US1556321A - High-frequency multiplex signaling system - Google Patents

Description

Oct. 6, 1925. 1,556,321 1. ESPENSCHIED HIGH FREQUENCY MULTIPLE SIGNALING SYSTEM ginal Filed Sent. 30. 1919 ave "01 filfsp ensdlkd 3:51 abhor/14 Patented e. 6,1925.

UNITED STATES PATENT OFFICE.

LLOYD nsrnascmn, 0F QUIIIS, NEW YORK, ASSIGHOB '1'0 AMERICAN TELEPHONE LID TELEGRAPH column, A COBIOBATIOH OF NEW YORK.

mGH-FBEQUBIGY IULTIIILEX SIGITAIJNG SYSTEI.

(Mgiaal application fled September 80, 1919, Serial Io. 827,801. Divided and this application fled April a, 1:21. Serial Io. mass.

To all whom it may concern:

Be it known that I, Lnoro Esrnuscnmo, residing at Queens, in the county of Queens and State of New York. have invented cerl tain Improvements in High-Frequency Multiplex Signaling Systems, of which the fol lowing is a specification.

This invention relates to high frequency multiplex signaling system and more particularly to a terminal circuit arrangement embod the use of amplifiers adapted to 'ampli the side band and the carrier frequency oscillations received by the said terminal circuit. I

This application is a. division of my cogznding application, Serial No. 327501 filed ptember 30, 1919, entitled High frequency multiplex signaling system.

The broad object of the invention is to improve the transmission eflicicncy and the transmission quality of carrier current circuits. One feature is the provision of a carrier current amplifier for improving the transmission efliciency of the carrier circuit.

35 A further object of the invention is to provide means whereby the ratio of the unmodulated carrier current transmitted over the system to the modulated or side band component may be controlled for the purpose of insuring good quality in the carrier transmission circuit.

A comprehensive understanding of the invention will be facilitated by recognizing that in the ordinary form of carrier current transmission represented by radio, there are involved really two channels, one the unmodulated carrier current which is transmitted over the system at the original car rier frequency and the other the modulated or side hand component which is at a frequency differing from the original carrier frequency by an amount corresponding to the signaling frequency. These two channels are commonly treated in radio, for example, as a single channel, and at the receiving end are fed unseparated into the detector. The detecting action obtains, however, only by virtue of modulation between, that is, the beating together of, the currents of the two channels, the carrier and one or both side bands. The present invention is concerned with carrier current systems, both wire and wirelem, wherein the carrier is transmitted directly along with the side bands as per ordinary radio practice, as distlngulshed from the type of carrier system first employed for multiplex service over wires wherein the carrier channel is suppressed at the sending end and resupplied at the receiving end by .a control system.

One feature of the invention resides in the use of an am lifier in the high frequenc part of the circuit which amplifies simu taneously both the carrier and the side band currents. A given amplification inserted in this manner in the hlgh frequency circuit results in a twofold amplification of the detected current by virtue of the fact that the amplitude of the detected current is a function of the product of the amplitudes of th carrier and the side band currents.

It has been found that for the obtaining of good quality in carrier telephone transmission, it is necessary that the carrier supply current be large compared with the side band currents. This relation is necessary in order that in detection or demodulation, the product term of carrier and side band, representing the desired detected current of signaling frequency, be large in amplitude compared with the other product terms such as those resulting from modulation between the two side bands or between the component currents of one side band, which currents represent undesired detected currents tending to interfere with and depreciate the quality of the transmission. A further feature of the invention is the provision of means whereby the carrier and the side bands may be amplified in difierent proportions, that is, the ratio of the amplitudes of the to the side band currents may be varied for the purpose of improving quality in the manner indicated. This is accomplished by combining with the high frequency amplifying apparatus, selective circuits whi discriminate as between the carrier frequency and the side band frequency.

The drawing shows the application of the invention to a terminal circuit of the type characterized by a single translating circuit adapted to modulate and demod ate the outgoing and incoming currents. In the figure L represents the high frequency line over which it may be assumed that currents of the frequency n and n-f are being received. These frequencies are impressed by the transformer T upon the input circuit 1.

- the common conductor of the duplex modulating and demodulating device MD,. As. sociated with the high frequency output branch 2 is a high frequency band filter F F and F represent low frequency filters which are adapted to transmit currents of the signaling frequency. The mode of operation of this circuit is as follows: Let it be assumed that the carrier frequency at and a band of frequencies represented by n-f, are being received over the line L from the circuit at the opposite end of the said line, and are being. impressed upon the receiving branch 1 of the terminal circuit shown in the figure. The band of frequencies represented by n-f will pass through the filter F and will be impressed by the transformer T upon the modulating and demodulating device MD,. The carrier frequency at will be selectively amplified by the amplifier A and the amplified oscillations of this frequency will be impressed upon the translating device MD The low frequency signaling current resulting from demodulation will be impressed by the transformer T upon the output side of the terminal circuit and passing through the low frequency filter F will be impressed upon the low frequency signaling circuit L The low frequency signalng currents set up in the circuit L by the low frequency signaling apparatus associated therewith will be impressed upon the input branch 4 of the transmitting path and p ssing through the low frequency filter F, will be impressed upon the translating circuit by the transformer T These low frequency currents will modulate the amplified high frequency carrier current impres ed upon the translating circuit by the amplifier A and the modulated high frequency current resulting therefrom will be impressed upon the output circu t by the transformer T9. These modulated high freuency oscillations will pass through the hi h frequency band filter F and over the transmission line L,.

It will be seen therefore that by means of he arrangement shown in the figure the unmodulated carrier oscillations which are simultaneously transmitted together with one or more of the side bands based upon this carrier frequency may be separated from the said band or hands in the receiving branch of the terminal circuit and may be amplified separately from the side bands and impressed upon a translating circuit common to the transmitting and receiving paths of the terminal circuits.

It will furthermore be seen that bysuitable adjustment of the amplifier A, the relative amplitudes of the carrier oscillations and the side hand oscillations may be controlled. It will also be seen that by means of the balanced duplex translating circuit oscillations of the carrier frequency are suppressed therein and do not pass through the transformer T Consequently this tends to reduce the possibility of singing in case the balancing networks did not exactly bala'ncetheir corresponding line circuits. Although this invention is disclosed as embodied in a wire signaling circuit it is to be understood that it is equally applicable to radio transmission systems.

Furthermore, although this invention has been shown as embodied in certain specific formor arrangement of parts, it is to be understood that it may be embodied in other and differentforms and arrangements without departing from the spirit and scope of the appended claims.

What is claimed is: v

1. In a signaling system adapted for the transmission and reception of high frequency signals, the method which consists in simultaneously receiving from a common medium modulated high frequency oscillations and unmodulated high frequency oscillations, separating the two types of oscillations, amplifying the unmodulated type, and detecting the modulated oscillations by means of the amplified unmodulated oscillations.

2. In a signaling system adapted for the transmission and reception of high frequency signals, the method for improving the quality of detection for signals which consists in simultaneously receiving from a common medium modulated and unmodulated carrier currents, selectively separating the said modulated and unmodulated currents, amplifying the unmodulated carrier current, to a definite degree, depending on the amplitude of the modulated current, and detecting the modulated current by means of the amplified carrier current.

3. In a signaling system adapted for the transmission and reception of high frequency signals, the method for improving the quality of detection of signals which consists in simultaneously receiving from a common medium modulated and unmodulated carrier currents, selectively separating the said modulated and unmodulated currents, amplifying the unmodulated carrier current to a definite degree, depending upon the amplitude of the modulated current, detecting the signaling component of the modulated current by means of the amplified carrier current, suppressing the unmodulated carrier current and transmitting the detected current.

.4. In a signaling system adapted for the transmission and reception of high frequency signals, the method which consists in simultaneously receiving low frequency signaling Variations and unmodulated high frequency oscillations, amplifying the said oscillations, modulating the amplified oscillations by means of said variations, suppressing the unmodulated high frequency oscillations and transmitting the modulated high frequency oscillations.

5. In a signaling system, the combination with two line" circuits one of which has a source of unmodulated carrier current associated therewith of a four-wire connecting circuit having atranslating circuit associated therewith comprising means to modulate and demodulate impressed oscillations, filters arranged in the t'wo-wire branches of the four-wire circuit so as to provide proper paths for the transmitted and received currents and a by-pass circuit connected with one of said two-wire branches having a filter and an amplifier associated therewith adapted to select and amplify the unmodulated carrier current and means to impress said amplified carrier current upon the said translatin g circuit.

6. In a signaling system, a combination of two line circuits, one of which has a source of carrier current associated therewith and a four-wire connecting circuit characterized by a translating circuit common to the transmitting and receiving paths of the four-wire circuit and having means to modulate and demodulate the currents flowing through said transmitting and receiving paths, and further characterized by means to select and amplify the carrier frequency current before impressing it upon the said translating circuit.

7-. In a signaling system, the combination of two line circuits, having connected therewith sources of low frequency and high frequency currents respectively and a four-wire 8. In a signaling system, the combination of two line circuits each having sources of current connected thereto and having networks individual thereto adapted to balance said lines, a four-wire connecting circuit electrically related to said line circuits by conjugate transformers, a translating circuit bridged across the two-wire branches of the four-wire circuit, common to the trans mittin and receiving paths of the fourwire clrcuit, low pass and high frequency band filters in each of the said two-wire branches, and a by-pass circuit connecting one of said twofwire-branches and said translating circuit and having means to select and amplify currents from one of said "sources and to impress the amplified currents on said translating circuit.

9. In a high frequency signaling system,

the combination of a receiving circuit adapted for the reception of oscillations of the side band frequencies and oscillations of the carrier frequency, a detector, means for selectingand amplifying oscillations of the carrier frequency to the exclusion of the side band frequencies and means for impressing simultaneously upon the said detector oscillations of the side band frequencies and amplified oscillations of the carrier frequency.

In testimony whereof, I have signed my name to this specification this 7th day of April 1921.

LLOYD ESPENSCHIED.

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