US1733583A - Submarine carrier telegraphy - Google Patents

Description

Oct. 29, 1929. A. M, CURTIS SUBMARINE CARRIER TELEGRAPHY Filed Feb. 2, 1927 Patented Oct. 29, 1929 lUNITED STATES PATENT OFFICE AUSTEN M. CURTIS, EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, F NEW YORK, N. Y., A CORPORATION 0F NEW 'YORK SUBMARINE CARRIER TELEGRAPHY Application led February 2, 1927. Serial No. 165,282,

This invention relates to carrier telegraph systems and more particularly to systems employing a submarine cable.

The primary object of the invention is to improve the operation of low frequency carrier telegraph receiving systems.

There are technical difficulties involved in duplex transmission of ordinary code impulses over long loaded submarine cables.

Since duplex operation has many advantages it has been proposed to employ carrier currents of a rat er igh frequency i. e., the range of 150 to 400 cycles per second or considerably higher. Such frequencies are spoken of as rather high in the sense that they are high for long submarine cable telegraphy. Viewed from the standpoint of carrier currents they are low frequencies, especially s ince only a few cycles will constitute a signal element.

2o Such a system has been found to necessitate the use of highly selective receiving circuits in order to prevet the outgoing carrier Waves from affecting the receiver. Since the use of such frequencies will permit the use of several channels, if the selectivity is sufficiently good, the invention also relates to plural channel submarine cable operation, either one-way or duplex. Therefore in reading this specification it is to be kept in mind that the receiving circuit referred to is especially adaptable for use in duplex or plural channel submarine cable telegraph operation. Consequently, a further object of the invention is to improve the operation of duplex and plural channel submarine cable telegraph systems.

A preferred embodiment of the invention, specifically stated, resides in the submarine cable receiving system herein disclosed for the reception of carrier waves of relatively 4o" low frequenc but higher than the fre- "quency at which communication is to be effected, modulated for transmission of code signals. It comprises a sharply tuned selecting circuit having inductance and capacity elements, to select waves of a comparatively narrow band of frequencies. Circuits of this type do not permit the carrier current to build up quickly and therefore distortion is introduced in the signals in a manner analogous to the effect of a long cable on ordinary direct current sending and, as heretofore used, puts a limit to the speed of signaling. The distorted signals are then passed through an amplifier and a rectifier into a filter Where the higher frequency carrier and harmonics are entirely suppressed. The relatively lower frequency signals which pass through the filter retain their distorted wave shape and in order to give these signals a more nearly squaretopped form such as they had when originally transmitted, a shaping network is provided in the circuit connecting the filter with a recording device. A type preferred in this invention comprises an arrangement in which a path containing a variable inductance and a variable resistance in series is connected across the output terminals of the filter and between this path and a terminal of the recording de vice is serially inserted a condenser shunted by a resistance followed by a serially arranged resistance.

The invention will be more particularly de- Ascribed in connection with the accompanying drawing, wherein Fig. 1 is a circuit diagram of a receiving system embodying the invention; and Fig. 2 is a diagram of the form of signaling waves before and after the Waves pass through the shaping network at the receiving station.

In Fig. 1 modulated Waves of a plurality of frequencies are transmitted through several channels over submarine cable l. Circuit 2 represents a single section highly selective selecting circuit which is adapted to be sharply tuned to waves of one of these carrier frequencies. This resonant circuit is regarded as typical of any one of a number of highly selective circuits of one or more sections adapted to transmit narrow ranges of frequencies, and is connected to the input circuit of a vacuum tube amplifier 3. The cathode of this tube is connected to the anode through the usual plate, or B, battery 4 and the primary winding of a transformer 5. The secondary winding of the transformer is or connected across the receiving circuit which extends at one side through a cathode and an anode of a rectifier 6 to a high frequency cut-off filter 7 and at the other side directly to the filter. The amplifier is used to magni- 1 fv theniodulated waves selected by the resonant circuit beforerectication, because the oscillations of the waves in the resonant circuit may be too weak to operate the rectifier. It has been found in a series of tests that if the resonant circuit is tuned sharply enough so that the low frequency and high frequency channels ,are satisfactorily separated, the

high frequency dots run together at a speed of about ten words a minute and therefore in order to avoid this condition and raise the speed of signa-ling, the carrier Wave is rectified. The rectified current is then passed through an integrating device such as the filter 7 wherein the carrier and the harmonies are suppressed and the direct current signaling waves are permitted to continue on to a receiving instrument 8 Which may be an oscillograph, siphon recorder, or any of the recording or indicating types adapted for telegraph reception. If the direct current signaling waves were to be recorded on the receiving instrument immediately upon leaving the filter, the record Would show the signals rounded off in a manner analogous to the signals received over a long cable with ordinary direct current sending, because the distortion introduced by the resonant circuit is carried through the amplifier, rectifier and filter. This distortion is corrected by passing the signaling current, after it leaves the filter, through a shaping network consisting of a variable inductance 9 and a variable resistance 10 connected in series andarranged as a shunt path across the output circuit of the filter, and a shunted condenser 1l and a resistance l2 arranged in series in one side of the output circuit and connected between the shunt path and the receiving instrument.

In Fig. 2 A represents a graph of the signal Wave When it is recorded immediately after passing through the filter and B represents the same Wave after it has passed through the shaping network and is recorded. Assuming, that the curves are plotted to the same scale it will be noted the Waves in passing through the shaping network, under- -go a considerable reduction in amplitude, but this reduction is anticipated an-d provided for in the amplifier.

This invention has been used satisfactorily in tests made over a 1500 mile dummy loaded cable in Which the highest carrier frequency employed was approximately 150 cycles, al-

though in cables of somewhat shorter lengths,

the carrier frequency may be as high as 400 cycles. The carrier current was modulated by direct current signals which effected a frequency range in the combined current of about one-third of the frequency of the carrier. It has also been tested and operated satisfactorily on an actual submarine cable about 2,000 miles long.

It is to be understood that selecting circuits other than a circuit containing single inductance and capacity elements may be used in place of circuit 2, and thatvarious other modifications of the system herein shown and described may be made without departing from the spirit and scope of the invention. Itis applicable also to considerably higher carrier frequencies than those herein mentioned.

l'Vhat is claimed is:

l. A low frequency carrier submarine telegraph system comprising a highly selective receiving circuit for selecting a received modulated carrier current, means including an integrating device to separate the low frequency signaling components from the carrier components of said current, and a network upon which said low frequency Waves are impressed to correct for the distorition introduced in the modulated carrier current by said selective circuit, said network including series capacity and shunt impedance.

2. A low frequency carrier submarine telegraph system comprising a highly selective receiving circuit for selecting a received modulated carrier current, means including an integrating device to separate the low frequency signaling components from the carrier components of said current, a low frequency translating device, a line for supplying said low frequency Waves to said translating device, and a. network upon which said low frequency Waves are impressed to correct for the distortion of the modulated carrier current of the selective circuit, said network consisting of an inductance and a resistance in series with each other and in shunt to said line and ca acity in series with the line.

l. A low frequency carrier submarine telegraph system comprising a highlyselectiveV receiving circuit for selecting a received modulated carrier current, means including an integrating device to separate the low frequency signaling components from the carrier components of said current, a low frequency translating device, a line for supplying said 10W frequency Waves to said translating device, a network upon which said low frequency Waves are impressed to correct for the distortion of the modulated carrier current of the selective circuit, said network comprising an inductance and a resistance in series With each other and in shunt to said line, a condenser in series With said line,`a resistance in shunt to said condenser and a second resistance in series with said line.

4. A carrier cable telegraph system comprising aline for transmitting a plurality of low frequency signal-modulated carrier currents, a receiving circuit for selecting one of said modulatedcurrents, means including an integrating device for deriving the si al component from said selected modulated current, and a network proportioned to attenuate the lower frequencies of said signal component more than the higher frequencies and to thereby correct for distoration introduced in said selected modulated current by said receiving circuit, said network including shunt inductance and series capacity and resistance.

5. A. carrier submarine telegraph system comprising a submarine cable for transmitting a plurality of low frequenc signalmodulated carrier currents, a hig ly selective receiving circuit for selecting one of said modulated currents, means including an integratin device for deriving the signal component irom said modulated current, a low frequency translating device, a circuit for supplying said signal component to said translating device,a network between said integrating and said translating devices proportioned to distort said signal component and correct for distortion of said selected modulated current, said network comprising an inductance and a resistance in series with each other and in shunt to the second mentioned circuit, a condenser in series with the second mentioned circuit, and a resistance in shunt to said condenser.

In witness whereoLI hereunto subscribe my name this 31st day of January, A. D.

AUSTEN M. CURTIS.

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