US1784176A - Equalization for carrier systems - Google Patents

Description

I Dec. 9, v CARPE EQUALIZATION FOR CARRIER SYSTEMS File d Jyily 2, 1929 INVENTOR mmlilg ATTORN EY Patented Dec. 9, 1930 UNITED STATES PATENT OFFICE" 7 ALLEN CAB-PE, or NEW YORK, N. Y., ASSIGNOR 'ro AMERICAN 'rELnrnoNE AND TELE- own column, a CORPORATION or NEW Your:

EQUALIZATION son canamn sYsrmrs Application filed Jul 2, 1929.: serial 1e. 375,463.

This invention relates to the equalization of carrier systems so that'all channels will be brought to substantially a common transmission level, the common level being maintained constant. with changes in transmission con ditions. 7.

In a transmission conductors, the attenuation of the current valies-with frequency, the attenuation increasing as the frequency goes up. Thisbecomes a very series matter in a multiplex carrier system, as the channels having the higher carrier frequencies will be much more attenuated than the channels transmitting at lower carrier frequencies. If, in such a system, the attenuation is plotted against frequency,-the

resultant curve will,ewithin reasonable fre- 'quency limits, approximate a straight line having a slope depending upon the character of the circuit and-the existing transmission conditions. This slope varies with different transmission conditions, and the variation in slope will, moreover, be different for different types of circuits.

a The need of compensation so that the transmissionat a given frequency is maintained at a desired level, and further compensation so that all'channels are brought at all times to thatlevel, and means for accomplishing this, are given" in the patent of Green, No. 1,743,132, January '14, 1930. More specifically, in that application use is made of two pilot "frequencies existing on the pilot line at all timesfone of these being usedto control the gain introduced by repeaters,and the two together being used difierentially to correct for changes in the slope of the attenuation characteristics of the "line.

This invention is an improvement on the method and means of the application referred to-and has for its object the simplification of the circuit. arrangements and the elimination and consolidation of certain of the otherwise necessary apparatus. More particularly in my invention 1' make use of two pilot frequencies, but instead of sending these out on the pilot line continuously, I send themalternately. In view of this, there need be but one oscillator at the transmitting "GP system employing line frequency changed periodically in anypredeterminedmanner. Also, atithe further .terminal of the transmission line or at the intermediate repeater stations, it is sufiicient to have onereceiving circuit for both of these frequencies, the receiver at any onestation I being alternately altered, as by tuning, to be receptivefor the onepilot frequency or the other. By suitable switching mechanism, then, it is possible to operate on gain control mechanism or on equalization control mechanism atone time or another, depending upon which particular pilot frequency is being re- 7 ceived at'the v moment.

The figure of the accompanying drawing shows a circuit arrangement for carrying out my invention. Referring more particularly to this drawing, there s shown a transmitting station A and an intermediate repeater station B, the two being connected by a transmission line, this line continuing to subsequent repeater stations. At the station A, there will be associated apparatus for transmitting messages over the transmission line L and apparatus'for receiving messages coming over this same line. Also, at this station, there is connected to the line an oscillator O the frequency of which may be altered periodically in any suitable manner, such as, for example, by connecting and disconnecting the condenser C in parallel with the condenser 0,. This change may be produced in any desired manner, such as by the'rotation of a make-and-break device 11 which in turn may be operated by clock mechanism. The

frequency at which this change occurs may be varied'over a wide range, but might very well be of the-order of once in five minutes As a result, there is impressed on the line L alternately twofrequencies f1 and f pref- At the station B, transmitting apparatus is associated with the line as at the station A. In addition, in the transmission line itself, there is introduced a potentiometer which controls the gain of the repeater end,- this oscillatofbemg adapted to have its Also in-the input circuit of the repeater R there is introduced an equalizer E by means of which an adjustable loss may be introduced, which is a function of the frequency. By suitable adjustment, then, of the potentiometer GP, it is possible to bring the level of transmission at a givenfrequency f to any desired value, and, by adjustment of the equalizer, it is possible to bring the level of all frequencies in the desired frequency band to the same level, all as described in the above-mentioned patent of Green.

Associated with the output of the repeater R is a branch circuit 13 associated with .the rectifier-amplifier 15. This association may be obtained in any of a number of ways, and, in the drawing, is shown as an inductive coupling from the coil 16 to the coil 17. Associated with the coil 17 are condensers 18 and 19, the one of these, 18,'being permanently connected in parallel, yielding a circuit tuned to the frequency f 0f the oscillator O. The condenser 19 is connected in parallel to 18 periodically in, a manner hereafter described, and, when so connected, yields a circuit tuned to the frequency f Associated with the output of the rectifier 15 is a galvanometer 21, of any suitable form such as the well known DArsonval galvanometer. The pointer 22 of this galvanometer will take up a position depending upon the size of the current flowing through the galvanometer 21, and, as it changes its position, may pass over strips 24, 25 and 26, which-bars are movable and adjacent to contacts 27. 28 and 29. Adjacent to the pointer is a bar 30 which, by some independent mechanism, may be pressed against the pointer 22 which in turn bears on'the contact strips 24, 25 or 26 to close contact with 27, 28 or 29, depending upon the position of the pointer 22.

Associated with the contactmembers 25 and 28 is a relay circuit including the battery 32 and relay 33. The armature 34 of this relay engages with a ratch t wheel 36 to step this around for a purpose to be described later.

The contact members 24 and 27' are associated; with a relay circuit 40 includingthe battery 42 and the relays 43 and a l, these latter being connected inparallel. The circuit also includes a switching member 46 constituting an armatureof a relay 38 which latter is included in circuit with the battery and. theratchet wheel 36.

In a similar manner, the contact members 26 and 29are associated with a relay circuit 50 including the battery 52 and the parallel relays 53 and 54, and including, also, a switching member 56-which constitutes a second, armature of: the relay 38. Finally, a third armature 59 of the relay 36 is used for connecting and disconnectingv the condenser 19.

The, relays. 4A and 54-v are used for controlling the gain control mechanism GCM which in turn is associated in any suitable manner with the potentiometer GP. The relay 44 operates on the potentiometer in a manner to increase the gain of the repeater, and the relay 54L operates to decrease this gain. Similarly, the relays 43 and 53 control the equalization control mechanism ECM to step the equalizer E in the one direction or the other.

The ratchet wheel 36 has its alternate teeth or segments connected to a common point, and by means of the battery 39 is used to control the relay 38. Thus, when the armature 34 is in contact with one of the segments just referred to, circuit for battery 39 will be closed and the relay 38 is operated. On the other alternate segments, however, circuit 39 will be broken.

The limits of motion of the pointer 22 are determined by stops 61 and 62, the stop 61 corresponding approximately to the position of the needle for Zero current through the galvanometer, whereas the stop 62 corresponds to approximately the maximum current which it is intended shall flow through the galvanometer. With this maximum current, the pointer 22 is still above the member 26 and in position to contact with that member upon the motion of the bar 30. The member 24, however, is fore-shortened so that the needle 22 is not in a position to contact with it if the current through the galvanometer falls below a certain specified minimum.

The methodof operation of the circuit will now be given. Consider the circuit to be adjusted initially for proper gain and proper equalization. In this invent, the current of either frequency f or f as taken off by the branch 13, is of such a magnitude as togive galvanometer current which will bring the needle 22 over the member 25 and periodically it will be pressed against themember 25 to close contact with 28, and thus the circuit of relay 33 will be closed. Each of these closures will cause the ratchet 36 to be movedone step and thus alternately opens. and closes'the circuit of relay 38.; This operation changes the tuning, whereuponthe needle goes to zero and awaits the next frequency. During this wait, nothing occurs, however, in the circuits 40 or 50, V

If, now, some change in the line. occurs so that the attenuation for the frequency f increases, then the current through the galvanometer 21 is below normal during the reception of this frequency f t It may be that it falls off suiiiciently to bring; the needle '22 above the member 24:. Let us consider this to occur while the relay 38 is operated, in which case the condenser 19 is connected in circuit andv the input, of the rectifier 15 is adjusted for reception of the frequency f Upon pressure of the bar 30 the circuit 40 is; closed at 24 and 27 tomake contact through let the relay 44 which then operates .GCMto step up the gain of the potentiometer GP. 1 It will be noted that during this time the circuit 50 cannot beoperated; As long as the needle 22 remains above the member-24, there will be an operation of the relay 44 and a correspondingjstepping up of the potentiometer each time thatthe bar 30 moves down to close :contact between 24 'and27, and, with each step thus made, the current through the galvanometer' 21 increases and finally the needle comes above the member 25. Upon the next movement'of the bar 30, .contactismade to operate the relay 33 which then moves the ratchet 36 one ste forward, disconnecting the relay 38 and re easing its armatures. Upon this movement, thecondenser 19 is disconnected and the input-of the rectifier 15 is now in tune for the frequency 72. If the frequency f is stillbeing given by theoscillator O, the current in the galvanometer willfail to practically zero value, and no operation of the circuits will occur. :In due course, however, the frequency of U willbe changed to f, and substantial current will now flow through the galvanometer 21, bringingtheneedle over, let us say, the member 24. If it stays over this member for an appreciable time, contact will be made through the pressure bar 30, thus closing the circuit 40 through the relay 43, thus stepping the equalizer control mechanism in such a direction as to increase the gain over the transmission line as a whole for the frequency f and step after step of this change will occur until the current for this frefrequency f brings the pointer 22 over the member 25, whereupon the ratchet 36 will be moved another step to operate the relay 37 and make it possible to close circuits for the relays 44 or 54 which control GCM. In the event, however, that the gain for this frequency f, is already too large, the pointer 22 will quickly move over the member 26, and, in due course, the pressure bar 30 will close the circuit 50 through the relay 53 which will then operate on ECM in the reverse direction to decrease the gain for this particular frequency.

From the above, it is seen that through the mechanism as thus described it is possible to control the gain either upwards or downwards for the frequency f,, bringing this to a predetermined desired level and also to equalize the gain for the frequency f either by upward or downward adjustment to bring it to the same level as the gain for the frequency f If these two frequencies are chosen at appropriate points in the total frequency range over which equalization is desired, then the departure from the desired gain for all the frequencies in this band will be substantially zero.

It should be noted that no synchronization is required between the operation at the translaced in the speech ranges,

mitter which changes the frequency from f to f and the motion of the ratchet 36; This is'made possible by the fact that no adjustments at the station B will take place if the iwrrent-throthgh the galvanometer'is below a quency for which the rectifier 15 is at the time tuned; This circuit will therefore await theproper change at the oscillator O and will "then resume operation and adjust the current in' the galvanometer 21 to the normal value, operating, now, upon equalization if the previous adjustment was a gain, or vice versa;

When thisvalue is reached, the cycle'of operation will be repeated.

,Ainother advantage of having a minimum value of current below which the needle 22 makes no contacts is that of protection of the apparatus from falsesignals, it being assumed that these false signals would never attain a value comparable to those necessary for the operation of the mechanism as a whole. fv While reference has been made to the-control mechanism for one ,pair'oftwires only, it is to be understood that if there are aplurality of such pairs of wires, each having a repeater R the gain of which-is to be controlled, the one set of controls GCM I and ECM may be used for all such re aters.

This invention has been descrifid specifically with reference to carrier frequency signaling but it is equally applicable for signaling in the normal telephone range, the two pilot frequencies selected being suitably "It willbe evident that many modifications and ch ng s m y e in the details of this i i withoutd parting from the. spirit of the invention,

For instance, instead of using inlays, it wouldbe possible to carry outthe changes with motor apparatus, habit is t be unders ood that these and oth v iat-ions cemewith u he s p f hi iin entio VVhatiS claimed is: Y v 1. In a 'm'ultivfrequencytern,"a transmission line, the method of equalilation of the transmission over arange of; frequencies, which consists in transmitting two pilot frequencies alternately, observing the amplitudes of these after transmission, adjustingthe gain for all frequencies in accordance with and byone of these observations, and adjusting the frequency equalization in accordance with and by theother observation to make the transmission equivalent of the system the same at all frequencies.

2. In a multiffrequencysignaling system,

a transmission line, means for transmitting over the line a plurality of pilot frequencies in sequence, means at a repeater intfor observing the amplitude of the received pilot requ ncies, a d-me ns con rolledhy in- I transmission syscoming pilot signals for introducing gain or loss in proportion to these amplitudes to bring the levelof transmission for the clifferent frequencies to a desired value.

' 3. In a multi-frequency signaling system, a transmission line, means for transmitting over the line a plurality of pilot frequencies in sequence, means at a repeater point for observing the amplitude of the received pilot frequencies, and means controlled by the pilot signals for introducing gain for all frequencies in accordance with the amplitude of one of the pilot frequencies, and for introducing equalization in proportion to another observed amplitude.

4. In a multi-frequency signaling system, a transmission line, means for transmitting over the line two pilot frequencies alternately,' means at a repeater point for observing the amplitude of the received pilot frequencies, and means for introducing gain for all frequencies in accordance with the amplitude of and controlled by one of the pilot frequencies, and means for introducing equalization in proportion to and controlled by the other observed amplitude.

5. In a multi-frequency signaling system, a transmission line, means for transmitting alternately over the line two pilot frequencies, means at a remote point on the line for receiving these, again control mechanism, and an equalization control mechanism, and means for automatically controlling these alternately in proportion to the amplitude of and by the received pilot frequencies.

6. In a multi-frequency signaling system, a transmission line, means for transmitting alternately over the line two pilot frequencies, means at a remotepoint on the line for receiving these, again control mechanism, and an equalization control mechanism, and means for automatically controlling these -alternately in proportion to the amplitude of the received pilot frequencies, the one mechanism being operated on and by receipt of the one pilot frequency, and theother on and by receipt of the other pilot frequency.

7. In a multi-frequency signaling system, a transmission line, means for transmitting alternately over the line two pilot frequencies, both in the signaling range, a receiver at a remote point on the line adapted to selectively receive one pilot frequency at a time, a gain control mechanism, and an equalization control mechanism, and circuits automatically controlled by the pilot signals for operating upon one mechanism or the other, depending upon the pilot frequency being received.

8. In a multi-frequency signaling system, a transmission line, means for transmitting alternately over the line two pilot frequencies, both in the signaling range, a receiver at a remote point on theline adapted to selectively receive one pilot frequency at a time,a gain control mechanism, and an equalization control mechanism, and circuits automatically controlled by the pilot signals for operating upon one mechanism or the other, depending upon the pilot frequency being received, and means for automatically shifting the receiver circuit to the other pilot frequency when proper adjustment has been made for the first frequency.

9. In a multi-frequency signaling system, a vtransmission line, means for transmitting alternately over the line two pilot frequencies, both in the signaling range, a receiving circuit adjusted at one time to effectively receive one pilot frequency, a galvanometer associated with the receiving circuit giving deflections in proportion to the amplitude of the received pilot frequency, and comprising three sets of contacts; one for increasing gain; one for decreasing gain; and one for shifting the receiver to the other pilot frequency when adjustment in accordance with the first pilot frequency has been made.

In testimony whereof, I have signed my name to this specification this 1st day of ALLEN CARPE.

' July, 1929.

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