ITU-R REPORT BT 961-2-1994 Terrestrial Television Broadcasting in Bands Above 2 GHZ《2 GHZ以上的地面电视广播》.pdf
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1、-1- Rep. ITU-R BT.961-2 REPORT ITU-R BT.961-2 TERRESTRIAL TELEVISION BROADCASTING IN BANDS ABOVE 2 GHZ (Questions ITU-R 1/11 and ITU-R 49/11) (1982-1986-1994) 1. Introduction Experimental amplitude-modulation terrestrial television broadcasting systems in Band 10 at 12 GHz have been set up in the Fe
2、deral Republic of Germany CCIR, 1974-78a1, in the Netherlands CCIR, 1974-78b1, and in Switzerland CCIR, 1974-78cI for system G, and in Japan for system M CCIR, 1974-78d and e. Further, an operational station for the same broadcasting system has been working in Japan since 1979 CCIR, 1978-82al. The W
3、orld Administrative Radio Conference for the Planning of the Broadcasting-Satellite Service (Geneva, 1977) (WARC BS-77) has established for Regions 1 and 3 a frequency and orbital position Assignment Plan for the broadcasting-satellite service in the 12 GHz band shared with the terrestrial broadcast
4、ing service. The Regional Administrative Radio Conference, Geneva, 1983 has established an analogous Plan for the broadcasting-satellite service in Region 2. An efficient means for the provision of television services to relatively small communities, (for example as an alternative to, or as an exten
5、sion of, cable television networks) is the microwave multipoint video distribution system (MVDS) Yard, 19921. Within Europe, the CEPT has recommended 40.5 - 42.5 GHz as a harmonized frequency band for MVDS CEPT, 19911. In the United Kingdom a performance specification has been produced for 40 GHz MD
6、VS transmission equipment United Kingdom RA, 19931, and propagation studies are being undertaken to develop appropriate planning parameters. 2. Technical characteristics 2.1 Systems using amplitude modulation 2.1.1 Characteristics of the radiated signal Both amplitude modulation and frequency modula
7、tion are applicable to terrestrial television broadcasting in the 12 GHz band. A system of amplitude modulation requires higher transmitting powers but will allow more television channels. Amplitude modulated television signals in the 12 GHz band should conform to the standards given in Recommendati
8、on ITU-R BT.470 so that they can be received by a conventional television receiver equipped with a frequency converter. 2.1.2 Protection ratio The ratio of wanted-to-unwanted signal power at the receiver input is an important factor in planning terrestrial television systems. The protection ratio re
9、quired when considering interference between two amplitude-modulation vestigial-sideband (AM-VSB) television signals is given in Recommendation ITU-R BT.655. The protection ratio between two frequency modulation television signals can be found in Report ITU-R B0.634. of a terrestrial system in the 1
10、2 GHz band, it is necessary to take into account both signal fading and the frequency stability of transmitters. With regard to the latter, an experiment in Japan has shown that it is not practicable to use precision offset techniques for AM-VSB systems in the 12 GHz band CCIR, 1978-82bI. The requir
11、ed ratios are essentially independent of frequency band. However, in applying them to the planning -2- Rep. ITU-R BT.961-2 2.1.3 Equipment characteristics 2.1.3.1 Transmitter Specifications of AM-VSB transmitters for a terrestrial television service in the 12 GHz band can be virtually In order to si
12、mplify the transmitters, the vision carrier could be amplified together with its accompanying sound carrier, but this may cause intermodulation. In Japan, the ratio of sound to vision power has been altered from 1/4 in Bands III, IV and V, to 1/10 in the 12 GHz band in order to reduce the 920 kHz be
13、at between the sound carrier and the colour subcarrier. the same as those in Bands III, IV and V. 2.1.3.2 Receiving equipment In experiments so far reported, the frequency converters used at the receiving points have only to change the frequency from the 12 GHz band to a frequency within Bands IV an
14、d V. The converter has been mounted directly behind the parabolic reflector, giving rise to negligible feeder loss. Experience gained has led to the conclusion that a converter noise figure of 7 to 10 dB can be realized without excessive cost, and that considering transmitting power, converter noise
15、 figure, mounting facilities, beamwidth and influence of wind, an antenna diameter of 40 cm is reasonable. For establishing the standards for terrestrial television broadcasting in the 12 GHz band in Japan, a converter with a noise figure of 10 dB, equipped with an antenna of 40 cm diameter, was ass
16、umed. In practice, converters with noise figures of 6 to 8 dB have been used in Japan. 2.2 Systems using frequency modulation For FM television systems further studies are required. However, some tests CCIR, 1982-861 to determine basic propagation conditions have been carried out in the United State
17、s of America. 2.2.1 Characteristics of the radiated signal Frequency modulation will normally be the preferred analogue modulation method for systems using 40 GHz, taking account of transmitter output power and available bandwidth considerations. Frequency modulated television signals in the 40 GHz
18、band should provide for compatibility with those radiated in the Broadcasting-Satellite Service (BSS) or the Fixed-Satellite Service (FSS) to enable existing indoor receiver units to be used in conjunction with 40 GHz antennas and down-converters. 2.2.2 Protection ratio The protection ratio between
19、two frequency modulated television signals can be found in Recommendation ITU-R B0.792. 2.2.3 Equipment characteristics 2.2.3.1 Transmitters The transmitter parameters for the 40 GHz analogue MVDS service proposed in the United Kingdom are as shown in Table 2. The limits for the spectrum of the modu
20、lated signal, using either IPAL or D2-MAC signal formats, are as shown in Fig. 1. For the United Kingdom 40 GHz FM MVDS service it has been proposed that a 64“ horn will provide an approximately circular coverage area at the desired service availability (when fed from the perimeter). Such antennas a
21、re considered desirable for frequency planning. However, it is likely that omnidirectional antennas may be specified in certain cases. The maximum gain for these types of antenna is shown in Table 3 and the antenna gain reference patterns for the 64“ antenna are shown in Figs. 2 and 3. 2.2.3.2 Recei
22、ving equipment The receiver parameters for the 40 GHz analogue FM MVDS service proposed in the United Kingdom are as shown in Table 4. The positions of the local oscillator within the MVDS spectrum are shown in Fig. 4 and the envisaged 40 GHz channel plan is shown in Table 5. -3- Rep. ITU-R BT.961-2
23、 2.3 Systems using digital modulation It is envisaged that MVDS will be attractive as a delivery medium for digital televisions services, which will benefit from increased spectrum efficiency over analogue systems. Only limited information on the specific application of digital techniques in Bands 1
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