US2264510A - Telegraph signaling system - Google Patents

Description

Dec. 2, 1941. J.vw. COX

TELEGRAPH SIGNALING SYSTEM Filed June 6, 1939 3 Sheets-Sheet l V INVENTOR. JOHN 7725M ATTORNEY Dec. 2, 1941. J. w. cox

TELEGRAPH SIGNALING SYSTEM Filed June 6, 1939 3 Sheets-Sheet 2 5 4 INVENTOR. I jmv M 60X BY. 7%

w m A Dec. 2, 1941. J. w. cox

TELEGRAPH SIGNALING SYSTEM Filed June 6, 1939 3 Sheets-Sheet 3 Q W I K .QukVQQQRW ATTORNEY.

Patented Dec. 2, 1941 TELEGRAPH SIGNALING. SXSTEM:

John W. Cox, Berkeley, Calif., 'assignor to Radio Corporation of America, a corporation of Delaware Application-June 6, 1939, Serial No..2!7 7,607

6Claims. v (Cl. 250-9) i cxpensive and the maintenance costs are; quite material.

It is:one obiect of my invention to devise a telegraph system for multiplex telegraphy that requires no synchronously running distributors at the transmitter and receiver.

Another object of the invention is to send messages by periodicallyinterrupting the carrier Wave by low 1 frequency alternations.

Another object ofthe invention is to simultaneously transmit a pluralityof signal messages by interrupting a carrier .wave to form mark and space. indications for each message andinterruptingv the mark indicationsfor each signal at apredeterminedlow frequency, the frequencies of interruption being. different for eachsignal message.

Another object of the inventionis to transmit a pluralityof 'messages withmark and space interruptionscof a carrier wave in which themarkingparts of the wave areinterrupted at a plurality of predetermined low frequencies and separating... the signal currents of the messages at the receiver by filtering.

Another object is. to transmit a .plurality of signal 'messages each acting on thesame carrier wave toform mark and space interruptions in which themarking Wave for each signal message is interrupted 'atapredetermined low frequency, the interrupting frequencie being different for eachsignal message.

Another'object is to'transmit a plurality of signal-messageseach alternately acting on the sameca-rrier'wave --to form mark 'and'space indications andinterrupting the marking portions of the wave at predetermined frequencies, there being-a diiferent frequency for each signal message and separating the signal messages by filters at the receiver.

Another'object of the invention is to assign a carrierwave successively toeach of a plurality of transmitting channelsand transmitting mark and space indications in the carrier wave while 55 interrupting. the marking; portion'of the wave at apredetermined low frequency the frequency of interruptions being different for each chann91.

Otherobjects will appear in the following. descriptiom. referencebeing had to the drawings, in which:

Figil is one form: of transmission system. for carrying out my invention. g t Fig. 2 is a modified form of transmissionrsys- Fig; 3.,is;a receiving system; for carrying out my'in-vention.

Fig. 4 is a series'of 'graphs showing a portion .of the carrierwavefor making the indications.v

Referring to Fig. 1, thelowfrequency oscillator consists of a condenser l havingone terminal connected to the negativeterminal of a battery 2.-'a'nd:the other one. connected to two adjustable resistances, 3'and 4 which are joined .to live'contacts 5 and 6 of well known perforated tape transmitters generally indicated at land 8. The tongue -9 of tape transmitter l is connected to segment. ID of a distributor or commutator H haying rotating brush I2; The brush l3 of this distributor is adjustably connected to potentiometer I4, l4, connected across battery 2; The tongue. l5" of relay 8 is connected to the remaining segment I 6 of the distributor; The distributor may be run at any desired speed by motor I! but it should have a frequency of interruption materially less than the frequency of the oscillations produced by the condenser l. A vacuum tube-type of distributor such as the multi-vibrator described'in patent to R. E. Mathes, No.

1,979,484, November 6, 1934, could also be used, as the invention is not dependent upon any particular type.

Neon or equivalenttube l8 is connected across condenser I through primary [9 of a transformer having secondary 20 connected to appropriate amplifiers 2!. The output lines ofthe amplifier are connectedto transformer 22 feeding the tone keyer stage 23. The secondary of this transformer is connected'between the grid 24 and filament 25 through'a negative bias 2B. The value of this bias is such that the tube-is blocked except during the positive alternation of the oscillations produced by the oscillating condenser I, as hereinafter described.

The plate 21 of the tone keyer stage 23 is coupled to transmitting keyer 28 through adjustable resistance 30 connected to positive terminal 3!; Tube'28 is blocked when-tube 23 conducts and it passes current when tube 23 is blocked. The plate 34 of keying stage 28 is connected to one end of resistance 35, the other end of the resistance being connected to positive terminal 36. The first mentioned end of resistance 35 is connected to the primary 3'! of a radio frequency transformer and the other end of this primary is connected to the plate 38 of modulator tube 39. The radio frequency oscillator 40 is connected between the grid 4| and filament 42 of tube 39 and the filament is connected to the negative terminal. The secondary 45 of the output transformer of tube 39 is connected to appropriate power amplifiers 46 and the output of the amplifiers is connected to an appropriate antenna 4'! and to ground.

The amplifiers 2| and 46 and the oscillator 40 may be of any type well known in the art and are therefore shown only in block diagram.

In the modified form of transmitting system shown in Fig. 2, I have omitted the distributor II and the perforated tape transmitter 'l and 8 are connected to individual oscillating condensers with their respective neon tubes l8. Devices similar to those of Fig. 1 have been given similar reference characters, so they need not be described in detail. The outputs of the oscillators [8 are connected through apparatus to and including the antenna that is exactly the same as shown in Fig. 1 and hence it has not been illustrated.

In the receiving circuit shown in Fig. 3 one antenna may be used but on account of general fading usually met with in radio systems, I prefer to use the diversity receiving antenna well known in the art and described in the patent of H. H. Beverage, No. 1,874,866, August 30, 1932. This may be generally described as consisting of three antennas 48, connected to three receivers 49, which may have well known receiving apparatus consisting of radio frequency tuning stages, heterodyne oscillators, intermediate frequency tuning stages and detectors which are well known in the art and hence have not been specifically illustrated. The receiving apparatus 49 is connected to appropriate amplifiers 59 and the amplifiers are connected to current or voltage limiters to further overcome the effects of fading. The limiters of the three circuits of the diversity receiving system are all similar and a description of one is sufficient. In the limiter, the grid 52 is connected through a negative bias of sufiicient value to cut off the desired part of the negative Wave in the limiting action. Resistance 54 in the plate circuit of this limiting tubeis of such value as to cut a similar part of the positive half cycle due to electron saturation efiects in the tube.

The output of each limiter is connected to mixing tubes 55 which may be the same in each of the three circuits. Each mixing tube has a negative bias 56 of such value as to block the tube for the negative half of the low frequency cycles of the condenser-neon tube oscillator and thus permit the passage only of the positive cycles. This prevents cancellation due to any difference in phase conditions of the currents in the three circuits and permits proper summation of the signals.

The plates 51 of the mixing or combining tubes are connected in parallel through the primary of a transformer 58 to positive terminal 59 and adjustable resistance 60 may be connected in this lead for obtaining the proper plate potential. The secondary of transformer 58 is connected in parallel to two limiters 6i and 6| and the output of each limiter is connected to band pass filters 63 and 63, one of these filters, say 63, being adjusted to pass one of the low frequencies, say, that controlled by perforated tape transmitter I, and the other one, 63' being adjusted to pass the low frequency controlled by the other perforated tape transmitter 8. The output of the band pass filter 63 feeds into rectifier 64 and the rectified output passes through smoothing filter 65 and is impressed across the grid filament circuit of coupling tube 66.

The output of the band pass filter 63 passes similarly through rectifier 54, smoothing filter and coupling tube 65. The output of coupling tubes 66 and 66' feed into a signal regenerating circuit shown as the well known locking circuit 51, 61' of the patent to Finch, No. 1,844,- 950, February 16, 1932. The regenerated signals from the locking circuits pass into utilization devices such as recorders 68 and 68' of any kind.

The limiters BI and El may be like the limiters 5| or they may be of any other type. The band pass filters 63, B3, are well known in the art and need not be illustrated or described except to say that it is preferable to design these filters with a narrow, band width to pass the frequency initiated by one perforated tape transmitter and exclude that of the other. The rectifiers 64, 64' may be of the usual vacuum type, or any other type.

The operation is as follows:

Referring to Fig. 1 when tongue 9 is brought into engagement with contact 5 by the perforated tape mechanism, condenser I charges by current passing from the positive terminal of the battery through resistance l4, to brushes [3 and [2, the latter being assumed to be in engagement with segment Ill. The current then passes through tongue 9, contact 5, resistance 3, condenser I, and back to the negative terminal of the battery. As the condenser charges, its voltage increases and finally the potential is sufiicient to discharge across neon tube l8 through transformer coil [9 after which it recharges. The time constant of the condenser l and circuit may be made anything desired by adjusting resistances 3 and I4, but for purpose of explanation and illustration it will be assumed to be such as to produce a frequency of 500 cycles per second. Assuming that distributor I2 is run at say, 60 cycles, the brush I 2 will be in engagement with segment in for a sufiicient length of time to permit the condenser-neon tube oscillator to produce a plurality of cycles at the frequency of h of 500 cycles per second. The secondary 20 of the transformer connected in the circuit of the neon tube I8 will therefore feed the low'frequency oscillations into the amplifiers 2| and then into the vacuum tube stage 23, which in this case has sufficient negative bias to block the plate current on the negative half cycle.

The fiow of plate current in tube 23, when a positive half cycle voltage is impressed across the input circuit, places such a heavy drop in resistance 30 that tube 28 is blocked by the negative voltage. There being no plate current in tube 28 during this positive half wave of the voltage wave initiated by perforated tape transmitter I, the drop in resistance 35 produced thereby is removed and tube 39 passes current under influence of the radio frequency impressed across its input by oscillator 49. A radio frequency wave is thus radiated from antenna 41 during the time of this low frequency half cycle. This is indie 39:v being. virtually short-circuited. Therefore,

during the negative half cycle there is no radiation from'antennar l'l, as indicated at 10 in Fig. .4.

Since the frequency of the. condenser-neon tube oscillator is considerably higherv thanthe frequency of interruption by distributor II, a number of groups-of highfrequency waves-69, H, 12, will be radiated before brush1.l0- leaves, segment l0. When the brush leaves this segment and engages contact I6, condenser I and circuit then has another time constant by virtue of the substitution ofresistanceA for resistance 3 and another low frequency, 1000 cycles, per second, for example, is produced. by the. condenser-neon oscillator in secondary and the radio frequency carrier of oscillator isradiated from antenna M in a numberof groups starting at 13. These groups have" the frequency f2 or 1000 in the example given. In thisway the perforated tape transmitters 1 and 8 will cause alternate groups of radio frequency waves to be radiated, the one group having a frequency of f1 and the other f2.

The mark indications of the two transmitters l and 8 may start at any time as they are independent of each other, but by way of example, I have indicateda mark for transmitter 1 as starting with group 69- and ending with group 14. Similarly themarkfor transmitter 8 is illustrated as commencing with group 13 and ending with group 16. Graph A is broken away at H to indicate that there are more groups. for the marks than can be shown in the drawings with a suitable scale.

The radiated wavesare-received and detected at 19 and amplified at 5B in all three of the channels in the diversity receiver. The amplified audio currents are then limited at 5| to cut off the desired amount of the positive and negative cycles to reduce fading effects. The output of the three limiters are mixed in the plate circuits of the rectifiers and introduced into the two channels through limiters 6|, 6|. Band pass filter 63 passes the low frequency alternations f1 and excludes f2 while band pass filter 53' passes f2 and excludes f1. lated and when rectified at 64, 64 will appear as indicated by the dotted line 15 in graph B. At this point the voltage will have positive pulses of frequency f1, broken up at the lower frequency of the distributor I l. However, when the voltage passes through the smoothing filter 65 it will be smoothed out as indicated by line 13. Similarly the rectified voltage of frequency f2 and the smoothed out voltage will be indicated by M and respectively, of graph G, which indicate the marks of the respective signals. The spaces of these signals are caused by the tube 28 normally shorting the plate voltage of amplifier 39 when no signals are being sent out by tape transmitters i and 8.

The signals after being rectified could be used to operate the recorders 68, 58, directly but it is preferable to square up the marks by a regenerating device such as the locking circuits 67, 61. Referring to graph B, when the voltage 13' is The two signals are thus isoapplied to. tube-fifirit produces a drop in resistance 16 by the. plate; current and condenser 16, previously charged toifulljline voltage, discharges through the platezfilament circuit of tube 66 to the center of --the.battery Hf, through one-halfof the battery and resistance 18 to the other side of the condenser: The drop in resistance 18 places a heavy biasonthegrid of tube-19 and blocks the tube. Tube 86 was, previously blocked by the drop; in resistance -8-l caused by the plate current of tube l9'.and when'it is removed the voltage of the grid: oftube 8.0 rises to full positive value. Tube-8ii-then draws. plate current and instantly blocks tube-J9 by; theinegative drop applied to its grid by resistance 82.v This happens at a predei terminedvalue'of the, signal voltage, say that indicated at the point 83 of graph B. The voltage: across lines-8G, 85, of the recorder, rising instantly to the value. 86 in graph B, will remain constant until the balance of the locking circuit is; disturbed by the decrease of the'sign-al to a predetermined value 81. It will be noted that at this time outputline 844s positive and line is negative.

When .point 87 in. the voltage curve 13 is reached, the chargingcu-rrent through condenser 7%., due to decrease of drop. in resistance 76, becomes heavy enough to place-a .suflicient positive drop in the grid of tube. 79, to cause that tube to conduct current. Thisinstantly causes tube 88 to block due-to the negative voltage placed on its grid due. to the-drop in resistance 8|. The voltage acrosslinestt and BEimmediately reverses at point .87 and the space fiaistarts to form. This space will continue until the beginning of another mark starts to fornnwhereupon the balance will be again disturbed by the condenser again discharging, it havingbeen charged to fu1lbatteryvoltage while the space was being formed.

The signal initiatedby tape transmitter 8 after the, currentv passes through smoothing filter E6 will operate locking circuit 61" in exactly the same way locking circuit 6'! was operated and the final square signal wave at the input terminals of recorder 58" will be as indicated by 89, 96, of graph C. No distributorisrequired at the receiver and hence synchronization between transmitter and receiver is entirely absent.

In the modified transmitting system of Fig. 2 the distributor ll of Fig. 1 has been omitted and two condenser-neon tube oscillators have been used. Condenser l of the respective channels will each oscillate at a low frequency depending upon the constantsof the circuit as in Fig. 2. The tape transmitters 1 and B will cause these oscillators to generate alternating voltage each time a marking contact is made. Each oscillating circuit is independent of the other and the low frequency output of the secondaries 20 are superposed on each other, and from there on the circuit to and including the antenna will be as described in connection with the apparatus of Fig. 1 except for the interrupter II. The receiving operation will also be as described in connection with Fig. 3 with a similar exception in respect to the interruption of the distributor Ii which will be absent. The modified form in Fig. 2 will be satisfactory but it is not preferred because the signal of one channel modulates the signal of the other by interaction. However, there will remain sufficient pulses at the band pass filters to enable the latter to separate the signals at the receiver and they will produce a suitable record.

In both forms of transmitting systems I may use any kind of low frequency oscillator, the one disclosed being by way of example only. Various other modifications may be made without departing from the spirit of the invention.

Having described my invention, what I claim 1. In multiplex radio telegraphy, a generator of high frequency oscillation, means for generating a plurality of alternating electromotive forces each having a different low frequency, signal transmitting devices each having means to send mark and space signals by interrupting current from the first-mentioned means for one of a plurality of messages, means for rectifying the interrupted currents of the generating means, a distributor connected to the signal transmitting devices for interrupting the signals therefrom at a frequency below the frequency of the low frequency generating means, and means for transmitting said high frequency oscillations only during the time periods of the current pulses in said rectified currents.

2. In multiplex radio telegraphy, an antenna, a generator of high frequency oscillations, means for generating a plurality of alternating electromotive forces each having a difierent low frequency, signal transmitting devices each having means to send mark and space signals by interrupting current from the first-mentioned means for one of a plurality of messages, a distributor connected to the signal transmitting devices for interrupting the current therefrom at a frequency below the frequency of the low frequency generating means, means for rectifying the output of the generating means, and means for passing the high frequency oscillations to the antenna only during the time periods of the pulses in said rectified current.

3. In signaling systems having a plurality of channels, a high frequency oscillator, means for producing a plurality of currents of different low frequency, means for modulating each current in accordance with a message, a rectifier, means to pass the modulated low frequency currents to the rectifier in timed succession for a uniform time interval materially longer than the periodic time of the lowest frequency of the first-mentioned means, and means for modulating the high frequency oscillator by the rectified low frequency currents.

4. In signaling systems having a plurality of channels, a high frequency oscillator, means for producing a plurality of low frequency currents, means for rectifying the low frequency currents, means for modulating the high frequency oscillator successively by each of the rectified low frequency currents during an interval of time greater than the periodic times of the frequencies, and means for interrupting the low frequency currents to form mark and space signals of materially greater time length than said time intervals.

5. In signaling systems having a plurality of channels, a high frequency oscillator, means for producing in each channel current of a low frequency differing from the frequency of the other current. means to interrupt each low frequency current to form mark and space signals, a rectifier, means to pass each interrupted low frequency current in succession to said rectifier for uniform periods of time materially longer than the periodic time of any of said low frequencies and shorter than the time length of the shortest signal, and means for modulating the high frequency oscillator by the rectified low frequency currents.

6. In signaling systems having a plurality of channels, a high frequency oscillator, means for producing in each channel current of a low frequency differing from the frequency of the other current, a modulator connected to said oscillator, means to pass each low frequency current in succession to said modulator for uniform periods of time materially longer than the periodic time of any of said low frequencies and shorter than the shortest signal, and means to interrupt each low frequency current to form mark and space signals, said modulator having means for causing said oscillator to oscillate only during alternate half cycles of said low frequencies.

JOHN W. COX.

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