1、ERC REPORT 38 European hdiocommunicdtions Committee (ERC) within the European Conference of Postal and Teiecommunicdtions Administrations (CEPT) HANDBOOK ON RADIO EQUIPMENT AND SYSTEMS VIDEO LINKS FOR ENG/OB USE i, x “, x. ,., Stockholm, May 1995 STD*CEPT ERC REPORT 38-ENGL 1995 232b4L4 0015492 127
2、HANDBOOK ON RADIO EQUIPMENT AND SYSTEMS VIDEO LINKS FOR ENG/OB USE CONTENTS 1. 2. 3. 4. 5. 6. INTRODUCTION ENG/OB TERMINALS THE BUILDING BLOCKS ENGIOB LINKS USED REGULARLY LINK MARGINS PROPAGATION DISCUSSION APPENDIX 1: ANTENNAS FOR ENG/OB LINKS APPENDIX 2 LINK BUDGET FOR ENG/OB VIDEO LINKS APPENDIX
3、 3: KNIFE-EDGE DIFFRACTION APPENDIX 4 ENG/OB TRANSMITTER SPECTRUM MASK Copyright 1995 the European Conference of Postal and Telecommunications Administrations (CEPT) ERC REPORT 38 Page i HANDBOOK ON RADIO EQUIPMENT AND SYSTEMS VIDEO LINKS FOR ENG/OB USE 1. INTRODUCTION Over the past few years, there
4、 have been various definitions of ENG (electronic news gathering) and OB (outside broadcast), and the various operations have been ascribed to either ENG or OB. Within the CEPT, definitions for ENG and OB have been agreed and are as follows. ENG : Electronic News Gathering (ENG) is the collection of
5、 television news stories without the use of film, using small hand held, electronic, colour cameras with microwave links to the news room and/or portable video tape recorders. (CCIR report 803-2, annex to Volumes x and XI, parts 3). OB : Outside broadcasts is the temporary provision of programme mak
6、ing facilities at the location of on-going news, sport or other events, lasting from a few hours to several weeks. Outside Broadcasts are generally planned in advance, but it is often necessary to accommodate. short notice changes of venue or unforeseen requirements. Video links are required for mob
7、ile links, portable links and cordless cameras at the OB location. Additionally, video links may be required as part of a temporary point to point connection between the OB van and the studio. (CEPT Project Teams SE 19 and FM 20). It can be seen that the definitions are not mutually exclusive. Certa
8、in operations could equally well reside in either or both categories. Added to this potential confusion, is the fact that equipment manufacturers, in line with the terminology used in the USA, refer to everything as ENG. Clearly, it is not possible to discriminate between ENG and OB, without becomin
9、g ambiguous. Therefore, for the purposes of this document, to avoid confusion, all types of operation will be considered under the general term ENG/OB. Having decided to treat ENG/OB collectively, which type of operation best describes an ENG/OB video link ? The simple answer is none. It is impossib
10、le to describe ENG/OB in terms of specific video links. A more accurate view is probably to consider ENG/OB as a set of building blocks or modules. These modules consist of transmit terminals, receive terminals, and combined receivdtransmit terminals (for mid-point applications). To service any part
11、icular requirement and provide the necessary connection between the location of an event and a destination, planners and operators will use the modules at their disposai as they consider most appropriate. This modular approach also simplifies the task of explaining the technical characteristics of E
12、NGIOB links. When the role of each module is understood, the required technical parameters become self evident. In the context of ENGOB, the destination is normally an established receiving installation although finally the signal will end up at a studio centre. The link from receiving installation
13、to studio (either cable, fibre or permanent fixed links) is beyond the limits of ENGIOB involvement. ERC REPORT 38 Page 2 2. ENG/OB TERMINALS THE BUILDING BLOCKS This section depicts graphidly a selection of building block modules currently utilised in ENG/OB links. Accompanying each drawing is a br
14、ief explanation where necessary and the antenna types that might be used. Antenna types are grouped into five basic categories, Low Cain; Ai to A3. Omni-directional; B 1 to B4. Low to medium gain end-fire; CI to C4. Medium to high gain reflector; D1. Special Antennas; El. Full details and representa
15、tive radiation patterns from each antenna category are shown in Appendix 1. Where the use of a module is unique to a specific type of link (i.e. cordless, portable, mobile or temporary point-to- point) this is shown, otherwise the module is defined as multi-purpose. STD*CEPT ERC tEPORT 38-ENGL 1775
16、H 232briL4 0015495 93b I Figure I: Cordless Camera Transmitter E Description: One Man Radio Camera Antenna Types: Omni-directional, i34 Special Antennas, El Figure 2: Portable Camera Transmitter a Description: Two Man Radio Camera Antenna Types: Low to Medium Gain End-fie, CI ERC REPORT 38 Page 3 ST
17、D-CEPT ERC REPORT 38-ENGL 1995 232b414 00l1549b 872 = ERC REPORT 38 Page 4 Figure 3: Mobile Camera Transmitter Description: Motor Bike Camera Antenna Types: Low Gain, Al, A2, A3 Figure 4: Mobile Camera Transmitter Description: Racing Car Camera Antenna Types: Low Gain, Al, A2, A3 STDmCEPT ERC REPORT
18、 38-ENGL 1995 232b4L4 O015497 709 9 ERC REPORT 38 Page 5 Figure 5a: Airborne Mobile Camera Transmitter I Description: Remotely Controlled, Gyro Stabilised Camera in Helicopter Antenna Types: Omni-directional, B1, B2, B3 Figure 5b Airborne Mobile Camera Transmitter Description: Cameraman in Helicopte
19、r Antenna Types: Omni-directional, BI, B2, B3 STD-CEPT ERC REPORT 38-ENGL 2995 m 2326434 0025498 645 ERC REPORT 38 Page 6 Figure 6: Multi-purpose receiver Description: Manually tracked receiving antenna located at any convenient point at ENG/OB site Antenna Types: Low to Medium Gain Endfire, C1, C2,
20、 C3, C4 Medium to High Gain Reflector, D1 Figure 7: Multi-purpose Receiver, Transmitter or Mid-point VI I Description: Golf buggy, commonly used on a golf course as a mid-point Antenna Types: Low to Medium Gain End-fie, C1, C2, C3, C4 ERC REPORT 38 Page I Figure 8: Temporary Link Transmitter Descrip
21、tion: Heavy duty vehicle with telescopic mast Antenna Types: Low to Medium Gain End-fire, C3, C4 Medium to High Gain Reflector, D1 ERC REPORT 38 Pap 8 Figure 9: Multi-purpose Receiver, Transmitter or Mid-point Description: Hydraulically elevated antenna platform Antenna Types: Low to Medium Gain End
22、-fire, C2, C3 Medium to High Gain Reflector, D1 ERC REPORT 38 Page 9 Figure 10: Multi-purpose Receiver, Transmitter or Mid-point Description: Roof of communications vehicle, a environmentally safe platform with convenient access, so manually tracked antennas are often located here. Becomes the home
23、of a wide range of antennas at an ENG/OB event. Antenna Types: Low Gain, Al Low to Medium Gain End-fire, C1, C2, C3, C4 Medium to high Gain Reflector, D1 STD-CEPT ERC REPORT 38-ENGL 1995 = 232b414 0015502 9Tb ERC REPORT 38 Pap 10 Figure 11: Multi-purpose, Airborne Mid-point Antenna types: Low Chin,
24、Al, A2, A3 Omni-directional, B1, B2, B3 Low to Medium Gain End-fire, C1 Figure 12: Temporary Point-tepoint Receiver Description: Existing Radio Tower. Normally fitted with remotely panned antennas Antenna Types: Medium to High Gain Reflector, D1 ERC REPORT 38 Page 11 Min Ikant. pin IdBi 5dBi 3dBi 13
25、dBi 3. ENG/OB LINKS USED REGULARLY Min Rxant. gain dBi 17dBi I3dBi 17dBi Table 1 is reproduced from the ERC Draft Recommendation on ENGIOB. It shows typical technical characteristics for ENG/OB links. The column headed type of link is grouped into four categories; cordless, portable, mobile and temp
26、orary point-to-point. This subdivision simplifies matters when frequency and power requirements are under consideration. lOGHz limited by precipitation fading. Description Handheld camera with integrated transmitter, power pack and antenna. Handheld camera but with separate body- worn transmitter, p
27、ower pack and antenna. Mounted in helicop- ters, motorcycles, pedal cycles, cars, racing cars and boats. One or boih link terminals may be used when moving. Link terminals are mounted on tripods, temporary platforms, purpose built vehicles or hydraulic hoists. Two-way links are often required. As a
28、series of examples, typical ENG/OB links in each of the preceding categories are constructed using the modules outlined in the previous section. STDmCEPT ERC REPORT 38-ENGL 1795 232b4L4 0015504 774 ERC REPORT 38 Page 12 Figure 13: A cordless camera link Description: One man radio camera to on site r
29、eceiver Suitable Frequencies: Less than 12 GE, (future systems at 22 GHz and 47 GHz may be achievable) I Figure i4 A portable link Description: Two man radio camera to roof of communications vehicle Suitable Frequencies: Less than 5 GE STDOCEPT ERC REPORT 38-ENGL 1995 = 232b!l14 0015505 b05 D ERC RE
30、PORT 38 Page 13 Figure 15: A mobile link Description: Motor bike to helicopter Suitable Frequencies: Less than 5 GHz Figure 16: A temporary point-to-point link Description: Hydraulic platform to radio tower Suitable Frequencies: Less than 10 GHz for long hops sTD.CEPT ERC REPORT 38-ENGL 3995 9 232b4
31、14 00L550b 54L 9 ERC REPORT 38 Page 14 Figure 17: A temporary point-bpoint link Description: Fast response vehicle to radio tower Suitable Frequencies: Less than 10 GHz t STDaCEPT ERC REPORT 38-ENGL 1995 2326414 001507 488 W ERC REPORT 38 Page 15 If transmit and receive terminals are not line of sig
32、ht a mid-point may be necessary. Figure 18: A cordless link feeding a mobile mid point link Suitable Frequencies: First hop less than 12 GHz, second hop less than 5 GHz i STD-CEPT ERC REPORT 38-ENGL 3995 2326434 0035508 334 W ERC REPORT 38 Page 16 Figure 19: A mobile link feeding a mobile (aeronauti
33、cal) mid-point link Suitable Frequencies: Fst hop less than 5 GHz, second hop less than 5 GHz Figure 20: A temporary point-to-point link feeding a temporary point-to- oint link P I 7 Suitable frequencies: First hop less than 10 GHz, second hop less than 10 GHz STD.CEPT ERC REPORT 38-ENGL L995 = 232b
34、414 0015509 250 ERC REPORT 38 Page 17 Of come things will become even more complicated when the whole operation is considered! Figure 21: Radio Links that may be used simultaneously for coverage of motor racing STD-CEPT ERC REPORT 38-ENGL 1995 m 2326434 0015510 T72 ERC REPORT 38 Page 18 4. LINK MARG
35、INS Appendix 2 derives the link margins for the four categories of operation; cordless, portable, mobile and temporary point-tepoint. The transmit E.I.R.P. and typical range values are obtained from Table 1. For all situations, the receiving antenna is considered to be a 1.2m parabolic dish, so the
36、margins are not frequency dependant. in the case of cordless and portable links, especially at frequencies above 10 CHz, it will be difficult to manually track an antenna of this size due to its narrow beamwidth. If it is considered more appropriate to use a 0.6m parabola instead, the margins will b
37、e decreased by 6 dB. It has already been explained that a wide selection of antennas are available, so in practice a high margin may be traded off against a more convenient antenna. The margins are calculated assuming that the terminals are in free space or line-of-sight (with first Fresnel Zone cle
38、arance). In general, any radio link used in ENG/OB will be planned to be clear lineof-sight; however in reality this may not always be the case. Someone always walks between a cordless link and its receiving terminal, a racing car always goes under a bridge when the helicopter is receiving best pict
39、ures, a news event always occurs in the centre of a cluster of high rise office blocks and so on! There will always be a time when a reliable radio link is required but the path between the terminals is obstructed. During these times the margin will decrease dramatically sometimes, unfortunately to
40、levels where pictures are unusable. 5. PROPAGATION Experience gained using ENG/OB links in a wide range of frequency bands shows clearly that the higher the frequency, the greater the attenuation produced by an obstruction. This is may be. attributed to a combination of increased absorption and diff
41、raction losses. Absorption losses are rather difficult to calculate and could well be the subject of further study. Difiaction calculations for well defined geometric structures produce exact solutions and are widely used in propagation models. A simple model considering a single obstruction in a sh
42、ort radio link is shown in Appendix 3. Such obstructions may be approximated to a knifeedge, and the results of the classical calculation of knife-edge difiaction loss at typical ENG/OB frequencies are show in Table A3-I. In general, once the radio path becomes severely obstructed, the diffraction l
43、oss increases monotonically with frequency. Another characteristic of cordless, portable and mobile links which may significantly decrease their coverage is multipath propagation. Consider an example where a cordless link with an omni-directional transmitting antenna, is operating in a stadium. The
44、radiation from the antenna is not only illuminating the area of the receiving antenna, it is also illuminating the rest of the stadium, much of which will be metallic. Reflections will occur, re- radiating the signal in many directions. The levei of received signal is the vector sum of the direct si
45、gnal and all the reflected signals arriving at the receiving antenna. It is not uncommon for complete cancellation to occur either at spot frequencies within the bandwidth of the signal, or over the entire bandwidth. The consequence of this, ranges from picture impairments to complete loss of signal
46、. Multipath effects may be alleviated by one of the two different methods described below. (i) Circularly polarised transmitting and receiving antennas may be used. As the direction of POkdnSdtiOn of a circularly pola-ised radio-wave changes on reflection, the receiving antenna can discriminate betw
47、een direct and reflected signals. This is not a complete solution as the signal resulting from multiple reflections may be either direction of circular or elliptical polarisation. Also the design and construction of a compact, lightweight antenna producing good circular polarisation over 360“ of azi
48、muth is by no means trivial. (ii) The use of directional transmitting and receiving antennas. STD-CEPT ERC REPORT 38-ENGL 3995 232b414 OOL5531i 909 W ERC REPORT 38 Page 19 These may be either manually, mechanically or electronically tracked. The narrower the transmit beamwidth the less energy is dir
49、ected towards reflecting surfaces, the narrower the receive beamwidth the fewer reflecting surfaces are visible. In principle this sounds simple, but antenna pointing requires extra personnel or expensive equipment. For cordless cameras, having only one operator, the tracking of the transmitting antenna must be automatic. This requires an additional radio link carrying antenna control data from the receiving point, back to the camera man. Suitable equipment is complicated and expensive, however Broadcasters and Programme Makers consider these o
