US2514889A - Automatic code selector - Google Patents

Description

W. W. MCGQFFKN AUTOMATIC GODE SELECTOR Filed March 2&3, 1,947

POD

Patented July 11, 1950 AUTOMATIC CODE SELECTOR William Walter McGofln, New York, N. Y., as-

signor of one-fifth to S. S. Baker, New York, N. Y.

Application March 28, 1947, Serial No. 737,905

Claims.

This invention relates to an automatic selector of Morse code signals and more particularly to an apparatus designed to respond to a particular combination of such signals.

An object of this invention is to provide an apparatus which automatically responds to a predetermined series of dot and dash signals in such a way as to exclude any undesired combination and to perform this function in an accurate and simplified manner requiring a minimum of component parts. Thus, two relays perform four elements of timing, that is, dots, dashes, intervals and spaces, the time between the dots or dashes of a letter being designated as intervals and the time between letters being designated as spaces. rlhe provision of the two timing relays in the manner hereinafter described permits the apparatus to operate over a wide variation of code speeds so that when the apparatus is set for a particular speed, it will respond correctly although receiving code signals which depart considerably from the predetermined speed setting.

Another object of this invention is to provide an automatic code responding apparatus which re-sets itself to starting position upon` the reception of any undesired letter component, such a component comprising either a dot, dash, interval or space, andy wherein the apparatus remains re-set until another letter is started. Thus, a part of a letter will not restore the apparatus to activity whereby false responses are avoided.

Another object of this invention is to provide an apparatus wherein two mechanically ganged stepper switches respectively respond to dots and dashes on the one hand, and intervals and spaces on the other hand, so that such signal components may be swiftly and accurately recorded thereby permitting faster and simpliiied operation as well as adaptability to varied code speeds.

Still another object of this invention is to provide neutral reception means whereby the letters of a signal will be accepted and a response produced whether or not the proper spacing between such letters is observed. This feature is of considerable importance in S O S signals where the letters are often run together without including letter spaces. Under such varyingcondtions of sending, the apparatus will nevertheless respond so as to sound an alarm when an S O S signal is received.

A further object of this invention, as represented by a modification, is to provide an apparatus of this type which in large measure automatically adapts itself to the code speed of reception. This is accomplished by the use of a 55 represented by interval wire lll.

condenser element which sets the delay time of a relay so that the length of dashes, as opposed to dots, or, of spaces as opposed to intervals, can be measured. The condenser element is arranged to carry a charge which is inuenced by the rate of code speed so that the delay time or the relay is correspondingly iniiuenced and the signal characters are measured with the code speed as a factor.

This application is a continuation in part of my prior application Serial No. 550,862, liled October 28, 1944, now Patent Number 2,446,943.

Other objects of my invention will be apparent from the following description, it being understood that the above general statements of the objects of my invention are intended to describe and not limit it in any manner.

Fig. l is a schematic representation of the apparatus.

Fig. 2 is a schematic view illustrating a modied form of a delayed relay action.

The selector or stepper switch is of the dual type which, upon relay actuation, progressively wipes over a radially disposed series 0f contacts arranged at two levels designated herein as switchesl Sl and S2'. Switches Sl and S2 have their main or relay actuated arms ganged together for simultaneous movement. Each series of contacts are further selectively connected to one of a bank of switch positions, the selection depending upon the call which the apparatus is set up to respond. Thus, switch Sl, upon which the dots and dashes are set up, includes a series of selector arms 25-29 etc. which may be set on any one switch position of the switch banks such as bank l5. The arms 25-29 etc. are normally set on the release or reset circuit i6 and when they are switched to one of the other circuits as hereinafter set forth, they select the dots and dashes of the desired combination. Thus, if the first character of the predetermined call is a dot, the switch arm 25 is set at the first switch position of the bank l5. .lf a dash follows, the arm 2S is switched to the second switch position of bank Il.

During the operation of the apparatus, arm 3l of switch Sl successively wipes over the contacts 3|-36 etc. each of which are selectively connected to the reset, dot or dash circuits according to the predetermined call.

The selector arms Iil-I etc. of the banks of switches of switch S2 are progressively set at either interval or space, the normal position of arms IBG-|05 being at the interval position as Thus, switch series S2 is likewise provided with switch bank positions although each bank in series S2 has four positions as hereinafter set forth. The last space of the desired call is not set at space but the last used arm of the selector arms H-E05 etc. is set at alarm instead. It will be seen, therefore, that the call is set up by alternately proceeding from Si to S2, setting up the dot and dash characters on Si and the intervals and spaces at S2 where they occur in the call.

The dot and dash pulsations are appliedI through dash wire SS or dot wire S9 to the dot and dash interpreter circuit 22 which is identied in Fig. 1 by broken lines. This enables each incoming pulsation to be checked as to its dot or dash character and the stepper switch is advanced or reset according to the correspondence of such character with the predetermined and pre-set call.

Pulsing relay ll is connected to the output of an ordinary radio receiver which is tuned to the call frequency. Thus, pulsing relay tl delivers the received signal to the apparatus for interpretation and alarm action if indicated. In the initial action, each incoming pulsation is applied to main switch arm 3l through wiret and contacts 39 and l0 of pulsing relay i. If the incoming pulse coincides with the selector switch arm setting to the interpreter circuits, the arm 31 is allowed to advance through the action of the spring 42 which pulls the dog 43 against the action of the'return spring IM at thev end of the pulsationyStepper relay l5 is Yenergized by the relay il through the contact 39 so that relay 45 receives the same potential that is applied to arm 3l. This pulls armature 46 and drops the dog 43 into the next tooth. Then when relay l5 is released, dog 43 pulls the toothed wheel stepper :t1 forward a notch through the action of spring ft2. vanced position by pawl e8 whichis controlled by reset relay 63. Mechanical armature 46a operated by reset relay 03 and through the linkage shown simultaneously disengages the dog 03 and the pawl 48 allowing thespring ed to return to the stepper wheel lll to starting position.

Simultaneously with applying the pulsation to the relay 135, it is also applied to the dot and dash timing relay 50 through the contacts 65 and Relay 50 is'of the delayed closing type accom- Yplished by the condenser 5| which is effectively interposed across the relay winding when it is not energized. The time delay includes there- Vsistors EZ-Et either one of whichemay be switched into the circuit so as to regulate the delay time of relay 50. In a practical embodiment, resistors 52-5il were 5000, 10,000 and 15,000 ohms respectively, while condenser 5l was l0 microfarads. The winding of relay 50 was of 10,000 ohms direct current resistance. It is understood, of course,

Ithat the values of these elements will be selected according to the delay required. This time delay permits relay 50 to closeon a pulsation which is of dash length but not of dot length and the length is adjustable by selecting the proper resistor. When relay 50 -does close, condenser 5l is effectively removed from the coil E50-by opening of contacts 200 and 201 allowing the relay to have instantaneous release action. This release is eifected at the end of the pulsation because the return lead from lrelay 50 goes -through contact E5 ordinarily to arm 66 which is connected to the negative source ofspower through'contactf l'l of reset relay 68.Y However, when relay lll releases, contact l(i5 is removed from' the negative Stepper wheel il is maintained Ain its-ad- .which would make the delay time of coil 50 variable. In the modified embodiment, advantage is taken of this variation but in the instant embodiment, the condenser is substantially discharged Y at the end of each pulsation.

When arm 25 is set on the dot circuit, negative potential originating at electrical line Ll is applied to stepper arm 3l at the beginning of a pulsation and is immediately placed on relay arm 'i5 through the dot wire 69. Since relay 50 is fed with each pulsation through contact 65, it starts timing the pulsation but isnot allowed to close unlessy a dash is received. Therefore, if the inn coming signal is a dot and conforms to the switch Si setting, the reset is not operated and the stepper is advanced. However, if a dash'is receivedand relay 50 allowed to`close, relay arm 'l5 which has negative potential makes contact with relay arm i6 which in turn operates the stepper reset relay 60. As hereinafter explained, this causes the stepper switch to reset to starting position because the vproper sequence of call characters has not been observed. During the rst pulsation, therehas been no checking for interval or space as the stepper arm lll has not yet advanced to the first position. It will be observed that this second level of the stepper represented 'by switch S2, follows one step behind the dot and `dash level as represented by switch S l.

Dot and dash acceptance and rejection When selector arm 25 or any other selector arm of switch Sl is set to the dash circuit in accordance with the desired call, the negative potential is applied to Vand immediately operates relay 82 which is energized through contact 0l and armature of relay A50 and locked in closing position byrelay 85. In the drawing, those terminals marked are connected directly to lead line 88 which is normally connected to the negative source Ll through contacts |55 and I52as hereinafter described. Until the alarm is operated, line 381s always negative. The relay immediately closes on each incoming pulsation following a letter space and remains closed vuntil another letter space. is received. As will hereinafter be described, relay S5, which is delayed in-releasing, interprets, together with its .associated relay Sli), intervalA and space signal components and `provides anelectri-cal lock on relay through contacts 83 and 84.v

- Simultaneously with the operation of relay 82, the negative potential placed on the dash circuit wire 89, is applied through armature 9i and con- Relay ill being thus far closed, no potential gets to reset relayli. If the incoming pulsation is a dash sol that sufcient time is given relay 50 to close, contacts B and 8i are opened, which opens the groundcircuit of relay 82releasing it notwithstanding theprevious locking effect secured by armature and vcontact v96 through the contacts 83 and 84. However, if a dot is received and contacts 80 and lStare-not opened, relay 82 remains locked in 'through contacts 95 and 36l and contacts 83 and B4. Sinceafter the beginning of the pulsation,

negative potential was placed through contacts 9|-, 92 to contact` 93, the reset 68 is operated at the end of a dot pulsation when the armature 9'1 returns to normal position. This shows that at the beginning of a pulsation when SI. is on the dash circuit, relay 82 is immediately-closed and negative potential placed on contact 93 through contacts 9i and 92 so that if only a dot is received, the reset will be operated when armature Sl makes contact with $3 at the end of the dot pulsation. Since the negative potential supplied relay 32 is broken at the end of the dot pulsation, it is necessary to have an electrical lock on relay 82 through contacts 95 and 96 and through contacts 83 and 84 in orderto maintain negative potential on s3. Thisy negative potential will remain on 93 until a dash is received so that anything else than a dash will operate reset relay 68 and return the selector or stepper switch to starting position. When, however, a dash is received suicient to close relay 5?, contacts 8D and 8l are opened so that relay 82 releases removing the negative potential from contact 93., Hence, it can be seen that if the pulsation is of suiiicient length to constitute a dash, subsequent opening of relay 4I will not operate the resetting relay ES. The stepper, however, is operated at the end of the pulsation as hereinabove stated. The acceptance or rejection of dot character pulsations follows the explanation hereinabove set forth. Thus, with each advance of the stepper, the next pulsation is checked to see whether it corresponds to the original setting of the selector switch arms.

Interval and space acceptance and rejection Relay 4I supplies the potential of the incoming pulsations not only to the dot and dash relays but simultaneously to the interval and space relays contained in the interval and space interpreter circuits S8. Switches SI and S2 respectively represent a series of switches which are mounted on a common support. Switch arms 'I1 and 3l are ganged for simultaneous movement so that as arm 3l advances, arm 'l'I similarly advances along the successive switch contacts wil-|35 etc. Switch arm I7 is directly connected to the negative lead Li so that it has negative potential on it at all times. It will be observed that the initial position of switch arm Tl is at contact Hill which is not connected to any circuit inasmuch as spaces and intervals are checked only after the rst letter component, i. e. either a dot or dash, has been received so as to advance switch arm 'll to the switch contact Illl. At this point, timing for spaces and intervals commences. Assuming now that switch contact lill is on an interval circuit as illustrated in Fig. 1, negative potential is placed on contact IBS which is not engaged with armature I0? as relay 85, due to its delayed action is still closed for a period of time not exceeding interval time. Ii a space is made allowing relay 85 to release, armature Iill engages contact Iti completing the circuit to reset relay 68 bringing the selector relay to starting position by its spring return dit. Thus, it can be seen that if the selector switch S2 is placed at interval and a space sufficient to release relay 85 is received, the apparatus will reset and reject the call. lf the interval was not of sufficient duration to cause contacts IDS and lol to engage, then the next pulsation would maintain relay 85 energized through contact 8S so that reset potential would not get to the relay 63. When S2 is set to the space circuit, negative potential. is immediately placed on armature l Ii) which is not engaged with contact Ell because of the delayed release time of relay 535. Negative potential is, however, placed on contact Il2 and through armature IIS to contact IIll. Contact I I4 does not engage armature @l until the beginning of the next pulsation. If a space is not received, however, when the switch arm is set for space, as set forth, then relay S5 is not given suilicient time to drop out before the beginning of the next pulsation. It will be recalled that relay 90 is associated with relay S6, such relay SE is energized only when relay 85 is released. Therefore, contacts II2 and I iii are engaged and negative potential from the space circuit is on contact Il4 so that at the beginning of the next pulsation, armature 'l applies the potential to reset relay 68.

Ii, however, a space is made allowing relay c5 to drop out, engaging contacts Il@ and III, relay 9U is operated removing the negative potential from contact Iiil by opening the circuit at Il and H3. Thus, when a space is made when the switch is set for a space, there will be no rejection and the stepper arms will advance another step. It will be noted that when relay closes, it will electrically lock itself through contacts IE5 and IIi through arm II'I and contact H3 of relay iii. At the beginning of the next pulsation it is evident that engagement between contacts l iii and I I I would be broken by the operation of relay 5:5. This would release relay 9G which would operate the reset through the contacts ll2 and i it through the armature Ill and contact I it. it is necessary, however, that this is not effected and, accordingly, relay QG is locked so as to remain energized through its contact H5 and armature IIG which receives negative potential from the armature l il and contact lill. At the end of the pulsation, when armature lil' returns to normal position, the lock is broken, arm ll' advances to the next circuit position and timing procedure repeats for the next position.

It will be noted that the provision of switches SI and S2 as described, makes speciic wiring for a predetermined call unnecessary because the individual switch arms can be set as required for practically any condition. In the bank or switches of selector S2, each switch bank of four terminals has a neutral terminal which precedes the other switch positions. When a baril; switch arm is on the neutral position, any time between pulsations will be accepted whether it is en interval -or a space. It will be appreciated that the flexibility of the apparatus is considerably enhanced thereby. Two advantages of the neutral position are the following:

l. In S O S signals, the letters very often run together without regard to intervening spaces. Automatic transmitters of S O S signals usually run the letters thus together. Ii the `apparatus were set to receive a space between the letters, a rejection would be ei'iected and the apparatus `would not respond. However, using the neutral position between letters and intervals etween the letter components, the S 0 S will come through whether or not the letters are duly separated. It will further be observed that the event a space is received during part ci a letter, it will be rejected because the switch is at the interval setting.

2. Experienced radio operators of code transmission often run letters together which cannot possibly form a false letter. Thus, A and N yare never run together becausD tb ey would form Reset operation As the reception of the switch arms progresses, switch larms 3l and ll advance so as to wipe over the selector switch contacts. As hereinabove stated, if any improper letter component is received,A the spring 44| returns the toothed wheel and its switch arms to the home or initial position. The operation of the reset relay 68, which through its mechanical action accomplishes this, also carries electrical contact armatures |25 and |26 and contacts |21 and |28. Upon operation of the reset relay, armature |25 is disconnected from contact |21 which removes the negative potential from armature d and 66, thereby stopping all further operation of stepper relay 45 and timing relay U. This results because negative potential Awhich is on armature 40 from contact |21 ordinarily supplies closing potential for relay 56 as well as relay B5. However, after a release or reset has been effected, it is necessary to disable the apparatus until a space is received. Otherwise, the apparatus might reject part of a letter and then proceed on the next part as if that next part were a complete letter in itself. By requiring a space to be observed after each rejection, whole letter operation is assured. The disabling of the apparatus until a space is received is accomplished by means of the electrical lock on relay 68 through contacts |30, |3| of relay 85 which is itself slow to release and will not drop out until a letter space is made. Thus, when a rejection is made, all circuits save the relay 85 are disabled and the release of relay 85 starts the action again. This is accomplished by relay 68, contact |28 and armature |26, which provides an electrical lock on the reset relay `63 through armature |36 and contact |3| of relay 85. It will be remembered that relay 85 is maintained energized by means of the incoming pulsation through contact 86 and arm '31. When a sufficient letter space is made allowing relay 85 to release, armature |36 leaves contact |3| opening the electrical lock on relay 68 which also restores Iarmature |25 to contact with |27 which restores negative potential to armature lill. Thus, the next letter is ready to be checked since all circuits are in operation.

Alarm When the proper signal for which the apparatus is set up is received, the alarm bell |50 is sounded so as to provide an audible indication of the reception of a call. This is accomplished in the following manner:

Originally, when setting up the call on the selector switches, the last switch representing a letter space is set at the alarm contact instead of a space. This means that after the switch arms have progressed through the call, switch arm l1 with its negative potential Iwill be effectively applied to the alarm circuit, as represented by the switch contact |04 of the Switch S2 according to the set-up in Fis. 1.. Negative potential is applied to relay |5| through contacts |69 and |6| when relay falls out with the last letter space so as to attract the armatures |52 and |53 of relay |5|. Negative potential from lead L| is thereby applied through armature |53 to contact |54 so as to operate the bell |56. Simultaneously, attraction of armature |52 disconnects the negative potential from contact |55 which cuts off any further current to the apparatus. This stops all operation of the apparatus except for the relay |5| which is connected to the negative lead L| through selector switch arm 'Vl connected thereto. This connection is not shown on the drawing for purposes of clarity. The bell |50 lwill then continue to ring until manually operated reset switch |56 is closed. Manual operation of this switch applies the negative potential to reset relay 66 which thereupon closes and resets the stepper the same as resets are made by rejections. This returns arm ll to switch Contact lill) so as to remove the negative potential from the alarm circuit whereupon relay |5| is released and the bell stops ringing.

It Will be understood that the last letter must not be followed by a dot or dash as otherwise it would constitute a different letter for which the apparatus was not set. Therefore means are provided to reset the switches if a letter space is not made when arm 'il engages the alarm circuit and another dot or dash is added to the last character instead of a space. This is accomplished by setting the selector switch following the last dot or dash setting to the reset circuit which goes directly to relay 68. Thus, if another dot or dash is applied through the switch arm it will energize relay 68 so as to reset the stepper switches. In this event, no alarm will be sounded.

It will be recalled that resistors 525| are selected in order that the closing time of relay 56 may be predetermined depending upon Whether faster or slower speeds are to be accommodated. In the same manner, the interval interpreter circuit as represented by relay 65 is provided With timing condensers H5, ll and lll in order that the delay time oi' relay 'd5 may be adjusted. This is for the purpose of presetting the apparatus in accordance with the expected speed or" reception. lt is, of course, understood that the apparatus Will operate satisfactorily over a considerable ldeviation trom a predetermined setting. This is made possible by the delayed closing and releasing relays which start timing all pulsations as dots until they extend to dash length. In other words, a dot may be any length, however short, until it extends to dash length whereupon it is, of course, considered a dash, and a dash may be oi'- any length as long as it exceeds the dash time which is set by the resistors til-5s. Similarly, the interval time may be as long as desired until it becomes space time. This provides extremely wide variation in code speed reception since dashes are normally three times as long as intervals. The time delay relays are set to operate at va timing point one-third the normal dash length 'and one-third of' the letter space time so that a signal component which does not effect operation of the two timing relays is a dot or an interval respectively.

In a modified embodiment, I have devised means to render the apparatus substantially automatically responsive to the desired signal irrespective of any settings of relays in anticipation of code speed conditions. This is accomplished by selecting a value of resistor l2 which will delay the leakage time of the condenser 5|. Ordinarily, resistor l2 may be o l a value of 500 ohms, While 9 condenser is 10 mid. However, by increasing resistor 'l2 to a much higher value, i. e. approximately 500i) ohms, the discharging of the condenser 5i is determined by the operating speed of the pulsing relay il which effects continuous making and breaking ci the contacts 'I0 and If the operation is very fast, the condenser charge will not have an opportunity to leak ofi between pulsations and a partial charge will always remain thereon decreasing the delay time and increasing the closing speed of the relay 5i] to conform with the speed of the incoming signals. This action will render the dot and dash interpreter circuits automatically adaptable to varying speeds. It is also necessary to similarly control the space and interval time. Referring to Fig. 2, the required modification of the delayed release relay 85 is illustrated. The feature of adaptability is accomplished by inserting resistor |35 in series with condenser |85 across the relay winding so that the condenser is not immediately fully charged. In addition, contacts |81 and |88 are provided to short out resistor |35 when piusing relay 4| is released allows condenser |86 to hold relay 85 closed for the duration of time in proportion to the charge received through resistor |85 while relay il is closed. If the operation of relay 4| is fast, condenser |86 is correspondingly charged to a lesser degree which allows relay 85 to drop out more rapidly at signal interruptions, the term interruptions referring to either intervals or spaces.

While there has been described what at present is considered a preferred embodiment of the invention, it will be evident that many changes and modifications may be made therein without departing from its spirit. It is therefore aimed in the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.

I claim:

l. In a signalling system for identifying a transmission of Morse code letter pulsations constituting a desired call, the combination of an alarm, electrical circuit means to operate said alarm, a selector device operating to progress in steps from a starting position to a position where it closes said electrical circuit means when a complete predetermined transmission has been received, release relay means for returning said selector device to said starting position when an undesired call is received, said selector device comprising a first series oi switch elements for preselecting the desired dot and dash characters, a second series of switch elements for pre-selecting the space and interval interruptions and switch arm means for progressing along the respective series of switch elements as the proper pulsations from said transmission are applied to said system, a slow closing relay energized by said pulsations and operative to close when a pulsation of dash length is received, said release relay means being operated by said slow closing relay through said first series of switch elements according to the preselection o said dot and dash characters thereon, a slow releasing relay energized at each received pulsaticn and operative to open at a signal interruption of space length, said release relay means being operated by said slow releasing relay through said second series of switch elements according to the preselection of said space and interval interruptions thereon, nonmoperation of said slow closing and slow releasing relays respectively determining the dot and interval natures of a received pulsation, and said second series of switch elements including a neutral position by which its switch elements remain unconnected to either space or interval positions so as to prevent operation of said release relay means through said second series of switch elements.

2. In a signalling system for identifying a transmission of Morse code letter pulsations constituting a desired call, the combination of an alarm, electrical circuit means to operate said alarm, a'selector device operating to progress in steps from a starting position to a position where it closes said electrical circuit means when a complete predetermined transmission has been received, release relay means for returning said selector device to said starting position when an undesired call is received, said selector device coinprising a first series of switch elements for preselecting the desired dot and dash characters, a second series of switch elements for pre-selecting the space and interval interruptions and switch arm means for progressing along the respective series of switch elements as the proper pulsations from said transmission are applied to said system, a slow closing relay energized by said pulsations and operative to close when a pulsation of dash length is received, said release relay means being operated by said slow closing relay through said first series of switch elements according to the preselection or" said dot and dash characters thereon, a slow releasing relay energized at each received pulsation and operative to open at a signal interruption of space length, said release relay rneans being operated by said slow releasing relay through said second series of switch elements according to the preselection of said space and interval interruptions thereon, non-operation of said slow closing and slow releasing relays respectively determining the dot and interval natures of a received pulsation, said selector device including an actuating relay, said actuating relay being directly fed by said pulsations, a pair of contacts on said actuating relay, said pair of contacts being electrically interposed between said rst series of switch elements and said slow closing relay and being normally closed, said pair of contacts energizing said release relay when a dot is received when said first series of switch elements is set for dash operation.

3. Apparatus according to claim 2 and including a second pair of contacts on said actuating relay, said second pair of contacts being interposed between said iirst series of switch elements and said slow releasing relay and being normally open, said second pair of contacts energizing said release relay when an interval occurs when said first series of switch elements is set for space operation.

4. In a signalling system for identifying a transmission of Morse code letter pulsations constituting a desired call, the combination of an alarm, electrical circuit means to operate said alarm, a selector device operating to progress in steps from a starting position to a position where it closes electrical circuit means when a complete predetermined transmission has been received, release relay means for returning said selector device to said starting position when an undesired call is received, said selector device comprising a irst series of switch elements for pre-selecting the desired dot and dash characters, a second series of switch elements for pre-selecting the space and interval interruptions and switch arm means for progressing along the respective series of switch elements as the proper pulsations from said transmission are applied to said system, a

slow closing relay energized by said pulsations and operative to close when a pulsation of dash length is received,lsaid release relay means being operated by said slow closing relay through said rst series of switch elements according to the preselection of said dot and dash characters thereon, a slow releasing relay energized at each received pulsation and operative to open at a signal interruption of space length, said release relay means being operated by said slow releasing relay through said second series of switch elements according to the preselection of said space and interval interruptions thereon, non-operation of said slow closing and slow releasing relays respectively determining the dot and interval natures of a received pulsation, a condenser and resistor in the circuit of said slow closing relay for regulating its closing time, said slow closing relay including a normally closed pair of contacts connecting said condenser to the winding of said slow closing relay, operation of said slow closing relay opening said contacts so as to remove the condenser from the relay circuit and permit instantaneous release thereof.

5. In a signalling system for identifying a transmission of Morse code letter pulsations constituting a desired call, the combination of an alarm, electrical circuit means to operate said alarm, a selector device operating to progress in steps from a starting position to a position where it closes said electrical circuit means when a complete predetermined transmission has been received, release relay means for returning said selector device to said starting position when an undesired call is received, said selector device comprising a first series of switch elements for preselecting the desired dot and dash characters, a second series of switch elements for preselecting the space and interval interruptions and switch arm means for progressing along the respective series of switch elements as the proper pulsations from said transmission are yapplied to said system,

a slow closing relay energized by said pulsations and operative to close when a pulsation of dash length is received, said release relay means being operated by said slow closing relay through said rst series of switch elements according to the preselection of said dot and dash characters thereon, a slow releasing relay energized at each received pulsation and operative to open at a signal interruption of space length, said release relay means being operated by said slow releasing relay through said second series of switch elements according to the preselection of said space and interval interruptions thereon, non-operation of said slow closing and slow releasing relays respectively determining the dot and interval natures of a received pulsation, condensers in the circuits of said slow closing and slow releasing relays for determining the time constants of said slow closing and Slow releasing relays and means to feed said condensers by incoming pulsations so as to adjust the time constants of said slow closing and slow releasing relays according to the speed of incoming pulsations.

WILLIAM WALTER MCGOFFIN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,287,396 Morse Dec. 10, 1918 1,597,763 Chauveau Aug. 31, 1926 1,655,689 Chauveau Jan. 10, 1928 1,930,631 Thompson Oct. 17, 1933 2,334,574 Neiswnter Nov. 16, 1943 2,334,575 Neiswnter Nov. 16, 1943 2,446,943 McGon Aug. 10, 1948 FOREIGN PATENTS Number Country Date 555,664 Great Britain Sept. 1, 1943

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