Definition – Aerial (also known as antenna) the part of the television system by means of which radio waves are transmitted or received.
There are three main types of aerial used in the reception of TV radio waves, these are –
Yagi – Most UHF aerials are based on the Yagi design. The aerial has good signal gain and directivity. The design is based on a ?/2 dipole with a reflector at the back and a specified number of directors in front. Directors are metal elements which channel the incoming signal. The spacing between the directors is arranged so that they re-radiate their energy in such a way as to increase signal strength.
Yagi aerials are normally specified according to the total number of elements. 10, 18, 32, 52 and 100 are the most common types used by Commercial Technical Services.
Log Periodic – The log periodic aerial has elements of progressively different lengths and spacings of the dipoles, which reduce towards the front of the aerial. Compared to the Yagi design, with the same amount of elements the log periodic aerial has less gain but picks up less interference from the side and back. It is a design which is especially useful in aerial where signal strength is good but interference from other transmitters is high.
Grid or Panel Aerial – With these types of aerials several dipoles are stacked vertically or horizontally in front of a grid reflector. The main use for grid aerial is in areas where identical channels are being received from two transmitters or where signal reflections occur. Both these circumstances create a ghost effect on the TV picture. The grid aerial minimises this effect.
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