US2209273A - Carrier frequency system - Google Patents

Description

July 23, 1940. J. l.. HILLS 2,209,273

- CARRIER FREQUENCY- SYSTEM I Filed Feb. 1e, 1939 {Buffe/@dar i gli .Second III-G I. Huazo f7@ uency 28 Q fatwa l0 mp/Hier) F5 if! den/ice 3) l from un) (Wimafz'ng` of Vara/e spe-ed' maior za aperae de Vice /2) INVENTOR JOHN L. HILLS i BY 1 ATTORNEXS Patented July 23, 1940 UNITED STATES PATENT .OFFICE V CARRIER FREQUENCY SYSTEM Application February 18, 1939, Serial No. 257,259 In Great Britain March 2, 1938 12 claims. (o1. 25o-"6) This invention relates to carrier frequency electric systems for communication, signalling, indicating, remote control and other purposes.

According to the present invention the carrier n frequency of a transmitter-receiver station or each transmitter receiver station, whilst arranged so as to be continuously variable within the predetermined frequency spectrum band, is normally maintained constant at. any fortuitous or predetermined frequency within said band, but is caused to vary when and only' when another transmitted carrier is received which produces at or before the second detector of the station an interference predetermined as to frequency and preferably also as to amplitude, which interference in the case of a speech-modulated carrier may be a heterodyne interference of, say, 5,000 cycles per second or even less. The frequency is thus either increased or decreased so that the aforesaid frequency interference is automatically removed whereupon the frequency variation is discontinued so that the transmitted frequency is now caused to remain constant at a new value until a fur-ther interference may arise when the 25l process above described is repeated, and so on.

Preferably the speed of the .frequency shift is approin'mately proportional to the amplitude of the heterodyne interference so that ifa strong interfering signal is suddenly received the interference is the more quickly and more Widely removed than is the case of a relatively weak signal.

Thus by this invention a plurality of signals may be simultaneously received which are automatically segregated into separate fixed frequency channels separated appropriately in accordance with their signal strength on the receiving. aerial. It is, of course, understood that the receiver is substantially aperiodic with respect to the predetermined frequency spectrum band.

In order that the utility of the present invention may be the more fullyappreciated it-may be helpful here to state that as at present considered, the main object of the invention is to enable a carrier wave to be radiated continuously -wvithin a predetermined frequency spectrum band without preventing reception of one or more other carrier waves radiated Within said band and from stations at predetermined distances or of predetermined radiation strength, thus enabling an instrument to be produced which will immediately indicate when another transmitter is radiating at a frequency within the aforesaid band and within the rangeof sensitivity of the receiving instrument. The instrument may thus be called a radio-proximity indicator for use for example by aircraft and by ships at sea. It will be appreciated that since a frequency band for a system in accordance with the invention will require to be allotted by the appropriate government department, the mean Wavelength will at the present time haveto be short, say i'lve metres. Since the range of such order of wavelengths is inherently short, apart from the power of the transmitter, the instrument according to the invention has great utility in connection with aircraft operating in the neighbourhood of for example an aerodrome or airport since it can provide to that airport or to aeroplanes within its vicinity an indication of one anothers proximity. The system is entirely automatic in its warning and is such that the radiations from one craft cannot affect the'ability of that craft to receive signals or radiations from another craft. When modulation of the carrier waves is taking place since each station definitely abandons all adjacent channel selectivity, all the modulations are capable of being heard simultaneously. Such is what is implied by a multiplex system in the present specification, as distinct from the transmission of several independent messages simultaneously over' a single channel such as by the plural high frequency modulatio-nof a single carrier wave. Thus the system may more aptly be called conference system.

Another important use of the invention may be in military operations where for example it is desired that communication should existbetween several units, one of which may be a commandingv 'unit from which orders are issued which are required to be received simultaneously by all the otherunits, which latter may reply at any time andeven interrupt the orders if necessary, Whilst furthermore the subordinate units can intercommunicate with each other;

To enable the invention to be fully understood it will now be described with reference to the accompanying drawing in which:

Figure 1 is a block diagram illustrating the invention and the requirements thereof.

Fig. 2 is a diagram of a convenient arrangement for varying the transmission frequency and holding it at different values.

Fig. 3 is a circuit diagram illustrating how the braking devices shown in Fig. 1 may be supplied with current and,

Fig. 4 is a diagram showing an alternative aradapted to operate in accordance with the invenr tion. The rectangle I represents conventionally a radio transmitter having a transmitting aerial 2 and a frequency control device 3 which is adapted under the conditions hereinbefore set forth to maintain the transmission frequency normally constant but to shift itwhen required. The rectangle iv is amoptional frequency Wobbler unit .the purpose of which will be hereinafter described.

'I'he station illustrated by Fig. 1 further com-L transmitter.

prises the receiving aerial 5A feeding the rst de tector or mixing valve device 6 whichfeedsyin.,

the well known manner Yan intermediate frequency amplifier 'I followed by a second detector 18,

followed, if desired, by an audio? frequency `arnplier 9 which feeds the telephones I0, indicating orcontrol devices.

In Fig. 1 of the accompanying drawing is shownat II the interference beat selector or frequency l responsive device which is fed from theris't 'dtector '6. and which is connected to the frequencyy control unit 3 in the manner hereinafter specifically described.

3 The operationr of the systemshown in .1 i isv'as hereinbefore set forth, it being understood.

that-the. input circuitpf the first detector 6 is aperiodic to -thepredetermined frequencygspectrum band but isv not responsive tov frequenciesi outside said band, whilst the intermediate fre.v i 3.0: quency amplifier 'I has a band pass characteristic responding to thedifference frequencies between carriers-from; .remote stations received by the.

aerial .5 and the'local carrier wave acting as the local `oscillatorfor the superheterodyne receiver. 1 It willbe appreciated that it might be possible, although '-unlikely, for' a` zero beat heterodyne effectftoarise for a shorttime in the receiver between-:the carrier of a.remote station and that of'. the local transmitter in which case whilst there may be violent distortions due to the mix-.-v

ing of the modulations; there would be no voltage acting througl'i the interference beat selector I I to operate the frequency control unit 3 for separating the frequencies( example thefrequency Wobbler unit 4 may coml- 50: prise merely a relatively minute' trimming condenser. havingan element adapted to be moved,

conveniently rotated such as by clockwork or an electric. motor. vSuch condenser ymay be in parallel with` the variable tuning device in the uniti g3l-g1fl`he frequencywobble affected by the unit 4 is not 'criticaljand it isimmaterial whether. its

vrange varies slightly such asl at different settings ofy-thefmain frequency control unit which is 'con'- veniently a condenser. The wobble rate should i603'. be either sub-audio or supersonic.l

`165the transmitter I.. It is common knowledge that Referring, now to Fig. 2,"at I2 is shown aY varilable condenser incorporated in the transmission frequency determining unit 3. This .condenser may be the main `or the: trimming condenserfof instead of a condenser any other means; may be provided vfor silently varying the transmitted frel 'quency within the predeterminedv frequency spectrum band, such forfinstance, as a distortableini IOfllductance coil forl an armature Ymovable relatively T clyavvspifingdriven: clock mechanismhaving a;

to an inductance coil or in other ways which are comnion-` knowledge, :for example, im the art of automatic tuning-in radio reception. f

KI' 3 .is indicated a motor which is coni/'enier'it-` or'A other Such zero beat effect can' .L5-,readily be prevented by continuously wobbling' the transmission frequency over a rangev of say small pinion I4 and a large one I5. The small pinion I4 meshes with a gear train comprising a large wheel I6 which meshes with a smaller. wheel II which is rigid with the moving element of the condenser or other variable tuning device I2. The arrangement is therefore such that the motor I3 normally causes to rotate the moving element of the tunin'g'device I2r so :as to-,Lvary the frequency back and forth cyclically within the predetermined frequency spectrum band of the 'Ihelarge wheel l5 of the motor I3 drives the v exemplified soft iron toothed wheel I8 through n the multiplyinggear'train consisting, for example; of the system illustrated at I9. The soft iron toothed wheel I 8 co-operates with an. elec- `tromagnetcomprising the yoke 26, polesZI and anode circuit. of a triode 23 in series with a limiting. resistance 22a which is preferably adjustable, and lwith an anode battery 25; The grid ofthe triode,23 vis-fconnected to the loadresistance 24 cfa the 'diode,25a, the negative end ofthe resistance 24` being connected tothe anode .of the.

diode' 25dthrough the resonant'circuit 26 whichv isjtunedlto. a frequency slightly higher than'the. highest modulation frequency for which.l the sys.-4

tem is` designed. Inl accordance'with the example hereinbefore given the circuit 26 is tuned to be resonantv at 5,000cycles per second.` In the cathv ode circuit of thevv diode 25a. is a delay bias; battery 2'I for preventing the diode from passing currentypuntilthe. heterodyne interference voltage attains a value. which will impair the intelligibility ofthe speech, received. VBy such means the vsystem canv be made.' to ignore interfering signals which'fare of insufficient strength to lcause undesirable interference compatible with the purpose for which the systemis being used such for example as either. o'f the'purposes hereinbefore stated v by way fofexample..`

Thean'odev Yof the diode 25a is kconnected by.,

thef-lead 2 8 to the first detector 6 shown in Fig. 1. Itwill be appreciated that-.when.theheterodyne voltage :exceeds the predetermined value, the.. y normally unbiased grid of the triode 23 will become'negative'toreduce the current flowing in the winding 22 of the rmagnet 23 (Fig. 2) .the

triode 23.nor1nally. passing su'icient current to hold ythe toothed; wheel I8 stationary and thus canarise `inpracticev except that forshort periodsk zero beat Vconditions may arise and such vcan be y prevented! by the wobbling unit A4 vpreviously vreferrea to# itfis .desirable-furthermore that the statiohs'snouid rearranged toir'un at dinerent normal maximum` speeds and'fthat the llaws of the variablejtuning-devices, such as I2 should not be identical-fin the colopelratirigv stations? Referring lastly to Fig. 4 of the accompanying drawing, which illustrates an alternative arrangement to that shown in Figs. 2 and 3 but in which the same reference numerals designate similar parts, the anode 2.0i the triode 23 includes in a balanced bridge arrangement the winding 29 of electric motor .(not shown) and resistances 3B, 3l, and 32. This motor may be of any known and convenient type such as the motor of an electricity meter and it is preferably of the variable speed type and adapted to rotate or to operate the moving element of the variable tuning device I2 at a speed in accordance with the extent of energisation of the motor winding 2S which as will be appreciated varies in accordance with the voltage of the audible heterodyne which may arise at the first detector (Fig. 1)` except for the presence of the delay bias 2 of the diode 25a, which, as with the arrangement shown in Fig. 3, is provided for the purpose of preventing frequency shift unless the heterodyne interference volume is sufficient to impair speech intelligibility.

I claim: 1. The method of conference type carrier frequency intercommunication between a plurality of transmitter-receiver stations, which consists in continuously transmitting from each station a carrier at a frequency which is normally maintained constant somewhere within a predetermined frequency band, effecting aperiodically with respect to said predetermined band the supersonic heterodyne reception of the carrier of at least one of the other stations whilst using the local carrier for the heterodyning, and effecting an automatic shift of the local carrier frequency to another fixed place within said predetermined band when a received carrier produces a heterodyne interference of predetermined frequency.

2. The method of conference type carrier frequency intercommunication between a plurality of transmitter-receiver stations, which consists in continuously transmitting from each station a carrier at a frequency which is normally maintained constant somewhere within a predetermined frequency band, effecting aperiodically with respect to said predetermined band the supersonic heterodyne reception of the carrier of at least one of the other stations Whilst using the local carrier for the heterodyning, and effecting an automatic shift of the local carrier frequency to another fixed place within said predetermined band when a received carrier produces a heterodyne interference of predetermined frequency and predetermined amplitude.

3. The method according to claim l, wherein the rate of the carrier frequency shift is substantially proportional to the amplitude of the heterodyne interference.

4. The method of conference type carrier frequency intercommunication between a plurality of transmitter-receiver stations, which consists in continuously transmitting from each station a carrier at a frequency which is continuously wobbled through a small range about an average frequency which is maintained constant somewhere within a predetermined frequency band, effecting aperiodically with respect to said predetermined band the supersonic heterodyne reception of the carrier of at least one of the other stations whilst using the local carrier for the heterodyning, deriving from said receiver a voltage only when any heterodyne interference of predetermined frequency arises in the receiver, and utilizing said derived voltage to shift the local carrier frequency to another fixed place within said predetermined band.

5. A transmitter-receiver station for conference type carrierY frequency intercommunication, comprising in combination a carrierwave transmitter having means adapted to vary the carrier frequency cyclically over a predetermined band, a supersonic heterodyne receiver arranged to utilize the local carrier as local oscillator said receiver having an intermediate frequency circuit substantially aperiodic to the range of intermediate frequency variation with respect to said .predetermined band, and means adapted automatically to actuate said carrier frequency varying means when a received carrier of frequency within said band produces a heterodyne interference of predetermined frequency so as to shift the carrier to another xed place within said band.

6. A transmitter-receiver station as claimed in claim 5, wherein said last mentioned means is responsive also to the amplitude of said heterodyne interference.

7. A transmitter-receiver station for conference type carrier frequency intercommunication, comprising in combination a carrier wave transmitter having means adapted to vary the carrier frequency cyclically over a predetermined band, a supersonic heterodyne receiver arranged to utilize the local carrier as local oscillator, said receiver having an intermediate frequency circuit substantially aperiodic to the range of intermediate frequency variation with respect to said predetermined band, means for deriving from said receiver a voltage only when a received carrier of frequency Within said band produces a heterodyne interference of predetermined frequency and amplitude, and means adapted to actuate said carrier frequency varying means in response to said derived voltage and at a rate substantially proportional to said amplitude.

8. A transmitter-receiver station as claimed in claim '7, having additional means for continuously wobbling the carrier frequency over a range small compared with said predetermined band.

9. A transmitter-receiver station for conference type carrier frequency intercommunication, com.- prising in combination a carrier wave transmitter having a tuning element which is normally fixed but is adapted to vary the carrier frequency cyclically over a predetermined band, a supersonic heterodyne receiver arranged to utilize the local carrier as local oscillator said receiver having an intermediate frequency circuit substantially aperiodic to the range of intermediate frequency variation with respect to said predetermined band, a resonant circuit for deriving from said receiver a voltage only when a received carrier of frequency within said band produces a heterodyne interference of predetermined frequency, and a motor adapted to actuate said tuning element to a new fixed position in response to said derived voltage.

10. A transmitter-receiver station for conference type carrier frequency intercommunication, comprising in combination a carrier wave transmitter having a tuning element adapted to vary the carrier frequency cyclically over a predetermined band, a source of power tending to actuate said tuning element continuously, electroresponsive means for normally holding said tuning element against such actuation, a supersonic heterodyne receiver arranged to utilize the local carrier as local oscillator said receiver having an. intermediate yfrequency circuit substantially aperiodc to the range of intermediate frequency variation with respect to said predetermined band, means for deriving lfromsaid receiver an electrical effectfoniy when a received carrier of frequency within said band produces a heterodyne interference of predetermined frequency,. said electroresp'onsive holding means being energised from said deriving means. l

11. A transmitter-receiver station for conference type Vcarrier frequency intercommunication, g

25:f frequency within said band produces a heterodyne interference of predetermined frequency, and meansI adapted to energise said motor in accordance with said electrical effect so as to shift the transmission frequency to another xed place Within said band. .l 7 v 12. Atransmitter-receiver station for conference type carrier frequency intercommunication, comprisingfn combination acarrier Wave transmitter having-means which are normally fixed but are adapted to fvary the carrier frequency" cyclicallyover a. predetermined band, a supersonic heterodyne receiver arranged to utilize the local carrier as local oscillator said receiver having an intermediate frequency circuit substantially aperiodic to the range of intermediate frequency variation with respect tosaid predetermined band, means forv deriving from said receivera voltage.: onlyvwhen a received carrier of frequency Within said band produces a heterodyne interference of predetermined frequency, said/means comprising a biased -recti'er connected to some partofthe'receiver after the rst detector thereof with a load resistance and a circuit tuned to the predetermined interference frequency', and means adapted to actuate said carrier frequency varying means in respo-nse to said derived voltage so as to shift the transmission frequency toanother fixed place Within Said band.

J OI-IN LIONEL I-IILLS.r

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