Wireless Systems for Sound and Video Transfer from Camera

By Seguey Karpov

Review contents:

Wireless Systems for Sound and Video Transfer from Camera Systems of Wireless Signal Transfer DynaPix Triad of DTC Communications Company Equipment of GMS Company Digital wireless system of receiving-transfer of sound and image signals of Grass Valley a Thomson Brand Company On-camera WRP20 System of IRTE Company (Italy) Wireless Transfer of Data from DY-DV5000 Camera with the Help of KA-DV 5000 Adapter Link Wireless Camera System is New Equipment form New Manufactures Swiss Wireless COFDM Systems Livetools in Russia Miniature Color Microdic Video Camera with Transceiver Wireless Systems of Video Transfer from Premiere Wireless Tandberg Wireless Operators’ Systems Reporter’s Radio Extender Teleview Reporter is Wireless Digital System of Video Signal Transfer “Camera-MTU” Transvideo wireless systems

Portable microwave transmitters are widely spread in contemporary television industry. Western specialists call such systems differently: radio cameras, wireless cameras, and digital wireless camera systems. We got used to call such systems “on-camera relays”. In any case wireless on-camera system performs a simple task: transfers images and signals of sound accompaniment from video camera to monitoring or recording facility. Such system is used in cases when signal transfer through the wire is impossible due to some reasons, for example, during sports broadcasting, or undesired, like in security systems or special techniques. Facilities. Produced by different manufactures are similar in many ways in their construction.

At present analogous and digital systems are produced. And both types of systems can be unidirectional as well as bidirectional. During last period of time amount of produced digital systems increased. There can be accounted more than ten such systems based on OFDM and COFDM modulation. About five systems are produced in series, are wide spread and are considered to be the standard for big broadcasters. In our country due to some reasons the most spread are analogous systems. The main factor for such choice in their price, it is literally on an order cheaper than digital. Also the problem of free frequencies and certification is typical for Russia and it leaves it own footstep on the choice of the system. Never the less, some big Russian broadcasters are interested exactly in digital systems and NTV TV company even bought portable on-camera system based on COFDM modulation working in 7 GHz diapason not so long ago.

After dividing on-camera wireless systems on analogous and digital let’s continue the review by the types.

To analogous systems correspond widely spread facilities, which operate in 2.2…2.7 GHz diapason, more rarely can be found systems, which operate in diapasons up to 8.5 GHz and more. Outlet power of such facilities is 3 mW…1 Wt. Distance of work can achieve 1 km with direct visibility and good weather, however usually standard distance of systems is 300..500 m. These are the simplest systems that use frequency modulation. In such systems transfer of composite NTSC or PAL sound and one (rarely two) sound channels is carried out. Real width of video field is about 5 MHz, of sound is up to 15 kHz. Usually analogous microwave on-camera systems have an opportunity of choice of operating frequencies in limits of own operating diapason. Usually these are four frequency values, which can be chosen by DIP-switch. For example, systems of Wireless Video Company, which work in 2.4…2.48 GHz diapason there is a choice of four operating frequencies: 2.412, 2.432, 2.452 and 2.472 GHz. So there appears an opportunity of use of few uniform systems of one producer on one filming area.

Transmitter mounted to the camera

For receiving of necessary direction diagram and ratio of effort receiving-transmitting antenna of on-camera systems can have different shape. The most spread is antenna with circular direction diagram. Antenna attaches directly to the transmitter. In that case signal receiving is done independent from how operator with camera are oriented in relation to transmitter and quality of received signal can be valued as satisfactory. During filming of static planes image will be stable, however during quick moving of camera there can be image ’blowing up’, what can be explained by modulation type and type of used antenna. For improve of receiving quality there are experiments with different types of antennas on transmitting and receiving sides. On receiving side there can be set systems on few antennas connected to one transmitter. These antennas receive signal of rectilinear and reflected waves. Then manufactures offer different solutions. Some companies produce receiving systems where signal are combined into resultant, which corresponds to exponent of maximum quality. Others set level measuring device, which choose maximum strong signal and switch, which gives that signal on demodulator. In both cases an opportunity of “blowing up” during signal receiving from moving camera becomes smaller. Sometimes you can see that on sports broadcasting are used transmitting antennas systems, set on high poles apart from camera, but following it. In such systems are used directed transmitting antennas, which are constantly oriented on the receiving part by an engineer who carries the pole independent from operator’s position. On receiving part in that case also are used systems of few antennas. All that is done for the reason to exclude image “blowing up” opportunity totally even during very quick movements of camera.

Wireless signal transmission system in use

Not less important is the way of on-camera relay fastening and its power supply. The most comfortable in use and so the most spread on-camera systems are fastened to the camera on slots of accumulator batteries. This can be a construction of “sandwich” type, when on-camera transmitter from the both sides there are squares of Gold Mount Anton Bauer standard: for fastening to the camera and for setting of battery on the transmitter. In that case camera and transmitter power supply is done from one battery, what is highly convenient for operators of mobile cameras, as the weight and overall dimensions of the entire complex are relatively small. On cameras with accumulators of NP type setting of transmitter directly on NP-holder is possible, which has screws for different additional fastenings including transmitters. In that case it is necessary to work a little with power supply to transmitter. Producers offer different variants of solution: from separate accumulator, which fastens on transmitter to external accumulator belt for operator. However the most refined decision is received by the ones who use cameras with special DC 12 outlet for cutoff points of Hi-Rose type. In that case transmitter is powered by the cable directly from the camera and additional weight and overall dimensions are minimal.

One of variants of wireless system mobile use - signal transmission from helicopter

Digital on-camera transmitter first were applied in out of studio TV production till the end of 1990s. Wide use of such systems started in 2001, from the moment when it became possible to put MPEG-2 coder and OFDM modulator in the body comparable in sizes with on-camera Betacam SP PVV-3P recorder. Produced digital systems operate mainly in the same diapason as analogous, i. e. 2.2…2.7 GHz. Power of these systems is 10 mW…100mW.

Application of digital wireless systems highly increased quality of transferred signal. Main enemy of analogous on-camera systems is wave reflection, which is the reason of image and sound “blowing up”. Digital systems ue OFDM modulation adapted for DVB-T, in which the signal transfers on 2000 or 8000 carriers and for which wave reflections are not dangerous. Digital systems are more stable towards errors due to multiplexing when the flow of transferred data is divided in between large number of carriers. Errors correction system during receiving corrects distortions in majority of cases. Used in DVB-T scheme foresees use of one of three different types of carriers modulation: QPSK, 16QAM, 64QAM. When using QPSK modulation together with errors correction algorithm flows with the speed of 5.58…8.78 Mbit/sec (the value is proportional to algorithm efficiency) can be received. When using 16QAM modulations flows with speed of 11.7…17.56 Mbit/sec are received. Starting from listed flow values producers recommend to use QPSK modulation of carriers. At the same time the majority of systems have an opportunity of switch of modulation type (QPSK, 16QAM, 64QAM).

Wireless systems in sports coverage are irreplaceable

Except for modulation the important part in digital on-camera systems plays compression. Today in systems are used three well-known compression formats: MPEG-2, DVCPRO, and Wavelets. MPEG-2 format with 4:2:2 or 4:2:0 algorithm and flow of 4…50 Mbit/sec provides broadcasting quality at the flow of 15 Mbit/sec. DVCPRO compression forms flows of 25 and 50 Mbit/sec. The factor of choice of compression type is the standard in which the signal passes through the section before the beginning of formation, through drive, before recording. Usually this is MPEG or DVCPRO. However Wavelet compression is characterized by more “careful” relation to the signal and smaller coding-decoding time, and so smaller delay period, what is important during operating on the air. At present manufactures in their systems use all three kinds of compression.

Digital systems have their own peculiarities, such as signal delay provoked by compression. In some cases when digital systems are used in broadcasting together with triax cameras, video signal delay can be seen easily, especially during commutation of cameras with similar planes. Offered today systems have delay of 40…50 ms. The best index is delay of 20 ms in systems with Wavelet compression. Exactly systems based on that type of compression are characterized by the highest quality of image and technical parameters, what can favor wide spread of such systems in broadcasting.

Constructively the majority of on-camera digital systems is done as separate content to the camera head facility, which replaces camera triax or multiple-strand adapter. There can be also found constructive decisions, which repeat transmitters of analogous systems.

In our country the use of portable on-camera transmitting systems both digital and analogous is highly limited. Most more important reasons for such limitations are absence of standards, detailed fields of frequencies and certification barriers. In Russia, differently from the rest of the television world there is now standard field of frequencies, detailed for use in out of studio TV production. That is why each one who wants to buy such system first of all faces the problem of frequencies. Western manufactures produce products for operation in 2.2…2.7 GHz field. And exactly these frequency in Russia is taken by different services. If you want to buy digital system which operates on the frequency that you have, for example, on 7.5 GHz, that producer can perfom a complex of scientific research works what is going to take about 4…6 months and after that make a system for the frequency necessary for you. As a result the cost of the system will increase on 20…35%. Besides you will have to certify this system. The ones who at least once tried to get a certificate for System of electric communications understand, what we are talking about. If you want to buy analogous system, then you have to hope that manufacture produces systems with frequency that nobody in your city uses. Sometimes there is no variant as the cost of analogous systems is low and for the purpose of selling of one on-camera relay in Russia none of the producers is going to change formed and perfected with years technology of production.