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april 2009
Installing a single fixed satellite dish Want to see more?
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Installing a single fixed dish A simple fixed satellite dish isn’t difficult to put up if you follow our step-by-step guide The majority of satellite systems in the UK use a single LNB on a single dish, feeding a single receiver. Most of these basic systems are fitted and aligned on the satellite by a professional installer – but anyone with some basic equipment and DIY experience can do the job themselves. How to fix the dish in place
01 Although the dish will come with assembly instructions, how you fix the mount in place depends on the individual situation. Most often, the dish will be mounted on a house wall, and this is largely a matter of drilling the requisite number of holes in the wall (using the mount itself as a template or one supplied) and fixing the mount in place with masonry fixings. It’s simple enough, but you should follow some rules. Only drill into brick, concrete or stone – not the mortar joints in between – and never fix to wooden parts of the building. Make sure that the mount is vertical and keep it at least three courses of bricks from the top of the wall. Use the right
fixings (nylon plugs and coach bolts for brick, steel expansion anchors for concrete), and if you’re fixing to a rendered wall make sure the fixings are long enough to grip the wall itself, not just the render. If the mount is going at ground level you should use a tripod or similar, fixed to paving slabs or kerbstones, or a king post with at least a third of its length concreted in the ground. For a flat roof use a tripod on paving slabs (if the roof can take the weight) – don’t be tempted to bolt directly to the roof.
How to find the satellite
The first rough alignment 02 With the mount and dish in place, adjust the bolts that lock the elevation and azimuth adjustments just tight enough to hold the dish but allow movement. You now need to point the dish in roughly the right direction for the satellite you want to receive. This will usually be for the Astra and Eurobird satellites at 28.2°E but you can find the elevation and
Hunting for the satellite: Sweep the dish left and right by a few degrees and up and down a fraction of a degree until the satellite signal is detected 2 What Satellite & Digital TV April 2009
azimuth for other satellites such as Astra 19.2°E and Hot Bird 13°E using the software and websites detailed in issue 271 (February 2009). Remember that offset dishes (as most Sky, Freesat and other domestic dishes are) appear to ‘look’ much lower in the sky than they actually do, so you should go by the elevation markings on the dish mount, and not the angle of the reflector. Alternatively, if there is a dish next door that points at the satellite you want, then simply aim yours to point in the same direction.
03 If you have a signal strength meter, now is the time to connect that up. You can also use the onscreen signal strength and ‘quality’ meters that your satellite receiver displays, but they are not so responsive, they’re inaccurate and require you to either have the receiver, a TV and mains supply close at hand by the dish, or communicate with a loyal and patient helper watching the TV screen elsewhere. A meter is so much better if you can beg,
Polarity Offset map for Astra 28.2°E – the angle to turn the LNB (clockwise when facing the dish) and the Preset zones
abc guide to... Toolkit What you need n Compass for azimuth and inclinometer for elevation measurements n Spirit level n Drill and masonry bits n Fixings and suitable spanner n Tripod, paving slabs or pole and concrete for ground mount n Cable and clips n F-connectors and cable tool n Mastic to fill holes n Self-amalgamating tape or rubber F-connector ‘boots’
or the bit error rate (BER) or quality display from the receiver. The signal level should decrease slightly as you pull the dish off-target. If the signal increases at all, then re-aim the dish very slightly in the direction of the side you pulled. Repeat this until pulling all the sides drops the signal level a little. Now you can tighten the mount adjusting bolts fully (tighten them evenly to avoid inadvertently changing the aim) to lock the dish in position. Adjusting the skew
borrow, steal (or even buy) one. Starting from your rough alignment, swing the dish a few degrees left and right – slowly. At the end of each sweep increase the elevation by a tiny amount and when you have covered a few degrees above your original position decrease the elevation to hunt below it. When the meter shows a satellite is being received fine-tune the dish aim to get the largest signal strength. If you have covered several degrees in all directions around your estimated position and have found no signal (and you’re sure all the equipment is working and connected correctly), sweep out a larger area of the sky. Is it the right satellite?
04 There are dozens of satellites serving Europe in orbit above the Earth and they are quite close together along the satellite arc, so it’s entirely possible that the first signal you find will not be from the right satellite(s) – in which case you must hunt again for another signal. Digital signal meters and analysers will identify the satellite received but simple signal strength meters will not. Without a smart meter the best way to check you have pointed your dish at the right satellite is to connect up the receiver and see if you can receive the expected channels. If you have a Sky Digibox then accessing the Signal Test menu page (press Services – 4 – 2) will show the ‘Network ID’ of the signal received – ‘0002’ means that you are correctly aimed at Astra 28.2°E (aimed at Astra 19.2°E it will show ‘0000’ or ‘0001’ and at Hot Bird, ‘013e’). How to peak your aim
05 When you know you’re on the right satellite, you should accurately aim the dish to get every bit of signal that there is available, otherwise you may lose the picture when a heavy downpour cuts the signal level reaching the dish. To do this tighten the mount adjustment bolts so the dish cannot be easily moved and pull on the sides of the dish – top, bottom, left, and right – in turn, and observe the effect on the meter
06 The final adjustment is the skew – the rotation of the LNB in its mount to align its polarity selection probes with the signal from the satellite. Again, this depends on your position on the Earth’s surface. For a Sky or Freesat system, trained on Astra 28.2°E, the minidish LNBs are fitted with an adjuster with numbered preset positions or they are turned to line up numbered markers with the mounting clamp ring – you simply adjust the LNB according to the correct preset position for your location on the polarity offset map. With other LNBs, or when aligning a dish on another satellite (or if the dish is not horizontal in the first place), you should find the optimum skew position manually. If your meter can tune to a specific frequency (rather than just report the strength of the whole spectrum) set it to the frequency of an active transponder using, say, horizontal polarity and set the LNB to vertical polarity – adjust the LNB angle for the minimum signal strength. If you don’t have such a meter then you can do the same with the receiver’s onscreen BER display. When the skew is set don’t forget to tighten the LNB clamp screws fully to lock the LNB in place. Cables and connections
07 The last task is to fit the cable from the LNB to the receiver in its final resting place next to the telly. The key thing here is to use the best cable you can; don’t skimp on cable quality or you’ll likely regret it later (or even immediately). Use double-screened copper co-ax cable, preferably benchmarked by the CAI as suitable for digital signals. All cable used outside must be UV stabilised. Use one piece of cable all the way from the LNB to the receiver. Plan for the shortest run you can but keep the cable out of sight as much as possible. Run it straight up and down, and horizontally across walls – not diagonally – fixing it with the correct size cable clips every 35cm, and don’t bend the cable sharply around corners but use a curve (see diagram).
Make a hole through the wall (not a window or door frame) for the cable to enter the house, drilling from the inside with a drill bit no wider than is necessary to accommodate the cable. Seal the hole around the cable with a suitable mastic. Inside, if the cable must cross the room tack it around the skirting board – don’t ever run it under the carpet. Secure the cable to the dish feed arm and mount using cable ties and leave a loop under the LNB and where the cable enters the house to drip water harmlessly away. Fit F-connectors to each end of the cable for connection to the receiver and LNB and, finally, thoroughly waterproof the LNB connection with selfamalgamating tape, or fit rubber ‘boots’ to the connection n Geoff Bains
A co-ax cable should not be bent sharply – keep to a radius of 10 times the diameter to avoid kinking the innards
Glossary Azimuth
The true bearing of a satellite, or the aim of the dish in the horizontal plane. Usually expressed (in the Northern hemisphere) as degrees east or west of due South. The bearing read from a compass will differ by a few degrees because of local ‘magnetic variation’.
Elevation
The aim of the dish in the vertical plane – the angle between the dish’s line of sight to the satellite and the ground (the horizontal).
Bit error rate (BER)
A measure of the accuracy of reception of a digital signal. It is basically the number of digital bits received incorrectly out of the total number of bits. Expensive digital meters and analysers measure BER directly and the onscreen signal ‘quality’ indicator of a receiver is usually based on BER.
April 2009 What Satellite & Digital TV 3