to latitude of 80 degrees the range is zero. from its vertical position as possible. You
those satellites that are located to the inclined towards the north so that it is in
take 24 hours for one full rotation (pre- Calculations we will perform at a later may always correct a slight north-south
east or west appear closer to the horizon parallel to the pole-to-pole axis.
cisely 23h 56m 04s). stage will provide a scientific framework deviation at a later stage when fine-tuning
until they disappear below the horizon.
for this statement. As antennas realisti- the complete system, whereas an impre-
cally can only be set up on the earth’s Because of the earth’s gravity spectators
In order to fulfil these conditions cise east-west alignment can only be
see the horizon as a horizontal line (see
Kepler’s third law of planetary motion surface the proportions and relations of
also Fig. 8).
adjusted by moving the antenna mast. Maximum
has to be applied: figure 3 apply.
The square of the orbital period of a Another underlying condition is know-
reception range
planet is directly proportional to the cube The antenna is installed at a certain ing the precise geographic longitude and Naturally, a general calculation exam-
of the semi-major axis of its orbit. position P on the earth, with a northern latitude of the antenna location – at least ple like the one above cannot take into
latitude φ. If we now align the antenna to everything except the decimal places. As account local factors such as buildings,
According the Kepler’s first law of plan- face precisely south, for example point- mentioned in the introduction these data trees etc. that might influence recep-
etary motion the orbit is an ellipse. In ing to satellite S1 and rotate it around can be obtained from specialists in the tion at the respective location. The only
our case the ellipse comes very close to the axis PP’ that has a pole-to-pole field or from friends owning a handheld value that can be calculated is the maxi-
Fig. 4 Fig. 6 mum angle that is limited by the horizon.
a circle. The great elliptic axis a is thus alignment until it points to satellite S2 GPS device. The geographic longitude Inclination towards the north against This angle is calculated from the south
replaced by the radius R, and the sat- it will not be able to exactly meet it as is of particular importance, as it plays
A very different situation emerges the horizontal level is: φ (conforms to towards east and west.
ellite’s mass m can be neglected when the antenna’s radius is smaller than the a crucial role for calculating the correct
when we deal with a polar mount geographical latitude)
compared to the earth’s mass M. Apply- distance PS2. It meets the equator plane elevation and determining the south-
ing Kepler’s third law we thus arrive at at point S2’, i.e. somewhat lower. This in antenna, as it rotates around the polar
ern direction. A compass should only be Inclination towards the north against
the following constants: turn suggests that the elevation (see fig. axis and ‘sees’ satellites next to each Fig.8
relied on as general guidance for identi- the horizontal level is: γ = 90 - φ
5) of the antenna has to be increased. other in a straight line (which is why
fying a southern direction, as its use it
U = 23h 56m 04s = 86 164 sec The bigger the deviation from a pre- polar mount antennas are used in the fist
U = rotation time cise southern direction, the bigger the place). However, when the dish rotates
too error-prone.
Inclination of the
G = 6,668.10-11 N.m2.kg-2 margin of error. A check calculation was the distance to the horizon changes, as
It is much better to look for a satel- antenna towards
G = gravitation constant performed to find out of this margin of Fig. 4b illustrates. Naturally, the antenna
cannot perform an arc-like movement,
lite that is positioned as closely to the the satellite
M = 5,976.1024 kg error that needs to be taken into account geographic longitude as possible. This of
Once the rotating axis is inclined to
M = earth’s mass in practice: At the geographic latitude of because it only rotates around a single course requires a TV or monitor to verify
the north by the appropriate angle the
47 degrees and a ω value of 60 degrees axis, which is aligned in parallel to the the result and to avoid pointing the
antenna has to be rotated downwards
the error is -0.41 degrees, which is neg- pole-to-pole line. antenna to the wrong satellite (as sat-
by the angle δ against the right angle
ligible. ellites can be positioned rather close to
towards the rotating axis, so that it
What we have learned so far clearly each other). Fig. 5 indicates the correct
‘looks’ directly to a satellite that is south
highlights the advantages of a motorised angles which are required for the calcu-
of the location.
polar mount antenna when it comes to lations that follow.
receiving a multitude of satellites and
their respective channels. Such a set-up M = centre of the earth
is not even very complex, with the single N = north pole
biggest issue probably being a suitable P = location of the antenna
location to install the antenna. What you φ = geographical latitude of the location
also need is a receiver which is capa- R = 6,371 radius of the earth
Fig.2 ble of controlling a motor, as an extra MS = 42,16 radius of the satellite’s orbit
The speed of the satellite is this: device for motor control does not make ε = elevation
sense. If you are computer-literate and
both your receiver and your PC feature The maximum reception range ω
(The satellites are positioned at 42,160 an RS-232 interface even the tiresome depends on the geographic latitude of
– 6,378 km = approx. 36,000 km above task of organising thousands of channels the location of the antenna, gradually
the equator) Fig. 3 becomes manageable quite easily and if Fig. 5 decreases the further north the loca-
144 TELE-satellite International — The World‘s Largest Digital TV Trade Magazine — 06-07-08/2012 — www.TELE-satellite.com www.TELE-satellite.com — 06-07-08/2012 — TELE-satellite International — 全球发行量最大的数字电视杂志 145

4. tion is situated, and reaches zero at 81
degrees northern latitude. The maxi-
A is required for these motors and can
easily be generated by suitable receiv-
able to really receive satellites between satellite can be received. We recommend Addendum
mum reception range can be achieved at ers.
the Hispasat 30 degrees west (azimuth
42.1 degrees west) and the Panam-Sat
Hotbird at 13 degrees east, as it almost
exactly (only 0.9 degrees deviation) cor-
Compilation
the equator at 81 degrees. Of course this 45 degrees east (azimuth 32.9 degrees responds to the geographic longitude of λ = geographic longitude
is only true for satellites with a geo-sta- Plus: No separate line to the antenna east). Between these positions there are Munich. To make sure you’re hooking to φ = geographic latitude
tionary orbit. required; DiSEqC via existing antenna approximately 20 satellites transmitting the correct satellite it is paramount to ε = elevation towards south
cable is used instead. If motor is more than 1500 free-to-air channels. select a channel from that particular sat-
The angle ω is calculated starting from detached for repair there is still recep- ellite. The following channel, for exam-
a southern direction towards east or Fig. 9 tion of one satellite, for example Astra. Next we have to perform all additional ple, can be used for Hotbird: δ = declination
west. In order to find the largest possible Minus: As the current for the motor is calculations, even though not all might
number of available satellites (azimuth) Motor control 13 V or 18 V depending on the polarisa- be needed, depending on the make and ZDF digital 11,054 GHz vertical
the following formula applies: tion level of the received signal, both the model of the antenna: Symbol rate 27 500 ω = reception angle from the south
Traditionally, motorised antennas are
speed and force of the rotation move- SID 8011 maximum no. of satellite positions
powered by an actuator which consists
Towards east: λ + ω ment vary. Not suitable for very large Video PID 570 (azimuth):
of a shaft whose length is varied with
(The correct algebraic sign has to be dishes. Audio PID 571 towards west: λ - ω
the help of a DC motor. Such a motor
used for the geographic longitude λ of PCR PID 570 towards east: λ + ω
has a uniform supply voltage of 36 V and
the location of the antenna)
changes its direction through switching H-H Inclination of the rotating axis towards
Towards west: λ - ω the north: Please make a point in setting all
the poles. A photocell is integrated in the So-called H-H motor controls have
(λ is positive for all positions east of φ = 48,1 degrees against the horizon- required parameters, as the same chan- inclination of the rotation axis towards
motor for exact positioning. It creates been promoted by various companies
the zero meridian.) tal line nel with the same name is also broad- north:
the impulses for positioning through a for some time now. However, they do
γ = 90 - φ = 90 – 48,1 = 41,9 against cast from ASTRA. Also make sure that against the horizontal level: φ
perforated disc. not fall into the polar mount category as
Polarisation their movement rather follows the circu- the vertical line the marking for south on the antenna against the vertical level: γ = 90 – φ
support is adjusted precisely while the radius of the earth = 6,371 km
Figure 4b illustrates that the eleva- When this technology first surfaced lar line-up of satellites above the horizon
Once all calculations are finished we complete construction is rotated on the orbit of the satellites = 42,160 km
tion changes automatically when the external control devices had to be used that is shown in figure 4a. The antenna
antenna is rotated. This at the same have to look for a suitable spot to install mast.
to control the antenna’s movements. cable transmits all control signals. Due to
time implies that the antenna’s orien- Soon, however, new receiver models their design H-H motor controls have to
the antenna. While perfect reception is
the number one focus we nonetheless Once you can confirm reception of
Technical terms
tation towards the satellites remains were introduced which were able to per- be physically attached to the antennas,
unaffected and the polarisation levels have to take into account other factors Hotbird all that is left to do is tighten Equator (Latin): balancer
form all required tasks and offered on- which means that any repair requires the
are the same for all receivable satellites such as a robust support for the antenna the fixing screws before you can rotate Azimuth (Arab): angle between the meridian
screen displays to set up the system in complete antenna to come down from of the location of observation and the vertical
and therefore need not be changed. mast (making it windproof and earth- the antenna for the first time to its limit circle of a heavenly body
the first place. the roof.
Nevertheless, most receivers with inte- ing it) and any restrictions or limitations stops, and check if the motor works sat- Declination (Latin): deviation
grated motor control come equipped that exist at the location. Of course all isfactorily using a soft stop mechanism DiSEqC (acronym): Digital Satellite Equipment
36 V power packs usually supply cur- Plus: Rather easy installation, because Control. Transmission of data via the antenna
with a device that corrects any possible regulations by local authorities must be that is available with most receiver types cable by way of impulse controls using the 22
rent with at least 2 ampere, while the all you need to know is the geographic kHz tone. Developed by Philips and offering
tilt of satellites. adhered to as well. and prevents the antenna from striking almost endless options. Even return channels
motors that are used generally require latitude and the southern direction. can be implemented for more complex control
any obstacle that might be in its way. set-ups.
less than 1 A. Unfortunately, however, Minus: If repairs are necessary there is
An LNB with built-in positioner can We recommend contracting a special-
these devices are disappearing very fast nothing left for reception. Only suitable Elevation (Latin): heightening, increase
achieve this with either a coil with elec- ised company for installing the antenna In case a satellite close to the limit
and in most instances are replaced by for small dishes. Geodetic system (Gea = Greek: earth): system
tric current flowing through it or an mast. This way you can make sure (i.e. stops cannot be received or comes in of imaginary lines covering the earth.
so-called H-H motors.
they must make sure) the mast can take only weakly you can slightly bend the
Practical example
Horizon (Greek): skyline, horizontal level
impulse-controlled tongue. Both options
high wind loads and is protected against antenna up or down to find out which of Kepler: Natural scientist 1571 – 1630. Kepler's
require a dedicated separate circuit Plus: sturdy design, hardly any laws of planetary motion:
We chose Munich is the location for our damage from lightning. Authorised busi- the two scenarios shown in figure 10 you 1. The orbit of every planet is an ellipse with the
from the receiver to the LNB. However, repairs needed, suitable also for larger sun at a focus.
practical example. First, we collected all nesses can also be expected to know are faced with. It is now that a less than 2. A line joining a planet and the sun sweeps out
such measures are mostly obsolete antennas. equal areas during equal intervals of time.
relevant data referring to our location local regulations and are responsible for perfect installation of the antenna mast
these days as satellites can be control- Minus: eparate circuit (5 wires) must
s
3. The square of the orbital period of a planet
and then performed all required calcula- is directly proportional to the cube of the semi-
not breaking any rules. shows its unwelcome consequences:
led much more precisely than what used lead to antenna, (+ and -36 Volt, ground,
major axis of its orbit.
tions we might ever need for installing
to be the case. +5 V for electronics, impulse circuit) LNB: Low Noise Block Converter (converter
our antenna: Now that all queries are solved the next positioned in the focal point of the parabolic
antenna and using an oscillator to convert the
Parabolic/offset DiSEqC Geographic longitude:
step is buying the technical equipment. If
you’re not the tech-savvy kind feel free
satellite frequencies into 950 to 2150 MHz,
which then are transmitted to the receiver via
the antenna cable)
antennas As more and more control functions λ = 12,1 degrees east to ask a specialist for assistance. Meridian (Latin): length, longitudinal circle.
(0-meridian: longitudinal circle from the north
Figure 9 compares two basic antenna had to be provided for one or more Geographic latitude: Fig. 10 pole via Greenwich near London to the south
pole. Generally acknowledged as the zero
types for wavelengths of a few centime- antennas and/or LNBs new and intelli- φ = 48,1 degrees north As far as assembly is concerned you a: The rotation axis is not enough to meridian since 1884).
tres (approx. 10 GHz). For professional gent ways had to be found for provid- Verification of the reception range: start out with the antenna support and the north Monitor (Latin): device for observing images,
video screen.
applications only parabolic antennas ing control impulses via existing antenna with adjusting the antenna according to b: The rotations axis is too much to
the calculated values with the help of the the north Polar (Greek): pivotal point; polar mount:
with a central reception unit (LNB) are cables. It then was a logical step to also mounted in a pole-to-pole direction.
in use, while for private reception offset integrate motor control into this system existing marking on the support. Next, c: The mast leans towards the east
Polarisation (Latin): direction (of waves).
antennas as shown in figure 9a are used and using the regular antenna cable for This means, in general the range to the support is attached to the antenna d: The mast leans towards the west
Satellite (Latin): companion.
up to a size of approximately 1.2 metres. impulse transmission (DiSEqC). As LNBs the east λ + ω = 12 +77 = 89 degrees mast and the antenna itself with the
Greek characters that have been used:
With its more upright position an offset are supplied with 13 or 18 V depending and to the west λ - ω = 12 – 77 = -65 LNB is attached to the support. You then Mishaps like these can be rectified by λ Lambda δ Delta ω Omega π Pi
γ Gamma ε Epsilon μ My φ Phi
antenna is less exposed to the elements on the polarisation level it made sense to degrees for the reception of satellites – need to connect a monitor or TV to the readjusting elevation and inclination of
Literature: Prof. Dr. Hans Heinrich Voigt,
(rain, snow) and thus more convenient to use the same voltage for the motors as azimuth +89 to -65 degrees. In actual antenna before you start rotating the the rotation axis – but always starting Göttingen university observatory „ Abriss der
Astronomie“ ("Abstract of Astronomy")
operate in the private sphere. well. A current of between 0.2 and 0.3 fact, however, we will probably only be antenna until signals from a southern from a southern direction.
146 TELE-satellite International — The World‘s Largest Digital TV Trade Magazine — 06-07-08/2012 — www.TELE-satellite.com www.TELE-satellite.com — 06-07-08/2012 — TELE-satellite International — 全球发行量最大的数字电视杂志 147