US1838268A

US1838268A - Biased carrier telegraph system

Info

Publication number: US1838268A
Application number: US475266A
Authority: US
Inventors: Ladner Henry; Welch Paul Vincent
Original assignee: American Telephone and Telegraph Co Inc
Current assignee: AT&T Corp
Priority date: 1930-08-14
Filing date: 1930-08-14
Publication date: 1931-12-29
Anticipated expiration: 1948-12-29

Description

Dec. 29, 193i. I ,H. LADNER ET AL 1,838,268

BIASED CARRIER TELEGRAPH SYSTEM Filed Aug. 14, 1930 INVENTORS BY W ATTORNEY mission line.

Patented Dec. 29, 1931 UNITED STATES PATENT OFFICE HENRY mm, or JERSEY CITY, amw JERSEY, AND PAUL vmciiirr WELCH, or BROOKLYN, NEW Yonx, ASSIGNORS '1'0 imnioAn 'rmirrnoim Am) 'rnnnomn OOMPANY, A oo ironA'rioiw or new YORK BIASED CARRIER TELEGRAPH SYSTEM Application tiled August 14, 1980. Serial ll'o. 475,266.

This inventionrelates to a biased carrier telegraph system adapted for diplex signal ing, and has for its object that of sending twotelegraph carrier frequency messages simultaneously with the same carrier frequency and inthe same direction over one trans- The invention will be better understood by reference to'the following specification and the accompanying drawings, inwhich Figure 1 shows one circuit connection for carrying out the invention; Fig. 2 gives in more detail a specific receiver adapted for use in Fig. 1; Fig. 3 shows the potential or bias of the carrier wave under different signaling conditions; and Fig. 4 shows the current an voltage relations in a detector of the kind shown in Fig. 2.

Referring more specifically to Fig. 1, there is shown at O a generator of carrier oscillations of any suitable frequency. This oscillator is connected to a line L by means of a transformer T. Associated with one side of the line is a keying device 1 and with the other side of the line a similar keying device 2. The upper contacts of these keys are connected with the midpoint of the secondary of transformer T in such manner that both sides of the line are thus connected to a point of zero or neutral potential. The lower contact of key 1 is connected through a battery 6 to one end of the secondary of the transformer, and the corresponding contact of key 2 is connected through a battery e to the other end of the transformer secondary;

ing a detecting device D in series with a relay, which relay may itself be a sounder 'or may be a device for controlling a receiving loop.

When the key 1 is operated, thus coming in contact with its lower contact, it impresses I on the line the voltage of the battery c and one-half the A. C. voltage induced in the secondary of the transformer. The detector D is so adjusted by some suitable bias that it becomes operative on the depression of ke 1 .by virtue of the battery e and the A. C. in-

duced in series with it. The detector D on the other hand, is not rendered operative by such voltage. Upon the depression of key 2 event that both keys are operated simultaneously, the batteries 6 and 6 neutralize each others efiect, but the complete voltage of the secondary of the transformer is now 1mpressed across the line and will be of such magnitude as torender both detectors responsive. v

This particular operation of the detectors will be made more evident by reference to Fig. 2 in which the detectors are shown as of the vacuum tube type comprising a tube with a filament, a plate and a grid. In the grid circuit of D is placed a battery 0 with its negative pole connected to the grid and adjusted to any suitable value, such as the cutofi value of the plate supply. Similarly, the detector D has in its grid circuit a battery e with its negative terminal connected to the grid and of such value as to bring this detector also to some definite operating point, such as the cut-ofi' value of the plate current. In the output .circuit of the detector D is connected a relay 6, and similarly, in the output circuit of D is connected a relay 7.

The operation of the system will be made more evident by reference to Figs. 3 and 4.- Thus, from Fig. 3 it will be evident that when key 1 is depressed there is impressed across the detector D the voltage 6 and one-half of the A. C. voltage of the transformer, so that the actual instantaneous Voltage across the detector I) is that corresponding to the portion a of Fig. 3. On the depression of age of battery e, is such that the operatin point of the tube is brought to the cut-o value N, and the voltage of e may suitably be made one-half of this so that when key 1 is depressed the D. C. voltage of the grid of D is one-half the cut-off value. Superposed on this grid, then, is the voltage corresponding to a, which will give rise to a current component in the output of the detector of sufficient value to operate the relay 6, the

instantaneous value of this current being represented by the portion I,

When the key 2 alone is depressed the instantaneous voltage of the grid of D is shown by the portion 6 of Fig. 4 and since this is at all times more negative than the cut-off value of the tube, no current will flow through the plate circuit of the tube and this portion would be represented'by 1 of Fig. 4. In the event, however, that both keys are depressed the batteries a and e neutralize each other but the A. C. voltage across each of the detectors is doubled and, as shown in Fig. 4, the grid takes on periodically large enough a potential to permit flow of current through the plate circuit, giving an instantaneous plate current represented by I which is sulfic'ient to operate the relay 6. l

The operation of the detector D is similar in every respect, but being connected in the reverse direction it is apparent that there will be no operation of D on the. depression of key 1, but on thedepression of key 2 the potential of the grid under the action of the attery a and one-half the A. C. voltage of the transformer will be such as to give rise to a periodic current in the output of the detector D of sufficient value to operate the relay 7. On the simultaneous operation of thetwo keys the detector D will again be rendered operative, all in a manner precisely as explained in connection with D From the above description it will be seen that we are enabled to carry on two simultaneous telegraph messages on a single carrier frequency and in the same direction with no interference of the messages, eachreceiver acting as though it were alone across the line,

' thus yielding a diplex carrier frequency teleexample, it would not be necessary to have the detector tubes biased to exactly the cut- 01f value but this bias might be somewhat greater or somewhat smaller without affecting the operationof the system. Also, it is to be understoodthat other than vacuum tube detecting devices might be used, either electrical or mechanical, but possessing characteristics which would yield substantially the same results as described above.

What isclaimed is:

7 1. In a carrier frequency telegraph system, the method of transmitting two messages simultaneously in the same direction which consists inactively biasing the line in one direction for one message and in the opposite direction for the other message.

2. In a signaling system, the method of transmitting two messa es simultaneously in the same direction whic consists in actively biasing the line in one direction for one message and in the opposite direction for the other message, the two biasings neutralizing when transmitting both; messages.

3. In a carrier,frequency telegraph system, a transmission line, ,a source of carrier frequency, a keying device on each side of the line, and circult connections such that when one ke is depressed a D. C. voltage plus one-hal of the carrier frequency voltage is impressed onthe line and when the v other key is depressed a reverse D. C. voltage plus one-half the carrier frequenc voltage is im ressed on the line and when 'oth' keys are epressed the D. C. voltages neutralize and the full carrier frequency voltage is im-- pressed on the line.

4. In a signaling system, a transmission line, a source of carrier frequency, two keythe ingdevices, and means for impressin ion carrier frequency voltage with an alding n a D. C. voltage for one message and the same carrier frequency voltage with an opposite D. C. voltage for the other message.

5. In a carrier frequency telegraph system, a transmission line, a source of carrier frequency, two keying devices and means for impressing across said line a ortion of the carrier frequency voltage wit a D. C. bias for one message and a portion of the carrier frequency with an opposite D. C. bias for the other message.

6. In a carrier frequency telegraph system, a transmission line, a source of carrier frequency, two keying devices, and means for impressing carrier frequency voltage with a D. C. bias for one message and carrier frequency voltage with an opposite D. C. bias for the other message, the D. C. biases neutralizing and the carrier frequency voltages adding for the two messages together.

7. In a carrier frequency teletgraph system,

a transmission line, a source 0- a single carrler frequency, two keying devices, means for impressing said carrier frequency voltage with an aiding D. C. voltage for one message,

and said carrier frequency voltage with an opposite D. C. voltage for the other message, and two receiving devices across the line at the remote end, one responsive to the one keying deviceand the'other to the other keying device.

8. In a carrier frequency telegraph system, a transmission line, a source of carrier frequency, two keying devices, means for impressing carrier frequency voltage with a 'D. G. bias for one message and carrier frequency voltage with an opposite D. C. bias for the other message, and two detector receiving device's across the line at the receiving'end connected in reverse direction and each biased to be unresponsive to voltage below a minimum value.

9. In'a carrier frequency telegraph system, a transmission line, a source of carrier frequency, two keying devices at the transmitting end, two detector receiving devices at the receiving end connected across the line in reverse direction and each biased to be normally unresponsive, a biasing means associated with each key opposite and substantially equal to that associated with the corresponding receiving device whereby when one key is operated the bias for one detector is neutralized and when the other key is operated the bias for the other detector is neutralized. a

In testimony whereof, we have signed our names to this specification this sixth day of August, 1930.

v HENRY LADNER.

PAUL VINCENT WELCH.