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US2471319A - Alternating-current signal transmitting system - Google Patents

Alternating-current signal transmitting system Download PDF

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US2471319A
US2471319A US670891A US67089146A US2471319A US 2471319 A US2471319 A US 2471319A US 670891 A US670891 A US 670891A US 67089146 A US67089146 A US 67089146A US 2471319 A US2471319 A US 2471319A
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current
signal
phase
terminals
carrier
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Gardere Henri
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Alcatel Lucent SAS
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Compagnie Generale dElectricite SA
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
    • H04L27/22—Demodulator circuits; Receiver circuits
    • H04L27/227—Demodulator circuits; Receiver circuits using coherent demodulation
    • H04L27/2275—Demodulator circuits; Receiver circuits using coherent demodulation wherein the carrier recovery circuit uses the received modulated signals

Definitions

  • SIGNALS (PHASE MoouLArso) -(J FI G 4 ADENTODULA'TQR l N VENTO@ HE/VE/ 3Q/Posee Patented May 24, 1949 ALTERNATING-CURRENT SIGNAL TRANSMITTING SYSTEM Henri ardre, Paris, France, assigner to Compagme Generale dElectricite, Paris, France, a corporation of France Application May 20, 1946, Serial No. 670,891 In France May 7, 1945 Section 1, PublicLaw 690, August 8, 1946 Patent expires May 7, 1965 4 Claims.
  • the present invention relates to the transmission of telegraph code signals and has for its object to provide a frequency change signal transmitting system of the so-called double current and phase modulation type, characterised by the fact that: at the transmitting end the direct current signals of both positive and negative types are converted into two types of alternating current signals having a phase difference of between 0 and 1r; at the receiving end the carrier current is reconstituted from the signals with a constant phase, and by means of said carrier current the alternating current signals are demodulated (i. e. reconverted into direct current) without any uncertainty as to their correct polarity and having durations which are independent of the amplitude of the alternating current signals.
  • a double current alternating current system there is transmission of alternating current during both the spacing keying intervals and the marking keying intervals.
  • the advantages of such double current telesignal systems are known, such advantages being due to the fact that the signals reconstituted at the receiving end are independent of the amplitude of the changed frequency current signals changed at the input of the receiver.
  • the known double current telesignalsystem operating by means of reversals of the phase of the alternating current in synchronism with the reversals separating the direct current signals has this advantage, but does not reliably give the signals with their correct polarity at the -beginning of a communication.
  • the receiver cannot determine the polarity of the direct current signals which correspond to the alternating current signals received, since the successive signals comprise reversals which indicate nothing regarding the absolute value of the polarity of the signals. Only the relative polarity of the signals is known, i. e. that a signal is of opposite polarity to the previous or to the following signal.
  • Fig. 1 shows one form of receiving circuit for receiving doubly phased modulated carrier signal currents and converting them into direct current signals, using a balanced demodulator, the pclarity of the initial direct current element corresponding to the polarity of the initial element of the signal applied to the transmitter;
  • Fig. 2 shows the vector relations in the receiving circuit of Fig. 1, when the first element of the received signal is a spacing element;
  • Fig. 3 shows the vector relations in the receiving circuit of Fig. 1, when the first element of the received signal is a marking element
  • Fig. 4 shows a modified form of circuit using a single demodulator for'accomplishing the same result as the arrangement of Fig. 1;
  • Fig. 5 shows the vector relations in the receiving circuit of Fig. 4, when the rst element of the received signal i9 is a spacing element;
  • Fig. 6 shows the vector relations in the receiving circuit of Fig. 4 when the rst element of the received signal is amarking element.
  • the signal changer at the transmission end produces alternating current signals which do not differ by a change of sign, but by a change of phase which is smaller than 1r in absolute value.
  • the alternating current corresponding to a negative direct current marking signal as produced by the key has a phase advance of an angle qs which is smaller than 1r with respect to the alternating current corresponding to a space signal.
  • the reverse convention viz. a mark signal having a phase lag of qs with respect to the space signal.
  • the direct current signals which are reconstituted at the receiving end are not dependent on the amplitude at the input of the demodulating receiving system, because the duration of such reconstituted signals is equal to the time between the reversals of the alternating current signals.
  • the same advantage is obtained, because the duration of the reconstituted signals is equal to the time between the changes of phase of the alternating current signals and is not dependent on their amplitude.
  • the absolute polarity of the signals cannot be determined, in the system according to the present invention, it is clear, as soon as the second signal appears in the receiving demodulator, whether said signal is a mark signal or a space signal- (i. e. negative or positive), according to Whether said signal has l an advance or a lag of the phase angle in accordance with the convention hereinbefore agreed.
  • the reconstituted signals have the same polarity as at the transmitting end, with means independent of the code of the signal or telegraph system used;
  • the change of phase. at the transmitting end can be obtained, according to the present invention, in the following manner: vtwo sources of alternating current of the same frequency and withfa phase difference equal to gb alternately transmit their current to the line through one or a plurality of dynamicI or static, electromechanical or electronic relays, which are controlled by the direct current signals of the signal or telegraph apparatus.
  • the mark signal or negative direct currentA operates the relay or relays which connect to the line the source of alternating current having such a phase advance of vqb.
  • Said vsource is replaced by the other alternating current source when the relay or relays are operated by a direct current spacing or positive signal.
  • the two sources could be replaced by a single source provided with two parallel leads connected to one or two dephasing devices producing at the output of said leads currents which are 4; out of phase, andl instead of connections being made tothe two sources, the co-nnections are made to the two parallel leads.
  • frequency change means producing signals which are out of phase by consists in permanently connecting the alternating current source to the line and inserting a dephasing device between the source and the line by means of relays controlled by the direct current signals. It is thus possible to obtain, applying one of the two (positive or negative) types of direct current signals, the phase difference of e in question.
  • Another example, according to the present invention, of frequency change at the transmitting end that is, the transformation of D. C. signals (zero frequency) into A. C. signals of the carrier frequency, consists in using a known frequency changer of the double current type as employed in the prior art operating by reversals of the alternating current, and in transmitting to the line, in addition to the double current alternating current signals produced by reversals, an auxiliary current which has a mld 4 phase advance with respect to one, and a phase lag with respect to ⁇ the other, of the two alternating current signals.
  • the auxiliary current must have an advance with respect to the space signal current, if adhering to the aforesaid assumed convention of a mark signal current having an advance of phase with respect to the space signal current.
  • Another example consists in using a variable phase source of alternating current and controlling the phase by. means of a relay controlled by the direct current keying signals.
  • the signals thus obtained from the transmit.- ter reach the input of the demodulating device at the receiving end in the form of alternating current.
  • the alternating current corresponding to a mark signal has a phase advance. of 4; with respect to the alternating current of the same frequency corresponding to a space signal. It is obvious that the converse convention could be made, but in order to simplify the explanation the rst mentioned convention will be adhered to throughout the remainder of the present specification.
  • Fig. 1 shows the diagram of a system according to the invention adapted to convert alternating current signals into direct current signals at the receiving end; the input terminals to which the alternating current signals is are fed are located at e.
  • fs is a preliminary filter for the signals which is particularly intended to separate the signals of various communications on several different frequencies, in the case of multiplex channels as known.
  • said preliminary ⁇ iilter passes a band of at least cycles, t being the elementary time,.i. e. the duration of the shortest possible interval; the maximum band width is determined by the illtering requirements or by the desirability of eliminating or attenuating parasites..
  • the filter maybe simple, this being an advantage involved in double current alternating current communication, as the filtering can be completed after demodulation, simply by a low-pass filter.
  • d1 is a parallel lead through which the signal current can reach either the input terminals of the signal amplier as, or the input terminals of the blocking devices br, bt.
  • These blocking devices are units which only allow signal current from di to pass from the input terminals to the output terminals (from the left-hand terminals to the right-hand terminals) when they are supplied with direct current at their control terminals (upper terminals).
  • Such blocking units are well known in weak current technique and may consist of a simple network of rectiers.
  • the output terminals of the blocking devices br and bt are in parallel, i. e. connected to one another. But Whereas the connecting leads are directly connected to the output terminals of br, the output terminals of bt are connected, ahead of the leads, to a dephasing device st which produces a lag of in the currents that pass through it.
  • the output leads are connected to the input terminals of the carrier current band pass iilter fp. Said lter, which is centered on the carrier frequency, should pass a band width of less than t being the duration of the elementary signal. But more often it will be an advantage to have as reduced a band width as possible compatible with the stability of the elements and of the carrier frequency.
  • the output of the carrier filter fp is fed direct to an amplier ar for the space signal carrier current and, through a dephasing device so producing a lag of to an amplifier at for the mark signal carrier current.
  • the aforesaid signal amplier as is connected to the input terminals of two demodulators in parallel, the space signal current demodulator mr and the mark signal current demodulator mt.
  • the output terminals of the demodulators (righthand terminals) are also connected in parallel.
  • the control terminals (upper terminals) of the demodulators mr and mt are respectively connected to the output terminals of the ampliers ar and at.
  • the demodulators are units of the known balanced type called carrier current suppressors. They are such that if a current i(t) is applied to the input terminals and a current I(t) to the control terminals, they produce at the output terminals a current of the form a.z ⁇ (t).I(t), a being a constant.
  • the output terminals of the demodulators are connected in parallel and are connected to a low-pass lter fc, the cut-olf frequency of which is at least equal to lgt, t being the duration of the shortest possible signal.
  • a control circuit dal is connected across the control terminals of the blocking devices br and bt through valves. or rectiers rr and rt which only allow current to pass in the direction of the arrows that represent them.
  • This control circuit d2 is connected in series in one of the leads connecting low pass lter fc to the output terminals of demodulators m1' and mt.
  • Fig. 1 enables an explanation to be given of the operation of the system illustrated therein by way of a non-limitative example, according to the present invention, of the receiving portion which converts the alternating current signals identical to those transmitted.
  • the rst signal is a space signal
  • the iirst signal is a mark signal
  • the iirst alternating current signal that reaches the input e of the receiver of Fig. 1 is a space signal current. It passes through the band-pass lter fs-which may be a simple one (the system enabling the signals which have been re-converted into direct current signals to be ltered by a simple low-pass iilter then the current reaches the parallel connection di.
  • One'portion of the current is amplified in the signal amplier as and is fed to the input terminals of the two demodulators in parallel mr and mt (lefthand terminals of the demodulators).
  • the other portion of the signal which is shunted at di passes through the blocking device br.
  • the blocking devices br and bt only allow current to pass between the input and output terminals when their control terminals are supplied with direct current, therefore if the blocking of br and bt is complete, the current is a zero current, save the initial signal current; in the initial state br has to be blocked.
  • the same is so designed that in the blocked state it allows a current to pass which is small compared with the current that would pass with br open.
  • the current having passed through br flows into the carrier current filter fp. At the output of the carrier current filter fp.
  • the signal current which is still of the same phase (space) is shunted towards the input terminals of two amplifiers: directly across the input terminals of the space signal current amplifier ar and, through a dephasing device sp which throws it
  • These two amplifiers respectively supply the control or carrier current terminals of the two demodulators mr and mt which, moreover, as hereinbefore stated, are fed in parallel through their input terminals by the signal current amplied by signal amplifier as.
  • the demodulator mr which is fed through its in-4 put terminals and through its carrier current control terminals with currents which are in phase, supplies a direct current across its output terminals; the connections are in a direction such 7 that said direct current flows through the lowpass filter ,fc and the output terminals s in the direction of the arrow which is assumed to be the positive direction.
  • the demodulator mt which is fedv with currents which are Lol s the valve rr and the blocking device br which is thus made open, whereas the blocking device bt, through which no current passes owing to the direction of the valve rt, remains blocked.
  • the blocking device br therefore allows the current derived at d1 to pass freely towards the carrier band pass filter fp, which only increases the weak current that it allowed to pass at the outset. This also increases the currents in the various circuits with their polarity and their phase as they were hereinbefore described.
  • the flow of this current involves (according to the assumed convention) a phase advance of in the alternating current forming the signals.
  • the phase and the amplitude oi the current at the output terminals of said lter fp can only change with a certain delay, so that the carrier currents amplified by amplifiers ar and at have not changed when the mark signal,
  • the demodulator ar which produced a positive current, now at this instant produces no current since the current at the input terminals and the carrier current are out of phase.
  • the demodulator mi, which produced no current is still supplied with a carrier current which has a phase lag of and now has at its input terminals a signal current which has a phase advance of but it passes through the blocking device bt which owing to this fact is open, i. e. has only a small attenuating eiiect on the signal current flowing from the parallel leads di.
  • the current (marking signal) passing through the blocking device br and reaching the carrier current lter fp it now passes through the blocking device bt and reaches the lter fp through the dephasing device st which imparts to it a phase lag of
  • the current representing a mark sign-al which, with respect to the previous signal, has a phase advance, next after passing through the dephasing device st, gets a phase lag, thus undergoes two successive equal and opposite changes of phase, the overall eect of which is nil. Therefore the current at the input terminals of the filter fp does not undergo change of phase.
  • this second signal produces (change from marl: to space) a phase lag of rola
  • the demodulator mi' whose input terminals were supplied with the signal current and the control terminals with a carrier current of the same phase, produced a positive current at the output terminals, whereas the demodulator mt, which 9 was controlled by a carrier current having a phase lag of produced no current.
  • the positive current at the output terminals of the modulator mr opened the blocking device br.
  • the demodulator m1* At the beginning of the second signal which has a phase lag of with respect to the previous mark signal, the demodulator m1* produces no demodulated current, and the demodulator mt (still supplied with carrier current having a phase lag of with respect to the rst signal.
  • the phase of the carrier current gradually changes, according to the time constant, from the phase of the rst signal to the phase of the second.
  • the two carrier currents which supply modulators mr and mt undergo the same change of phase (backward displacement of and the current z'mr demodulated by mr gradually changes from 0 to its normal positive value, whereas the current imt demodulated by mt gradually changes from its positive value to 0.
  • the two demodulators mr and mt as a whole, produce a positive total current and the blocking device br remains open.
  • the space signal is demodulated by the demodulator mi', whereas mt produces no current.
  • the system has thus returned to the state in which it was in the rst case when a rst space signal was being demodulated.
  • the system produces a positive current for the space signals and a negative current for the mark signals.
  • zsr represents the initial space signal applied to the system, i101 the carrier cur- 10 rent produced by the first signal and fed to the demodulator mr, pt which has a phase lag of representing the carrier current fed to the demodulator mt, zmr is the positive current produced from z'sr and z'pr in phase in the demodulator m1' and z'mt is the zero current demodulated from is? and z'pt in quadrature in the demodulator mi.
  • ist represents the mark signal following the initial signal
  • pr and zpt the carrier currents which remain permanently owing to the effect of the large time constant filter fp and of the opening of the blocking device bt instead of br
  • z'mr is the zero current produced from ist and z'pr in phase quadrature in m1'
  • zmt is the negative current produced from ist and ipt in phase opposition.
  • Fig. 3 have been shown for the circuit of Fig. 1 the signals and currents illustrating the second case of operation when the rst signal that arrives is a marking signal.
  • ist is the initial mark signal
  • z'pr and pt the carrier currents produced thereby and having a phase advance with respect to their normal position
  • mr the positive current produced from ist and zpr in phase in mr
  • z'mt the zero current produced from ist and zpt in phase quadrature in mt.
  • z'sr is the space signal current that follows the current of the initial signal, ipr and z'pt the carrier currents which have not yet had the time to change and are identical with those shown at d (Fig. 3). imr is now zero and z'mt produced from z'sr and z'pt in phase in mt is positive.
  • h and z' is shown the backward rotation of the carrier currents ipr and zpt during .the space signal zsr which has a phase lag with respect' to the previous signal.
  • the lower row of Fig. 3 are shown the corresponding variations ofthe demodulated currents produced.
  • z'mr which is Zero at instant acquires increasing positive values and imt retains positive but decreasing values.
  • y is again the space signal z'sr, the carrier currents have reached their normal phase, z'mr is positive and zmt is zero.
  • the system is in the state shown in Fig. 2 at d and is therefore ready to receive correctly the next mark signal.
  • Fig. Il shows the diagram of another nonlimitative example, according to the present invention, of a system which re-converts at the receiving end the phase modulated alternating current signals into direct current signals.
  • fs is a prefiltering filter having the same functions and the same characteristics as in the previous example of Fig. l
  • d1 is a parallel connection through which the current of the signals from js can reach, either the input terminals of the signal amplifier as, or the input terminals of the blocking devices br and bt in parallel.
  • Said blocking devices are units comprising rectier bridges which produce between their input and output terminals (extreme left-hand terminals for the input, extreme right-hand terminals for the output) a small or large decrease of intensity according to whether direct current owing in one direction or in the 11 other is fed to their control terminals (mid terminals on both sides.)
  • blocking devices br and bt produce a negligible decrease when direct current is passing through them in the direction of the arrow (arrow and at the output terminals of the blocking device bt another dephasing device st imparts a phaselag of (still assuming the convention of a mark signal current having a phase advance of with respect to the space signal current).
  • the circuits fed with the output of the two blocking devices are connected to the input terminals of the bandpass lter fp.
  • This band pass lter fp which is centered on the carrier frequency has similar characteristics to those ci the filter fp o the previous example of Fig. 1.
  • the output terminals of the, lter fp are directly connected to the input terminals of the carrier current amplier ap.
  • the output terminals oi the signal amplifier as previously referred to are connected to the input terminals (left-hand terminals) of the demodulator m, the f'' control terminals of the demodulator m (upper terminals) are connected to the output terminals of the amplifier ap.
  • the demodulator m is a unit of the typeY of those used in the previous example of Fig. 1.
  • the output terminals of the demodulator are connected to.
  • a low-pass lter fc having similar characteristics to those of the filter of the same designation in the previous example of Fig. 1.
  • a parallel lead d2 is connected to the control terminals of the blocking devices br and bt.
  • first signal is a. space signal.
  • the current of this signal passes through the lter fs, reaches the parallel lead di.
  • One portion of said current is amplifled in the signal amplifier as and is fed to the input terminals of the demodulator m.
  • the other portion of the signal which is shunted through di flows along two parallel leads and partly passes through the blocking devices br and bt which, owing to the initial absence of direct. current at their control terminals (mid terminals) are neither open nor lli Gil
  • the signal current then passes through the dephasing devices s1' and st, reaches the input terminals of the carrier band pass filter fp, passes through same and is then amplied by the carrier current amplier ap and fed to the control terminals of demodulator m.
  • the blocking devices br and bt should be so designed that their transmission properties, in the absence of direct control current, allow such currents to pass that at the output terminals of ap and at the control terminals of m, there is a current which diiers in phase by less than from the initial signal current at the input terminals of the demodulator m.
  • the demodulator m to the input and control terminals of which are fed currents that differ in phase by less than produces at its output terminals a positive direct current im (direction of the arrow at the output terminals of m).
  • Said direct current which is diverted at d2, passes through the two blocking devices br and bt by way of their control terminals and, owing to its polarity, opens br and blocks bt.
  • the signal current from the shunt lead di which was passing through the blocking devices br and ht now only passes through br, is given a phase lag of by the dephasing device sr, passes through fp and, after being amplified by ap, is fed to the control terminals of m,
  • the demodulator m to the input and control terminals of which are fed currents that differ in phase by less than produces at its output terminals a positive direct current im (direction of the arrow at the output terminals of m).
  • the flow of this current involves (according to the assumed convention) a phase advance of Owing to the large time constant of the carrier current filter fp, the phase and the amplitude of the current at the output terminals of said filter can only change after a certain delay, so that the carrier current amplified by amplier ap and fed to the demodulator m has not changed (still has a phase lag of when the mark signal is applied to the input terminals of the demodulator.
  • the mark signal has a phase advance of with respect to the initial space signal, the carrier current a phase lag of 13 This mark signal current and the carrier current are therefore out oi' phase by:
  • the space signal changes into a mark signal
  • the demodulated current im will therefore be negative as long as the mark signal current lasts.
  • the space and mark signals are thus reconstituted with their correct polarity.
  • the iirst signal is a mark signal. It is obvious that at the beginning of a message, that is to say as soon as an alternating current flows at the receiving end, the system cannot indicate the phase of such current, since a current only has a phase relatively to another current or relatively to a denite origin of time. For this iirst mark signal, the system this will therefore behave exactly as in the first case,
  • the blocking device br will again remain open and the signal current at the input terminals of the filter fp will have a phase lag of (relatively to What it was during the rst sig- I- nal).
  • the current at the output terminals of carrier amplifier ap and at the control terminals of the demodulator m will therefore gradually change its phase according to the time constant of the carrier band pass lter fp. Like the change of phase of the signal, this change will be a lag of rola but slower, the phase of the carrier current relatively to the signal current will therefore change from a advance to a lag. It follows that during any change of phase of the carrier, the demodulated direct current will remain positive.
  • Fig. 5 For the rst case when the first signa-l received is a spacing signal, the vectors representing the currents. At lc are shown the two vectors zsr rep-, resenting the alternating current space signals and ist with a phase lag of im is the positive demodulated current produced from isr and ip which are given a phase dierence of in the demodulator m.
  • ist represents the mark signal current, following the initial signal, ip the carrier current which does Vnot un- 15 dergo a change of phase and therefore has a' phase lag of with respect to ist owing to the eiect of the time constant of the filter fp, of the opening off the blocking device bt and of the dephasing device st.
  • im is the negative direct current produced from ist and ip which are given a phase lag of alga in the demodulator m.
  • Fig. 6 In Fig. 6 have been shown for the circuit of Fig. 4, the signals and currents illustrating the second case of operation when the rst ⁇ signal element received is a marking signal.
  • ist is the initial mark signal
  • ip the carrier current which results therefrom and has a phase lag of as in the rst case.
  • im is the positive and therefore, incorrect direct current produced from ist and ip in the demodulator m.
  • isfl is the space signal following the initial signale and having a phase lag cf with respect to same
  • ip is the carrier current which has not had time to change, an im the demodulated current resulting therefrom and which is always positive.
  • the system according to the present invention offers the advantage of giving unequivocally the polarity of the re-converted signals whose distortion is practically independent of the strength of reception.
  • the signals are re-converted according to their type in an exact and well-dened direction. This property involves the possibility, without impairing the transmission, of narrowing the frequency band allotted to each communication down to the requisite theoretical value.
  • the usual single current communications at the signal speed of 59 bauds, are allotted a frequency band of to 90 cycles with a serious distortion when the strength of reception varies, and owing to this defect there is a tendency to increase this band width to a value er;- ceeding cycles.
  • the system according to the present invention enables the same message to be transmitted, with a frequency band of only 50 cycles per second, therefore in a multiplex system, two or three times more messages to be transmitted, with better quality of reconstitution.
  • the system according to the present invention oiers the advantage, which is common to all double current signal systems, of being less sensitive to parasites; it requires during transmission smaller power than that used for single current signal systems, and thus has less effect on neighbouring communication.
  • the system according to the present invention is applicable to all signal systems in which it is an advantage to use alternating current rather than direct current signal, in particular in simple or multiplex signal or tele-communication systems, either wired or wireless.
  • the system can be applied equally well whatever be the transmitting medium and agent, for example: wire and electric current, space and Hertzlan or light waves, atmosphere and sound waves, and so forth, provided that at the transmitting end there is conversion of the electric current of the signals according to the present invention into the agent utilized, and the reverse conversion at the receiving end.
  • the systems described is to a great extent insensitive to fading.
  • a transmitted alterhating current signal consisting of successive short trains of two alternating currents of the same frequency but having a substantial determined phase diierence W which is substantially less than 1r
  • receiving terminals for receiving said trains of the so determined different phase
  • a carrier current suppressing balanced demo-dulator unit having input terminals and output terminals and control terminals, said input terminals of said demodulator unit being connected to said receiving terminals
  • a pair of blocking devices having substantial conducting asymmetry and each having input terminals and output terminals and control terminals and each being adapted to pass a relatively large current from its input terminals to its output terminals when rect current of a particular characteristic is applied to its control terminals and to pass only a relatively small current from its input terminals to its output terminals when its control terminals are not so energized
  • a carrier band pass lter of relatively large time constant
  • a receiver for receiving and reconverting into direct current signal elements of successively opposite polarity a transmitted alternating current signal consisting of successive short trains of two alternating currents of the same frequency but having a substantial determined phase difference W which is substantially less than 1r, receiving terminals for receiving said trains of the so determined diierent phase, a pair of carrier current suppressing balanced demodulators each having input terminals and output terminals and control terminals, said input terminals of said demodulators being connected to said receiving terminals, a pair of blocking devices having substantial conducting asymmetry and each having input terminals and output terminals and control terminals and each being adapted to pass a relatively large current from its input terminals to its output terminals when direct current of a particular characteristic is supplied to its control terminals and to pass only a relatively small current from its input terminals to its output terminals when its control terminals are not so energized, a carrier band pass lter of relatively large time constant, a rst connection between the input of said carrier filter and the output terminals of said blocking devices, said
  • a receiver for receiving and reconverting into direct current signal elements of successively opposite polarity, a transmitted alternating current signal consisting of successive short trains of two alternating currents of the same frequency but having a determined phase difference which is substantially receiving terminals for receiving said trains of Y the so determined different phase, a carrier current suppressing demodulator having input terminals and output terminals and control terminais, said input terminals of said demodulator being connected to said receiving terminals, a pair of blocking devices having substantial conducting asymmetry and each having input terminals and output terminalsv and control terminals, and each being adapted to pass a relatively large current from its input terminals to its output terminals when direct current of a particular polarity is applied to its control terminals and to pass only a relatively small current from its input terminals to its output terminals when direct current of opposite polarity is applied to its control terminal

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
  • Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)
US670891A 1945-05-07 1946-05-20 Alternating-current signal transmitting system Expired - Lifetime US2471319A (en)

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US (1) US2471319A (fr)
CH (1) CH254683A (fr)
DE (1) DE892460C (fr)
FR (2) FR996628A (fr)
GB (1) GB629532A (fr)
NL (1) NL62039C (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2819339A (en) * 1956-01-12 1958-01-07 William E Scoville R. f. phase shift keying system for teletype communication

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3078344A (en) * 1960-10-25 1963-02-19 Robertshaw Fulton Controls Co Phase demodulation of keyed carrier by use of synchronous gating, with phase lock driven step wise in response to forbidden output
DE1137759B (de) * 1961-09-19 1962-10-11 Siemens Ag Verfahren zur UEbertragung von Start-Stop-Telegrafiezeichen mit Hilfe einer quaternaer phasenmodulierten Traegerfrequenz

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1901642A (en) * 1929-12-23 1933-03-14 Rca Corp Signaling
GB453254A (en) * 1934-11-15 1936-09-08 Soc Et Liaisons Telephoniques Improvements in or relating to telegraph signalling systems
GB494099A (en) * 1937-04-19 1938-10-19 Standard Telephones Cables Ltd Improvements in or relating to telegraph systems

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1901642A (en) * 1929-12-23 1933-03-14 Rca Corp Signaling
GB453254A (en) * 1934-11-15 1936-09-08 Soc Et Liaisons Telephoniques Improvements in or relating to telegraph signalling systems
GB494099A (en) * 1937-04-19 1938-10-19 Standard Telephones Cables Ltd Improvements in or relating to telegraph systems

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2819339A (en) * 1956-01-12 1958-01-07 William E Scoville R. f. phase shift keying system for teletype communication

Also Published As

Publication number Publication date
FR56738E (fr) 1952-10-03
GB629532A (en) 1949-09-22
NL62039C (fr)
FR996628A (fr) 1951-12-24
CH254683A (fr) 1948-05-15
DE892460C (de) 1953-10-08

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