US1714567A - Telegraph circuit - Google Patents

Description

H. NYQUIST May 28, 1929.

TELEGRAPH CIRCUIT Filed Dec. 9, 1927 IN V EN TOR.

\@,X I I I E 8 BY W 1 ATTORNEY Patented May Y NYQUIST, or iarnnnuan, NEW anasnr, Assienon 'ro AMERICAN 'rnnnrnonn I aria? ant oas s.

\ AND TELEGRAPH COMPANY, A CORPOTION E NEW Y0.

TELEGRAPH CIRCUIT.

Application filed December 9, 1927. Serial No. 238,803.

This invention relates to telegraph systems, and more particularly to improvements in a method of and means for insuring symmetrical signals and, hence, lack of distortion in the loop circuits of such systems.

It has been found that it is a common experience with telegraph subscribers loops that the wave shape is not the same on opening as it is on closing the subscribers key.

This lack of symmetry gives rise to distortion of the signals transmitted by the subscriber and in some instances it has beenfound necessar to go to considerable lengths to obviate t ese effects. It is the primary object of this invention to present and illustrate a method for insuring symmetrical signals in tele raph subscribers loop circuits. The met 0d of the arrangements of the invention comprises so constructing the loop circuit that its impedance as seen from the subscrib ers key is a constant resistance at all fre quencies. It will be seen from the discussion hereinafter given that this will result in symmetrical signals in the loop circuit. Other objects and features of the invention will appear more fully from the detailed description of the invention hereinafter iven. The invention may be more fully understood from the following description, together with the accompanyin drawing, in

the Figures 1 to 8, inclusive, ot which the invention is illustrated. Figs. 1, 2oand 8 are schematic showings of telegraph loop circuits embodying the principles of the invention. Figs. 3, 4, 5, 6 and 7 are curves showing the wave shape of the signals. Like reference characters have been utilized to denote like parts in all of the figures.

In Fig. 1 is shown symbolically a telegra h loop circuit comprising-the battery B, key and inductance L to represent the inductance of a series relay, or sounder. To illustrate the method of the invention, which consists in so constructing the loop that its impedance as seen from the subscribers key is a constant resistance at all frequencies, it has been assumed that all the reactances in the loop'are negligible except inductances of series relays or sounders. Furthermore, only one such series relay, as illustrated by the inductance L is shown. The individual relays or sounders will now be equipped with compensating shunts. For example, let a given relay have the inductance L and the resistance 1'. It may be convenient as a preliminary to add a resist'ance as shown in series to bring the total reslstance up to B. When the shunt which is connected in parallel with the combination of relay and resistance consists of a condenser and resistance in series, the resistance is given the value It and the condenser the value C. The impedance of branch LR as seen from key K is ZLR and the impedance of branch GR is,

- a E" to The impedance of the combination as seen from K would be symmetrical in shape, reference is had to Fig. 2. In the loop of Fig. 2, the opening of key K efiects the instantaneous insertion of a resistanceless battery B into the circuit whose voltage is so chosen as to bring the current to zero. This is true because since the circuit looks like a resistance at this point, there are no transients in the battery branch, or in other Words, that portion of the circuit external to points A and B. Furthermore, the closing of the key K removes this battery. Accordingly, in the loop circuit of Fig. 2, considered external to the points A and B, the opening and closing of the key is equivalent to varying the potential in a constant impedance circult in equal and opposite steps and will give .rise to a symmetrical wave of the shape shown in Fig. 3. It is obvious that in the loop of Fig. 1, considered external to points A and B, the openingand closing of key K is equivalent to the operation already described with respect to Fig. 2 in that it will also give rise to a symmetrical wave of the shape of the curve of Fig. 3. Accordingly, the two loop circuits external to the points A and B are equivalent.

Considering that branch of the loop in Fig. 2 between the points A and B designated b LR, it will be seen that the closing of key l results in applying a positive potential across terminals A and B. This would give rise to a wave in branch LR of the form shown by the curve of Fig. 4. The application of a negative, instead of a positive, potential across terminals A and B would obviously give rise to a wave of the same form but in reverse direction, .as shown by the curve of Fig. 5. Let us assume a direct current I flowing through the branch LB- due to a positive potential across terminals A and B in Fig. 2. If we now, without removing this positive potential, apply an equal negative potential by closing key K in Fig. 2 at the time indicated by point P, the wave shape will be illustrated by the curve of Fig. 6. This curve is obviously of the same form as that of Fig. 5 except that it starts from I instead of zero. The continued opening and closing of key K would give rise to a signal wave of the form illustrated in Fig. 7, in which the building up of the wave is symmetrical to its decay. In other words, the opening and closing of the key in Fig. 2, which is equivalent to varying the potential in equal and opposite steps in the loop circuit which has been made of constant impedance will give rise to a symmetrlcal wave.

It has been pointed out heretofore that the two loop circuits of Figs. 1 and 2 considered external to points A and B are equivalent. But the two loop circuits between points .A and B are identical with each other. Accordingly, as they are equivalent outside of points and B and are identical between points A and B, the operation between points A and B must be the same. Accordingly, the operation of key K of Fig. 1 will give rise to a wave of the form shown in Fig. 7, in

which the building up of the wave is symmetrical to its decay. In other words, the wave shape of the signals in the relays will be symmetrical and distortion will be obviated.

It is pointed out that the above discussion has dealt with only one relay or sounder such as illustrated by the inductance L..

However, if a plurality of relays or sounders existed, each would be provided with a compensating shunt comprising a condenser and a resistance so that the impedance would equal a constant resistance at all frequencies.

It might be desirable to make certain adustments in thatportion of the loop looking in the other direction from the key K, such as to the left, so that the impedance looking in this direction might be equal to a constant resistance at all frequencies. Accordingly, reference may be had to Fig. 8. In this loop circuit, an inductance L is shown. This might represent the sending relay. The equivalent capacity between conductors may be termed C. The d. c. conductor resistance the spirit of the invention as defined by the appended claims. 1

What is claimed is:

1. The method of insuring symmetrical signal waves in telegraph circuits, which comprises constructing the circuit so that its impedance as seen from the telegraph key or sending contacts is a constant resistance at all frequencies.

2. A telegraph circuit comprising a key, a resistance and a relay having a certain inductance in series in said circuit, and a shunt circuit around said relay and resistance, said shunt including a condenser and a resistance, the values of said inductance and capacity and resistances being so chosen that the impedance of the combination as seen from said key will equal a constant resistance at all frequencies.

3. A telegraph circuit comprising a ke a resistance B and a relay having an in uctance L in series in said circuit, and a shunt circuit around said relay and resistance, said shunt including a condenser C and a resistance R, the values of C, L and B being so chosen that L/U=R 4:. The method of insuring symmetrical signal waves in telegraph circuits, which comprises constructing the circuit so that its impedance as seen from a telegraph key or sending contacts in either direction is a constant resistance at all frequencies.

In testimony whereof, I have signed my name to this specification this 7th day of December, 1927.

HARRY NYQUIST.

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