US1468687A

US1468687A - Transmission regulation

Info

Publication number: US1468687A
Application number: US558447A
Authority: US
Inventors: Herman A Affel
Original assignee: American Telephone and Telegraph Co Inc
Current assignee: AT&T Corp
Priority date: 1922-05-04
Filing date: 1922-05-04
Publication date: 1923-09-25
Anticipated expiration: 1940-09-25

Description

H. A. AFFEL.

TRANSMISSION REGULATION Sa 25,1923 L46$9687 Fi\led May 4, 1922 Sheets-Sheet 1 mzm ZHM AAA AAAAA M Sept. 25, m3.

. H. A. AFFEL,

TRANSMI S S I O N REGULATION Filed May 4;, 1922 2 Sheets-Sheet 2 Kelqfi? releases 0107122129 )1 22 n v 5 v A TTORNEY Patented Sept, 25, E923.

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w methods and arrangements for controllingthe transmission over such circuits. I

In a wirecarrier or radio telephone system, the fluctuations in attenuation of the transmissionmedium or line produce correl flsp'onding variations in the over-all transmission equivalent of the voice circuit. In one well known type of carrier system, the carrier-.freque'ncy itself is suppressed at the modulator end in connection with each which is relatively low, is transmitted to the receiving end of the circuit, and by harmonic regeneration, caused to produce a s chronous carrier supply for the respec- 't1ve demodulator's. The carrier supply in this case 'is transmitteol at a ire uency which. is substantially independent 0 ordinary line attenuation. fluctuations and the variation in line attenuation at the side band frequency causes a "directly roportional variation in the over-all equivalent there being substantially no fluctuation oi the equivalent of the circuit due to the carrier component itself. 1

ever, in whicha carrier frequency is trans mitted along with the side'band tions may be even more; serious, since in t demodulation the resultant voice output may, for normal operationofi the demodulator, be proportional to the-product at the the modulated side band. It, therefore, the attenuationot the intervening line or other transmission-medium varies,

carrier and approximately the same variation'will take place for both the carrier andthe modulated side hand, i and the resultant voice circuit lji pr portionalfto the prod Application filed may 3, 1t22.- tlerlal l lo. 558,447.

at Brooklyn, in the county ofchannel, and the fundamental frequency,

With the type of carrier system, how-- of eachindividual channel, the transmission fluctuat 'of one transmission circuit of. a carrier telegraph system,

shown) not involved in the present not of these two factors, will be approximately doublegthat of the'line attenuation itself. i p

In accordance with the present invention, it is proposed to overcome the dificulties encountered in connection with transmission fluctuations. in the type of circuit in which the carrier frequency is transmitted along with the side band, by controlling some ele-" ment of the transmission'channel or circuit to vary the transmission of such element in accordance with the amplitude of the carrier frequency of the channel. 1 Preferably, the control thus exercised will be applied to an element in thereceiving channel at a receiving station by selecting the carrier frequency component, rectifying the selectedcomponent to produce a direct current whose amplitude will depend upon the transmission conditions to which the carrier has been subjected, and controllin the transmission element by the rectified current. The control exercised byfthe rectified current may be efiected either electrically or mechanically, but in the preferred form herein disclosed, a mechanical system is illustrated. v

The invention may now be more fully understood from the following description, when read in connection with the accompanying drawing, lFi res 1, 2 and 3 ct which show circuit iagrams' illustrating three difi'erent'lorms of the invention.

Referring to Fig. 1, so much of a carrier system is shown as is necessary to an understanding of the present invention. lln this figure,']ltl.| desi ates a receiving channel said channel being connected, other similar channels not too. common transmission e (not shown) over-which carrier frequencies are transmitted mitting channel is not together with illustrated-as it is invention. The receiving channel RL includes a band filter RF for selecting the desired side band and the corresponding carrier, a detector D and a receivingamp 1 lhe'corresponding trans fiafsarecentn J J may be of any well known type, such as a vacuum tube detector, and is adapted to detect the voice currents corresponding to the side band by beating the side band with the carrier. The recelvi'ng amplifier RA may be any well known type of amplifier,

but is illustrated as being a vacuum tube amplifier and is arranged to amplify the detected. voice currents as well as the unmodulated carrier appearing in the output circuit of the detector. receiving amplifier RA includes a transformer 11 by which the low frequency circuit 13 (which may be associated with a low frequency transmission line) is connected to the receiving channel.

'- the unmodulated carrier.

The circuit 13 includes a low-pass filter LPF b which voice frequency currents are selecte into said circuit to the exclusion of the higher frequency components such as The carrier frequency component may be selected by'means of a tuned circuit or filter 12 throu h which the carrier frequency is impresse upon a rectifier .R. The rectifier may be of any well lmowfln type but is illustrated as a vacuum tube arrangement adapted to translate the selected carrier component into a direct current. In systems of this type, this direct current is ordinarily used to control the operation of a si nal relay SR which is illustrated as being mcluded in the output circuit of the rectifier. This signal relay is adapted to operate a ringing signal when the carrier is interrupted at the sending -station, the interruption of the carrier (which is normally transmitted) resulting in the cessation of the flow of direct current in the output circuit of the rectifier.

- In thev present invention, this circuit is i also utilized to control the transmission eificiency of the receiving channel RL and for this purpose a polar relay PR is included in .the output circuit of the rectifier R. The polar relay PR may be arranged with its armature so biased that the direct current flowing in'the output circuit of the rectifier R, when the transmission efliciency of the transmitting medium is normal, will be just sufficient to hold the armature at a neutral point against the tension of the biasing means. An increase or decrease in the direct current, in response to an increase or decrease in theefficiency of the transmitting medium, will therefore result in shifting the X armature tov its upper or lower contact.

:Inorder to adjust the transmission efliclency of the receiving channel RL, the potentlometer 14 is included in the receiving channel upon the input side of thedetector vD. This potentiometer may be adjusted by means of an arm 15 which may be rotated by a motor 16. The motor-16 may be energreed fromthe power mains 17 and its circuits are-controlled by means of relays 18 The output circuit of the.

raeaeev and 19, so that when either of these relays is operated, the armature circuit is closed, and

when one of the relays is operated, the field circuit is completed in one direction, while when the other relay is operated, the field circuit is completed in the opposite direction. These relays are controlled by the contacts rier frequency assigned to the receiving channel RL will be selected by the band filter BF and will be transmitted from the po-' tentiometer 14 to the input circuit of the detector D. The-detector D detects the voice currents corresponding to the sideband by beating the side band with the carrier, and the detected voice currents,- together with the unmodulated carrier. component, are impressed upon the amplifier RA; When these currents are' amplified the low frequency voice currents pass through the transformer 11 and the low-pass filter LPF to the lowvfrequency line. The carrier frequency com- 'ponent, however, is selected by the filter or select ng device 12 and impressed upon the rectifier R. The carrier frequency is transmitted at all times, regardless of whether or not a side band is being transmitted, and the output direct current of the rectifier R will correspond in amplitude to the amplitude of the carrier. The amplitude of the carrier will in turn depend uponthe transmitting conditions of the transmitting medium so that the rectified current flowing through the polar relay PR will fluctuate in amplitude as the efiiciency of the transmitting medium fluctuates.

If the efliciency of the transmitting meof the, polar relay PR, sothat if the armadium is decreased,the'armature of the polar relay PR will be shifted to one of its contacts. say the lower contact, thereby energizing the relay 19 which completes the field and armature circuits of the motor 16.110 cause the motor to rotate in one direction and adjust the potentiometer 14; to gradually increase the'transmissi'on" to the; detector, until acondition is reached such that the amplitude of the carrier. frequency will be sufiicient to produce a rectified. current in the rectifier R, whose strength. will be of such value as to again shift the armatureof' the polar relay PR to neutral position, w ereupon the operation of the motor will neeaeer:

cease; The adjustment of the. i-"ission of thereceiving channel Rh is now such-that the change'in transmission of the transmitting niedlum has been compensatedtor, and

the low'frequencyvoice currents detected by the detector will be of normal am litude.

ill" the efliciency oi the transmitting rue-i diuin is increased, the-unmodulatcd carrier component would increase in amplitude, thereby causing a greater direct current to flow through the polar relay PR and this would shift the armature to the other contact and energize the relay 18, causing the motor 16 to rotate in the. opposite direction and adjust the potentiometer it so that the transmission efliciency to the receivin channel BL is gradually decreased. This results in a-gradual decreasing otthe amplitude of the carrier frequency until a point is reached Where the direct current flowing a potentiometer 20 included between the detector D and the receiving amplifier RA, as

- shown in Fig. 2. llhe net result rvill be the same as in the case of Fig. l, aid in this case, the adiustment of the potentiometer, instead of afi'ecting the carrier and the side hand before detection, produces a change in the amplitude of the unmodulated carrier component of the detector, and of the low trequenc voice signal. The change in the amplitu e of the. unmodulated carrier component in the detector, in response to adustment of the otentiometer, causes the current through t e relay PR to vary in amplitude until the current becomes normal,

after which. the adjustment ceases. lhe

amplitude otthe low frequency voice cur rent component-is adjusted by the potentiometer at the same time, so that when the final adjustment is reached, the amplitude F of the voicgiirurrent will be normal.

llnstead' iof arranging the circuit'so that the rectified direct current will be autoerratically restored-t0 its normal value by the adyusting means thesystem may be so arranged that the direct current will at all time depend in amplitude upon the. amphtude of the "carrier frequency, and the a u tit-t i ur nt-me; b utilized to ady just the transmission eciency ot the cir onl Such an-jarrangementisillustrated H1 ig'. 3. "ln thiegcasat. output circuit cuitfor the lovv frequency voice. currents f h m ds ti.- us s a polarized relay PR, includesaseries of marg nal cold-V521,;22and 23. The contacts of these. relays. are arranged to control a shunt circuit 2% including resistances 25 26. and .27 brid across the low frequency circuit 13; Whenthe rectified current in the output circuit of the rectified it falls below a certain minimum value, which for purposm of illustration may be taken as. El

nails, none of therelays 21., 22 and 23 is energized; lit. the "rectified current has a value betvveenfi mils and say-5 mils, only the. role 21 ,is energized. lit-the rectified current as a value between 5 mils-and say mils, relays 21 and 22 are energized, and for a value oi rectified current greater than '2' mils, all three relays will be energized.

Suppose new the trammitting el'liciency oi the transmitting medium is so low that the rectified carrier component flowing through the

relays

21, 22 and 23 is less than 33 mils. All three

relays

21, 22 and 23 will be deener 'ized and the: shunt path 24: will be opened at the contact of the relay 21, so that the full energy of the detected voice currents will be transmitted through the low-pass filter arr into the circuit 13. it

the transmission eficiency or the medium is increased, so that die rectified carrier com onent attains a value oi over 3 mils but ess than 5 mils, relay 21 Will be energized and relays 22, and 23 deenergized. Under these conditions, the bridge 24 will be closed at the contact of relay 21 and

resistances

25, 26 and 27 will be included in the bridge. This will shunt a certain pro portion otthe energy of the low frequency voice currents into the bridge, thereby reducing the voice energy transmitted to the circuit 13 to the noal value.

It the eliiciency of the transmitting me dium. is still further increased, so that the rectified current attains a value between 5 mils and 7 mils, relays 21 and 22 Will be actuated and relay 23 will be deenergized.

Bela 22 short-circuits resistance 25, so that the ridge 2t'will now be closed through

resistances

26 and 27 in series. Under these conditions, a still greater proportion of the voice current energy will be shunted through the bridge, so that the voice current energy transmitted to the clrcuit it Will be substantially normal. ll the amplitude or the carrier frequency is still furtherincreascd'by an increase in eciency of the transmitting medium, the rectified current ma attain a value of 7 mils or over, in WlllCll case the relay. 23 will be: energlaed, in addition to relays 21.1 and '22.: Bethunsistances25" and .2dtvvill nova bershort-cir.=.

the circuit 13 substantial eater proportion of the voice energy abridge and maintaining the energy hhviousthat the general principles herein disclosed-may be embodied in many other organizations widely difi'erent from those illustrated, without departing from the spirit of the invention as defined from the selected carrier component a current having characteristics depending upon the transmission conditions to which the carrier has been subjected, and a mechanical switching device operated by the current carrier is transmitted alon with the side thus produced to adjust a circuit element of the receiving channel in accordance with the characteristics of thercurrent thus produced to compensate for the change in eiiiciency of the transmitting medium.

2. In a system for controlling transmission, a transmitting medium over which the carrier is transmitted together with the side band, the transmission efliciency of said medium being variable under different conditions, a receiving channel including a detector upon which the side band and carrier may be simultaneously impressed to detect the low frequency signaling currents represented by the side band, means to select from the output of the detector the unmodul'atd carrier frequency component, means to produce from the selected carrier component a direct current whose amplitude depends upon, the transmission conditions to which the carrier has been subjected, and mechanical switching means operated by the direct current for adjusting a circuit element of the receiving channel in accordance with the amplitude of said direct current to compensate for the change eiiiciency of-the transmitting medium.

3. In a system for controlling transmission, a transmitting medium over which the band, the transmission e clency of said medium being variable under different conditions, a receiving channel includin a detector upon which the carrier and si e band may be simultaneously impressed, means for selecting the carrier, means for producing from the carrier a current whose characteristics depend upon the transmission condi-=.

tions to which the carrier has been subjected,

- afcircuit element in said receiving channel and mechanical switching means controlled in accordance" with the characteristicsbf band, the transmiss'on eflicienc having an amplitude depending upon the means? said current to adjust said circuitelement to compensate for the change, in efficiency of the transmitting medium. a. In a system for controlling transmission, a transmitting medium over which the carrier is transmitted. along with the side band, the transmission efficiency cf "said medium being. variable under difierent conditions, a receiving channel u on which the carrier and side band *maye impressed,- means for selecting the carrier, a rectifying device to rectify the selected carrier to pro- 1 duce a direct current having an amplitude depending upon the transmission conditions 8'03 to which the carrier has been subjected, a circuit element in said receiving channei, and mechanical switching means controlled in accordance with the amplitudeof the rectified current to adjust said circuit ele-- ment to compensate for therhangein efiiciency of the transmitting-medium.- g

5. In a system for controll'ng'transmis sion, a transmitting medium over which the carrier is transmitted alon with the side band, the transmissione ciency of said medium being variable underdifierent conditions, a receiving channel includin a detector upon which the carrier and si e band may be impressed, means for selecting the carrier, means for producing -from these lected carrier a current whose characteristics depend upon thetransmission conditions to which the carrier has been subjected, a potentiometer in said receivingchannel, and means for adjusting-said potentiometerain accordance with the characteristics of the i current produced from the" selected carrier to com ensate for thechange -'in-transmission e ciency of the transmitting medium.

. 6. Ina system for controlling transmission, a transmitting medium over which the carrier is transmitted along with the side of said medium being variable under di erent conditions, a receiving channel including a. de'-" tector upon which the carrier'and side band may be impressed,.means for' selecting-"the carrier a rectifying device to rectify the selecte carrier to produce a direct current transmission conditions to which the carrier has been subjected,- a potentiometer in said receiving channel, and means to adjust said 12d for the change in efliciency of the transmit potentiometer in accordance with the amplitude of the rectified current to compensate ting medium.

7. In a system tor -controlling}transmis= sion, a transmitting medium over which the carrier is transmitted together-withthe side band, the transmission eficiency of said medium being variable under different conditions, a receivin channel including a deteptor upon whic the. side band may impressed together with the carrier to detect and essee the low frequency signaling currents represented by the side band, means to select the unmodulated carrier component from the output of said detector, means to produce from said selected carrier component a direct current Whose amplitude depends upon the transmission conditions to which the carrier has been subjected a potentiometer in said receiving chennei, and means to adjust seid potentiometer in accordance with the amplitude of'said direct current to compensate for the change in transmission eficiency of said transmitting medium.

lntestimony whereof, I have signed my name to this specification this 3rd day of Mey, 1922,

HERMAN A. AFFEL.