US2416791A - Radio receiver system - Google Patents

Description

H. H. BEVERAGE RADIO RECEIVER SYSTEM Filed oct. 1o, 1942 March 4, 1947.

2 Sheets-Sheet 1 mvENToR Izroh/IZl/ezago ATrQRNEY March 4, vH947.

H. H. BEVERAGE RADIO RECEIVER SYSTEM Filed oct'. 10, i942 2 Sheets-Sheet 2 ATTORNEY Patented Mar. 4, 1.947

Radio Corporation of America,

Delaware a corporation of Application October 10, 1942, .SerialNd 461,527

11 Claims.

My lpresent invention relates to Aultra-high frequency radio receivers, and more particularly -tc radio receiving -systems capable of receiving .ann plitude modulated carrier energy `free of `undesired frequency modulation effects.

It is the usual practice at relatively low radio frequencies to stabilize the yiftransmitter, vand to place radio frequency selectivity ahead of a superheterodyne receiver first detector 'thereby to improve the signal to noise ratio -atitherst -detector. vAt very high radio frequencies, however, this is impractical at present, because of the lack of devices that Willamplif-y satisfactorily-,at these frequencies. This makes it impracticable tosta bilze the frequency of build a radio frequency amplifier ahead of Vthe rst converter. Accordingly, .in the prior art when radio transmission yhas been practiced .in the extremely .high .radio `frequency range, it Vhas been necessary `to allow the transmitter 4to vary ,over a comparatively wide band of frequencies. Consequently, .the Ysignal vselector vcircuits of Vthe Vassociated -superheterodyne receiver .were .d e.-

signed so that the acceptance bands thereof -were wideenough to accept Vthesignaling modulations plus the yfrequency variations of the transmitter and the receiver .localoscillaton This results .in a relatively .poor .signal -tofnoise ratio fat the .re' Cever output.

It may, .thereforabe stated that it is-one ofthe main objects of my present invention ,to provide communication at ultra-high radio frequencies and 'to use .a narrow intermediate frequency Dass band which is only wide .enoughtoselect the necessary modulation frequencies; the noise .being greatly reduced ,due to the narrow intermediate frequency (LF.) band since the noise 'is a function of the band width.

Another important object of my vinvention may bestated to reside in the provision -of a system of receiving amplitude modulated signals without theusual difficulties .caused by .coincidental undesired yfrequency modulation (F. MJ).

Another `important object of this invention to make possible the use of a fsuperheterodyne receiver in which the 'band width of the I. F. .network does notneed to be `excessivelywide thereby making it possible Vtofobtan Afreedom fromin.- terference and to lsecure an Limproved signal to noise ratio.

Another object of .my invention is to provide an arrangement for receiving ,amplitudemodulated signals which eliminates the difficulties caused by coincidental undesired 'frequency ^modulati r n,` wherein 'the' local beat oscillator 'has the transmitter, for to s the same frequency variations as ,thesig'nal with the result that ,the intermediate frequency .energy has no frequency variation.

uYet another object is to provide Ea receivingsystem for amplitude modulated signals with -coincidental undesired frequency modulation wherein the frequency variations are 4removed by deriving local heterodyne energy from the signal energy.

Still another object of my invention is to provide a receiving system .for amplitude modulated signals which eliminates coincidental undesired frequency modulation ,at the intermediate 5fre,- quency by beating the signals with local v.oscillations derived from the .signal energy, and passing said local oscillations:through a limiter to remove amplitude variations thereby obtaining linear ,respense. V

It is still necessary in the receiving systems disclosed in this application to .have the input circuit to the rst converter sufficiently wide to allow for the variationsof the transmitter. However., the noise lat Vthe first detector may be .considered as a continuous spectrum of noise which is in effect scanned by the I. F. vamplifier in accordance with the .frequency variations :of the received signal so that at any instant the I. F.. network sees only a comparatively narrow band of frequencies thereby .resulting in .an improved signal to noise ratio at the receiver output.

`Stated generally, in `my receiving 'system undesired frequency modulation effects of the received signals are completely eliminated at the operating I. F. of the receiver by an varrangement whereby the high frequency `oscillations which beat with the received signal to produce the I. E'. energy is derived from a combinationof Y,

high frequency energies. These energies `are those of the 'local oscillator and the ,incoming `signal so that vthe conventional .high lfrequency oscillator of Va heterodyne system .is replacedfby oscillations `having exactly the .same nfrequency variations as the received signal itself. Consequently, thebeat derived from the .local oscillations .and .the Asignal yhas noneof. the frequency variati-ons of Vthe original signal, and the I. F. amplifier need be only wide .enough to transmit the essential modulation side bands.

The novel features which I believe to becharacteristic of my invention are set forth with lparticularity in the appended claims; the invention.

itself, however, as to bothits organization and method of operation will best be understoodfby reference to the following description taken `in connection with the drawing inywhich haverinrlicatedv diagrammatcally several circuit organzations whereby my invention may be carried into effect.

Y In the drawing:

Figs. l, 2, 3 and 4 schematically show respectively different embodiments of the invention.

Before describing the circuits in detail, it is pointed out that it has been the practice to stabilize the frequency of the transmitter in radio frequency communication by the use of' stable master oscillators. For example, resonant lines and crystal-controlled oscillators have been uti' lized for frequency stabilization. Generally,lthis' is a desirable solution to the problem since itr conserves frequency space, and makes possible the use of a simple receiver. However, at frequencies of the order of thousands of megacycles (mc.) it is frequently very difcult, and in some cases practically impossible, to stabilize the frequency of the transmitter, since a very high degree of frequency multiplication would be required if conventional stabilized oscillators were employed. In other cases, unconventional devices are required to generate these very high frequencies efficiently, and, therefore, conventional methods of frequency stabilizationare not applicable.

Referring now, specifically to the schematic radio receiving system shown in Fig. 1, let it be assumed that there has been radiated from an ultra-high frequency transmitter an amplitude modulated carrier wave whose carrier frequency is chosen at 2,000 megacycles. As is well known to those skilled in the art, the signal energy may be radiated from a parabolic antenna, andthe radiated signal energy may be received by a parabolic antenna I. The collected modulated carrier wave energy is concurrently applied to the first converter 2 and auxiliary converter I3 of a superheterodyne receiving system. A crystal-controlled oscillator I5 is provided, and this oscillator functions to provide stable oscillations at a fundamental frequency of mc. It is not bclieved necessary to show the circuit details of such a stabilized oscillator, since those skilled inthe art will readily be able to construct an oscillator 'of this type. The 20 mc. oscillations are of substantially constant amplitude, and are applied to frequency multipliers I3, I2 and IIY in succession.

- These frequency multipliers I3, I2 and II respectively multiply their respective input frequencies by factors of 5, 5 and 3. In this way the 20 mc. energy is stepped up in frequency to a Value of 1500 mc. The output energy of multiplier II at r1500 mc. is applied to the rst converter. Hence,

there is provided at the output ofthe iirst converter 2 intermediate frequency energy of 500 mc. The 500 mc. I. F. energy output of the converter 100 mc. energy can be reduced to 20 Since the frequency variations of the 500 mc. and 400 mc. energies are identical, the second I. F. energy of ,100 mc. will not have any of the incidental frequency variations which existed in the original signal.

Prior to impression of the rst I. F. energy upon the converter 4, the 500 mc. energy is passed through a band pass filter 3 to remove undesired heterodyne combination frequencies, The 100 mc. energy may be amplified by an I. F. amplifier 5, and the resulting I. F. energy of 100 mc. is then applied to a third converter 6. If desired, the

mc. by utilizing the output of oscillator II-i In this case, frequency multiplier I7 multiplies the 20 mc. oscillations to the fourth harmonic, and the re vsulting 80fmc. signal energy is applied to the third Y converter 6 thereby to provide the third I. F. en-

ergy of 20 mc. The latter may be amplified as at 7, and after a fourth conversion at network 8 the resulting modulation signals` can be amplified and reproduced.

In order to make the response of the receiving system linear,l there is shown a limiter 20 which follows filter network I9. The function of this limiter is to prevent any amplitude varia- -tion |being applied to the converter 4. Hence, the 400 mc. energy applied to converter 4 has no amplitude variation no matter what the variations of the incoming -amplitude modulated carrier energy may be. This is an important advantage of the present invention, because if the limiter were omitted, and if amplitude variations were allowed in both the 400 and 500 mc, energies, it is obvious that theresponse in converter 4 would not be linear. y I

In Fig. 2 I have shown an embodiment of the receiving system which requires less equipment.

.2 is modulated, of course, in accordance with the Ysignal modulations which existed on the carrier energy applied to antenna I. In like manner, the output of crystal-controlled oscillator I6 is multiplied by successive frequency multipliers I3, I 4 and I5 to a frequency of 1600 mc. These multipliers have respective multiplication factors of 5, land 4. The latter energy of 1600 mc. is applied to auxiliary converter I8 along with the original amplitude modulated carrier wave energy of 2,000 mc. Hence, there is produced at the out:

put of the auxiliary converter I8 amplitude mod` .A

ulated carrier energy of 400 mc. f,

As is well known, the heterodyning process does not alter the total frequency change. Accordingly, if the signal energyoutputs of converters 2 and I8 are combined, the output signal energies thereof will provide a second I. F. of 100 mc.

Instead of using the crystal-controlled oscillator I6, frequency multiplier I'I and the frequency multipliers I I to I5, there is 'employed an oscillator 40 which provides oscillations of constant amplitude at 1550 mc. fed to a modulator 39 along with constant amplitude oscillations from the 50 mc. oscillator38. The modulator 39 Vis so constructed that the carrier frequency of 1550 mc. is suppressed, while the sidebands of 1550 plus or minus 50 mc. are passed. Filters 33 and 34l respectively pass the resulting 1500 mc. sideband or the 1600 mc. sideband. The filter 33 feeds Ythe 1500 mc. energy to the rst converter 2, while the filter 34 feeds the 1600 mc. energy to the auxiliary converter I8. The outputs of converters 2 and I8 are treated as shown in Fig. 1. The third converter ,6 is` fed with the'100 mc. energy, and is suit` ably supplied with mc. oscillations (as from networks similar to I6, I'I of Fig. 1) in order to reduce the mc. energy to the 20 mc. value.

' Those skilled in the art are fully aware'ofv the Vmanner of constructing frequency multipliersv of the type shown in Fig. 1. Furthermore, theA limiter 20 may be'of any desired type, such as, .for example, a readily-saturatable amplifier. V The modulator circuit 39 of Fig. 2 is well known `to those skilled inthe art. The system of Fig. 1 may be Vfurther simplied as shown in Fig. 3. In this case, a suppressed carrier modulator 55, similar yto the modulator 39 of Fig. 2is fed with energy at 1550 mc. from oscillator 56. Oscillator 51 provides modulator 55 with the 50 mc. energy. The resulting output of modulator 55 contains frequencies of 1500 mc. and 1600 mc. These two `frequencies beat with the collected 2000 mc. energy in the first con- These oscillations are aua-791 I verter 2. The output of converter .'2 will, therefore, contain both v500 mc. beat energy and 400 mc. beat energy. The filters 41 and 48 respec.- tively select the 500 mc. beat energy and the 400 mc, beat energy. The 400 mc. signal energy is passed through an amplitude modulation limiter 43. The limited 400 mc. signal energy and the 500 mc. signal energy are applied tothe second converter fi. The resulting 100 mc.'signal energy is then treated by the successive stages 5, 6, 1 and 8 as shown in Fig. l. In the system of Fig, 3, the networks H to l5, i8, I9 and 2i) of Fig. 1 are omitted. The third converter l, fed with 'amplified 100 mc. energy from amplifier 5, has applied thereto the 80 mc. oscillations from multiplier l1 thereby to reduce-the frequency of the 100 mc. energy -to the lower frequency value as shown in Fig. l. The oscillator i6 supplies 20 mc. oscillations to multiplier I1, as in Iig` 1. In Fig. 4 there is shown another modification in which there is employed a relatively high frequency oscillator 11. This oscillator 11 is followed by a minimum number of frequency multipliers 16, 15 and 14. The output of the multiplier 14 is the twelfth harmonic of oscillator 11. The twelfth harmonic energy is heterodyned with the received modulated 2000 mc. energy vat the first converter 2. The resulting 800 mc. I. F. energy is combined with the 100 mc. oscillations from oscillator 11 at a second converter E1 to produce a modulated beat output of 700 mc. i The 200 mc. output energy of multiplier 15 is combined with the 800 mc. I. F. energy at the third converter 68 to produce a modulated carrier output of 600 mc. The 100^mc. energy is passed through a filter 6i), and the filtered energy is then applied to a fourth converter`1. The 600 mc. energy output of third converter 68 is ltered as at 1l. The filtered energyis `then subjected to amplitude limitation at '19, and the output of the limiter 19 is applied tothe fourth converter 1i). The beat output energy ofthe fourth converter 16 is the signal modulated' carrier .energy reduced to a carrier frequency of 100 mc. The latter energy may thenbe ysubjected to further conversion for the production of the modulated signals as shown in Fig. l. 'Ihat is to say, the fifth converter is fed with 80 mc. oscillations from a source of oscillations such as is exemplified by oscillator l5 and multiplier l1 of Fig.r -1. The lresulting 20 mc. output of the fifth converter is then amplified, and further converted as shown at networks 1 and 8 of Fig. 1.

While .Ifhave lindicated and Vdescribed several systems for carrying my invention into effect, it willbe apparent to one skilled in the art that my invention is by no meanslimited to the particular organizations shown and described, but

that `many modifications may be made ,without departing fromthe scope of my invention.

What I claim is:

l. A method of signalling with amplitude modulated carrier waves having incidental frequency modulation effects which includes providing stable local oscillations of constant amplitude and of a relatively lower frequency than the carrier frequency of said modulated carrier waves, frequency multiplying the local oscillations to a frequency differing from the carrier frequency by a predetermined value, heterodyning the modulated carrier waves and multiplied oscillations to produce a beat frequency, frequency multiplying said local oscillations to a second frequency differentfrom the at high frequency first' multiplied value, combining the modulated carrier waves and the second multiplied oscila tions to provide a second beat frequency dif,- ferent from the rst beat frequency, .amplitude limiting the current of one of Asaidbeat frequencies to remove amplitude variations therefrom, and after said limiting combining ,the two beat vfrequenciesto provide a third beat frequency sub.-

stantially free of said modulation. l

.2. A method of signalling at high frequency with amplitude modulated carrier Waves ,having incidental frequency modulation which includes providing frequency-stable local oscillations of constant amplitude and of a relatively lower fre,- quency than said carrier, frequency multiplying the local oscillations to a frequency differing from the carrier frequency by a predetermined value,

rheterodyning the modulated carrier waves and multiplied oscillations toproduce a beat frequency having said incidental frequency modulation, frequency multiplying said local oscillations to a second frequency different from the first multiplied value, combining the modulated carrier waves and the second multiplied oscillations to provide a second beat frequency different from the first beat frequency but having said incidental frequency modulation, amplitude limiting the second beat energy to remove amplitude variation thereof, and combining after said limiting the two beat frequencies to provide a third beat frequency substantially free of said incidental frequency modulation.` Y

`3. A method of signalling at high frequency with amplitude modulated carrier waves having incidental frequency modulation which includes providing frequency-stablelocal oscilla,- tions of constant amplitude and of relatively lower frequency thanthe carrier frequency of said modulated carrier waves, frequency multi-,- plying the local` oscillations to a frequency dif.-

fering from the carrier frequency by a predeterf f mined value, heterodyning the modulated carrier waves'and multiplied oscillations to produce a beat frequency having said incidental frequency modulation, frequency multiplying' said local oscillations to a second frequency different from the first multiplied value, combining the modulated carrier waves and the second multiplied oscillations to provide a second beat frequency different from the first beat frequency but having i said incidental frequency modulation, subjecting one Vof the beat frequency currents to amplitude l1mit1ng,combining the two beat frequencies after said limiting to provide a third beat frequency substantially. free of said incidental frequency modulation, reducing thethird beat energy tol-a lower frequency value, and demodulating the reduced frequency energy. A

4. A method of signalling at ultra-high fre- '.quency with amplitude modulated carrier waves which have incidental frequency modulation, which includes providing frequency-stable local oscillations of constant amplitude and of a relatively lower frequency than the carrier frequency f of said modulated carrier waves, changing the local oscillations to a frequency differing fromY the carrier frequency by a predetermined value, heterodyning the modulated carrier waves and changed oscillations to produce a beat frequency having said incidental modulation, changing4 said local oscillations to a second frequency different` from the first value, combining the modulated carrier waves and the second ,oscillations to provide a second beat frequency different from the first beat frequency but having like incidental` variations in the current of the secondbeat frequency, and combining after said :elimination `the two beat frequencies in such relation as to provide athird beat frequency free of saidlincidental modulation.

5, A method of signalling at high frequency with amplitude modulated carrier waves Which includes providing local oscillations, frequency multiplying the local oscillations to a frequency differing from the carrier frequency by apredetermined value, heterodyning the carrier waves and multiplied oscillations to produce a beat frequency, frequency multiplying said local oscilla-V tions to a second frequency dierent from the rst multiplied value, combining the carrier waves and the second multiplied oscillations to provide a second beat frequency different from the first beat frequency, amplitude limiting the energy of the second beat energy to remove all vam Y plitude variation thereof, and combining the two beat frequencies in such relation as to provide a third beat frequency which is solely amplitude modulated.

V6. A methcdof receiving amplitude modulated ultra-high frequency carrier wave energy which has incidental undesired frequency `modulation consisting in reducing Jthe carrier frequency of the'Y received wave energy to a lower lcarrierfrequency, deriving from the received wave energy Y local oscillations whose frequency is substantially dierent from said lower carrier frequency but which oscillations have the same undesired frequency modulation as said received Wave energy, completely removing amplitude variations from said localoscillations, and heterodyning the lower carrier frequency energy with said local oscillations after said amplitude variation removal to produce intermediate frequency energy having said amplitude modulation but being free of said --incidental frequency modulation.

7. A method of receiving amplitude modulated carrier wave energy which has undesired incidental frequency modulation which includes `the steps of deriving local oscillations from the received carrier Wave energy which have a frequency different from the Vcarrier frequency of the wave energy, removing all amplitude variations from the local oscillations, beating thereceived carrier energy with saidlocal oscillations derived from the received carrier wave energy Yafter said amplitudeV variation removaL'and demodulating the resulting amplitude modulatedintermediate frequency energy which is free of said incidental frequency modulation. i

f e. A method of eliminating undesiredfrequency modulation from lreceived amplitude modulated carrier wave energy which includes the steps of deriving local oscillation energy subject to said undesired modulation from the received carrier energy, combining the received energy with the amplitude modulated intermediate frequency energies of different frequency but of like incidental frequency variation, amplitude limiting one of the intermediate frequency energiesv to remove amplitude variation thereof, beating the two intermediate frequency energies together .to provide a third beat energy free Vof incidental frequency variation, and demodulating the beat energy.

10. In an ultra-high frequency receiver, the method comprising the steps of heterodyning receivedV amplitude modulated ultra-high frequency carrier waves subject to undesired incidental frequency deviation with a pair of separate local oscillations of different frequency to provide separateamplitude modulated intermediate frequency energies of different frequency but subject to said incidental deviation in like manner, limiting one ofl the intermediate fre-V quency energies to remove amplitude variation, beating the limited intermediate frequency energy together with the other intermediate energy to provide a third beat energy free of said deviation, and demodulating the beat energy.

l1. A method of receiving ultra-high frequency carrier energy which is modulated in two different types of modulation,l one type being desired and the other undesired, which includes the steps vof converting the received energy into at least twomodulated carrier energies of different frequencies and modulated in the same manner as the received energy, removing from one of the two converted energies all variation representavtive of the desired type of modulation, and heterodyning the two carrier energies of different frequencies thereby to provide a resulting modulat ed beat energy which is free of the undesired type of modulation. A

' HAROLD H. BEVERAGE. REFERENCES CITED vThe following references are of record in the file of this patent:

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