Kitplus - The TV-BAY Magazine

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Antenna cables matter. So, you have invested in an antenna distribution system and a nice pair of remote directional antennas. Very good, but these antennas now need to be connected to the RF input of your antenna splitter. It is imperative that good quality, low loss 50 Ohm cables are used. The cable lengths should be identical and the cable runs should be short as practically possible. For RF system installations where the cable runs have to be quite long then use of antenna cables with a solid core is recommended. RF boosters or amplifiers can be useful in situations such as this, but it is important to note that they should only ever be used to compensate for losses along the length of a cable. Using boosters on short cable runs is, generally, counter-productive as the RF input stage of the receiver can be overloaded. Any properly designed antenna system will deliver to the RF input of each receiver the ‘normal’ signal level that it is designed to accept. Too much RF input level can be as problematical as too little. In mobile deployment situations antenna cables should be checked regularly. It’s all too common for a flight case to be rolled over an antenna cable resulting in a non-visible break in the copper conductor inside the cable sleeving. One obvious symptom of this is RF being received from one antenna, but not from the other. I’m still running my wireless systems in channel 69. Well, you shouldn’t be. The finite resource that is UHF spectrum is divided up into TV bands – each 8 MHz wide. Channel 69 (854-862 MHz) used to be the nationally available 8 MHz TV band that was available for wireless microphone use, across the UK, subject to the user having a shared operator’s licence. This is, emphatically, no longer the case. Channel 38 (606-614 MHz) has been designated in the UK (but not for the rest of Europe) as ‘the replacement channel’ for channel 69. Indeed, all of the TV bands from Channel 61 (starting at 790 MHz) right up to channel 69 (ending at 862 MHz) are, at time of writing, off limits for use by wireless microphones. This is because the licences to use most, but not all, of these frequencies have been sold to mobile network operators in order that they can roll out new 4G mobile networks. Assuming that take up of these new services is adopted by the public at large then more and more interference will be generated by the base stations and user equipment, rendering the operation of wireless microphone systems in these bands impossible. There is another reason why users should not be operating in these bands. You would be breaking the law. Arqiva PMSE (Program Making and Special Events – a generic term used to describe our industry’s wireless activities) are legally prevented from issuing PMSE licences for any of the frequencies between 790 MHz and 862 MHz – therefore, if you use any of these frequencies, you are an outlaw. I don’t need a licence to run wireless systems, right? Wrong, at least with one very small exception. Whilst the wireless equipment itself needs to conform to rules, regulations and common standards that are laid down by various bodies and institutions, all PMSE equipment users in the UK are subject to the Wireless Telegraphy Act. With the exception of a very small slice of UHF spectrum, specifically 863-865 MHz, all other frequencies between 470-790 MHz need some form of licence for the equipment to be legally operated. It currently breaks down thus; 470-606 MHz – Interleaved spectrum. A licence is required, in simple terms, on a where, when and for how long basis. 606-614 – Channel 38. A shared licence is required. Users have to coordinate frequency use between themselves at any given location. 614-790 MHz - Interleaved spectrum. A licence is required, in simple terms, on a where, when and for how long basis. KITPLUS - THE TV-BAY MAGAZINE: ISSUE 95 NOVEMBER 2014 | 53 TV-BAY095NOV14.indd 53 06/11/2014 13:05