摘要:

In the point-to-point relaying of 405-line television signals, the objective is to provide a transmission system having a video-frequency bandwidth of 3 Mc/s over which the gain and delay are substantially constant, and satisfying certain requirements with respect to noise, linearity and gain-stability; in addition, a high degree of reliability is essential. Experience up to the present time in the United Kingdom has shown that excellent results can be obtained either by cable or by radio transmission, and the choice between the two systems must therefore be largely a question of economics.Two coaxial cables are already in operation; one is between London and Birmingham and uses 1-in coaxial pairs transmitting frequencies in the band 3-7 Mc/s with a carrier of 6-12 Mc/s, whilst the other is between Birmingham and Manchester and uses 1-in coaxial pairs transmitting frequencies between 0-5 and 4 Mc/s with a carrier of 1 Mc/s, asymmetrical-sideband methods being used in both cases. A radio link between London and Birmingham, operating at about 900 Mc/s, has also been in service for an extended period, and a 4000-Mc/s microwave link has been installed between Manchester and Edinburgh, frequency-modulation being used in both systems.The cost of television transmission by cable depends largely on how the provision of a system fits in with the development of the trunktelephone network. Where a television-relay system and a large number of new telephone channels are required over the same route, composite cables can be laid to carry both services, thereby spreading the cost of the cable-sheath, ductwork, repeater buildings and local services between the two systems, with considerable economy. On routes where there is no requirement for telephony, however, a radio link is generally the cheaper system. When radio links for the simultaneous transmission of both television and multi-channel telephony have been developed, the present economic advantages of cable links on combined television and telephone routes may be nullified.

DOI:10.1049/pi-3a.1952.0039

出版商:IEE    

年代:1952

数据来源: IET

摘要:

Early experience showed flexibility to be essential in temporary television links for outside broadcast purposes, and both land-line and radio links were developed to meet the various requirements. As the technique of temporary land-line connections is dealt with elsewhere, the discussion here is limited to the particular part it plays in link facilities required. The relative merits of metric- and centimetric-wave equipment are briefly examined to show that both can be usefully employed. The application of centimetric-wave equipment is dealt with in greater detail since it has satisfactorily provided the longer temporary links which have been used.

DOI:10.1049/pi-3a.1952.0040

出版商:IEE    

年代:1952

数据来源: IET

摘要:

In certain respects the transmission characteristics of a communication channel designed for television service differ somewhat from those of a channel designed for telephony. Such differences entail the easurement of parameters not adequately covered by the usual transmission measurements.The paper is intended to indicate the manner in which the problem has been at least partially solved by providing special test apparatus utilizing television-type waveforms.

DOI:10.1049/pi-3a.1952.0041

出版商:IEE    

年代:1952

数据来源: IET

摘要:

A systematic method of design for delay equalizers with frequency ranges having a moderate ratio of maximum to minimum frequencies is outlined, and a description is given of the delay equalization of the 3–7-Mc/s carrier channels of the London-Birmingham coaxial-cable television relay system. For the transmission of B.B.C. 405-line television signals, the delay of each channel (as measured by noting he envelope delay of a variable-frequency carrier modulated by a 100-kc/s signal) has been equalized to within ± 0.06 microsec over the frequency range 3–7 Mc/s.

DOI:10.1049/pi-3a.1952.0042

出版商:IEE    

年代:1952

数据来源: IET

摘要:

Transmission by long-distance cable and repeaters using a vestigial-sideband carrier is becoming standard practice in television. The paper describes some factors affecting the performance of coaxial cables in such an application. A brief description of the inherent properties of a typical coaxial cable and their effect on system design is given. The main part of the paper describes an experimental programme for evaluating the irregularities of coaxial cable, and an estimate is given of their effect on television transmission. It is found that the most probable magnitude of the distortion from this cause is lower than the distortion from other causes.

DOI:10.1049/pi-3a.1952.0043

出版商:IEE    

年代:1952

数据来源: IET

摘要:

The development of reflex-klystron oscillators suitable for use as f.m. transmitter valves in links operating in the 3600–4200-Mc/s band is described; details of the performance in this and neighbouring bands are given. Since the valves use the copper-glass construction with external resonant circuits, their use is not limited to the applications described.

DOI:10.1049/pi-3a.1952.0044

出版商:IEE    

年代:1952

数据来源: IET

摘要:

A method is described for applying loop negative feedback to flatten the gain/frequency characteristics of three-stage amplifiers employing tuned-anode intervalve couplings resonant at the geometrical mid-band frequency of the pass-band.A comparison is made with the responses of amplifiers employing different types of intervalve couplings. Apart from the well-known advantages of negative feedback, the performances of the amplifiers described should be superior to those of the other amplifiers, since they are simpler and easier to align.Two typical feedback amplifiers, using this design method, are described. They are employed for the transmission of television signals over coaxial cables.The possibility of feedback amplifiers operating as regenerative modulators at high levels of signal is discussed.

DOI:10.1049/pi-3a.1952.0045

出版商:IEE    

年代:1952

数据来源: IET

摘要:

The equipment described constitutes a radio link for transmitting one video and two audio signals from an outside-broadcast site back to base. The power output is 4 watts at 4400–4800 Mc/s with paraboloids 4 ft in diameter. Double frequency-modulation is used for the audio signals to reduce cross-modulation. Details of the r.f. equipment and of the mechanical design are given in the paper, which concludes with information on some actual field trials.

DOI:10.1049/pi-3a.1952.0046

出版商:IEE    

年代:1952

数据来源: IET

摘要:

The paper describes the transmitting and receiving terminals of a portable equipment operating in either the 3600–4200 or the 4400–4800-Mc/s band, designed for the transmission of the British Standard television waveform over paths up to 40 miles in lengthThe considerations governing the design of the various parts of the system are stated, and the paper concludes with a brief review of operational results.

DOI:10.1049/pi-3a.1952.0047

出版商:IEE    

年代:1952

数据来源: IET

摘要:

A description is given of the requirements and design of a line amplifier for use with 3/8-in diameter coaxial cables, which is suitable for the transmission of either 405-line television on a 1-Mc/s carrier or 16 supergroups of multi-channel telephony. From a discussion of the noise and harmonic requirements it is shown that an amplifier having a gain/frequency characteristic which equalizes the attenuation of six miles of cable is necessary. The circuit design of the line amplifier, and also that of a flat amplifier for use at the terminals, is described. Some of the practical difficulties which limit the performances of the amplifiers and the associated transformers are discussed, and an indication is given of possible improvements which may be incorporated in a future design.

DOI:10.1049/pi-3a.1952.0048

出版商:IEE    

年代:1952

数据来源: IET