US2363571A - Radio signaling - Google Patents

Description

Patented Nov. 28, 1944 RADIO SIGNALING l Joseph G. Chaffee, Hackensack, N. J., assignor to Bell Telephone Laboratories, Incorporated, New

York, N. Y., a corporation of New York Application January s, 1943, SerialNo. 471,389 r Claims. (01. 250-.6)

This invention relates to radio signaling systems and more particularly to two-way radio telephone systems for short rangecommunication at ultra high frequencies. i a

The general objects of the invention are the simplification of the circuits and controls in twoway signaling systems and the reduction of the size andweight of the equipment necessary for reliable communication over short distances. Another object is the improvement of the noise characteristics in radio telephone systems super-regenerative receivers.

In accordance with the invention, a super-regenerative oscillator directly coupled to the antenna at each terminal of a two-way system, is

using used both for transmission and for reception of a the high frequencycarrierwave. This oscillator is arranged to generate waves of an ultra high frequency,which may, for example, be of the.

order of several hundredmegacycles per second, and is alternately quenched and activated at a from the following detailed description-and by rate of several million cycles per second. a The oscillators atthe two terminals operate at approximately equal high frequencies, but with quenching rates which differ by a substantial amount, for example, 400 kilocycles per second.

Signaling is effected by modulating the frequency of quenching in accordance with speech, the radiated wave partaking of the character of a carrier wave modulated in amplitude by a frequency modulated subcarrier. At the receiving terminal the received wave, modulated in the.

above manner, is impressed on the super-regen erative oscillator, thereby giving rise in the wellknown manner to a current correspondingto the amplitude variations of its envelope, that is, to the quenchingfrequency at the sending end. I have found that there is. also produced a current corresponding to the difference in the quenching oscillation frequencies which,.slnce the quenching oscillation at the sending. endis 'frequenc'y modulated by. the speech signal, is likewise frequency modulated; In the systems of the invention, the signal is detected from this difference frequency current by any of. the well-known frequency 'modulationdetectors. "By subjecting,

the current to amplitude limiting a substantial reduction. .of the noise. commonly present in super-regenerative receivers is effected.

LAntenna switching is eliminated by the use of the super-regenerative oscillator for both sending and receivingand at the same time thesize and, weight of ,the equipment is reduced. The

power output and the receiving sensitivity ofla super-regenerative oscillator using a receiver type tube is such that reliable communication over moderate distances may be maintained.

The use of ultra high frequency waves in the systems of the invention has the advantage that high frequency quenching rates, such as several million cycles perfsecond,'can be employed without adverse effect upon the sensitivity of the super-regenerative:receiver. .Thisqpermits the quenching rates at the system terminals to differ .by'high super audible frequencies and thereby simplifies the construction .of the receiver circuits which carry the difference;frequency currents.

Similar circuits may housed in the receivers at both-terminals, or in all receivers if additional stations are included. The :high super-audible value of the differencefrequency makes it easy to provide circuits of sufficiently broad selectivity toaccommodatethe full swing-of the frequency 'modulation. l

Other features of, the invention will appear reference to the accompanying drawing where+ m; l l

.Fig. 1 is a block schematic of a'icomplete systemaccording to theinventiomand q Fig. 2 shows the circuit arrangement of the apparatus constituting one terminallstationa Referring to Fig. 1, which shows both terminals of a communication system, station A at the left-hand side of the figurecomprises a transmissionchannel including microphone I, audio transformer 2, frequency modulator 3, which may be. of the well-known reactance tube type, quenching oscillator, A, superregenerative oscillator 5 and antenna ,6,-all coupled in tandem.

The-receiving channel comprises an intermediate frequency selectiveamplifier 1, including amplitude limitingmeans, frequencymodulation detector 8, and telephone receivers 9. The superregenerative oscillatoris preferably designed to generate waves of ultra high frequency, for ex ample, of the order of 500.megacycles persecond.

The quenching oscillator may have a frequency of aboutfour millioncycles per second and its coupling toithe super-regenerative oscillator may with advantage be arranged so that the latter is activated during only a relatively small part of mean frequency of about400 kilocycles, which, as

the quenching cycle. In the receiving path ,amplifier (is selective to a fairly, broad band, preferably 30 kilocycles or: greater, in extent at 2.

already pointed out; corresponds to the difference Of'the quenching frequencies at the two terminal stations. Station B is identical with station A exceptthat the quenchingos-cillator operates at a different frequency. The two super-regenerative oscillations operateat substantially equal frequencies, but synchrlonism, is not necessary beyond the degree determined by the band Widths of the antenna circuits.

In the operation of the system, speech. currents from microphone l are impressed upon frequency modulatingdevice 4, thereby causing the frequency of the quenching oscillator toyary in accordance with speech. For telephonic communication a signal band of about 3,000 cycles per second i generally adequate; consequently a swing of [the quenching frequency. of. about 15 kilocycle's amplitude"permits substantial noise ref duction in the received signal. Assuming anormal quenching frequency of about 4 megacycles, this amplitude of swing is easily obtained by means of a reactance tube modulator coupledltc?v the frequency determining circuit of thetoscilgenerated by the sup ereregener lator.

The waves ative oscillator under control of the modulated quenching oscillator take theform of' a series-of will generally tend to be :discrete, :giving the radiated wave the'character oil-a train. ofzzpulses modulated in" their timing. 1 Narrowing the. .se-

lective characteristic of the'antenna-swill tend i l to lengthen the durationzofthe. pulses I and to give the radiatednwave 1 amore nearly continuous amplitude variation; Either type' of radiation may be used in the systems of theinve'ntion.

'lWhen waves from station EZB, modulated the above manner, "are "received upon -antenna =6, they'are' impressed upon the-super-regenerative oscillator, andprovided the local quenching oscillator" is active,-g-ive'-rise to a current in the oscillator circuit corresponding to the amplitude modulations of the'received wave, that is, to'the quenching oscillator frequency atlthe secondstation. This is theordinary well-known action of a super regenerative -receiver'. "There is also produced" a second current having 'afrequency equal to. the difierencebetween the frequency of the "received amplitude modulations and the frequency of thelocal quenchingoscillator, that is, to the difference between the quenching" frequencies of the two super-regenerative oscillators.

This latter current' is utilized in thesystems of the invention and is selectedby the receiving amplifier"! Whichflis tuned to the'appropriate frequency. Thus, if 'thequenching frequency-at stationA is 4- megacycles and that at-station'B is 3.6 'megacyc'les, the receiving amplifiers at both stations Would-be'tuned'to the difference frequency' of 400' kilocycles per second. "The-"difference. frequency wave, after 7 amplification" and amplitude limiting in amplifier 1, is 'passedto frequency modulation detector 8 'inwhich the signal-is detectedJ It is desirableth'at the meanfrequency ofthe difference frequency wave should be maintained at" a constant value in order thatth'e wave may be'kept'within' the passband of the receiving amplifier. This is accomplished-in the. system illustrated by .an automatic. control -cf-theylocal quenching "oscillator jfrequen {whereby it is caused .tovary insucha Waycs to counteract [an-y. tendencylof. the difference frequency to depart from ..the..assigned mean value. .For .this .purpose, the .detector. 8. may. be. of the. balanced the quenching frequency.

a way asto produce a compensating change of .,-antenna switching, and without requiring any great accuracy of tuning of the ultra high fre- Iiquencyj parts of the system. The system also has the advantage that side-tone is provided in .fthe-telephone. receiver at each station when the .quenchingoscillator at the other station is in operation. This will be evident since the diiference frequency current from which the signal is detected will follow the frequency modulations of both of the quenching oscillators.

:Typical 1. circuit arrangements for a complete d;erminah'stationtasuch asis-shown in Fig. 1;are illustrated;schematically inFig. 2. The superregenerative oscillator comprises. a triode vacuumtube lllbetween the gridjand-plate termina-ls ot which-is connected an oscillatory'loop circuit tuned by'variable. condenser 12. The circuit *is:of-' the :typeshoWnin -Fig. 3 of my. earlier Pat.- .ent;;2l,-l41-,376,;:issued December .27, l938,-.and-.is suitable forthexgeneration of oscillations of'fre- :quencies. asxhigh as 500.:megacycles per; second or more. Inductances 13,. l3'.-and .13". in the oathode, grid.1and;plate leads are ultrahigh. frequency chokes which-prevent the loss .of high frequency energy tothe lowerfrequency portions of theuci-rcuit. A 1oop l4.-coup1ed'to the oscillatorywcircuit supplies the/high frequency oscillations toan antenna for other radiator,. not shown. The cathode. heating rcircuits of the oscillatoretube:andalso. of. the other tubes are omitted for; the :sake of. simplicity. Quenching oscillations-are impressedon the grid of tube "10 throughzgrid resistor 15 from coil l6 which is .adjustably :coupled .to the quenching oscillator circuit. 'A fixed normal biasvoltage isapplied to the-oscillatorrgridq'fromsource |l-,-the magnitude of which determines the duration of the active period: of the oscillator-'inceaoh quenching cycle.

=;'Ihe quenching oscillator. is; of the. Well-known -Ha-rtley=type. It comprises triodexvacuum tube l8 and an oscillatory; circuit. constituted by variablezcondenser I9, inductances 20 and'2l, re-

sistor .22,:.and blocking condenser 23. 24 is a grid leak resistor and'25 is a blocking condenser .in the-'gridlead-to the oscillatory circuit. Ad- :justmentof the quenching oscillator "frequency to itsrdesired .normal or mean value is controlled "by variable condenser l9.

'Modulation of the quenching oscillator fre- "quency in accordance with speechsign'als is effected by reactan'ce tubev 26, the grid circuit of "which is coupled to microphone I through audio transformer 2. Voltages-of'the quenching frequency in quadrature relationship with each other are impressed on th plate-cathode and the grid-cathode circuits of the modulation tube 'through leads12l, 28 and- 29, connected to the terminals of .inductance 2| and resistor; 22 .inthe quenching oscillator circuit- 30,. is ahigh frequency by-pass. condenser .of low capacitywhich prevents. the diversion of, signal energy fromtthe speech input path. The operation. of the reactiv'etube .as. a frequency. modulating. device is .now wellknown and understood and neednot'be described here. It may b noted, however, that sits range of control, is suchas to enable the impressed speech voltagestos produce a frequency .deviation of. the. controlled oscillator of at least 15,000 cycles per second from a mean frequency of about 4 megacycles.

In the receiving channel, which is connected to the plate circuit of the super-regenerative oscillator, the intermediate frequency amplifier comprises coupling filters 3| and 32 and amplifier tubes 33 and 34. This amplifier, as already noted, selects currents of frequencies of the order of four or five hundred kilocycles per second corresponding to the difference of the two quenching frequencies. The filters should have pass-bands at least as wide as kilocycles to accommodate the full range of the frequency modulation.

magnitude is proportional to the amplitude of the oscillations in the'receiving channel and its action on the super-regenerative oscillator is such as to produce a compensating amplitude variation. Resistance 41, choke 48 and condenser 49 constitute a filter circuit which may be adjusted to pass only slow variations of the voltage, thereby providing an automatic volume control.

What is claimed is: l. A two-way radio telephone system comprising at each terminal a super-regenerative oscil- Tube 34 acts not only as an amplifier but also i i to suppress amplitude variations of the oscillations and noise resulting therefrom in the signal output circuit. For this purpose a choke coil 35 or other suitable means having a high impedance at frequencies in thesignal range is connected in the cathode lead as described in United States Patent 2,218,526, issued October 22, 1940, to O. E. DeLange. If desired, a similarconnection may also be used for tube 33 to increase the suppression of amplitude variations.

The frequency modulation detector is of the type well known as a phase discriminator. It

comprises a pair of coupled tuned circuits36 and 31, both tuned to the mean frequency of the im.

pressed waves, and two balanced rectifiers 38 and 30 differentially connected to equal output resistors 40 and 4|. Theoutput voltage of the tuned circuits is impressed upon the rectifiers in series and the input voltag is impressed upon the rectifiers in parallel through couplin condenser 42. The operation of the detector is such receiver 9 through filter 44. This filter should pass only the desired signal frequencies, for example from 200 to 3000 cycles per second, and l should suppress all higher frequencies.

The detector in addition to detecting the signal currents, provides two control voltages which are applied to the regulation of the transmitter circuits. The first of these is a frequency-regulating voltage which is obtained from the normal output of the detector and is applied to the grid of modulator tube 26 through lead and resistance capacity filter 46. The time constant of a the latter is such that only very slow variations of the detector output voltage can pass. The

variations of the controlvoltage, which repre-,

sent changes in the mean frequency of difference frequency waves in the receiving channel, act

the summation of the rectifier outputs through a connection to the junction point of resistors 40 and 4|. This voltage is applied tothe grid of the super-regenerative oscillator through resistor 41, choke coil 48 and coupling inductance l0. Its

which comprises modulating the frequency of lator circuit an antenna coupled to'said circuit,

means for periodically quenching the oscillations .in said circuit at a high frequency rate, the quenching frequencies at the two terminals differing from each other by a super-audible frequency, means for modulating the quenching frequency in accordance with speech signals to be transmitted, a selective circuit coupled. to said oscillation circuit responsive to oscillations of frequency equal to the difference of the quenching frequencies at the two terminals, a signal detector responsive to frequency variations of oscillations impressed thereo'ver, and means for impressing on said detector oscillations selected by said selective circuit.

2. A system in accordance with claim 1 in which there is included in at least one of the terminals means responsive to slow derivations of thefrequency of the oscillations in said 'selective circuit from an assigned value for producing a compensating change in the quenching. frequency. i

3. A system. in accordance with claim 1 in which there is included-in at least one of the terminals means for deriving from the'signal detector a control voltage corresponding in sense and in magnitude to slow variations of the frequency of the oscillations in said selective circuit from an assigned value, and means for impressing, the control voltage on said modulating meansin such polarity as to produce a compensating change in the quenching frequency.

4. A system in accordance with claim 1 in which there is included in at least one terminal means for deriving from the signal detector a control voltage proportional to the amplitude of the oscillations in said selective circuit, and means for impressing slow variations of the control voltage upon said super-regenerative 'oscillation circuit to produce a compensating change. in the average amplitude of the generated oscillations. 5. In a two-way radio telephone system comprising at each terminal an ultra high frequency super-regenerative oscillation circuit, an antenna coupled to said circuit, and quenching oscillation generators coupled to said circuits operating at different highfrequency rates at the two terminals, the method of communcation the quenching oscillations at one terminal in accordance with speech signals, radiating the.

quenched ultra high frequency oscillations, receiving the radiated oscillations at the second terminal, deriving from. the super-regenerative circuit at the second terminal oscillations of the difference frequency of .the quenching oscillations at the two terminals, and detecting the signal from the frequency variations of the dif-. ference frequency oscillations,

l i JOSEPH G. CHAFFEE.

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