Handheld field-test instruments have become critical to today's communications and broadcasting networks, performing tasks ranging from performance verification to problem solving. For example, an application note from Anritsu Co. focuses on the single-frequency networks (SFNs) pertaining to digital terrestrial broadcasting. It details the measurements that should be performed during installation, commission, and maintenance. Titled "Understanding Single Frequency Network Measurements," the 13-page note focuses on measurements associated with Digital Video Broadcasting-Terrestrial/Handheld (DVB-T/H) and Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) technologies.
Historically, broadcasters have enjoyed access to large swaths of the very-high-frequency (VHF) and ultra-high-frequency (UHF) bands. Yet the mobile-wireless communications industry is now asking regulators to force broadcasters to relinquish much of that bandwidthspecifically in the UHF range. As a result, broadcasters must start planning for single-frequency networks (SFNs). Simply put, broadcasters or network operators will have to transmit the same amount or even more information in fewer available channels. The note looks at how they can accomplish this goal while providing some basic information on digital terrestrial television technology.
Among the practical considerations provided is commentary on a key test, the impulse-response or delay profile measurement. In a multi-frequency network (MFN), only significant co-channel signals are likely to form echoes of the main signal. As a result, delays should be measured slightly in excess of the longest allowable guard interval for the respective orthogonal- frequency-division-multiplexing (OFDM) mode.
Conventional approaches, which use the OFDM structure's pilot signals, are reliable enough to calculate delay and relative levels with decent accuracy. For an SFN, however, it is necessary to check for relative signal delays over a much longer periodespecially during installation. Transmission delays at the transmitters can then be calculated and programmed to make sure that co-channel receptions occur within the guard interval. The note focuses on these and other measurements as they would be performed on Anritsu's handheld field test instruments (the MS2721B, MS2712E, and MS2713E Spectrum Masters and MT8212E and MT8213E Cell Masters). However, knowledge of these instruments is not necessary to glean knowledge from this document.
Anritsu Co., 490 Jarvis Dr., Morgan Hill, CA 95037-2809; (408) 778-2000, FAX: (408) 776-1744, www.us.anritsu.com.