摘要:

The interference between the direct ray and a ground-reflected ray gives rise at the receiver of a communication link to a sinusoidal field pattern in the vertical plane consisting of nodes and maxima. The position and pattern wavelength of this field depend on the receiver and transmitter heights and spacing and on propagation conditions via an effective curvature parameter,C. This parameter varies in time, and is the cause of most fading at a single antenna. Its upper limit, which may be as high as 2.5 for a small percentage of the time, determines minimum antenna heights for line-of-sight transmission under extreme conditions.Cis normally about ¾. Its range of variation determines the optimum spacing of a pair of diversity antennae, and suitable design formulae are given. Experiments using a pair of mirrors, a varying transmitter frequency, and photographs of oscillograph traces indicate an extreme lower value ofCover water of −1.5. A moving-film display shows that conditions can vary rapidly from minute to minute, although at other times the display is steady for hours at a time.An automatic phasing junction has been designed for insertion in the feed from two diversity antennae, the drive for the phasing element being taken from the receiver. A combined signal nowhere smaller than the greater of the received signals is obtained from the combining unit, and when the diversity spacing is chosen with regard to the extreme values of curvature obtained on the path, an excellent overall response is ensured. Some preliminary figures are given for the performance of an improved combining network and phase-control apparatus operating in conjunction with a height-diversity microwave system over a 69-mile overwater path.

DOI:10.1049/pi-b-2.1962.0203

出版商:IEE    

年代:1962

数据来源: IET

摘要:

A method is described of combining two or more carrier signals, which may be from a space-diversity aerial system, in such a way that the output power is always the sum of the individual signal powers. This gives the optimum signal/noise ratio under the commonly assumed Rayleigh distributed fading conditions.The control signals are taken from the i.f. amplifier of the main receiver; no extra detecting facilities are therefore required. However, a standby receiver can be incorporated, and the combiner can easily be adapted to act as a change-over switch, if required.

DOI:10.1049/pi-b-2.1962.0204

出版商:IEE    

年代:1962

数据来源: IET

摘要:

The paper describes an investigation into three similar methods of reducing the bandwidth required for the transmission of television pictures. The three methods all involve the isolation of the essential brightness changes in the picture; these are redistributed to occur at a uniform rate for transmission. A second signal must be transmitted in order to allow correct repositioning of the brightness changes in the final picture. Partial instrumentation has been carried out, and the methods have been assessed with regard to their bandwidth requirements and resultant picture quality.

DOI:10.1049/pi-b-2.1962.0207

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Measurements of the X-band magnetic properties of a series of nickel ferrite-aluminates, as a function of applied magnetic field, are described, together with static magnetization measurements. The results show considerable departures from simple theoretical (Landau–Lifshitz) behaviour, especially in the compensation region of small magnetization, which are probably due to porosity and anisotropy eftects.Resonant-cavity measurements of permeability and permittivity have been made on various nickel ferrite-aluminates and nickel-zinc ferrite aluminates, and compared with transmission measurements for thin slabs of the same materials placed in rectangular waveguide. A general correlation was obtained in all cases, but this was insufficiently precise for exact prediction of waveguide propagation data from intrinsic ferrite parameters. Possible reasons for this are discussed.

DOI:10.1049/pi-b-2.1962.0210

出版商:IEE    

年代:1962

数据来源: IET

DOI:10.1049/pi-b-2.1962.0211

出版商:IEE    

年代:1962

数据来源: IET

摘要:

A brief summary of the principal features of waveguide characteristics is given and with the help of the main conclusions a system assessment is carried out. The effect of attenuation and dispersion is discussed and a new approach to mode conversion-reconversion phenomena is proposed, by treating the phenomenon as a form of noise.Criteria for repeater spacing and their characteristics are examined in the light of the modulation system used. It is shown that for short-distance applications there are a number of possible modulation systems, but that for long distances only quantized systems can be considered; of these only pulse-code modulation has received any detailed attention, but the analysis given is applicable to any quantized system.It is shown that it is not necessary to use perfect regenerative repeaters, but if repeaters incorporate non-linear amplifiers such that the random amplitude and time jitter can be decreased by a factor of about two there will not be any limitation on the overall circuit length. Design criteria for such amplifiers are given.

DOI:10.1049/pi-b-2.1962.0212

出版商:IEE    

年代:1962

数据来源: IET

摘要:

The theory of a single directional-coupler reflectometer having two auxiliary tuners is reviewed, giving emphasis to precision-measurement possibilities.Problems in setting up this system for measurements in coaxial line are discussed, and a system for measurements in the frequency range 3.95–5.85 Gc/s is described.The development of λ/4 short-circuit reflection standards and sliding terminations is presented.The results of measurements of the reflection from connectors and various loads at 4Gc/s are given.

DOI:10.1049/pi-b-2.1962.0214

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Chain codes are a form of digit sequence which have error-correcting properties when suitably arranged, and methods of finding the best code for any particular application are detailed.A particular equipment is described in outline which would be suitable for transmitting the contents of one computer store over a telephone line and into another store.The paper shows that chain codes with less than 2ndigits in the major chain can be effectively used to transmit 2nmessages with a specified amount of error correction.

DOI:10.1049/pi-b-2.1962.0215

出版商:IEE    

年代:1962

数据来源: IET