A b r i d g m e n t o f

Radio Telephone Service to Ships at Sea BY WILLIAM WILSON1 and LLOYD ESPENSCHIED 2

M e m b e r , Α. I. Ε. E. M e m b e r , Α. I. Ε. E.

Synopsis.—The paper discusses the American end of the ship-to- short waves. The station facilities which have been provided for this shore radio telephone system and the connecting equipment on service on the New Jersey coast are described also the equipment board the SS. Leviathan. There is given an outline of previous which has been developed for the ship. Finally, the results are given work in this field and of the technical problem involved in the use of of the first trip of commercial service of the Leviathan.

THE ship-to-shore radio telephone system here described was opened for public service between the SS. Leviathan and the United States on Decem­

ber 8, 1929. This was the first extension of the public telephone service to a ship at sea, and enabled calls to be made between the vessel and any Bell System sub­scriber. The system as set up is intended primarily for giving telephone service to the larger passenger-carry­ing vessels as an extension to the wire network, and should be distinguished from the more simple uses which have been made of radio telephony in the marine field, such as enabling a coastal station operator to talk with coast guard vessels, fishing trawlers, etc.

It is significant of the wide-spread interest in this service that developments have also gone forward rapidly on the European side where the British, Germans, and French are preparing coastal stations and equipping some of the larger ships for public tele­phone service. The British have initiated service to the SS. Majestic and the SS. Olympic, and service to these vessels has been extended also from the American side. Before the summer is over, it is likely that half a dozen of the larger transatlantic vessels will be under­taking this service, connecting with both the American and the European telephone networks.

EARLY DEVELOPMENTS Following the long-distance, point-to-point radio

telephone experiments of 1915, what is believed to have been the first trial of two-way radio telephony from the wire telephone system to a vessel at sea was conducted by Bell System engineers in 1916, in cooperation with the Navy Department. In the years 1920-1922 there was undertaken an extensive development of ship-to-shore radio telephony, looking toward the linking of ships at sea with the land line telephone network. 3

At that time there was built a coastal radio telephone station at Deal Beach, N. J., and several ships were equipped on a trial basis. Extensive engineering tests

1. Bell Telephone Laboratories, New York, Ν. Y. 2. American Telephone and Telegraph Company, New

York, Ν. Y. 3. "Radio Extension of the Telephone System to Ships at

Sea," by H. W. Nichols and Lloyd Espenschied, / . R. E. Pro­ceedings, 1923, Vol. 11, No. 3.

Presented at the North Eastern District Meeting of the A. I. E. E.t

Springfield, Mass., May 7-10, 1930. Complete copy upon request.

were made and a number of demonstrations carried out which proved the physical feasibility of establishing such connections at that time. The waves in the range of 300-500 meters, which had fcesn used in these early trials, were soon thereafter assigned for broad­casting.

More recently the development of short-wave radio systems has greatly increased the message carrying capacity of the radio spectrum, and has made it feasible to maintain communication over a greater range of distances than was previously practicable for ships. Transoceanic radio telephone services have been in­augurated, and with the large increase in steamship travel, there has arisen a renewed interest in the exten­sion of telephone service to ships at sea.

For purposes of point-to-point as well as for ship-to-shore telephone services, and as part of a general program intended to obtain fundamental data upon short-wave transmission, there was undertaken a series of measurements of the strength of electric fields re­ceived aboard ship from a shore transmitter. These tests were first made in 1925 on vessels running between New York and Bermuda. Further measurements were made in subsequent years on other ships.

Along with this study of transmission conditions there was carried on the development of short-wave apparatus technique for telephony. The first applica­tion was in the field of point-to-point transatlantic operation; and the considerable art built up there, including the design of transmitters, receivers, direc­tive antennas and the working out of two-way operating methods, served as a very useful basis from which to develop the coastal and ship stations for the maritime system.

With this background of development, preparations were made to set up a two-way, short-wave radio telephone system for commercial service. This service was centered upon New York because of the large concentration of ocean-going traffic at that port.

T H E TECHNICAL PROBLEM One of the most important problems to be solved in

the design of a short-wave system is that of determining the frequencies necessary for giving the service involved. The frequencies which are best suited to the different distances, time of day, and season of the year for trans-

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July 1930 WILSON A N D E S P E N S C H I E D : RADIO T E L E P H O N E SERVICE TO SHIPS 543

mission over the North Atlantic are indicated in the curves of Fig. 2. Fortunately, there is a considerable band on each side of the curves shown for the longer distances in which good transmission can be obtained, and this enables one to choose in the short-wave range a small number of frequencies which are adequate to cover the conditions. Actually, it is found that a set of about four frequencies is required to cover the North Atlantic.

By reason of the fact that the transmission appears

FIG. 2—DISTANCE-FREQUENCY CHARACTERISTIC

to take place in the upper regions of the earth's at­mosphere, for distances greater than a few hundred miles, these characteristics obtain irrespective of whether the transmission is over water or land. Closer in to the transmitting station, however, there is the so-called surface component, the attenuation of which is much less over sea water than over land. It will be seen that the surface wave may be relied upon for dis­tances of the order of 200-300 mi., for frequencies of about 4000 kc*. The transmission of this component is much more stable and reliable than is the transmis­sion of the sky wave. It seemed important, therefore, to utilize the surface wave to the maximum extent possible. Measurements have shown that to avoid seriously sacrificing the effectiveness of the surface wave, it is necessary to locate the coastal transmitting and receiving stations immediately upon the seacoast or a salt-water bay.

An important factor in connection with radio re­ception on shipboard is that of electrical interference. The operation of the electrical machinery and the radio telegraphic services produces interference in a ship­board receiver which is much in excess of that normally encountered in a suitably located shore receiving station. Furthermore, there is on the ship another source of disturbance which is due to charging and dis­charging of various parts of the rigging in the strong electromagnetic fields of the various radio transmitters. These factors make it desirable to employ at the shore end as powerful a transmitter as is available, and to use whatever benefit is obtainable from antennas designed to be directive along the transatlantic ship lanes. A transmitting set of the type used in transatlantic communication, but adapted for ship-to-shore wave­lengths, is therefore employed.

Since the shore receiver may be located in a compara­tively quiet situation, and since use can also be made of directive receiving antennas, it is not necessary to transmit as large an amount of power from the ship as from the shore. The actual power radiated by the Leviathan's transmitter is of the order of 500 watts.

T H E SHORE SYSTEM

The general set-up of the system is illustrated in Fig. 3. The coastal stations, sending and receiving, are located about 60 mi. south of New York on the New Jersey shore, at Ocean Gate and Forked River.

In general, the whole coastal station, including the transmitting and receiving units, together with the wire line connections and control position in New York, is similar to one end of a transatlantic point-to-point circuit. The transatlantic facilities have been described in previous papers 4 and reference should be made to them for more detail than is given below. The trans­mitting set has a power of a 15-kw. output of un­modulated carrier and is capable of delivering 60-kw. peak power. Actually, a similar transmitter, located two miles inland at Deal Beach, is being used for this service pending the completion of the new transmitting station on the waterfront at Ocean Gate.

The receiving station at Forked River has been in operation since the opening of commercial service last December. The receiver is of the double-detection type, of high gain and selectivity, and employs screen-grid tubes. It is provided with automatic gain control. The apparatus at the receiving station includes not only the receiving set proper but also the equipment which is

FIG. 3 — U . S. COASTAL STATION CIRCUIT B E T W E E N N E W YORK AND SHIP

required for monitoring the circuit and for connecting with the wire line into New York. The receiving di­rective antennas are of the same general type as those used in the transatlantic system, but less sharply directional. A photograph of the station at Forked River and two of the antennas is shown in Fig. 8.

The control and operating terminal equipment in New York is identical with that in use on the trans-

4. Papers on Transatlantic Telephone Service, by Messrs. Miller, Bown, Oswald and Cowan, presented at Winter Con­vention of the Α. I. Ε. Ε., New York, Ν . Y., January 27-31, 1930.

544 WILSON A N D E S P E N S C H I E D : RADIO T E L E P H O N E SERVICE TO SHIPS JournalA. I. Ε. E.

oceanic radio telephone circuits. The control positions include voice-current operated switching devices which prevent the speech received from the ship from being re-radiated from the shore transmitting station and permit independent adjustment of amplification in the circuits leading to the transmitting and receiving

The quartz plates used in the crystal control system are circular, approximately one inch in diameter, and are clamped rigidly in the holder. The holder, with its crystal, is mounted in a small oven, the temperature of which is held constant at 50 deg. cent, to better than + 0 . 1 deg. cent.

FIG. 8—ILLUSTRATION FORKED R I V E R STATION WITH A N T E N N A

stations. This enables full modulation of the trans­mitter to be obtained for over-riding noise on the ship despite variations in speech volume received from dif­ferent land line subscribers.

The circuit terminates as an operating facility before a traffic operator at one of the long-distance telephone ' boards in New York. This telephone operator talks directly with the ship operator, passes and receives information as to calls, and is generally responsible for completing the connection between the ship circuit and the land line subscriber. She is assisted by a second operator who is concerned more particularly with the land line subscribers, themselves, getting in touch with and holding land line subscribers for inbound calls, answering inquiries and recording calls outbound to ships.

T H E S H I P STATION

The Leviathan's radio transmitter is designed to supply about 500 watts, 80 per cent modulated radio frequency power to an antenna a t frequencies from 3000 to 17,000 kc. A schematic of the circuit is shown in Fig. 11. The transmitter unit comprises a crystal oscillator and associated amplifiers designed to main­tain the carrier frequency within close limits; namely, 0.01 per cent. This minimizes interference with other services, facilitates the establishment of contact between the ship and shore stations, and obviates the necessity for frequent retuning of the shore receiver.

The thorough electrical shielding which is necessary between amplifier stages to prevent singing makes the changing of coils, required for the changing of wave­lengths, very unhandy. Hence, the crystal control and amplifier system, except in the last stage, is provided in duplicate, one amplifier system being used for the two longer and the other for the two shorter waves. Wave changing is then aôcomplished by connecting the proper amplifier to the power stage and resetting the output circuit of the power stage.

As shown in the figure, the crystal is connected be" tween the grid and filament of a five-watt vacuum tube-The radio frequency voltage developed by the crystal oscillator is applied directly to the grid of a 7J^-watt screen-grid tube which can be used either as an amplifier or a frequency doubler. The output of this tube, except in the case of the higher frequencies, is applied directly to the grid of a 50-watt screen-grid amplifier and thence to the final amplifier stage. For the higher frequencies, a second frequency doubler is switched into the circuit. The power amplifier consists of an air-cooled,

7-j WATT AMPLflER OR

HARMONIC GENERATOR

H I l i IH

Ec E. Ec E. E B

F I G . 11—SHIP TRANSMITTER'S SCHEMATIC DIAGRAM

three-element, one-kilowatt tube. Neutralization is ac­complished by the familiar balancing arrangement shown in the figure. Modulation takes place in the plate cir­cuit of the final amplifier stage by means of two 250-watt tubes, connected push-pull and fed by a 50-watt amplifier. The power supply is obtained from motor-generator sets operated from the 110-volt d-c. ship supply.

A reduction of the receiving disturbances due to stray noises and better discrimination against the trans­mitted carrier is obtained if the transmitting and receiv­ing antennas are widely spaced. In the case of the

July 1 9 3 0 W I L S O N A N D E S P E N S C H I E D : R A D I O T E L E P H O N E S E R V I C E T O S H I P S 545

Leviathan installation, the transmitter and receiver are located in the same room and the transmitting antenna is located directly above the radio room, between the second and third stacks, with the receiving antenna placed as far behind the third stack as possible. The receiving antenna is connected through a suitable step-down circuit to a shielded transmission line and thence to the receiver, the receiver itself being very thoroughly shielded to avoid direct interference from the trans­mitter. On account of limited space, only two re­ceiving antennas are provided to handle the four fre-

circuit is to be seen also in Fig. 1 3 . It consists of re­peaters, volume-control devices, and volume indicators, by means of which the levels of the incoming and out­going signals can be properly adjusted. Keys are pro­vided which enable the technical operator in the radio room to talk either over the radio circuit or to the ship subscriber. On a lower deck is located the subscriber's booth and a position for an attendant. The attendant has facilities by which he can talk either to the sub-criber or to the technical operator and has a connection with the ship's telephone system for the purpose of locating persons on the ship and calling them to the telephone booth.

FIG. 13—RECEIVER ON S S . LEVIATHAN

quencies, each antenna representing a compromise be­tween the most efficient antennas which could be put up to handle the separate wavelenghts.

The receiver itself is of the double-detection type, using heater type tubes throughout. Screen-grid tubes are used for the first detector and intermediate fre­quency amplifiers and three-element tubes in the re­maining positions. A reproduction of a photograph of the receiver and associated voice-frequency equipment, as it is installed on the Leviathan, is shown in Fig. 1 2 . The high-frequency selective system consists of four separately shielded, tuned circuits, coupled by small capacities. The purpose of these selective circuits is to prevent overloading in the first detector. The intermediate frequency amplifier stages are coupled by means of double tuned circuits. The use of properly designed circuits of this type makes it possible to obtain a high degree of selectivity against undesired frequen­cies while obtaining sufficient band width to maintain ease of tuning and to pass the desired frequencies. Auto­matic gain control is provided in which a certain amount of the carrier is taken at the end of the intermediate frequency stages, amplified, rectified, and applied to the grid of the first detector in such a manner that an in­crease in the intermediate frequency output brings about a reduction in the total set gain, and vice versa.

The voice-frequency equipment for controlling the

DEC. 1929 TIME OF DAY* EST

AM NOOH PM 2 4 6 8 K > 1 2 2 4 6 β «0

NO. OF CALLS

NOON 0I5T.

AMBROSE

SUN. N.Y.-SHIP 8 SHIP-N.Y.

,^Λ,ν . . . . . . i . i i i

10 170

SUN. N.Y.-SHIP 8 SHIP-N.Y.

*9 P U 10 170

SUN. N.Y.-SHIP 8 SHIP-N.Y. 4

Λ I · ι «S . 4 10 170

MON. N.Y.-SHIP 9 SHIP-N.Y.

4

Λ I · ι «S . 4

5 7 2 0

MON. N.Y.-SHIP 9 SHIP-N.Y.

5 7 2 0

MON. N.Y.-SHIP 9 SHIP-N.Y.

4

4 j * iHiohNe'tae is ι 4 5 7 2 0 4

4 j * iHiohNe'tae is ι 4

3 1 2 7 0 10 SHIP- N.Y

3 1 2 7 0 10 SHIP- N.Y

4 ' * Heavy (irackUs 4

Nois«_ _4

Nôîse" 4 Low Fields, Yggj A

Low Fields, Noise

Arrived Cherbourg

3 1 2 7 0

WED. N.Y.-5HIP 11 3HIP-N.Y

4 ' * Heavy (irackUs 4

Nois«_ _4

Nôîse" 4 Low Fields, Yggj A

Low Fields, Noise

Arrived Cherbourg

0 1Θ20 THUR.UY-SHIP

12 SHIP-V4.Y

4 ' * Heavy (irackUs 4

Nois«_ _4

Nôîse" 4 Low Fields, Yggj A

Low Fields, Noise

Arrived Cherbourg

0 2 3 9 0

FRI. 13

4 ' * Heavy (irackUs 4

Nois«_ _4

Nôîse" 4 Low Fields, Yggj A

Low Fields, Noise

Arrived Cherbourg

EASTBOUND

WEST BOUND

T U E . 17

WED. N.Y.-SHIP 18 SHIP-N.Y.

THÜR. N.Y.-SHIP »9 SHIP-KY.

FRI. N.Y.-SHIP 20 SHIP-N.Y.

5AT. N.Y.-SHIP 21 5HIP-N.Y.

SUN. N.Y.-SWIP 22 5HIP-N.Y.

MOM. N.Y. -SHIP 23 SHIP-N.Y.

TUE. NY.-SHIP 2 4 SHIP-N.Y.

TOTAL NY-SHIP ENTIRE 5HIP-RY. TRIP ,

Left Cherbourg 9

Low Fields, Ship IMtr None — ! -L_*

Low Fields' - ΓΓ~ Crétkl**

ORM Ship* Set is

Hioh Noise β

iQRMShi FitfcU β

lo* Fields β 4_ Crack

Arrived Lieht

Small figures denote approximate Frequency in Megacycle; I I I I I I I I I I L

8 10 12 2 NOON

T I M E OF DAY EST

2100

FIG. 16—TRANSMISSION RESULTS BETWEEN SS . AND N E W YORK

T H E

LEVIATHAN

W A V E L E N G T H SITUATION AND SIMULTANEOUS

T E L E P H O N E AND TELEGRAPH OPERATION

Communication between ship and shore is carried out by the use of a pair of frequencies, one for transmission in each of the two directions, separated from each other by about 3 per cent. The specific frequencies which were first assigned by the Federal Radio Commission to the shore station and the Leviathan were in the ab­sence of any comprehensive wavelength plan for this new service necessarily chosen on more or less of a makeshift basis. The Commission has recently had under study the setting up of more adequate provisions

5 4 6 LYONS: R E D U C T I O N OF E D D Y C U R R E N T LOSSES Journal Α . I. Ε. E.

for ship-to-shore telephone channels, whereby it is hoped a series of frequencies may be designated for telephone service exclusively and whereby there may be established the relation between the telephone and the telegraph frequencies necessary for the avoidance of interference between the two services. Difficulties of fitting in the two services were encountered in the early work on the Leviathan and although the problem has not yet been worked out to final solution, sufficient progress has been made in cooperation with the engi­neers of the Radio Corporation of America, to enable the telegraph and telephone services to be conducted simultaneously without undue interference. The whole question of marine frequency allocations is in need of being further developed not merely on a national but also on an international basis.

TRANSMISSION R E S U L T S The transmission results of commercial service

which have been obtained with the SS. Leviathan on her first trip are summarized in Fig. 16. It will be noted that practically continuous 24-hour communication was maintained for distances within 1000 mi. of the shore, corresponding to two days out. The service at greater distances was more intermittent, due largely to the fact that during this first trip the effort was concen­trated on the more important nearer-in distances, and the ship was not prepared to transmit on frequencies above 8000 kc. The service proved to be much in demand by the passengers, as is indicated by the number of calls completed each day, particularly on the return trip. A like number of test and demonstration calls was made during the voyage.

A b r i d g m e n t o f

Reduction of Eddy Current Losses by the Inverted Turn Transposition and the Twisted Lead

Transposition BY JOHN M. LYONS*

Assoc ia te , Α . I . Ε . E .

Synopsis,—The first section of the paper contains a brief review of the general theory underlying the determination of extra copper losses in armature windings carrying alternating current. Simpli­fied methods of calculation are then described.

The second part extends the study of the inverted turn transposi­tion to the special case of three-phase windings, with two phases connected in series to form a single-phase winding and the third phase left idle. Formulas and tables are presented to show what reductions in copper losses may be expected for this connection, and

to aid in deciding what type of transposition is best for a given winding.

The final section of the paper deals with the twisted lead trans­position, and presents formulas and tables showing reductions in extra losses to be gained from this method of inversion and con­nection. Details of the derivations of the formulas and examples of the use of the twisted lead transposition are contained in appen­dixes at the end of the paper.

* * * * *

I . INTRODUCTION

THE problem of determining the extra copper losses in rectangular conductors composing the armature windings of large alternators has been covered in

detail in the well-known papers listed in the references. From these and many other investigations several methods have been adopted commercially for reducing the parasitic eddy current losses and the extra heating which they produce. The methods now in use group themselves into two general classes. One class includes transpositions of the conductor laminations in the slot, and the second includes inversions or twists of whole conductors or leads in the end portions. This paper is concerned only with the second class.

The inverted turn transposition, described by I . H.

"Turbine Generator Engg. Dept., General Electric Co., West Lynn, Mass.

Presented at the North Eastern District Meeting of the A. I.E. E., Springfield, Mass., May 7-10,1980. Complete copy upon request.

Summers 1 in a previous Institute paper, is now used to advantage on practically all multi-turn coils in large generators. The loss reductions to be expected from the use of this transposition in standard two-phase and three-phase windings can be found from the for­mulas and tables contained in Mr. Summers' paper.

This transposition can also be applied equally well to various special windings, and one purpose of this paper is to extend the general treatment to cover one such case. The winding to be considered is the standard three-phase winding in which two-phases are connected in series to form a single-phase winding, and the third phase is left idle. Formulas and tables for finding loss reductions in such a case are given herein, while the general method of calculating these factors with the latest simplifications is detailed in the complete paper.

1. Reduction of Armature Copper Losses, by I. H. Summers Α . I. Ε. E..TRANS., Vol. 4 6 , 1 9 2 7 , p. 1 0 1 .

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