TV Reception and your Antenna
What is a TV signal?
A TV signal is an audio and video electrical representation of a TV program that gets transmitted through the air by a broadcast tower and is picked up by your TV Antenna or satellite dish. TV stations currently broadcast two types of signals; analogue and digital.
How are TV signals broadcasted?
A TV station sends the TV signal to a transmitter site where it’s converted to a high power radio frequency. It’s then broadcast in the form of electromagnetic waves through a broadcast antenna. Broadcast antennas are generally placed on top of high buildings or towers so the signal can cover a wide area without much interference. Each radio frequency signal occupies 7MHz (megahertz) wide channels. For Analogue broadcasts each channel carries a single program, on a digital broadcast several programs can fit onto the same channel space.
What is an antenna and how does it work?
The antenna (or aerial) converts the electromagnetic waves back into an electrical signal. The antenna’s gain, expressed in dB, is a measure of how well it does this. The higher the gain, the better the electrical signal is received.
A standard outdoor TV antenna features several metal rods called "elements". The size of the element determines the frequencies they cover. Longer elements cover low frequencies and short elements cover high frequencies.
The elements on the antenna are arranged so that the antenna favours signals arriving from the front over signals coming from different directions. This is called “directivity” and it’s the measure of how well an antenna can reject interfering signals and noise.
Coaxial cable (or "coax") is used to carry the electrical signal from the antenna to the TV receiver. It has a centre conductor surrounded by an insulating layer and then one or more screening layers made of metal braid and/or foil. An outer plastic jacket protects the cable from weather or sunlight. For digital reception, high quality double or quad screened coax is a must. Inferior cables lose some of the signal and pick up noise that corrupts the digital data causing the picture to freeze.
Indoor antennas are smaller than outdoor antennas and aren’t as effective. They can be usable where there is a clear line of sight to the transmitter at distances of several kilometers, but performance on lower channels is usually poor.
How do I choose an antenna?
Primarily your antenna needs to cover the range of channels used in your area. In capital cities, combinations of VHF and UHF antennas are used to receive channels 2 to 12 and all UHF channels such as SBS (28). In some areas, all channels are broadcast on UHF so a UHF only antenna is needed.
If the channels you want to watch don’t all come from the same direction, you might need two antennas pointing in different directions with their signals combined using a combiner or “diplexer”. In some areas VHF and UHF signals come from different locations.
In any case when you consider the time and effort involved installing an antenna you’re better off buying the best antenna you can afford, made from high quality materials, so you get the best possible signal. Similarly, cheaper coax cables can connectors can also spoil a great signal.
Environmental conditions that can affect your outdoor antenna
In high wind areas, placing an antenna under the roof and above the ceiling area (the attic) may be an option, but may also effect the signal strength.
If you live in high wind areas, consider spending a bit more money for a longer lasting professional antenna. Make sure that the antenna mast has plenty of supporting guy wires and stays. Consult with our Dick Smith Mobile Techxperts for the proper equipment and installation if strong winds are a problem in your area.
Living near a beach has its advantages but sea air and salt will lead to corrosion of any exposed metallic structure and may call for a good professional antenna coated with epoxy paint.
Epoxy will not much affect the electrical performance, and may keep the salt air out. Alternately, you can have the antenna spray painted with a coating of clear lacquer or epoxy before installing the antenna.
Check with the Dick Smith Mobile Techxperts for advice and installation.