Satellite dish work can be a profitable sideline for electricians, as the tools and expertise are already in place. David Herres offers an overview.

 Construction workers of all types are severely affected when the economic climate is uncertain and demand for new building blows hot and cold.

Electricians seem to survive downturns fairly well. One coping mechanism is to reach out into closely related fields such as refrigeration and data networking. Electricians have tools and knowhow that are applicable wherever electrons or photons are being moved about.

Communications circuitry is one area that has a lot in common with power and light. Design, installation and repair concepts are simple, but task-specific demands have a way of becoming complex and detailed. Of course, electricians are used to that.

Many homes in the developed world have TV and an internet connection using cable or a satellite dish.

Audio, video and data transmission operate at much higher frequency than the 50Hz or 60Hz we are accustomed to in power and lighting. For home owners it’s a mysterious world of bandwidth, harmonics and duty cycles.

For an electrician it’s not a very big step beyond Ohm’s law and familiar notions of capacitance and inductance. There is abundant information available in textbooks and on the Internet.

Otherwise you could find some malfunctioning equipment and dive right in. You may not have an oscilloscope or spectrum analyser just yet, but bring along your multimeter.

If a TV is completely dead – dark screen, no sound, no illuminated LEDs on the front panel – it probably means the internal power supply is defective. (Occasionally the problem is as simple as a defective power cord or tripped breaker.)

If the set shows signs of life but the video and/or audio quality is poor or the video has difficulty staying in synch, there will be a range of possible faults.

The way to proceed is to examine the transmission line, including modem, cable box and antenna. (A satellite dish is technically a type of antenna.)

A good tool in this endeavour is a field strength meter. It can measure the transmitted signal in space or at various points along a transmission line. This can also be done using a small portable TV with an RF port on the back panel that accepts a coaxial cable connector.

Troubleshooting consists of moving along the transmission line and watching for an abrupt change in signal strength, indicating the fault location.

For campus-style buildings under single ownership, the coax is usually mounted on power poles some distance below the grounded conductor associated with the high-voltage circuit. You will need a cherry-picker.

To make this type of transmission cable work, inline amplifiers are located at less than 100m intervals to make up for signal attenuation, and these amplifiers need power to bias the semiconductors.

The power is carried along with the RF signal in the coax. It may be AC or DC and is typically about 60V. The power can be introduced at either end of the transmission line or anywhere along the way. All that is needed is a small cord and a plug-connected AC-powered transformer connected to the coax.

If this power is out, the good news is that AC voltage can be used for troubleshooting the line using a standard multimeter.

Many users, especially residential, receive television programming via a satellite dish. Large hotels and similar facilities, often with multiple buildings some distance apart, are also good candidates for this technology.

The troubleshooting techniques mentioned for coaxial cable are relevant because the signal has to be conveyed to the receiver in the building. However, installation, maintenance and overall troubleshooting are somewhat more complex.

Satellite dishes are generally used in remote locations. They function well, with video and audio quality equal to, or better than, those of cable – notwithstanding occasional weather-related outages.

The defining feature of a satellite system is the parabolic metal antenna. A parabola is one of Euclid’s conic sections, and reflectors conforming to that particular curve are widely used. Light bulb reflectors and remote listening devices are other examples.

The dish gathers the signal contained in electromagnetic energy coming from the satellite and focuses it at the input end of the feedhorn, which is mounted at the dish’s focal point.

This segment of the signal path provides lots of passive amplification, the amount determined by the diameter of the dish. (With higher power transmission in recent years, it has become possible to reduce the size of the dish.)

The dish must be precisely aimed so as to pick up the signal from the satellite, which occupies a fixed position in the sky directly over the equator. The satellite must be at a specific altitude – 22,236 miles (35,786km) ­– to avoid crashing into the earth or flying off into space. Small on-board rockets maintain the position.

There are thousands of satellites in geostationary orbit, and additional satellites are launched as needed.

Satellites contain transponders, typically numbering 24. Each of these is a semi-autonomous transmitter/receiver connected to a power supply and antenna. Programming is beamed up from transmitters on earth and the transponders rebroadcast 100-plus channels, multiplexed and at a different frequency so as to avoid blanking out the incoming signal.

Separate transponders serve different areas on earth with slightly overlapping footprints, providing complete coverage of the assigned geographic region.

Installation of a satellite dish is straightforward except for the aiming process, which is highly exacting. It’s like hitting a rubbish bin lid at a distance of five miles. If the dish is not pointed correctly, performance will be compromised.

You can use the on-screen signal strength meter or a portable instrument made for the purpose.

It’s not feasible to point the dish in various directions and watch the meter for a response. You probably wouldn’t find a signal, or you would lock onto a signal from the wrong satellite.

The correct procedure is to look up online the setting for your location. Aim the dish in that direction then tweak it in to lock onto the strongest response.

If the dish is pier-mounted, the metal post should extend well below grade (depending on local soil, wind and frost conditions) and set in concrete. If it’s roof or wall mounted, it is important to lag-screw the mount securely into sound timber framing. If it is spongy or loose, long-term alignment will not happen.

Apart from pointing the dish, installation is not difficult but you need to understand the circuitry. The signal from the satellite is high-frequency electromagnetic radiation that carries audio, video, synch and metadata for the programming.

Because the frequency is high, parallel capacitive and series inductive losses are great, and transmission via ordinary cable is precluded.

For that reason, the signal at the dish’s focal point must travel through a waveguide to the location of the down converter. A waveguide is a bolted and gasketed pipe of rectangular cross-section with a polished reflective inner surface that channels the signal about 1m to where it enters the low-noise block.

Inside the feedhorn is a polariser. Its purpose is to double the number of available channels by sending two separate signals on each frequency. These signals are either vertically or horizontally polarised, and they occupy the same frequency. The desired signal is chosen in the feedhorn.

In early satellite dishes a servo motor rotated a polariser to select the channel, but now the mechanism is electronic.

Because the low noise block contains semiconductors, power supply voltages are needed. A DC supply voltage originates in the building, and travels over the coaxial transmission line to the site of the dish. Two voltage levels (typically 13V and 17V) select the type of polarisation (horizontal or vertical).

In circular polarisation, clockwise or counter-clockwise rotation is selected, doubling the number of channels available.

The signal, reduced to a frequency compatible with coaxial cable and correctly polarized, travels to the receiver in the building where four operations are performed.

First, the desired channel is selected. Some signals are encoded to prevent unauthorised access. A smartcard, inserted into a slot in the receiver, performs the decoding function. Proprietary microchips enable menu interactivity with suitable on-screen graphics.

The signal frequency is reduced to RF compatible with the television set and fed into it through a short coaxial cable. When there is stereo capability, colour-coded cables with RCA jacks are used.

Satellite dish systems are also used for internet access where cable is not available. This is a more expensive and elaborate system compared with TV, and more expertise is required for installation and troubleshooting.

For one thing, the dish has to be aimed more accurately, because any attenuation will show up in the quality of the internet connection. Also, unlike TV, an internet installation involves transmission up to the satellite so that there can be interactivity.

Two coaxial cables connect the modem in the building to the low noise block that is part of the feedhorn/dish assembly. This is usually a twin cable with a grounding wire included.

When working on an internet dish, you must beware of radiation burns, which can occur if the system goes into transmission mode while you are at the focal point.

Then there’s the sometimes difficult matter of configuring the owner’s computers and mobile devices, which involves installing cabling or enabling wireless with the network name and password in each device.

TV and internet satellite dish providers offer extensive online training with examinations and certification. Lots of technical data is included, plus practical information on installation with particular emphasis on mounting and aiming the dish.