US1871740A

US1871740A - Method of receiving radio signals and apparatus therefor

Info

Publication number: US1871740A
Application number: US144244A
Authority: US
Inventors: Walter Van B Roberts
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1926-10-26
Filing date: 1926-10-26
Publication date: 1932-08-16
Anticipated expiration: 1949-08-16
Also published as: GB279808A

Description

Aug.V 16, 1932.

W. VAN B. ROBERTS METHOD OF RECEIVING RADIOSIGNALS AND APPARATUS THEREFOR Filed Oct.

lNvr-:NToR W.VAN B.' ROBERTS v Egw f,

Patented ug. 1.6, 1932i. i

WT ED? i leeren-T ,y orme-Ei WALTER VAN is.

aoB-RTsyor BRoNXvITLnINnW YORK, Asistencia', To RDI'- confio- RATIO-N ore-Munten, nreoaroaeriou or natewartn METHOD or RECEIVING. Ennio siennes AND APPARATUS THERFOB Appncsfmmed, october es, 192e; Ysensi im 144,244.7

n signal but another signalfdiffering from the heterodyne frequency by the sarneanijount as' does the desired signal'.A i'

it is a further' object of inventionto eliminate `a number ofstagesfof circuits tuned 1u to the signa-las now employed 1n super#heterof-` Y dyne reception. p .Y

Y it is the present practice to use a nuinber Vof tuned circuits to suppress lthis undesired signal whichllwill call the firnage signal because it lies onthe other side of the heter-"o dyne frequency just as far thev desired signal liesonthe one side; ,j Y

To more clearly illustrate what I. meanby the term fiinage signal, assume' a signal freit.l quency of GOO `kilo-cycles'. Ifthe local voscilflator has afrequency of .G50 kilo-cycles, then' the interniediateV frequency', will bef 50' kilocycles. VBut it alsoisjtrue thataifrequency of 700 kilo-cycles will beatv with the' l'o'c'a'l if oscillatorto 'produce the intermediate ffre` quency of .50 kilo-cycles, an-d'rthis frequency of 700 cycles is the imagefr frequency ofthe GOO kilo-cycles. Now if itis desired toafect the enormous attenuation of tlie image fre- 31 quency with respect to the` signal frequency suchas isfnecessaryin or'derto receive weakL signal through strong interference without noticeable beats being produced, an undesir-v ably large number of circuits inustbe kept', in tunewith the signal. This invention con;` templates using' a heterodyne frequency enough greater than thes'ignal frequencyvso that the range of l'inagef frequencies corref spending to the range' of broadcast: frequen- W cies lies so far above the' range of broadcast frequencies that theV twov ran-ges doinot overlap and are preferably separated by a considerable amount. For example, if we cond siderthe broadcastrange to extend'froind'() 4"" to V1500 hilo-cycles and if we choose an intermediate frequency of 3000 kilo-cycles",then

the range of imagefrequencies entends;A p fromV 6550 to 7 500 kilo-cycles winch latter fre-f quencies are out-side of thebroadcast' rar'gef.v JO These two ranges are separated a wide margin so that a IOW pass l-terinay 'be used instead :of circuits tuned to the signal .frequency. `'This' low pass lter' offers free-passage to all frequencies in the broadcast range but attenuates to' any desired extent the fre'- quencies lying in the range of"irnage"s. The extento'f this attenuation depends upon the number of,` sectionsv in the filter and other known factors. l Y

It is desirable to'clio'ose' the high inter`L mediatefrequeucy of Sonie valuethat is ,not twice or equal tothe frequency of ldesired signal, that is,1ess than 5,50 or greater' than 370,00', votherwise some one' stat'i'o'ri'iwoi'lld,not` be received-properly. il 550 'er less is chosen, the lo'w'p'ass Vfiltering' will be' dilicu-'l' while chosen, itwill bein'o'r'e diiicult" j to suppress' thelsecond image?.

n will be newsfeed that. the use orari? frequency. Therefore in its preferred forintV i the, invention also providesfor a'second heterodyne to1 step downv fronithev high intermediate frequency to a second intermediate frequency lowenou-glr to' giver' the ful-lest advanta-ge in selectingA between` stations lying' close together 'in frequency;.y Thev secondA thissecond' intermediate-frequency introduces anew image frequency lso that/it isi-neces! sary to" attenuate this to the degree-as'` the ytype or"niage` first considered', Heteever, if a selective-'hegt vrintermediate rre-LY queneylainplifier is used theisecon l"image ,will bejdiscrirninat'ediagainst' so i'snot necessary togo back to circuits' tun'c'dto the"l signal', although such circuits again will help c and one or tvvo of them are desirable as eX-V plained before. y

c In addition to being Vhighly selective against interference the intermediateL frequency amplifiers shouldy transmit as nearly equally as possible a band of frequencies twiceas wide'as exists in the audio. range so' as to maintain goodquality, and to this end I prefer the use of a band pass filter in connection with, a vbroadlytunedlow intermediate frequency amplifier. Thev high Sintermedivate frequencyamplifier is'not likely to be so 15 is coupled tothe` frequency changingde-Y .c5 vice 16 which combination with the appa-i Figure c 3 shows a particularfcircuit arrange# ment for carrying out the idea of Figure 2.

Y Referring to

lFigure

1, 1 indicates -a signal pick-up device kWhichmay be of the usual loop type or any other suitable aerial device. Tothis pickup is connected a lovv pass 'filter 21Which passes the received'signal Vto the frequency changing device` 3 and from there to the high intermediate frequency; amplifier l; f(` lloWing-vvhichY the signalis detected at 5*;'and then passed through thefaudiofrequency amplifier ,6. c .10 indicates any ,vvell known loud speaker devices which is operated by the output of the amplifierff.V

`'Ylhe systemV shown in Figure 2 operates similarly 'to that shown inFigure 1exceptV that there is provided a secondheterodyne of fixed frequency 7. This second heterodyne frequency isused, as explained above, to' step `dov'vn from the high intermediate" frequency to: 'a second intermediate frequency loW enough to permit the most suitable selectivity' between stations lying close together in Wave lengths.' The low intermediate frequency amplifier Vshown jat 'v8 isV used in connection" With the secondfrequency changercto provide suitable amplification for` the signal.'v The high intermediate 'frequency amplifier is made highly selective inorder to'reject theV second image' frequency producedby the use of a second intermediate frequency-- In AFigure 3fI have shown diagrammatically a particularV circuit which is suitable for carrying out thez above describedin'vention. 11 indicates a loop of thevvell knovvn type now usedlin connection with super-k heterodynes. 12Vindicates a low pass filterV Which` communicates With lthe vacuum Vtube 13 where beat notesare ,produced -by thev device 14, which beat notes are then supplied to the vacuum tube'15 for the purposes of amplification... The output of the. ampllfier Y:1,871,7445 Y hij ratus 17 produces a second heterodyne beat. Coupled to the frequency changer 16 is a low intermediate frequency band filter 1S which is in turn coupled to the amplifier 19,

Where the lowintermediatefrequencies are amplified. Following thisstage of amplification the low intermediate frequency is impressed upon the detector 20, Which detector coupledto a suitable audio frequency amplifier 21, yWheretheaudi'o frequency is :amplified toitheldesired degree and is then made to actuate the loud speaker device V22. It is to be understood, that the invention is v not limited` to thesev arrangements, but mightemploy amplification at the signal frequency and would use as many sections in AVeo both filters as desirable andas many stages e l ofzam'plification at eachfrequ'ency, andmight useeither the ordinary three electrodeV tube withv propervneutralizing'"arrangements or the shielded-grid'tube as shovvn in certain parts of Figure 3. v Y i i IclaimV as, my invention: c

"e 1.' In a methodof receiving `radio signals within' agiven range of frequencies by the e superheterodyne method in which the signal equencyis made to produce'an intermediate difference frequency by` beating with local oscillations, the step of producing an inter-y mediate ldifference frequency which is above said range whereby it can'v be produced by only Lone signal frequency Within the said range. -v

2.' In the;method'ofireceiving radio'isign als by causin'gapredetermined range ofk L signal frequencies'toheterodyne with localA osclllations izo-'produce an vintermediate difference frequency, the step of producing said intermediate beatojfsuchI frequency thatit is above the highest frequency of said range and cannot ,belproduced' by any other signal frequencyivi'th the ,said range beating with saidlocal oscillations. Y, c i

3.1 The method ,of radio reception which comprises, producing an intermediate differencefrequency betvveen van incoming signal of a predetermined. range of frequenciesy and local oscillations, said signal frequencyhgw;`

ing an image frequencyvvhich differs from the frequency of said local oscillationsjby an amount equal to the difference ,between said signal frequency and said local oscillations, saidimage frequency being greater than the highest frequency in saidv predetermined range of frequencies by an amountV greater than-said range.

" L The method of radio Vreceptionfvvhich comprises, producing' an intermediate dierence frequency of' a magnitude of the order of 55,0 kilocyclesubetvveen an incoming signal of a predetermined range of frequencies and local oscillations, said signal frequency-V having an image frequency which differs from said local koscillations by an amount equal tothe' intermediate frequency andv saidf- I n de image frequency being widely separated from said predetermined range.

5. In the method of receiving` radio signals within a` predetermined range of frequencies by producing an intermediate difference frequency between a signal frequency and local oscillations, the'step of producing saidV intermediate frequency of a frequency not less than the lowest frequency of said range and greater than the highest frequency of said range whereby there is noimage frequency corresponding thereto within said predetermined range.

6. A method of receiving signals which comprises collecting signal energy of a frequency within a predetermined range of frequencies, generating local oscillations of a frequency such that the magnitude of the differencefrequency between the signal and local frequencies is above the said range and can be produced by only one frequency within said range, combining said local and signal energies, amplifying the said difference frequency, and attenuating frequencies which are images of said signal frequency.

7. A method of receiving signals which comprises collecting signal energy of a frequency within the broadcastV range of frequencies, generating local oscillations of a frequency lying outside said range, the value of said local frequency being such that the difference frequency resulting from the combination of the local and signal frequenciesv has a value above said broadcast range and can be produced by only one frequency within said range, combining said local and signal energies, and amplifying said difference frequency. y

8. The method for the hetercdyne reception of radio signals which comprises selecting a range of frequencies to be received, applying a range of frequencies thereto to produce a constant beat frequency therefrom throughout said range, said beat frequency and'said range of oscillation frequencies being such that an image frequency range is produced thereby which is separated from the range of signal frequency to be received by a range greater than the range of signal frequencies.

9. In a heterodyne receiver, the combination with a radio frequency circuit, for the reception of a certain range ofsignal frequencies, of means for producing local oscillation frequencies and a beat frequency therefrom which beat frequency added to said range of oscillation frequencies provides a range of image frequencies separated from said range of signal frequencies, and means for attenuating frequencies within said image frequency range including a low pass filter adapted to transmit currents of frequencies within said si gnalfrequency range, said filter being providedv with adjustable terminations for increasing the voltages of said signal frequency currents.

*.11 10. In combination,lwi`th means:y for colleotingasignal energygdisposed in the broad-v cast rangemeans for combining the-collected energy with local oscillations, to` produce a beat v,frequency close tov the low freipie'ncy.v

end of the broadcast range,'means for amplifying'the said beat energy, meansfor-combining the, anipliiied'beatenergy with local oscillations to produce a'beat frequency lower I than the first beat frequency, means for amplifying said second beat energy, a` band pass network connected between said last mentioned amplifying means and the means for producing the second beat frequency, and means for detecting said amplified .y second beat frequency energy. Y

11. In combination wi ing signal energy disposed in the broadcast range, adjustable means for combining the collected energy with localV oscillations to produce a' beat frequency close tothe low kfrequency end of the broadcast range, means for amplifying the said Vbeat energy, means for combining the amplified beat energy with local oscillations to produce la beat frequency lower than theiirst beat frequency, means for amplifying said second beat energy, a band pass network connected between said -last mentioned amplifying means and the means for producing the second beat frefied second beat frequency energy.

12.l A method for reception of radio signals consisting in selecting a range of signals to be received, applying a range of frequencies thereto to produce a constant beat frequency therefrom throughout said range of a value of the order of 550 kilocycles,

amplifying the beat energy, Vchanging thek frequency of the amplified energy to a lower intermediate frequency, and detecting the latter.v

thimeans for collectes i,

roo

13. A method for reception of radio sig- A nals consisting in selecting a range of signals to be received while attenuating undesired image frequencies, applying a rangeof frequencies thereto to produce a constant"V Y beat Y frequency therefrom throughout said range of a value of the order of 550 kilocycles, amplifying the beat energy, changing the frequency of the amplified energy to a lower intermediate frequency, and detect ing the latter. y

Y 14. A method for reception of `radio signals consisting in selecting a range of signals to be received, applying a range offrequencies thereto'to produce a constant beat frequency therefrom throughout said range ofa value chosen from a range of the order of 550 to 3000 lrilocycles, amplifying the beat energy, changing the frequency of the amplified energy to a lower intermediate frequency, and detectingy the latter.

quency, and means for detecting said ampli# *signals` to loef'reoeved, applying arrainge otk' `frequencies the beat frequency reto to produce a; constant ltherefrom -throughout said range ofraA value ofthe orderso 550 kilo- 5 cycles, amplifying the beat'energy, changing thefrequency of the amplified energy to a e energy, andf'det lower intermediate frequency,

Wide band char imparting a aoterlstlc Vto the'lntermedlate ec'ting lthelatter. Y

W. VAN B. ROBERTS?