US2127525A - Radio receiving system - Google Patents

Description

Aug 23, 1938. T. A. MARSHALL RADIO RECEIVING SYSTEM Filed July l, 1936 @E /wam Patented '23, 1938 `fill?INIT,ITD STATES Q; 2,127,525;` Y Revio @GEW-ING SYSTEM* f w n. Thomas A. Marshallr'vSaPiedro, Calif?` l u "Appli'ca'tionfJulyi, ,ieserseghNgffsssaf iciaivms. (crest-8) A y l(ri-mitm'. 'under the mi, 'of "March 3, i883, 'as

and atmospheric disturbances in thereception of signals.

One of the objects of my inventionis topro- 1 'vide' a 'radio Areceiving system which will' clearly and efliciently receive signals of lvary high` carrierffrequencies which arev especially subject Vto distortion and'critical under )control so that reliable reception thereof is diicult.

" Another/'object of myinvention isto,v provide a raidioreceiving circuitA for'thefreception of high 'frequency signal energy in which the use of highly selective circuitsuis made possible byfthe'ad- Jjustment of the carrier frequencyover consid- "e'rable, ranges of variation to pass the selective circuits to the exclusion of dstortingand linterfering energy.

Al further object ofmy inventionl isgto make possible thev employment of tone discrimination inthereception of continuous Wave signals at vultra-lngh frequencies. l

" Still another object of my inventionv is to provide a superheterodyne radio-receiving system fory the reception of ultra-high frequency signals, 'wherein tonel discrimination is made possible by modulating the intermediate frequency current at a stable audio frequency and keying the audio modulation by the signal received.

A still further object of my invention is to provide vasuperheterodyne radio receiving system 'for-the reception of ultra-high frequency signals, wherein the signals are impressed on the first detector-and are effective in the intermediate frequency amplifier -under the controlr of Van, loscillating-current operative to iniiuence the output of thconversion oscillator; the' intermediate Vfrequency' amplifier beingr particularly selective to pass only the desired frequency band. l

' Another object of my invention is to provide' a ys'uperlfieterodyne radio receiving system for the reception of ultra-high frequency signals Wherein the signals are intermittently passed vto the intermediate frequency amplifier, and 4all distortion, atmospherics, andman-made static are effectively excluded from the output during the periods between the intermittently passed signals. f' Other and further objects of my invention reside in -the circuit arrangement and modifications 'thereofl hereinafter more fully described, with reference to the accompanying drawing, whichis a..schematic diagram :of the circuit employed v-in the receiving system of my invention.

` .;In the reception of signals at ultra-high'fre-l Llective circuit in the receiving system in vorder -to'exclude distortion arising from frequency l Y ,amendedAprilB 1928;,370 O. G4757) lfil/[yfnvention relates broadly tcsuperheterovtlyfneradio receivers and more particularly to a modulationand rharmonics of the modulating signals, andjalsof.V interfering energy such asarises from atmospheric disturbances,`manmade static,

orinterinali'circuit'imperfections.y In C.'W. re-

-ception, the lpractice "known, as tone discrimination is extremelyus'efuland has been' made practical in the reception of'comparatively low frequencies. ,But so far, k,tone discriminationhas not vbeen satisfactorilyaccomplished in the field of ultra-highfrequency Vreception due to variations in the local oscillator frequency and in the transmitter'frequency. Any variation in the oscillator frequency for obtaining `heterodyne reception of the incoming frequency'will change the beat frequency, which is usually made 1,000`cycles 'and amplifiedv in a peakedaudio'- amplifier. Should the beat frequency bechanged even slightly, tone discrimination Willnorlongerbe useful, and'if the frequency of lthetransmitter varies,'the sig- -nall will likely not be heard; For vlovv frequency reception, better stability of frequency and less percent variations'in ther operation of the transmittlers and local oscillator are obtained and tone discrimination is practical.

,In the reception of voice modulated high frequency Waves, the vpractice of tone discrimination is Anotapplicable but/an analogous operation, employing the same circuit arrangement, is possible ywith merelyan adjustment of the frequencies of operationas will `hereinafter be more fully set forth. n

ATone discrimination in C. W. reception at high and'ultra-high frequencies is obtained in the system of my invention v'by using atuned audio system, and a super-heterodyne receiver,l and byk modulating thel intermediate frequency current by varying theoscillator output With a modified type `of relaxation oscillator which is adjusted to 1,000 cycles. Thel intermediate frequency currentl is therefore modulated at '1,000 cycles, and is detected by an ordinary rectier'instead of by the -beat frequency oscillator method. Thus, all signals are receivedas if they were actually transmittedwith a-modulation of 1,000 cycles, and tone discrimination isvpossible.y

Referring -to the drawing in more detail, I provide an antenna l and a pre-selector tuning circuit 2 connected With the input of a radio frequencyamplier-stage '3.th`roughfa coupling condenser 14. A balanced, non-oscillating rst dentector circuit employing electron tubesl 5 and 5' has the inductancel in the'input circuit thereof coupled with the inductance 1 which is connected in ,the voutputcircuit of the radio frequency amplifler 3. An inductance 8 is connected between Ithe anodes ofthe tubes and 5 and hasl a center rtap connection -8 thereto for connection to vthe anodes of the lbalanced detector. The inductance J8.is coupledwith the input circuit of the first detector through the inductance 6, but oscilla- I and I0', inductance I I connected with the control grids ythereof and inductance IZ, coupled with inductance II, connected with the anodes thereof. in shunt with inductance Il, and is operable to control the frequency of oscillation of the conversion oscillator in the usual manner` through a gang control arrangementwith. tuning con-l densers I5 and I6 in the radio frequency amplier 3 and the first detector circuit, respectively, as indicated by the dotted line II..

, lIhe output of the conversion oscillator is coupled with the first detector, wherein it beats with energy at the received frequency to produce currents at'the desired intermediate frequency, through the inductace 8 via the high frequency coupling condenser I3, which isv of approximately 100 mmf. capacity, the conductor vI 9, and the center tap 8. The output of the first detector, at the intermediate frequency is Vfed through the tap 8' and conductor 20 to the intermediate frequency amplifier as will be hereinafter more fully considered.

In addition to and in cooperation with the usual functions in a superheterodyne receiver, I provide a relatively low frequency oscillatorY 2|, which is a modified relaxation type of electron tube oscillator and will generate an output of constant frequency. Means comprising a variable resistor 22, connected in the cathode circuit of the oscillator 2i, is provided for adjusting the frequency of operation of the oscillator 2l. In C. W. reception, as now being considered, this frequency may be an audio frequency of 1000 cycles per second. Measurements on thisoscillator, operatingat 1000 cycles, showed that its fre.-

quency varied but 3 cycles over a period of five hours. A variable anode voltage of volts plus or minus 10 percent gave a frequency variation of approximately 10 cycles. Novariation infrequency was observed by varying the heater voltage from 2 to 2.5 volts.

The low frequency auxiliary oscillator l2I is connected with the conversion oscillator through a high frequency choke coil 23, a low frequency coupling condenser 24, which is of approximately 1 mfd.' capacity, conductor 25, `and center tap I2' on the inductance I2, whereby the output of the low frequency oscillator 2l modulates the output of the conversion oscillator. In the case of C. W. reception, the output of the conversion oscillator is modulated by a constant 1000 cycle per second audio frequency. In'the first detector, this modulated current entering at 8lr divides between the two halves of the inductance 8 on either side of the center tap andqequally affects the control grids of the tubes 5 and 5 by reason Yof the coupling between inductances 8 .and 6. When no signal is received on antenna I and in inductance l, the modulation of 1000 cycles will not be heard by thev listener because of the absence of an intermediate frequency current. When a signal is received and passes through inductance 1, the control grids of the tubes 5, 5', are oppositely affected thereby because of the unbalanced coupling of the inductance l, and a beat frequency will be generated from the combination of the signal and the local oscillator output. The first detector thus produces an output at the beat frequency which is the intermediate frequency A variable condenser Iis connectedV auxiliary oscillator 2! current of the superheterodyne receiving system, and this intermediate frequency current is modulated at 1000 cycles from the output of the auxiliary oscillator 2|.

The modulated intermediate frequency current is fed through conductor 20 to the interrnediate frequency amplier stages 26 and 27 and to the second detector 28 in the output of which appears the 1000 cycle'modulation in the characterof the signal received. In the output of the second detector, I have provided a low pass filter 29 and a band pass filter 30 in order to effectively exclude all energy except the 1000 cycle signal. This is possible because of the stability of the 1000 cycle wave which is generated in the Peaked audio frequency amplifier stages 3| .and 32 complete the receiving circuit to the telephone receivers 34. The listenerhearing the constant 1000Ycycle note in the(characterV of the signal may therefore easily Y discriminate in tone between the signal and any interference that may be present in the telephones.

I have shown in the drawing merely the terminals of the power supply circuits and the connections at x, which interconnect the heater elements in the various tubes shown. 'Volume control means are shown at 35 and 36; and choke coils 3l and bias resistors 38 are shown distrib- ,uted in the power connections as required. Bypass condensers 39 likewise are provided `where necessary.

In the system of kmy invention as shown and described, static appears to be received as a highly damped oscillation and does not unbalance the detector by'aoting in the inductance 'I as a signal. It is, therefore, not heard in the telephones at 1000 cycles when Va tuned vaudio system isemployed as shown. It appears also that crashes and noise do not effectively unbalance the rst detector, so that clear reception is had on .all high `frequency bands. Thus, the system of my invention is extremely useful in the elimination of noise, static and internal amplifier noise, and reception at the 'high frequencies is, therefore, greatly improved.

A further useful advantage of the system of my invention will be seen in` ultra-high frequency multiple reception work, that is, intermittent receptionfrom a number ofcommunication stations all transmitting at or .near the same frequency. Heretofore such operation has not been successful on ultra-high frequencies due to the fact that crystals used for controlling the frequencies of the Several transmitters are not all `ground to the same frequency but to frequencies differing by several kilocycles. Higher accuracy in the grinding of the crystals to insure substantially identical frequencies of operation is irnpracticable. By employing a modulated intermediate frequency current in the superheterodyne receiver, the circuits can be made to cover as wide a range as 16 kilocycles by adjusting the intermediate frequency band pass tuning sys- "tem, or by obtaining from the second ldetector through the beating of incoming signals of various frequencies with the output of the conversion oscillator and the output of the auxiliary oscil1ator,'beat frequencies which will be passed by peaked intermediate frequency amplifier circuits.

-The latter instance will obtain, for example, wheny an oscillatorfrequency of 20,465 kilocycles isrnodulated by a 1000 cycleoscillation to produce beats ofV 20,466 and 20,464 kilocycles. Considering that these beat frequencies Will also beat to produce a 2 kilocycle note and that the second. harmonic of the modulation is 2 kilocycles, further beat frequencies of 20,461 to 20,464 and 20,466 to 20,469 kilocycles, as well as the fundamental frequency o-f 20,465 kilocycles, will be present in the first detector to beat with the signal energy. Signal energy therefore of any frequency between the limits of 19,996 and 20,004 kilocycles will produce a beat frequency in the output of the first detector of 465 kilocycles which will be passed by a peaked 465 kilocycle intermediate frequency amplifier.

Considering, now, voice modulated currents received at the antenna I from a single transmitter operating'at ultra-high frequency, and the frequency of which is susceptible of rather broad variation, such as within the range above noted in which a number of C. W. transmitters were considered operating. Such a voice modulated current, varying in frequency, can be received by the system of my invention in a manner similar to that just previously described. One important adjustment is required to be made, namely, in the frequency of the auxiliary oscillator which must obviously be of super audible frequency in order that the output thereof will not be heard in the telephones. This adjustment can be made by merely 'varying the resistance 22 in the cathode circuit of the auxiliary os'cillator 2l. Coupling condenser 24 may also be varied to transmit the higher frequency more efficiently; and the lters 29 and 30 also may be adjusted for the modified operation of the system. Also, as only one station is to be received, the intermediate frequency amplifiers 26, 21, may be limited to respond only to a narrow frequency band which embraces the voice modulations. The advantages of noise suppression, and distortion removal and prevention, noted with respect to the operation of the system of my invention in C. W. reception,

`obtain also in the reception of voice modulated currents.

While the system of my invention is primarily intended for use in C. W. reception on ultra-high frequencies, as hereinbefore set forth, I desire it understood that modifications may be made within the scope of my invention along the lines indicated with respect to the reception of voice modulated currents, and along other lines, and that no vlimitations upon my invention are intended except as are imposed bythe appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon.

What I claim as new, and desire to secure by Letters Patent of the United States, is as follows: y

1. In a superheterodyne high-frequency continuous wave signal receiving system, in combination, a first detector comprising a balanced electron tube circuit having a balanced input circuit and a balanced output circuit in coupled relation, a local oscillator, means for modulating said local oscillator at a constant audible frequency, means for impressing the output of said modulated oscillator on said first detector through said output circuit in balanced relation, means for impressing incoming continuous wave signals on said first detector in unbalanced relation whereby said electron tube circuit is unbalanced and current flows inthe said output circuit at-.

the beat frequency of said incoming signal and the local oscillation, in the character of the incoming signal, and modulated at said constant audible frequency, an intermediate frequency amplifier operative at said beat frequency, a second detector, and a peaked audio frequency amplifier for selectively amplifying said modulation.

2. In a superheterodyne high-frequency voice modulated signal receiving system, in combination, a first detector comprising a balanced electron tube circuit having a balanced input circuit and a balanced output circuit in coupled relation, a local oscillator, means for modulating said local oscillator at a constant inaudible frequency, means for impressing the output of said modulated oscillator on said first detector through said output circuit in balanced relation, means for impressing incoming voice modulated signals on said first detector in unbalanced relation whereby said electron tube circuit is unbalanced and currents of beat frequencies are produced in said first detector, an intermediate frequency amplifier, certain of said beat frequencies produced in said first detector corresponding to the frequency of operation of said intermediate frequency amplifier, a second detector, and an audio frequency amplifier for amplifying the voice modulations detected in said second detector.

3. In a superheterodyne high-frequency signal receiving system, afirst detector comprising a balanced electron tube circuithaving a balanced input circuit and a balanced output circuit, center-tapped inductances in said input and said output circuits arranged in coupled relation, and a third inductance coupled with said centertapped inductances, means including the centertapped inductance in said output circuit for impressing modulated local oscillations on said input circuit in balanced relation, means including said third inductance for impressing signal energy on said input circuit in unbalanced relation, and an intermediate frequency amplifier operatively connected with said first detector through the center tap of said inductance in the output circuit thereof for receiving modulated oscillations of beat frequency in the character of the signal energy.

4. AIn a superheterodyne high-frequency signal receiving system, a first detector comprising a pair of electron tube devices having input circuits connected in push-pull relation and output circuits connected in parallel relation, centertapped inductances in said input and said output circuits arranged in coupled relation, and a third inductance coupled with said center-tapped inductances, means including the center-tapped inductance in said output circuits for impressing modulated local oscillations on said input circuit in balanced relation, means including said third inductance for impressing signal energy on said input circuit in unbalanced relation, and an intermediate frequency amplifier operatively connected with said parallel connected output circuits for receiving from each of said electron tube devices modulated oscillations of beat frequency in the character of the signal energy.

THOMAS A. MARSHALL.

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