• Document: H Field Measurements MS2721B Spectrum Master MT8222A BTS Master
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Application Note DVB-T/H Field Measurements MS2721B Spectrum Master™ MT8222A BTS Master™ Introduction This application note describes the key measurements to perform on DVB-T/H digital terrestrial television transmitters during installation, commissioning and maintenance. It also describes how to monitor transmissions within the coverage area of a transmitter and how to interpret some typical measurement data and results. It focuses specifically on measurements pertaining to the DVB-T/H technology but occasionally references other digital television technologies where comparisons will aid understanding. The emphasis is very much towards the field measurement aspects of DVB-T/H and, as such, discusses the measurements as would be performed on Anritsu’s handheld field test instruments, notably the MS2721B Spectrum Master and the MT8222A BTS Master. No prior knowledge of these instruments is necessary to review this application note. However, full details, including specification data sheets, instrument User Guides and the Digital Television Measurement Guide can be found at the www.us.anritsu.com website. Brief History of Digital Television For most of the last century, analogue techniques were used for television transmission. Slight modifications were implemented when black and white pictures were replaced with color in the 1960s and later, too, when stereo sound was transmitted digitally. Essentially, though, the RF television channel had not changed much for many decades. A single channel of, typically, 5, 6, 7 or 8 MHz bandwidth was required to transmit the content of one television station. This worked reasonably well when the number of television stations was small. There was plenty of available bandwidth in the VHF and UHF spectrum and large geographical areas and, indeed, complete countries, could be served with judicious placement of transmitters and the re-use of channels at transmitter sites whose relative distances were likely to cause minimal or no interference. However, towards the end of last century the number of television stations was growing rapidly. In many countries, the VHF part of the spectrum had been reallocated for other uses and so it was recognized that, going forward, it would become more difficult to squeeze the growing number of services into a smaller available spectrum. About the same time, digital transmission technologies were being researched and developed and advances in data compression techniques on digitized video and audio information meant that it would be possible to transmit content from multiple program sources (stations) multiplexed together in the same RF channel. This improvement in bandwidth efficiency coupled with capacity needs being continuously variable depending on the level of compression and resolution of the required image meant that broadcasters could provide, say, a high definition television service or multiple standard definition services, multimedia or interactivity, all in the same bandwidth space. This was very exciting and the advance in transmission efficiency, in terms of information (bits) per second per Hertz of bandwidth, was obvious and compelling. Figure 1. The chronology of television. However, broadcasters could not just install new digital transmitters and immediately switch off the analogue ones. There would likely be a lag in the consumer industry before new receivers would be readily available and at a price that consumers themselves would feel comfortable adopting the new technology. So, in every country where digital television has been adopted there has been, or is ongoing, a transition period usually lasting some years where both analogue and digital transmissions co-exist at the same transmitter sites. It’s somewhat ironic that in trying to find more efficient transmission of an increasing number of television channels, broadcasters first have to accommodate the transmission of both analogue and digital versions of the same program material in the same limited spectrum, without causing interference between them. From the late 1990s and continuing today, the transition to digital is progressing. Some countries have completed the transition and achieved Analogue Switch Off (ASO), whereas others have not started yet. However, by far the majority of countries are in transition and will each have a target date for ASO. Some of those dates have been determined not only by the desire to offer digital television services but also by governments’ needs to re-use some of the spectrum traditionally used for public service broadcasting for other digital services unrelated to the broadcast field. Spectrum is a valuable commodity and the UHF spectrum in particular has long been coveted by other service providers.  Digital Television Basics As in analogue terrestrial television where there are many standards around the world (PAL, SECAM and NTSC), so there are in digital terrestrial television. The vast majority use multiple carrier Coded Orthogonal Frequency Division Multi

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