Mounting A Satellite Dish Or Rotor

1  General Introduction

Public broadcasting satellites orbit Earth high above the Equator once a day in the same direction as it spins, so appearing geo-stationary, motionless viewed from Earth.  Thus they lie in a circular arc across the sky reaching zenith over the meridian, for northern latitudes in the southerly sky stretching between south west and south east, and vice versa for southern.

Satellites orbit either individually or more usually in clusters, and henceforth here, 'satellite' should be taken to be interchangeable with 'cluster' unless context dictates otherwise.  Clusters are spaced approximately evenly around the Equator about 2-3° apart.

There are two main types of domestic installation, a fixed dish, the commonest, and a rotor (aka H-H Mount, Equatorial Mount or Polar Mount).  As implied, a fixed dish is permanently pointed at, aligned to in sat speak, a single satellite, while a rotor is aligned to the meridian and under the viewer's control can swing a dish as far as 40-70° either side to receive from a surprisingly large number of satellites.  (Additionally, a fixed dish can be converted to cover neighbouring satellites by mounting multiple receiving components, but this is rather too specialised to be covered here.)

Satellite TV - Axi-Symmetric Dish Diagram

Satellite TV - Offset Dish Diagram

Just as a concave mirror focuses light, the dish's concave reflector focuses the incoming satellite signal into the receiving component, a Low Noise Block (LNB).  This converts the signal into an electrical form in the downlead suitable for the satellite tuner at the other end to interpret.  Note that, unlike terrestrial TV where one aerial can serve multiple devices, each satellite tuner requires its own LNB, and to allow recording of one or more programmes while watching another, PVRs often have multiple tuner inputs, requiring an LNB with as many outputs, connected by as many downleads.  This should not be confused with loopthrough on some STBs, where the LNB signal is routed out via a second connector, to which can be chained a second STB, which can use the signal either when the first is in standby, &/or when both are tuned to the same transponder on the satellite.

There are three main dish types, hopefully having scales on the elevation adjustment:

Initial alignment must be accurate enough to receive the target cluster's signal, signal level itself being used for fine alignment.  This can be read using either a satellite meter (aka satellite finder), and/or the receiver's own signal data.  Clusters being so close, the likeliest error, and source of consequent confusion, is to align on the wrong one.  To avoid this, initial alignment must be accurate to within about 1°, but to realise the full range of a rotor, final accuracy will need to be a fraction of that.

To obtain alignment settings, directly or indirectly you will need to know some or all of the following:

The above completely determine the following setting angles, which must be calculated before work begins, and a workable method chosen for setting each of them sufficiently accurately …

Installation Requirements

To complete installation successfully, you will need the following:

  1. Beforehand:
    • Alignment details  -  Azimuth, possibly Tilt, Elevation, Skew  -  and a method of setting each;
    • A site for the dish with line of sight to the satellite free of obstruction by trees, buildings, passing high vehicles, washing lines, etc, out of reach of vandals or burglars, solid enough to hold it in a gale;
    • Satellite Dish, may be part of a kit  -  otherwise 50-60cm should be adequate for Freesat in the UK;
    • An LNB, may be part of a kit  -  if not, specify the type of dish, normal or mini, to ensure you buy to match; the number of outputs determines the number of tuners that can be simultaneously connected, remembering that multi-tuner devices require an LNB with at least as many outputs, each output requiring its own downlead;
    • Fixing bracket &/or mounting pole, may be part of a kit  -  if not, use industry standard satellite brackets or I or T&K brackets for wall mount(s), at least 40mm steel poles;
    • Fixing bolts, may be part of a kit  -  avoid the plastic-sleeved coach bolts often supplied, use something like anchor bolts having a wedge action to grip deep in solid masonry.
    • xx100 CAI Benchmarked satellite grade double-screened downlead cable, may be part of a kit;
    • Self-amalgamating tape for the cable join(s) to the LNB (and rotor);
    • Sealant for where the cable enters the house;
    • Cable clips for the downlead;
    • Optionally a double-screened F-Connector wall-socket and pattress;
    • F-Connectors for the cable ends;
  2. Installation:
    • Ladders, if the dish is to be mounted on the side of a house;
    • Electric hammer drill and masonry bits (10mm?) for the fixing bolts and cable entry hole, the latter long enough (400mm?) to drill through into the house, perhaps an extension cable, an RCD is always a good idea.
    • Ring spanners, may need pairs, for the anchor/coach bolts (10-13mm?), mountings/adjusters (13mm?);
    • Screwdriver for the LNB holder;
    • Sharp knife or wire stripping tool;
    • Wire clippers or pliers;
    • Hammer;
    • Electrical screwdriver for the wall-socket;
  3. Very nice to have:
    • Satellite meter  -  cheap ones squeal on signal and give an indication of its strength, but even that is very useful; expensive ones can tell which satellite they are receiving, but are probably overkill for DIY;
    • Spirit level with vertical as well as horizontal scales;
  4. May be useful:
    • High scale map.  In the UK, Ordnance Survey (OS) Landranger 1:50000 or Explorer 1:25000 (Public Library);
    • Protractor;
    • Plumb Line;
    • Straight Edge.