Types Of Transmitters Research Articles

Experiences of the Measuring of Consistency

Measuring and control instruments for the pulp and paper process have been manufactured at the works of Kalle-Regulatorer, Sweden, for more than 40 years. In the course of time, certain experiences have been gathered, particularly in the field of consistency measurement. In step with development of stock process techniques, two main types of consistency transmitters have been developed, one for open systems working on part stock flow, the other is an inline consistency transmitter for direct measurement in the stock pipe line.

A new measurement technique for the study of the effects of rock pressure in mines

The article describes new developments in the research work of the Coal Research Institute in Ostrava (C.S.S.R.) in the field of measuring techniques. It discusses the advantages and design of electric indicators used in measuring some effects of rock pressures in situ. These indicators, equipped with a uniform type of resistance transmitter, make it possible to establish mine measuring and registering stations when performing complex mine research work.

Short-distance radio telemetry of biopotentials in occupational medicine

Two types of radiotelemetrie transmitters were designed for recording biopotentials in moving human subjects, especially during occupational work. The first type is suitable for potentials of order 1 millivolt and with frequency components in the range 0.5 to 160–300 c/s, e.g. electrocardiogram or summation electromyogram. The second type is designed specifically for heart rate counting, owing to the signal frequency band being limited from 4 to 30 c/s. The very high frequency oscillator (40 to 95 Mc/s) is frequency- or amplitude-modulated; no transmitting antenna is used, so that the radio-frequency energy is radiated only by the oscillator coil, electrode leads and the subject's body. This construction allows the transmitter to be worn under the subject's clothes, preventing thus damage to the transmitter from too high or low environmental temperature or other unfavourable factors (dust, corrosive substances, etc.). Moreover, carrying the transmitter under the clothes excludes the hazard of electrical injury due to accidental contact with mains supplies and makes the transmitter practically invisible to co-workers and other persons, reducing thus emotional stress from medical examination during work.

Interference Filters for the Far Ultraviolet (1700 Å to 2400 Å)

The transmission characteristics of Fabry-Perot type aluminum-magnesium fluoride-aluminum interference filters for the wavelength region 1700 A to 2400 A are described. Typical peak transmissions of 0.25 with bandpasses <300 A are obtained with first-order filters on fused silica substrates. Secondorder filters give narrower bandpasses. Methods of filter preparation are described briefly, and the effects of the optical properties of the aluminum reflecting layers on filter performance are discussed.

A note on the testing of a sheep heart-rate transmitter

Abstract A sheep heart-rate transmitter has been tested under field conditions. Measurements were made simultaneously on two unshorn wethers grazing in a secluded paddock over a period of 15 days. Factors affecting heart rate have been examined. Measurements made on two sheep before and after shearing using one transmitter only are included to illustrate the use to which this type of transmitter may be put.

Space tapaering of linear and planar arrays

The recent activity in electronically scanned arrays has stimulated interest in means of reducing both the quantities of elements required for a given size aperture and the number of different types of transmitters which would be necessary in an array using an illumination taper. One method of doing this is presented in this paper. The conventional amplitude tapered array is simulated by varying the spacing of equally excited elements, hence the name "space tapering." Space tapered arrays with predictable gains, beamwidths, and sidelobe levels can readily be designed using graphical techniques and simple mathematics. Reduction in the number of elements of from 50 to 90 per cent for moderate and large size planar arrays are possible while retaining good pattern characteristics. Although only linear and circular planar arrays are discussed, the technique can be applied to other planar and three dimensional arrays.

Transmitters

The evolution of the type, form and scope of radio transmitters is traceable from the nascent technology of not yet a century ago to today's elaborately sophisticated systems, among which are included radar, multichannel microwave, aircraft and marine communications and navigation and commercial broadcast. Apparatus and techniques progressed from the early spark and arc transmitters to alternators of various designs and powers, through the era of the first vacuum-tube transmitters to the later highly efficient vacuum-tube types. More recently, transmitter design has utilized high-power tetrode and klystron amplifiers. Although code signaling was the first practical method of communicating intelligence, interest in voice transmission resulted in concurrent efforts to adapt the then existing transmitters to this purpose. The discovery of ionospheric phenomena permitted advances into areas of transmitter development previously considered impractical for other than short-distance communications. Regulations governing transmitter power, frequency and use were established by government agency as the need became apparent. The regulations have been adjusted to keep pace with the increase in power capabilities and the use of the frequency spectrum as the trend continues toward higher-power transmitters.

Echo Capsule for Medical Use (A Batteryless Endoradiosonde)

A new type of a swallowable radio transmitter, ECHO CAPSULE, is described along with some clinical experiments. Unlike other similar capsules which have been reported, this capsule contains no battery and is energized from outside the human body. The energy is converted into dc by the transistor of the oscillator circuit itself, stored into a capacitor and then used as an energy source for the transmission of information on temperature, acidity or the like within the digestive tract.

A Novel Type of High Power Pulse Transmitter

A system of generation of radio waves is described which makes use of a symmetrical circular array of condensers charged through resistors and discharged through spark gaps in the manner of the Marx impulse generator. It is shown that exponential wave� trains of very high peak powers, of the order of 10,000 MW, may be radiated. The radiation resistance and radiation field of the structure are given and modification of the field pattern by parasitic elements is considered. Formulae and graphical aids are given which facilitate the design of such transmitters and experiments with various model transmitters are described. Consideration is given to circuit losses, particularly spark losses, and means are described to minimize these losses.

Radio propagation over a discontinuity in the Earth's electrical properties. Part I

The problem considered is that in which vertically polarized waves are propagated across a single straight-line discontinuity in the electrical properties of a smooth flat earth, the discontinuity being such as might occur at a (rather idealized) coastline. It is further specialized by the assumption that one of the media (e.g. sea) has infinite conductivity, and this is replaced by an infinitely thin, perfectly conducting half-plane lying in the interface of the air and the land medium, the latter now being taken to fill completely the region below the interface.With this model a method of solution is proposed which is a union of ray theory and rigorous diffraction theory. The presence of the land is accounted for by the introduction of a suitable image field and the problem thereby reduced to one in which two fields are incident upon a perfectly conducting sheet situated in free space. The technique is illustrated by application to the case of a three-dimensional plane wave, and this solution forms the basis for the later work.When the transmitter is at a finite distance from the coastline the solution can be obtained by expressing the incident field as an angular spectrum of plane waves the propagation of which has already been studied. This procedure is first applied to the two-dimensional problem of a line source and the results are shown to be in close agreement with previous work on the subject. On examination, however, the solution is found to be made up of the field of the actual transmitter diffracted at the coastline, together with the diffracted field arising from an image transmitter of strength equal to the Fresnel reflection coefficient appropriate to a particular angle of incidence, and this suggests an even more elementary way of tackling the problem. For any type of transmitter all that is now required is the solution of the corresponding Sommerfeld diffraction problem, and with this new approach the case of a point source is treated. The result is almost identical with that found by resolution into plane waves. Moreover, a comparison with the solution for a line source shows that the factor by which the free-space field must be multiplied to give the total field is of the same form for both transmitters, the factor for a point source being obtainable from that for a line source by replacing each two-dimensional distance by the corresponding three-dimensional one. In particular this justifies the application to each radial separately of the formulae for normal incidence on the coastline and enables the analytical difficulties associated with three-dimensional propagation to be avoided.The nature of the field is then studied with particular reference to the rapid changes of intensity and phase just beyond the coastline; the former is generally termed the ‘recovery effect’, whilst the latter gives rise to the phenomenon of coastal refraction. The use of height-gain factors is considered and it is shown that, for sufficiently small elevations of transmitter and receiver, the factors appropriate to homogeneous earths may be applied. Several numerical examples are given.

A Comparison of the Informational Capacities of Amplitude- and Phase-Modulation Communication Systems

In this paper are calculated the informational capacities and the optimum statistics of communication systems consisting of an amplitude- and/or phase-modulated transmitter; a medium, which may include the rf and IF portions of the receiver, and in which white thermal noise of the same bandwidth as the transmitted signal is added to the latter; and a receiver responding to the amplitude and/or phase of this received signal. Restriction of the transmitted signal or receiver response to amplitude modulation alone or to phase modulation alone reduces the informational capacity of the system below the full channel capacity found by Shannon, C = W log (1+r2), with W the bandwidth in cps and r the rms signal-to-noise ratio. It is found that at very high signal-to-noise ratios the capabilities of AM alone and of PM alone each account for half this full informational capacity of the channel. When the signal-to-noise ratio is much less than unity, however, PM has 79% of the full channel capacity, while AM can transmit no more than about 17% of the full channel capacity. If a receiver is used which responds to both amplitude and phase, on the other hand, the capacity at low signal-to-noise ratios equals the full channel capacity whatever type of transmitter is used. An AM signal received on a PM receiver is found to be able at low signal-to-noise ratios to convey as much information as a PM signal.

The 100-KW ERP Sutton Coldfield Television Broadcasting Station

This paper describes the planning, design, construction, and service performance of the 100-kw ERP Sutton Cold-field television broadcasting station built by the British Broadcasting Corporation as the first of the group of four new high-power stations required by the plan to extend the London television service to provide national coverage for the United Kingdom. It represents the basic general arrangement which has been used at the subsequent stations, although at each of these, some variations have been desirable because of differences and improvements in the type of transmitter and combining equipment. The relation of the operating channel of Sutton Coldfield to the over-all frequency-allocation plan for the 41-to 68-mc band used for television broadcasting in the United Kingdom, and the reasons for adopting a vestigial sideband characteristic for the vision signal, are briefly discussed. The construction details of the complete vision and sound transmitting equipment, transmission lines, combining diplexer, mast and antenna system are described, and information about the performance of the station in service is given.

Single-Sideband Transmission by Envelope Elimination and Restoration

A new type of single-sideband transmitter is described which does not require the use of linear radio-frequency amplifiers. Amplification is accomplished by a process in which the phase-modulation component of the single-sideband wave is amplified by means of Class-C amplifiers, and the amplitude envelope is restored at the final amplifier. Experimental results show performance equal to or better than conventional linear radio-frequency amplifier practices. The over-all efficiency is approximately the same as that of a double-sideband amplitude-modulated transmitter. This system is especially suitable for high-power operation.

Television broadcasting stations

The paper surveys the television transmitting-station distribution scheme by which the B.B.C. hope to provide the greater part of the United Kingdom with a television service using the 405-line 2: 1-interlaced-scanning 25-pictures/sec British Standard transmission. The basic factors underlying the choice of scheme are discussed, together with the arrangements for dividing the available 41–68 Mc/s frequency band into five separate operating channels using the receiver-attenuation system of vestigial-sideband transmission. The proposals for operating two geographically separated transmitters, one of high power and one of low power, on each channel to complete a 10-station plan, and the precautions needed to minimize co-channel interference, are explained. Some of the problems of site selection for transmitting stations are mentioned, and a brief account is given of propagation phenomena which influence the estimation of service area. The scheme for linking the stations with the London studio centre is briefly described.The general planning and design of the complete transmitting equipment used at the B.B.C.&apos;s new high-power television broadcasting stations and intended for use at the future low-power stations is surveyed, with particular reference to the different types of vision and sound transmitters, monitoring equipment, air and water cooling installations, vision/sound combining circuits, transmission lines and aerial systems, to indicate the progress so far made and illustrate the trend of future developments.

The Empire Service broadcasting station at Daventry

The paper describes the development of the short-wave broadcasting service in this country during 11 years from the initial experiments carried out at Chelmsford in 1927 to the present time. As a result of the initial experiments, the Empire broadcasting station was established at Daventry by the B.B.C.in 1932. The considerations underlying the design of this station are given, together with a brief description of it and the results obtained. Changes to the 1932 aerial system are discussed and an account is given of a series of experiments carried out at Daventry to determine the most suitable type of aerial for short-wave broadcasting. Details are given of the new aerial system erected at Daventry as a result of these experiments. The number and power of transmitters required for a shortwave broadcasting service which has to cover practically the whole world are discussed, and a detailed description is given of two types of high-power short-wave transmitter which have been installed at Daventry. The feeder and feeder-switching system to permit the connection of a number of high-power transmitters to a number of short-wave aerials is described. The paper ends with information on the performance of the station. An Appendix contains notes on the wavebands available for short-wave broadcasting services.

The Communication System of the Radiomarine Corporation of America

The coastal facilities and shipboard apparatus used in the communication system of the Radiomarine Corporation of America, are described in this paper. Long-range communication obtainable from ship to shore with moderate power at high frequencies has resulted in the development of several new types of short-wave transmitters. In addition to serving the marine field as an important communication facility and safety-of life factor, radio, through the direction finder, has become a valuable navigation aid. One of the standard Radiomarine direction finders is briefly described in this paper.

Some observations on the Orfordness rotating beacon

The following paper gives an account of observations which have been made during the past nine months on the Orfordness beacon which was established in July 1929 with the object of ascertaining the utility of this type of wireless aid to navigation when the observations were made by the personnel of the Mercantile Marine.The Orfordness beacon is of the rotating-loop type which operates on a wave-frequency of 288.5 kilocycles per sec. (wavelength 1040 m), and emits continuous navigation signals with special morse characters to indicate the N. and E. signal positions. Bearings are obtainable with any type of wireless receiver with the aid of a suitable stop-watch or chronograph. At the request of the Board of Trade, the masters and operators of many ships have submitted a record of the observations of bearings which they have made on the beacon, together with information as to the position and true bearing of the ship at the time the observations were made. The paper gives a summary of the results contained in the reports submitted by about 160 ships and discusses these results in some detail. It would appear from the results analysed that with a normal type of one- or twovalve receiver, as employed in modern ships, the reliable working range of the beacon is of the order of 100 miles by day or night. Within this range under favourable conditions about 80 per cent of the observed bearings are correct to within 2°. At greater ranges bearings of a slightly lower order of accuracy are obtainable in the daytime up to distances of about 250 miles with the same type of receiver, and with more sensitive receivers the working range may be anything up to 500 miles. At these larger distances, however, the reliability of the bearings is somewhat impaired during the hours of darkness by the phenomena of flat minima and wandering zeros which are characteristic of experience in direction-finding under similar conditions.Section (3) of the paper gives details of a series of observations which have been carried out at the National Physical Laboratory. From these it appears that the accuracy of the time of rotation of the beacon is well beyond the limit of any ordinary chronograph or stop-watch which is employed in bearing observations. From systematic readings obtained in the daytime over a considerable period, it is also to be concluded that skilled observers can obtain bearings from the beacon with a maximum error of 2°, and that a high proportion of the bearings are accurate to within 1°. These results, together with those (already referred to) taken on board ship, indicate that no definite error can be ascribed to the rotating beacon installation itself. Over the range of 93 miles overland between Orfordness and Teddington, observations taken at night show that the accuracy of bearings, even with skilled observers, seriously deteriorates and errors of as much as 20° may sometimes be experienced. Since it appears that the working range of the beacon might with advantage be increased above its normal value of Reprinted from 100 miles oversea, it will be desirable in future to develop the beacon along lines which will provide freedom from these night errors, which at present appear to be the only limitation imposed upon the accuracy and reliability of the bearings supplied by the rotating-loop type of transmitter.

The Development of a Visual Type of Radio Range Transmitter Having a Universal Application to the Airways

This paper deals with the development of a visual type of radio range which has universal application to the civil airways of the United States. Following a discussion of the relative merits of the aural and visual systems of course indication, the theory of the production of twelve courses by utilizing a three-phase radio-frequency source is presented, followed by a general description of the transmitter. The necessary requisites of goniometer design are touched upon, and performance curves of the final goniometer illustrate the effect of these factors on the results. The detrimental effects of cross-couplings between the loop antennas are pointed out, and methods given whereby these couplings may be eliminated. Further discussion covers the advantages of neutralization in the transmitter, the relative merits of various types of interstage coupling, and the method used to obtain and determine a three-phase radio-frequency supply. A description of the installation includes a discussion of the characteristics of the loop antennas used for transmission, together with a measured field intensity curve. A course indicator is developed which is useful in aligning and monitoring the courses. Polar space patterns of reed amplitude show the characteristics of the courses obtained with the two-, four-, and twelve-course ranges. The installation is designed to give continuous operation with a minimum number of interruptions due to failure of the apparatus, a condition necessary to the establishment of an aid to air navigation.

Development of the Visual-Type Airway Radiobeacon System

Research work on a visual-type radiobeacon system for use on the airways of the United States has been under way at the Bureau of Standards during 1926-1929. As a result of this work a system has been developed which fulfills the requirements for course navigation on the civil airways. A directional transmitter is employed on the ground making possible the use of simple apparatus on board the airplane. A single radio receiver is sufficient to make use of all the radio aids provided. Visual indication is provided by means of a tuned-reed course indicator. The pilot observes the vibration amplitudes of two reeds. On the course the amplitudes are equal. Off the course they are unequal, the reed vibrating with the greater amplitude being on the side to which the airplane has deviated. Two types of beacon transmitters are described, the double-modulation and the triple-modulation. The former is capable of serving either two courses at 180 deg. with each other or four courses at arbitrary angles. The latter serves twelve courses at arbitrary angles and is better adapted for use at airports located at the junction of a large number of airways. Reed indicators for use with the double-modulation and triple-modulation beacons are described. A discussion of the radio receiver and receiving antenna system employed is included. Airplane engine ignition shielding is also discussed. A marker-beacon system has been developed whereby the pilot is given visual indication of his exact position at definite intervals along the route.

A theoretical discussion of various possible aerial arrangements for rotating-beacon transmitters

In the following paper, three arrangements for a rotating-beacon transmitter are discussed from the theoretical point of view. These three systems are the single coil, the double-spacedcoil, and the Adcock aerial arrangement.In the case of the single-coil system it is shown thatunder night conditions, when wireless waves can be deflected from the upper ionized layer, the signal minimum as observed at the receiver can occur at such times during the rotation of the coil as to indicate an error in the observed bearing ranging up to 80 deg. It is shown that this error is of the same order as that observed on an ordinary direction-finder under similar conditions.The treatment of the arrangement of two co-planar spaced coils, as sometimes employed for directional reception, shows that, while the time of occurrence of the minimum giving the correct observed bearing remains unaltered during all conditions of night effect and downcoming waves, other secondary minima may be obtained under these conditions, the observed bearings on which maybe in error by the same amounts as those obtainable with the single-coil transmitter. As the observer at the receiver will, in general, be unable to distinguish between the main and the secondary minima, this double-coil system would appear to possess nearly the same liability to error as the single-coil system. The possibility of the two minima occurring close together will also detract from the accuracy of observation of the main minimum, even supposing it could be distinguished from the other.The third case to be considered is that proposed by Mr. C. E. Horton, viz. the use of the Adcock aerial system as a rotating transmitter. With this arrangement it is shown that a signal minimum is produced when the plane containing the pair of vertical aerials, or their equivalent in space, is perpendicular to the direction of the receiver. This minimum remains unaltered in thepresence of downcoming waves at night, and as no secondary minima occur it appears that this system will give correct bearings at all times when the signal is strong enough for observation.In searching for a type of rotating-beacon transmitter upon which the observed bearings are independent of night errors, it would appear that the Adcock arrangement is the most hopeful; and it is, therefore, proposed to consider this system in more detail from the practical standpoint.