US2491810A - Receiving system for phase-keyed pulse signals - Google Patents

Description

G. GUANELLA RECEIVING SYSTEM FOR PHASE-KEYED PULSE' SIGNALS Filed Sept. 18, 1946 2 Sheets-Sheet l mm. 2m w49 Filed Sept. 18, 1946 G. GUANELLA RECEIVING SYSTEM FOR PHASE-KEYED PULSE SIGNALS 2 Sheets-Sheet 2 .ATTORNEY Patented Dec. 20, 1949 RECEIVING SYSTEM FOR PHASE-KEYED PULSE SIGNALS Gustav Guanella, Zurich, Switzerland, assigner to Radio Patents Corp eration, New York, N. Y.,

a corporation of New York Application September 18 In Switzerland s claims. 1

The present invention relates to receiving systems for pulse modulated carrier signals, more particularly of the type wherein the signal pulses and spacing intervals are characterized by a phase change between two predetermined time phase positions of the carrier wave of substantially constant amplitude, such as a 180 phase reversal for the signal pulses and spacing intervals, respectively. The invention has many uses such as for the reception of telegraphic and facsimile signals, pulse time and variable pulse position modulated signals and in general all other signals utilizing pulse modulations for the transmission of intelligence, from a transmitting to a receiving station.

Devices are already known which employ phase keying for the transmission of telegraph signals, wherein the signal pulses are distinguished from the spacing intervals by means of a phase position shift of 180 for the continuously transmitted high frequency oscillation. This means of distinguishing the impulses and intervals may also be applied to speech and facsimile transmission using pulse time or an equivalent modulation. At the receiving end the signals are demodulated by superposing them upon an auxiliary voltage whose frequency coincides with the frequency of the received oscillation. Considerable diiiiculty is encountered in producing this auxiliary oscillation at the receiving end since the oscillation must be in exact phase or in phase opposition with the receiving oscillation. It is known to produce the auxiliary oscillation by means of a frequency-stabilized oscillator whose phase position is adjusted by hand in the desired manner. This manual adjustment makes the practical application of this method very diilicult. The disadvantages of this known device are overcome by the present invention.

According to the invention, means are provided for obtaining a harmonic from the receiving frequency wave, there being further provided means for synchronizing the auxiliary oscillation with this harmonic wave. The second harmonic is particularly suitable for this purpose. Other harmonics of a higher order may, however, also be used. Synchronization occurs independently of whether the phase of the received signal voltage is the same or opposite to that of the auxiliary oscillation. For the auxiliary oscillation it is thus of no importance whether the received wave is transmitting a signal pulse or a spacing interval between successive pulses.

The invention both as to its further objects and novel aspects will become more apparent 1946, Serial No. 697,767 October 4, 1945 (Cl. Z50-8) from the following detailed description taken in reference to the accompanying drawings, forming part of this specication and wherein:

Fig. la to Fig. 1dV are diagrams illustrating the shape of a known type of pulse signal char-4 acterized by successive phase reversals of a car-A rier wave, forming the basis of the invention;

Fig. 2 is a schematic circuit diagram for rel modification. of

further modifications of systems according to' Fig. 1;

Fig. 6 is a block diagram illustrating a modied arrangement for carrying out the invention;

Fig. 7 illustrates a special receiving device suitable for use in connection with the invention; and

Fig. 8 is a block diagram showing a modification of a system according to Fig. 6;

Like reference characters identify like parts in the different views of the drawings.

Fig. la shows a graphic representation of the telegraph or other pulse signals to be transmitted, and consisting of alternate signal pulses Z and spacing intervals P. The corresponding curve of the modulated high frequency oscillation at the output end of the transmitter is shown in Fig. 1b.

The high frequency oscillations incoming from the transmitter with constant frequency and amplitude but with phase reversals corresponding to the signal keying, reach the receiving antenna A of the receiving arrangement shown in Fig. 2 and then pass to the receiver and amplifier E in the form of an input voltage e1. This amplifier may be a multi-stage amplifier of known kind. The output voltage ea of the amplifier E is applied to the frequency doubler or' multiplier V. This frequency doubler advantageously may comprise two amplifier tubes in pushpull connection and having sharply bent characteristic curves, so that the second harmonic is strongly pronounced. The voltage e4 which is thus obtained and has double the frequency is halved again in the frequency divider T. Thislatter apparatus may be a regenerative vacuum tube generator which oscillates at the receiving frequency and is synchronized by the harmonic frequency of voltage e4.

not subjected to any phase reversals. The oscilshown partly in Voltage e5 thus con-- tains the same frequency as voltage e3, but is,

lations es, e4 and e5 are shown graphically in Figs. 1b, lc and 1d. At the instants 1, 3, etc., at which the signal pulses start, phase changes occur, these being for instance direct phase reversals of 180, as shown in the drawing. At the instants 2, 4, etc., i. e. at the end of the signal pulses, the original phase is restored again. The dotted parts of the curve represent the unkeyed or unaffected course of the high frequency oscillations. The oscillations may be raised to double the frequency in the multiplier V, for instance by means of double-wave rectification, as shown in the drawing. Other degrees of frequency multiplication may also be employed. By rusing rectication to multiply the frequency, an oscillation curve for the voltage e4 such asis shownin Fig. lc is obtained. This oscillation curve no longer contains any of the phase reversal of voltage es. The voltage e4 in turn has its frequency halved in the frequency divider T which follows; that is thefrequency is restored'to its original value.. The voltage-e5 which is'thus-obtained, is shown in Fig. 1d.

YThefrequem'sy of yvoltage es'coincides again with the frequency of voltage e3, with thedif-l ference, however, that the voltage e5 even with a phase keying'ofY voltage e3 does not exhibit any phase reversals7 sinceithe phase reversals of the signal, oscillations es, has no effect on the voltage e4. Voltage e5 can therefore'be used aste'.

an auxiliary voltage for demodu-lating the telegraph signals, inasmuch it coincides exactly with the frequency of the received oscillation. :Thus byl superposing the rvoltageies with the phasekeyed Voltage es in modulator 1M, adirectcur rent output voltage e7 is obtained which accordingto the phase reversalsoi voltage es. relativelto the voltage eachanges its sign betweenpositive and negative values. A diode. may `be used as a modulator having oscillatorycircuitsl inserted in its output circuit which are excited by the voltages esand e3, respectively, as shown in Fig..2. The resulting direct current linthe output circuit changesits directionl at the beginning and end of the signal .and can serveto actuate a recording ldevice or' the like. Modulator'lVlf may be of anyother type known in the art.

A-Isuperheterodyne receiver E havinga local oscillator O mayalsobeused as shownv'in Fig. 3. The intermediate frequency voltage e2 undergoes the same phaseV reversals-as the received signal voltage e1. Instead of doubling the frequency it` is-'also possible to multiply the frequency 'rn-times and to subsequently divide it by m.

Fig; 6 shows an arrangement, wherein the frequency divider T is replaced by a generator G. A harmonic wave es of the generator'has its phase corrected tov correspond with that of the multipliedreceived"voltage e4 by means of a discriminator and automatic frequency regulator-P.

The invention isnot limitedto keying by phase reversal; but equally applies to receiving' signals which arephase keyed by an angle 'Il' 7|" r 2 s or an even smaller amount frequency doubled or multipliedp-'times insuch .as well as auxiliary voltages of different phase which are obtained from the voltage e5.

Fig. 4 shows a constructional example of the invention for two messages with two phase changes of and 1r and -with Vtwo .corresponding modulators. 'Modulator Ma operates exactly like modulator M in Figs. 2 and 3. Voltage e5 is supplied to modulator Mb over a phase shift network N designed to eifect a phase shift of 7|' Phase changes in voltage eaA--a-mounting-to p=1r only produce pulse signals in modulator Ma, while phase changes of '12 f 2 only cause modulator Mb to operate. Modulators Ma and -Mb are shown to supply separateoutput devices, such as recording relays-Ra -and Rb, respectively, or the like.

When receiving telegraph signals from. transe mitters with keyed phase changes, itis possible to interchange the signalsv andthe intervals. Since generally the duration of-allintervals differs considerably from the dur-ation of all signals, the mean value of the signal current obtained -in modulator M maybe used to--actuate a pole-reversing relay R which is sensitive tothe direction of current flow, as shownin Fig. 5. Furthermore the difference between the sum of the duration of thesignals andY that of the intervals maybe determined automatically in a device which is located in the place of'relay R in the arrangement shown in Fig. 5. AA detailed-arrangement of such a device is shown in Fig. 7. In this figure Vi and V2 indicate two amplier tubes which may also be mounted in a common vessel. When the carrier frequency is transmitted, modulator M (Fig. 5) supplies a direct voltage to terminals l and 2 (Fig. 7). If terminal I is positive relative to terminal 2, then the cathode current of tube V1 exceeds that of tube V2 andv acts to pull the armature of the polarized relay X away from the position of rest, for instance to the direction O. The polarity at the terminals l and 2 is temporarily reversed by the keyed signals. If, however, compared with the time constant of condenser C1 or C2, respectively, together with that of the relay winding, the total duration of the intervals always exceeds thatV of the signals, the relay armaturewill remain inthis position. Tubes Vi and Vzvare additionally operated as socalled cathode follower amplifiers for the received signal in the mannery shown. Approximately the same voltage uctuations occur at the resistances Rxi and Rxz as at the resistances Rgi and Rgz. A high impedance current source, for instance a diode modulator, may thus be connected to the terminals l, 2. The internal resistance of the arrangement measured at the terminals 3 and t is comparatively very low and this is an advantage asA regards any recording device connected to this arrangement.

With a "directional "relay 'arrangement of the type shown in Fig. 7, it is thuspossible to maintain at the output terminals 3, 4, pulses of the same polarity, i. e., either positive or negative, independently of any interchange between the pulses and spacing intervals in the received carrier wave or the corresponding demodulated positive and negative pulses supplied by the modulator M and applied to input terminals l 2. Thus, if the pulses and spacing intervals are interchanged due to any cause, such as by a phase reversal of local oscillator or frequency divider, the relay X, due to the change of the average or integrated pulse current, will cause its armature and cooperating contacts to switch from the position o to the position u, or vice versa, thus maintaining the proper polarity of the output pulses supplied at the terminals 3, 4.

Another modified form of the arrangement for producing an auxiliary frequency which is independent of the phase keying, is shown in Fig. 8.

The received oscillations e3 which are amplified in the receiver E and the oscillator oscillations es have their frequency doubled or multiplied by means of the frequency multipliers Va and Vb and are applied to the modulator M1 acting as a phase comparator. The resulting demodulation voltage ee is used as a regulating voltage for controlling the frequency and phase of the oscillator O. By this means it is possible for the frequencies of voltages e1 and e'z to be continuously synchronized independently of the phase keying, so that the telegraph signal voltage ev may be obtained from the modulator M2 as a direct voltage with alternating polarity.

While the invention has been described with specific reference to a few desirable embodiments, it is understood that various changes in the construction and arrangement of elements, as well as the substitution of equivalent elements and circuits for those herein shown, may be made without departing from the spirit and scope of the invention as defined by the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than a restrictive sense.

I claim:

1. The combination with a system for receiving pulse modulated carrier signals of the type wherein the signal pulses and spacing intervals are characterized by a phase reversal of the carrier wave of substantially constant frequency and amplitude and comprising a signal input circuit and means for producing an auxiliary signal of carrier frequency to be combined with the incoming signal to derive demodulated output signals, said means comprising a frequency multiplier connected to said input circuit for multiplying the frequency of a portion of the incoming signal energy, a frequency divider connected tothe output of said multiplier for reducing the multiplied frequency to a value equal to the original signal frequency, and means for combining the received signal with output energy of said frequency divider to produce final output energy of amplitude varying between two limit values in accordance with the signal pulses and spacing intervals, re spectively.

2. The combination with a system for receiving pulse modulated carrier signals of the type wherein the signal pulses and spacing intervals are characterized by a predetermined phase change differing from 180 of the carrier wave of substantially constant frequency and amplitude and comprising a signal input circuit and means for producing 'an auxiliaryV signal of car--` rier frequency to be combined with the incoming signal to derive demodulated output signals, said means comprising a first frequency multiplier connected to said input circuit for increasing the frequency of the received signal to produce an intermediate signal subject to phase reversals according to the signal pulses and spacing intervals, respectively, further frequency multiplying means connected to said first multiplier for increasing the frequency of a portion of the intermediate signal energy, a frequency divider connected to the output of said further multiplying means for reducing the multiplied frequency to a value equal to the frequency of said intermediate signal energy, and means for combining said intermediate signal with output energy of said frequency divider to produce nnal output energy of amplitude varying between two limit values in accordance with said signal pulses and spacing intervals, respectively.

3. In a system for receiving pulse modulated carrier signals of the type wherein the signal pulses and spacing intervals are characterized by a phase shift of the carrier wave between predetermined limit values, a signal receiver includ` ing means for producing an auxiliary carrier signal of frequency equal to the signal frequency and having a constant phase to be combined with the received signal for deriving demodulated signal pulses, said means comprising frequency multiplying means connected to said receiver for increasing the frequency of a portion of the received signal energy, frequency dividing means connected to said multiplying means for reducing the multiplied frequency to a value equal to the signal frequency, and means for combining the received signal with output energy of said dividing means.

4. In a system for receiving pulse modulated carrier signals of the type wherein the signal pulses and spacing intervals are characterized by 180 phase changes of the carrier wave, a signal receiving including means for producing an auxiliary signal of frequency equal to the signal frequency and having a constant phase to be combined with the received signal for deriving demodulated signal pulses, said means comprising a frequency doubler-amplifier connected to said receiver for increasing the frequency of a portion of the received signal energy, a frequency divider connected to the output of said doubler-amplifier for reducing the multiplied frequency to a value equal to the signal frequency, and means for combining the received signal with output energy of said doubler-amplifier.

5. In a system for receiving pulse modulated carrier signals of the type wherein the signal pulses and spacing intervals are characterized by a pre-determined phase shift differing from 180 of the carrier wave of substantially constant frequency and comprising a signal receiver and means for producing an auxiliary carrier signal to be combined with the received signal for deriving demodulated signal pulses, said means comprising a first frequency multiplier connected to said receiver for increasing the frequency of the received signal to produce an intermediate signal subject to 180 phase reversals according to the signal pulses and spacing intervals, respectively, a frequency doubler-amplifier connected to the output of said first multiplier for increasing the frequency of a portion of the intermediate signal energy, a. frequency divider 7 con-nete cof-cheV output of vsaid multiplier-ampl-ier' 'for .reducing ,the multiplied frequency to ava1ue equal t'o the Aintermediate signal frequency, and means for combining said intermediate signal withfoutput 'energy of said frequerrcy divider to produce 'nal signal energy of amplitude varyingJetix/er1` limits in accordance with the signal pulses Aand spacing intervals, respe'ctively.

1 GUSTAV GUANELLA.

REFERENCES CITED The illwing referentes are of record in the Vthis patenti Number

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