摘要:

The paper describes the origin of the Gibraltar–United Kingdom circuit working on forward scatter in the ionosphere. Aerial input powers up to 40kW have been used and observations made on frequencies in the range 37 to 70Mc/s and at distances in excess of 1100 miles. The scope of the work undertaken by various interested organizations is outlined and the main conclusions are given in relation to the claims that have been made for this mode of transmission by the pioneer workers in the United States. Special reference is made to the serious interference problems arising from the reception of signals from other stations and noise sources by reflection from sporadic-E ionization, particularly in lower latitudes. Similar troubles, including the effect of back scatter and round-the-world echoes, have been met owing to normal F-layer reflection as the sunspot cycle has progressed from a minimum to a very high maximum of activity.

DOI:10.1049/pi-b-1.1958.0002

出版商:IEE    

年代:1958

数据来源: IET

摘要:

The paper describes a scatter signal analyser which enables level time-structure measurements to be made on scatter propagation signals. The analyser consists of several different units, the most important which is a level comparator of the sampling type whose speed response is sufficient to deal with the highest fading rates anticipated. The various units may be interconnected in different ways, and paper explains how the analyser may be used to measure amplitude distributions, median aerial gains, signal auto- and cross-correlations, fading rates and, in some circumstances, error rates.

DOI:10.1049/pi-b-1.1958.0003

出版商:IEE    

年代:1958

数据来源: IET

摘要:

In ionospheric scatter communication systems the angle of elevation at which signals should be transmitted and received depends on the circuit length, the height of the ionospheric scattering layer and the refraction which occurs in the troposphere. The effect of variations of these parameters is discussed, and it is shown that probable variations of ionospheric height and refraction are unimportant for circuits up to about 1100 miles in length.The concept of optimum height of aerial above a smooth reflecting foreground is introduced and is shown to be applicable to the partially incoherent wave which results from the scattering process.The additional question of adequate overlap of those regions of the ionosphere visible from the transmitting and receiving aerials is considered, leading to recommendations for circuit design. It is shown that the design of very long circuits presents difficult problems, and that to secure consistent performance on such circuits it might be advantageous to use two aerial systems at different heights.

DOI:10.1049/pi-b-1.1958.0004

出版商:IEE    

年代:1958

数据来源: IET

摘要:

The paper reports measurements of amplitude distribution, lateral correlation, diversity effects and error rates of ionospheric scatter signals at a frequency near 70Mc/s. The results are discussed and it is concluded that a markedly non-Gaussian signal occurs at some times. The effects of signal structure are examined, and it is shown that the only effect is that some loss of diversity action would need to be included when deducing the performance of a link from the median signal and noise levels The signal/noise ratio required for various error rates in a non-diversity system is derived, together with information of use in estimating the feasibility of h.f. communication links. Some information on the diurnal variation of cosmic-noise intensity is given.

DOI:10.1049/pi-b-1.1958.0005

出版商:IEE    

年代:1958

数据来源: IET

摘要:

The problem of radio interference is particularly acute when consideration is being given to ionospheric scatter communication. This is mainly brought about because of the low level of scatter signals and the consequent need for high-gain receiving aerials.A wide variety of both man-made and natural interference has been encountered in the United Kingdom during an investigation into the behaviour of scatter transmissions from Gibraltar. Furthermore, specific surveys have been made which have yielded valuable information concerning disturbances at other geographical locations.The problem resolves itself mainly into two categories: (a) disturbances which have their sources in the vicinity of the receiving aerial, and (b) disturbances which are propagated over great distances. Type (a) can be largely overcome by adequate separation of the receiving site from disturbing sources, and by careful design of the receiving aerial; type (b) could be overcome by raising the operating frequency.

DOI:10.1049/pi-b-1.1958.0006

出版商:IEE    

年代:1958

数据来源: IET

摘要:

The recordings of ionospheric scatter signals received at East Hanningfield, Essex, from the experimental transmitter at Gibraltar have been analysed, but, because of some disturbing factors, great care had to be exercised in accepting certain data.In general, the mean signal levels are a maximum between 0400 and 1200 G.M.T., while a fairly well-defined minimum occurs at about 1800 G.M.T. Signal bursts of duration greater than 1 min appear to have a diurnal variation similar to that of the observed mean signal levels.The time relationship between the first appearance of an identifiable burst at two receiving stations separated by a distance of 70 miles has been investigated. On an east-west route the mean lag at the west station is just over 2 min, the range being from +11 to −6 min; the latter represents a lag at the east station.A pronounced seasonal variation in mean signal levels has been disclosed by the analysis. Two sharply defined minima occur, one centred on March, the other on October; of the two maxima, that which occurs in December is the higher.The variation of transmission loss with frequency derived from the analysis confirms the American data obtained at a similar mean latitude. Compared with 37 Mc/s, the mean signal levels for corresponding months show a reduction of 10 dB for 48 Mc/s and 19 dB for 70 Mc/s.

DOI:10.1049/pi-b-1.1958.0007

出版商:IEE    

年代:1958

数据来源: IET

摘要:

The required polar diagram depends on four factors, namely the size and shape of the zone in the ionosphere which can be seen from both terminals, the effect of the angle through which the radiation is scattered, the allowable multi-path delay and the interference. Diagrams showing the mutually visible zone are presented for path lengths between 1200 and 1800km. The available information on the scattering properties of the ionosphere suggests that there is not much advantage in reducing the beam width in the horizontal plane below about 30° (between 3 dB points). Diagrams showing the delay in transmission for paths off the great circle are presented. The required polar diagram in the horizontal plane is discussed in detail for a path length of 1200km. For the polar diagram in the vertical plane it is important to ensure that the lowest lobes from each terminal overlap well, and that as much power as possible goes into the lowest lobe; rules for achieving this are given. Protection against interference to or from distant stations is discussed. Requirements for the reflecting surface (land or sea) are investigated, and it is shown that horizontal polarization is preferable; the size and allowable roughness of the surface are specified.

DOI:10.1049/pi-b-1.1958.0008

出版商:IEE    

年代:1958

数据来源: IET

摘要:

A study has been made of the angular distribution in the horizontal plane of the energy reaching Slough from a v.h.f. transmitter at Gibraltar by scattering in the ionosphere. The mean bearing of the energy distribution is found to vary with time of day, and is, on the average, zero in the middle of the day and 7° west by night with reference to the great-circle path. The spread in bearing of the incident energy at any time has a standard deviation with a mean value of about 6°.

DOI:10.1049/pi-b-1.1958.0009

出版商:IEE    

年代:1958

数据来源: IET

摘要:

The paper reports measurements made at Winkfield, near Slough, on signals received from a transmitter at Gibraltar operating on 37.3 Mc/s. A diurnal variation of the mean bearing of meteor-trail reflections is found, and the angles of elevation are consistent with those to be expected from the path geometry. The rates of reception are found to be consistent with an inverse amplitude law for the weaker reflections and with an inverse fourth-power law for the strongest. The bearing of the strong persistent reflections obtained from sporadic-E ionization lies close to the great-circle bearing. Applications to practical transmissions are briefly considered.

DOI:10.1049/pi-b-1.1958.0010

出版商:IEE    

年代:1958

数据来源: IET

摘要:

Observations have been made on short bursts of signal received at Cambridge from the Kirk o'Shotts television transmitter at a distance of 480 km. The time distribution, the distribution of amplitudes and the direction of arrival of these bursts are studied. The characteristics which would be expected if the bursts were produced by reflections from ionized meteor trails are examined and good agreement is found between these and the experimental results.

DOI:10.1049/pi-b-1.1958.0011

出版商:IEE    

年代:1958

数据来源: IET