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TECHNOLOGIES Everything you ever needed to know about WIRELESS LINKS (But were too afraid to ask) by Michael Coyler W ireless links - be it catapulting footage from the cockpit of a Formula One Car as it reaches 180MPH into a knifepoint turn, or feeding a screen in the serene landscape of Scotland’s world-renowned links for this year’s Ryder Cup - Radio Frequency (RF) links have taken a major foothold in recent years in the outside broadcast field thanks to improved reliability of the related technologies, such as the evolution of COFDM, better methods of compression, controllable guard intervals - or better focusing of emitted microwave radiation - to name just a few. In this article, we’ll be taking a look at the fundamentals of these links in order to gain an understanding of how they can be more effectively used. Early, analogue, methods of creating a wireless link are still indeed in common use today - and can prove a cost- effective method of passing data between two points - so long as a clear line of sight is maintained, and there are no structures that stand to refl ect the signal (i.e. a metal bridge, or a glass building), which could ultimately lead to signal degradation known as Multimode Propagation - which tends to manifest itself in terms of image jitter, or ghosting (in which images on screen have a ‘ghost’ of themselves to the right of the original image - caused when part of the signal is received on time and accurately, whereas another part of the signal refl ects off of on object, and thus takes longer to arrive at the antenna - causing the ‘ghosting’ effect.) Other types of wireless signal degradation (or ‘fading’) could include Path Loss - wherein a signal loses part of it’s intensity the further it travels through space - and Shadowing - whereby, again, the signal is attenuated - but this time as a result of a physical obstacle causing diffraction, refl ection and scattering. “FSK, ASK & PSK form the fundamentals of digital wireless transmission.” 70 | KITPLUS - THE TV-BAY MAGAZINE: ISSUE 96 DECEMBER 2014 Fig.1, A standard sinusoidal radio wave followed by those modulated with FSK, ASK & PSK. However, in the past two decades, we have seen the advent of digital-type wireless links utilising Coded Orthogonal Frequency Multiplexing (COFDM for short) - which not only removes the requirement to ensure line of sight transmission, but also affectively terminates the risk of encountering the effects of certain types of fading such as multimodal propagation thanks to advanced error correction techniques . In order to gain a better understanding of this advanced technology, we need to fi rst cover the fundamentals - namely - how do we wirelessly transmit digital data? In essence, there are three fundamental way of doing this; FSK, ASK - and PSK. Consider Fig. 1. above. At the top, we have a conventional RF waveform which contains no useful data. Under it, however, we have our fi rst method of modulating information onto the carrier - FSK. FSK stands for Frequency Shift Keying and essentially allows us to assign either a ‘1’ or a ‘0’ to a signal based on whether a high or low frequency is used (hence how in the example above, the higher frequency has a value of ‘1’, and the lower of ‘0’,