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Installing a 36V motorised dish

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Traditional 36V motors can drive large dishes and move between satellites faster than DiSEqC, but installation is also a bit trickier

Vertical ground pole: It is essential that the mount pole is accurately vertical for the motor to properly track the satellite arc

Although DiSEqC and USALS motors undoubtedly have mass appeal, ‘traditional’ 36V DC polar and horizon-to-horizon (H-to-H) mounts still find fans today. These older motorised mounts are less elegant and more cumbersome than DiSEqC motors, but they can cope with larger dishes and very exposed sites, and move between satellites much faster. The setup process for these mounts is also trickier than DiSEqC motors, not least because larger dishes have a narrower beamwidth and require more accurate tracking of the satellite arc. The installation process given here should also be used with polar mounts that use a DiSEqC actuator (with the exception of wiring issues) and all but the dish-mounting also applies to those smaller H-to-H 36V motors that mount on a ‘normal’ 1.5in mount pole and carry the dish on a short motorised spindle in a similar way to a DiSEqC motor.

Declination adjusment Inclination ( =. Latitude) ‘Jack’ actuator Azimuth adjustment (for South pointing)

Guy ropes hold pole vertical as concrete sets

2  What Satellite & Digital TV

Inclination adjusment

SOUTH Declination Motorised axis Declination adjusment Inclination ( =. Latitude) Inclination adjusment Azimuth adjustment (for South pointing)

Dish mounting pole

Spirit level to check pole is vertical

36V mount angles: A polar mount and an H-to-H mount both have the same three adjustments to set, to follow the satellite arc

Declination Motorised axis

How to support the mount

How to wire it all up

01 36V motorised mounts are usually

02 A 36V motorised dish requires more

heavy and are used with large, heavy dishes and are subject to huge wind loads, so a sturdy mount is needed. Many polar mounts and large H-to-H mounts fit to a 3in (76mm) or wider mount pole that requires hefty T&K wall brackets or concreting into the ground. For a high wall mounting you can combine a series of T&K brackets on a very long mount pole, with the base concreted into the ground at the foot of the wall. However it’s arranged the mount pole must be dead vertical for the dish to track the satellite arc. Poles that screw to a wall or floor surface can be adjusted to vertical by inserting shims or washers between the mounting brackets and the surface. A pole concreted into the ground must be positioned vertically as the concrete sets.

cabling than a DiSEqC or fixed-dish system and this is often undertaken before the dish and motor are put into position (maybe in concealed ducting). As well as the co-ax cables to the LNB(s) and, perhaps, separate polariser control cables (for variable skew), the motor itself requires four or five connections, usually in a special multi-core cable, although separate cables can also be used. The motor power wires provide the 36V motor drive that names the mount. This is supplied only when the dish is moving and reversed on the two cables for movement in the opposite direction. Large dish motors consume a heavy current (up to 3A or 4A) and the gauge of the cable should accommodate this. The wires must be connected the right


ABC guide to... way around to the motor terminals and receiver/positioner terminals. This is often achieved by trial and error; check the dish moves west when west is selected at the positioner. The motor also gives feedback to the positioner so its position is known, using pulses counted by the positioner as the dish is moved. The pulses are generated by a reed switch connected by two low-current wires to the positioner, or by an active Hall-effect switch that requires an additional 5V supply wire. Adjusting the motor’s inclination

03 Once the motor and dish are

assembled on the pole the first angle to set is the mount’s inclination. This is the angle between the axis of rotation and the horizontal, and is equal to the site’s latitude (read from an atlas or mapping website) plus a small offset. Use an offset of 0.5° for now, and tweak the inclination in the final stage. With a polar mount, use an inclinometer to directly measure the angle of the rotational axis as it is adjusted. H-to-H mounts have the main axis hidden inside but they usually have a flat surface at the top end of the axis. Use the inclinometer on this and adjust to 90° minus the inclination. How to adjust the declination 04 Declination is the small downward tilt of the dish, so it will point at the satellites in geostationary orbit and not off into empty space. UK declination varies from 7.3° at Land’s End to 8° in Orkney, so you can estimate the correct value or use 7.5° and fine-tune it later. The declination is usually set with a screw stop on the mount. A scale on the mount may be provided; otherwise, add the declination angle to the axis inclination angle and, with the dish in its apex position, make the declination East satellite

South satellite

Elevation: Measuring the elevation of the dish with an inclinometer and straight edge across the dish face, for centre feed and offset dishes

Elevation=ATAN((COS(RADIANS(f))-0.1512) SIN(RADIANS(f))* 57.296

where the factor, f is: f=(ACOS(COS(RADIANS(sat)RADIANS(long))*COS(RADIANS(lat))))* 57.296

Satellite elevation = 90° - I

Wooden straight edge and inclinometer

Satellite elevation = 90° + dish offset - I

How to make final adjustments

adjustment by reading the angle of the dish face (use the inclinometer on a straight edge right across the dish). Set inclination accurately first. This is harder with offset dishes because the dish face is not at right angles to the direction the dish is looking. Include the manufacturer’s elevation offset angle in your calculations. How to align the mount South

05 The satellites are used to align the mount to point south. Pick a suitable satellite (Astra 19.2°E is a favourite) and calculate the elevation at your site according to the MS Excel formula: West satellite

Use the satellite longitude for sat, and the co-ordinates of the site (west is negative) for long and lat. Use suitable software or websites to do the maths. Subtract the elevation from 90° to give the angle of the dish face (again with an offset dish, include the elevation offset angle). Either driving the motor with the positioner or by hand, move the dish round the motorised axis until the angle on the dish face reaches the required value. Keep the straight edge upright, measuring the vertical angle (don’t rotate it with the dish). When the dish is at the right elevation, rotate the whole mount on the pole until the correct satellite is found. Homing in on the exact spot, the mount is then pointing due South and can be locked off.

06 At least one of the three settings –

Angle corrections: Use this table to make the final adjustments as reception is tested from the three satellites

Correction required

(Movement required to increase signal) Up

Up

Up

Decrease axis inclination

Down

Down

Down

Increase axis inclination

Up

Down

Up

Decrease inclination

Down

Up

Down

Increase inclination

Up

-

Down

Rotate mount east

Down

-

Up

Rotate mount west

-

-

-

Mount is aligned

inclination, declination or south bearing – will need further adjustment. Test which direction the dish is ‘off’ for satellites at the centre and ends of the satellite arc – such as Turksat (42°E), Thor (1°W), and Hispasat (30°W). If you are using the positioner, save the three positions so you can easily find them again. If you’ve disengaged the motor and are turning the dish by hand, mark off the positions of the three sats on the mount. For each satellite, gently pull on the rim of the dish to test if the signal is stronger (use a signal meter or the onscreen display) when the dish is pointed a little up or a little down and then make corrections to the mount setting according to the diagram. Don’t ‘over-correct’. Once your dish tracks the arc accurately, you’ll have permanent access to any satellite n Geoff Bains

Glossary Polar mount

Open structure motorised dish mount allowing the dish to track the satellite arc with a single movement powered by a linear push actuator jack. Typically capable of 45°-100° movement.

H-to-H mount

Enclosed motorised dish mount that enables the dish to track the satellite arc with a single movement powered by an internal motor and worm drive gearbox. Gives 140°-170° movement.

What Satellite & Digital TV  3


Installing a 36V motorised dish