Telegraph Circuits Research Articles

Basic Principles of tne Varioplex Telegraph

A new kind of channel-sequencing system allots the full capacity of a telegraph circuit to the busy channels alone. A busy channel cuts itself out of its sequential position by becoming idle but may re-enter the sequence at will by offering one letter for transmission. Entry, mixing, and exit are accomplished by electromechanical control of standard start-stop and multiplex printing telegraph apparatus. Special signal or code combinations are used to denote changes in the pattern of subchannels cut in, and to act as a check on correct distribution. For greater efficiency, ordinary message letters, by a new method, may be interspersed among successive elements of switching combinations, and the cascading of combinations is also employed. Dummy channels, high-speed receivers, and other devices may be used to prevent or utilize unusual channel speeds. Varioplex systems may be repeatered either by subchannel storage or by storage involving several subchannels handled as a unit.

Basic principles of the varioplex telegraph

A new kind of channel-sequencing system allots the full capacity of a telegraph circuit to the busy channels alone. A busy channel cuts itself out of its sequential position by becoming idle but may re-enter the sequence at will by offering one letter for transmission. Entry, mixing, and exit are accomplished by electromechanical control of standard start-stop and multiplex printing telegraph apparatus. Special signal or code combinations are used to denote changes in the pattern of subchannels cut in, and to act as a check on correct distribution. For greater efficiency, ordinary message letters, by a new method, may be interspersed among successive elements of switching combinations, and the cascading of combinations is also employed. Dummy channels, high-speed receivers, and other devices may be used to prevent or utilize unusual channel speeds. Varioplex systems may be repeatered either by subchannel storage or by storage involving several subchannels handled as a unit.

The varioplex — A new development in telegraphy

The varioplex method of telegraphic operation provides each pair of stations connected together by it an ever-ready two-way channel for the exchange of traffic, which occupies a band width of zero when idle and of a variable width when busy, depending upon extent of simultaneous usage by other connected stations. It possesses certain advantages over, or in supplement to, other forms of manual and machine switching or repeatering. Adapted to the use of private subscribers through telemeter service, it is finding extensive application in the telegraph plant. A good deal of current effort in the telegraph engineering field is being directed toward the solution of problems of trunking and switching. Basically, these problems arise from the circumstance that important trunking centers, like Boston, Atlanta, or Los Angeles, have tributary to them most of the less important telegraph offices in their respective surrounding areas. That this is so with respect to the many branch telegraph offices and tie-line connections which dot the larger American cities requires no explanation; the growth of commerce along the railroads has made it no less true of cities and towns many miles from trunking centers. The existence of fanned-out local telegraph circuits around Boston as a hub, to take that city as an example, is inherent in the commercial relationship of most New England towns to its dominating city. It can be appreciated, then, why the Boston office, in years past, has acted not only as the terminal for a considerable day-to-day traffic between Taunton and Boston but also as the relay point for the less frequent messages between Taunton and New York. This situation exists the country over. Of recent years, improvements in the transmission qualities of these tributary circuits have made it possible to terminate them, almost universally, in printing telegraph equipment.

Empire telegraph communications

The paper deals with the engineering aspect of Empire telegraph communications. In order that the size and scope of these communications may be realized, the author begins by setting forth the components of the telegraph operating company, showing the systems contributed by each section.The engineering organization within the operating company is then dealt with, the training and necessary qualifications of telegraph engineers in the present service being outlined. Returning to the general aspect of Empire communications, the main traffic routes are discussed, with details of a number of main-line circuits. Some of the engineering requirements of the flow of traffic are touched on.Having dealt briefly with the system, the paper proceeds to enumerate the methods by which the collection and the delivery of messages are effected. The methods of signalling and the suitability of the different codes under varying circumstances are explained.The author then presents a short history of progress in cable telegraphy. Modern methods of signal shaping, balancing, and synchronous-regenerator working on cable circuits are reviewed. Where well-known methods are in use the descriptions are brief, full technical explanations being given only where information has not previously been published except in patent specifications. The items described in detail include the capacitance magnifier, the fork relay, the automatic bias corrector, and the automatic scrutinizer.There follow brief notes on recent progress and cable problems which are still being investigated.A brief outline of the methods of operating the wireless telegraph circuits is given, with details of the application of regenerator working to these circuits. A description of a method of double-frequency keying of wireless circuits follows. Finally, reference is made to the effects of varying cosmic conditions on wireless signals.

Single-Side-Band Telephony Applied to the Radio Link between the Netherlands and the Netherlands East Indies

An historical introduction reviews the initial long-wave telegraph circuit with the East Indies in 1923, the first short-wave telegraph circuit in 1925, and the inauguration of short-wave telephony in 1928, this being accomplished by means of the usual double-side-band and carrier system. The principal limitations attending this method of operation are discussed; viz., the phenomena of fading, susceptibility to frequency and phase modulation, and the fact that it does not lend itself to multiplexing, because of the presence of the high-powered carrier. The features which characterize the present system are, first, that of single-side-band as applied to high-frequency transmission, and, second, that of multiplexing, whereby a plurality of channels are enabled to be transmitted by means of a single power amplifier and directive antenna system. In the transmitter the group of channels which is to be transmitted, representing one telegraph and two telephone messages, is assembled at low power and low carrier frequency and is then stepped up in power and in frequency in a succession of stages. The spectrum transmitted comprises (1) the two telephone channels located in frequency as single bands on opposite sides of the suppressed carrier; (2) the telegraph channel superimposed thereon as two tone frequencies, one for spacing and one for marking, and transmitted on a double-side-band basis to obtain the advantage of frequency diversity; and (3) the pilot channel transmitted at a frequency 5000 cycles removed from the carrier position.

The Reliability of Short-Wave Radio Telephone Circuits*

From empirical measurements of noise-to-signal ratio made during the routine operation of short-wave radio telephone circuits there is obtained a general relation between percentage lost circuit time and transmission improvement in decibels. In this relation “percentage lost circuit time” is the percentage of time that the noise-to-signal ratio is considered unsatisfactory. No attempt is made to define such a standard quantitatively. If, from past experience with a long-range, short-wave telephone, telegraph or broadcast circuit, it is known that the circuit is unsatisfactory a certain percentage of the time, the above-mentioned relation may be used to estimate the effect of transmission improvement upon this percentage of unsatisfactory or lost time. For a given circuit the variation in percentage lost circuit time, as the standard for the tolerable service is changed by a given number of decibels, may also be estimated. There are included estimates of the relation between the number of lost time intervals of various lengths and transmission improvement.

Iron Armored Aerial Communication Cable

This paper describes a study of the application of an iron armored aerial communication cable as an inductive coordination measure permitting a high voltage transmission line to occupy jointly for a distance of about 20 miles the same railroad right-of-way with telegraph and telephone circuits. Calculations are given indicating the induction to be expected on open wire communication circuits, and the degree of reduction afforded by several different designs of cables, both armored and nonarmored. The effect of cable on the normal operation of the telegraph and telephone circuits carried through it also is considered.

A new carrier telephone cable

Three carrier telephone circuits and one telegraph circuit are provided by this newest cable linking the United States with Cuba. The design is such that still more carrier channels may be provided when the need for them arises.

Developments in Methods of Communication

A PAPER on modern communication systems, by Dr. F. Luschen, was read to the Institution of Electrical Engineers on April 7. Dr. Luschen pointed out that the rapid progress of invention has made modern communication systems very complicated to design. Few realise how difficult it was to solve the problem of the interconnexion of wired and wireless systems. This was first carried out in the telephone link between Great Britain and the United States. Further problems that have been solved are the multiple utilisation of lines for telegraphy and telephony, the control of electrical apparatus at a distance, and the electro-acoustic transmission problems involved in broadcasting and sound-films. These methods have widely extended the field of use of communication systems. The information contained in the spoken word is an extremely complicated function of the time. The transmission system is composed of widely different elements. At first, therefore, it appears to be a hopelessly difficult problem. Yet, with the help of a few simple mathematical principles, engineers have succeeded in visualising the transmission of signals. As an illustration of the pitch of perfection to which carrier-current telephony has reached in the United States, Dr. Lüschen described a pole line carrying twenty pairs of conductors, sixteen of which carry three high frequency channels each, in addition to their low frequency communication circuits, while the other four pairs are equipped with ten telegraph channels each. Twenty pairs of wires thus result in 150 communication circuits, 80 of them being telegraph circuits and 70 of them telephone circuits. Dr. Luschen also gave interesting particulars of tests made on a system of telephony and telegraphy linking Berlin with Buenos Aires. It is designed to transmit speech and two telegraphic messages simultaneously.

Police teletypewriter communication

PoLICE organizations throughout the country are rapidly adopting the latest development in record communication, namely, the teletypewriter. By this means alarms are typed at one point and simultaneously recorded in printed form at a large number of widely separated stations. The engineering for a modern police system involves not only the provision of the teletypewriter machine, but large networks of telegraph circuits with the associated switchboards, telegraph repeaters, power plants, and testing equipment which also must be designed, manufactured, and installed.

An automatic concentration unit for printing telegraph circuits

WHEN a number of lightly loaded telegraph circuits terminates at a central telegraph office, and the number of messages over each circuit is insufficient to keep the operator fully employed, these circuits usually are grouped together on a switchboard or “concentrator,” so that a single operator can send and receive messages over any line of the group.

Telegraph Power Plants

This paper mentions some of the early methods of providing electrical energy to operate telegraph circuits and contrasts these with a description of the telegraph power plant in the Western Union Telegraph Company's new building in New York City. It also describes the present general methods of distributing power to telegraph circuits and the equipment recently designed for maintaining continuity of power including engine generator sets for standby service.

A concentrator for printing-telegraph circuits

The termination in a telegraph office of a large number of “start-stop” printing telegraph circuits, requires some means for concentrating the circuits to enable incoming and outgoing traffic to be handled efficiently and economically. A multipleturret concentrator which permits any one of many circuits to be worked by any one of a few operators is described here.

Effect of Signal Distortion on Morse Telegraph Transmission Quality

In applying telegraph transmission measuring apparatus to the development and maintenance of telegraph circuits, it is desirable to correlate quantitative measurements of telegraph signal distortion with quality of telegraph transmission. Accordingly, a series of tests has been carried out in order to determine this relationship for the case of manual operation using the American Morse Code. These tests are described and the results, together with the conclusions reached, are given in summarized form.

A new electronic rectifier

G. W. Janson: Schemes such as that shown in Fig. 14 have been tried at various times by communication engineers, in their efforts to increase the output of telegraph circuits. The possibilities of these arrangements have, however, been generally limited by factors other than the effectiveness of available rectifying means. However, there are probably many other valuable uses for a rectifying element having the excellent characteristics described in this paper.

Line Current Regulation in Bridge Polar Duplex Telegraph Circuits

A mathematical analysis of the bridge polar duplex telegraph circuit, under the condition that the bridge arms are of equal resistance, shows that there is a particular bridge arm resistance which results in maximum received current. As the bridge arm resistances are increased beyond the value giving this maximum, the received current diminishes gradually. On the other hand, as the bridge arm resistances are decreased below the value giving the maximum, the received current drops off very rapidly. It follows that when necessary to limit line current, the maximum received current is obtained by placing the regulating resistance in the bridge arms. Also when the line resistance is large enough to limit the line current to less than the maximum allowable value, a gain may be obtained by increasing the bridge arm resistance to the value which corresponds to maximum received current. Experience has shown that in many situations where difficulty is encountered in operating a duplex telegraph circuit with the regulating resistances in the line, a very decided improvement is obtained by transferring these resistances to the bridge arms.

Neutralization of Telegraph Crossfire

With the simple means here described for neutralizing mutual interference between parallel telegraph circuits, it has been found practicable to effect a reduction to 10 or 20 per cent of the original values. This has improved considerably the operation of some circuits and made available others which were previously unsuitable. The resulting improvement in transmission has made possible the elimination of certain intermediate telegraph repeaters with material savings. The neutralizing apparatus has no material effect when crossfire is not present, that is, when the paralleling wires are idle. It has been found that the use of arrangements here described on certain long open wire circuits makes possible fast manual full-duplex operation where only medium-speed half-duplex operation was possible before. Furthermore, in the case of some cable circuits where it was impossible to operate more than two telegraph circuits per quad, it is now practicable to obtain four telegraph circuits.

Metallic polar-duplex telegraph system for long small-gage gables

In connection with carrying out the toll-cable program of the Bell System, a metallic-circuit polar-duplex telegraph system was developed. The metallic-return type of circuit lends itself readily to the cable conditions, its freedom from interference allowing the use of low potentials and currents so that the telegraph may be superposed on telephone circuits. The new system represents an unusual refinement in d-c. telegraph circuits, the operating current being of the same order of magnitude as that of the telephone circuits on which the telegraph is superposed. The metallic system is suitable for providing circuits up to 1000 miles or more in length, the grade of service being better than that usually obtained from ground-return circuits on open-wire lines for such distances. About 55,000 miles of this type of telegraph circuit are in service at present.

Voice-frequency carrier telegraph system for cables

Carrier telegraph systems using frequencies above the voice range have been in use for a number of years on open-wire lines. These systems, however, are not suitable for long loll cable operation because cable circuits greatly attenuate currents of high frequencies. The system described in this paper uses frequencies in the voice range and is specially adapted for operation on long four-wire cable circuits, ten or more telegraph circuits being obtainable from one four-wire circuit. The same carrier ferquencies are used in both directions and are spaced 170 cycles apart. The carrier currents are supplied at each terminal station by means of a single multi-frequency generator.

Voice-Frequency Carrier Telegraph System for Cables

Carrier telegraph systems using frequencies above the voice range have been in use for a number of years on open-wire lines. These systems, however, are not suitable for long toll cable operation because cable circuits greatly attenuate currents of high frequencies. The system described in this paper uses frequencies in the voice range and is specially adapted for operation on long four-wire cable circuits, ten or more telegraph circuits being obtainable from one four-wire circuit. The same carrier frequencies are used in both directions and are spaced 170 cycles apart. The carrier currents are supplied at each terminal station by means of a single multi-frequency generator.