US2151810A - Superheterodyne receiver - Google Patents

Description

March 128, l939. R. SIEMENS SUPERHETERODYNE RECEIVER Filed Jan. ll, 1937 Patented Mar. 28, 1939 UNITED STATES PATENT OFFICE i SUPERHETERODYNE RECEIVER.

Rudolph H. Siemens, Richmond Hill, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application January 11, 1937, serial No. 119,926 6 claims. (o1. 25o- 20) My present invention relates to superh-eteroin a schematic manner the various networks of a dyne receivers, and more particularly to a novel superheterodyne receiver embodying my present method of, and means for, increasing the freinvention; it being pointed `out to those skilled quency range of a short wave receiver by means in the art that the circuit details of the individual n of a fixed frequency oscillator. networks may embody arrangements well known lf'5 4It -is generally known that it is relatively diffikto them. It is not believed necessary for the last cult to construct a sharply tuned superheterodyne vnamed reason to show any of the 'circuit' details receiver which will give satisfactory results when of the different networks, since it is believed that signals of a frequency higher than 30 megacycles those skilled in the art can readily supply such 1() (mc.) are to bereceived. One of the reasons for details with the following description. The refri() such difficulty resides in the fact'that ythe heteroceiving system embodies the usual signal collector dyne oscillator drifts in frequency. Various solu- A of any type. It is to be further understood that ktions for this problem can be proposed. However, the signal energy received may be. modulated with they generally involve complicated devices, or cirvoice, or by pictures. In either case the collected f i cuits, which prohibit their usage in practical resignals are impressed upon the tunable input circeivers. cuit l of the first detector 2. Of course one, or

One of the main objects of my present invention more, stages of tunable amplification could preis to provide a superheterodyne receiver which cede the first detector 2, and in which case the embodies 'a local Yoscillator `of fixed frequency tuning devices of these: preceding amplifiers would utilizing accurate frequency control means; and be adjustable with the tuning condenser 3 .of the 20 the selection of signals being accomplished by input circuit l. means of a variable intermediate frequency (IF) The detector 2 may employ a tube of any deamplier whereby adequate stability of all cir- SiI'ed type, but it Will be especially eiective Wllen cuits involved is provided and the selectivity it emplCYS u tube Which lends itself for the decharacteristic secured is similar to that of receivtecticri function in the Operating Signal range 25 ers whose frequency range is limited to a maxi- Which ceVeIS 32' t0 60 mciHCluSVe. It will be mum of mc. A understood, therefore, that the tuning condenser Another important object of the invention isv to 3 iS alJ'uStefi t0 Very the tuning 0f the input cirprovde a superheterodyne receiver employing a @uit l OVel e Signal frequency Teuge 0f 32.150 60 So mst detector adapted to be ,tuned @Ver a, freimc. inclusive. The first detector 2 is fed with lo- 30 quency range higher than 30 ma, a, local 05011- Vcally produced oscillations from a local oscillator lator of a fixed frequency of the order of 30 mc. 4. The OScillaftOl 4 iS arranged t0 produce OScilbeing associated with the detector to produce siglutiOIlS having e frequency 0f the Order of I29.5

i nal energy over a wide range up to 30 mc.; and a mc., and as a consequence there will be produced 35 variable IF amplifier and converter network being in the Output circuit 5 cf the first detector 2 -IF 35 used toreduce the frequency of the resultant sigenergy in a range of 2.5 to 30.5 mc. It is not nal energy. thought necessary to show the circuit details of Another. object of the invention is to improve th-e local oscillator il, since it is well known how to generally the selectivity and operating efficiency construct an oscillator operating to produce enkff) of superheterodyne receivers, andmore especially ergy of 29.5 mc. It is desired, however, that the 40 to provide a highly selective superheterodyne relocal oscillator 4 be maintained at its frequency ceiver which is capable of giving efcient voperby means of an accurate frequency control device. `ation for signals above 30 mc., and which receiver For example, crystal control, or a very high Q is not only readily and simply operated, but is tuned tank circuit, can be employed tofiX the ai economically manufactured and assembled. frequency of oscillator 4 accurately at its oper- ,.45

The novel features which I believe to be charating frequency. Since those skilled in the art acteristic of my invention are set forth in parare fully aware of the manner of accurately fixticularity in the appended claims; the invention ing the frequency 0f an electron discharge tube itself, however, as to both its organization and Oscillator, it iS 110t thought necessary t0 describe oc method of operation win oost be understood by in any further detail the oscillator 4. -5'0 Areference to the following description taken in The IF energy produced in the Output circuit Connection with the drawing in which 1 have in- 5 of the first detector is impressed on the tunable dicated diagrammatically a circuit organization input circuit 6 of the first IF amplifier l. The A`whereby my invention may be carried into effect. variable condenser `8 is adjustable to tunethe :5 Referring now to the drawing there is shown input circuit 6 over a frequency range of 2.5 to 1,55

f2.5 Yto 30.5 mc.

30.5 mc., the latter range including the intermediate energy frequencies produced by the heterodyne action of the fixed local oscillator 4 and the first detector when adjusted through its tuning range of 32 to 60 mc. Of course, one or more tunable stages of IF amplification may be employed, and in such case the rotors of the tuning condensers will be mechanically unicontrolled with the rotors of condenser 8, and the rotors of condenser 3. The numeral 9 denotes in dotted lines the mechanical uni-control.

mechanism which varies the rotors of the tuning condensers 3 and 8 in proper synchronism so that at any setting of the rotors of condenser 3, the rotors of condenser 8 will be adjusted to tune input circuit 6 to the proper IF.

'I'he signal energy, amplied by the first IF amplifier 1, is then impressed upon the tunable input circuit I0 of the second detector il. The variable condenser I2 has its rotors mechanically ycoupled to the rotors of condenser 8 so that the input circuit I0 is tunable over the IF range of The numeral I3 denotes a variable local oscillator which feeds local oscillations to the second detector II so as to `produce 'in the output circuit I4 of the second detector the second IF energy. The second IF energy is chosen to have a frequency of 1650 kc., and for this reason the second, or variable local oscillator, I3 is tunable over a frequency range of 4.15 to 32.15 mc.

'Ihe numeral I5 denotes the tunable tank circuit of the variable oscillator I3, and the tank circuit may include a variable condenser I6 Whose rotors are arranged for mechanical unicontrol, if desired, with the uni-control adjusting mechanism 9. In this way adjustment of the common control device 9 results in actuation of the rotors of condensers 3, 8, and I2 and I6 in synchronism so as to tune their respective resonant circuits to the predetermined frequencies. 'I'he oscillator I3 may be of any desired construction, and it may feed the locally `produced oscillations to the second detector II in the same manner as the oscillations from network 4 are fed to the first detector 2. It is to be clearly understood that instead of utilizing separate detector and local oscillator tubes, each converter network may comprise a single tube having its circuits arranged to provide a composite oscillator-detector circuit. Such composite circuits are well known to those skilled in `tlie art, and tubes of the 6A7 type, for example, may be used in this connection.

'I'he beat energy produced in the output circuit III of the second detector II is transferred to the resonant input circuit I8 of the second IF amplifier network I1. Each of circuits I4 and vIt! is tuned to the second IF of 1650 kc., and it "will be understood that the network I 1 may com- 'prise one, or more, stages of amplification. Of course, if more than one stage of amplification I1 is used, then each of the second IF circuits will be tuned to the operating IF of 1650 kc. The amplified second IF energy is impressed upon a third detector, or audio demodulator, I9 by means of the network I8', and the latter may be a transformer which has its primary and secondary circuits each resonated to the operating second IF. The third detector I9 may be of the usual detector construction, and, if desired, an audio amplifier may be utilized in this circuit. Of course, the direct current voltage component of the finally detected signal energy may be employed for automatic volume control of preceding `ratio probably would fall to 500:1 at 1,000:1 at 32 mc., due to the loss of selectivity `it is 27 mc.

signal transmission tubes; such AVC arrangements are too well known to warrant further description. The audio voltage component of the finally detected signal energy may be impressed upon one, or more, stages of audio amplification, and then utilized in any desired manner. The final utilization device may be a reproducer for sound or sight.

The arrangement shown herein will provide adequate stability of all circuits involved, and give results similar to present types of receivers whose frequency range is limited to a maximum of 30 mc. 'I'he circuits between input circuit 6 4 and the demodulator I 9 may be those of the usual double detection superheterodyne receiver of the all wave type, and in such case the circuit between network 6 and demodulator I9 would be the aforesaid receiver when adjusted for short wave reception. In other words, the tunable radio frequency input circuits of such a short wave receiver would be used as the variable first IF amplifier circuits of the system shown in the drawing. In this way it becomes possible to use a receiver limited to a maximum frequency of 30 mc., in a higher range extending up to a frequency value as high as 60 mc. Furthermore, this is accomplished with minimum additional circuit elements.

Another advantage of the present system resides in the fact that the ratio of image rejection is never less than the minimum image ratio of the variable IF amplifier 1. This, of course, applies to interference frequencies differing by +33 mc. of the desired signal for the case described Such interfering signals would be given j above. the same attenuation, due to the selectivity of the first IF amplifier, as lower frequency signals which are within the range of the first IF amplifier. An illustration of this effect follows:

Suppose the image ratio of the first IF amplifier to be 1000:1 at 30.5 mc. and 10,000:1 at 2.5 mc. This would permit the reception of signals which are combined with the fixed oscillator 4,

-of 60 mc. and 32 mc. respectively. The image signals of 63.3 mc. and 35.3 mc. would be attenuated to the same extent as signals received on the IF amplifier alone of 33.3 mc. and 5.8 mc. This increased image ratio would not be possible if the 32 and 60 mc. signals were received directly in the first IF amplifier 1. The image 60 mc. and

of the first IF amplifier 1 at these frequencies.

Again, there exists an advantage in the present system in that the gain at 32 to 60 mc. is practically the same as the first IF amplifier gain at 2.5 and 30.5 mc. This, of course, would not be possible if the first ll amplifier 1 were tuned directly to the 32-60 mc. range. The selectivity of the input circuit I (32-60 mc.) for image reduction purposes is likely to be adequate, since there is a large difference between the desired and undesired frequencies. An illustration of this is as follows: For a 60 mc. input the image frequency is 1 mc., where as for a 32 mc. input A mechanical advantage is, also, secured in the present system in that a 4:1 ratio Vernier dial action over the 32-60 mc. band is secured, if the 2.5-30.5 mc. range of the first IF amplifier is divided into four separate bands.

It is preferred that the receiving networks employed with the oscillator 4 be Awell shielded and electrically isolated from it. In such case no unyas quency energy in the remaining circuit, or with signals in the 32-60 mc. band. One point of interference may occur when receiving a signal at 59 mc. At that point the fixed oscillator operating at 29.5 mc. coincides with the tuning of the first IF amplifier 1. This interference can be reduced, or eliminated entirely, by the use of a push-pull input to the first IF amplifier 1, in the manner disclosed and claimed by W. A. Harris in his application Serial No. 748,606, led Oct. 17, 1934, and granted on April 21, 1936, as Patent No. 2,038,285.

While I have indicated and described a system for carrying my invention into effect, it will be apparent to one skilled in rthe art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims.

What is claimed is:

1. A method of superheterodyne reception which includes the steps of selecting a desired signal frequency from within the 32 to 60 megacycles range, beating such signal with oscillations of an accurately controlled frequency of 29.5 megacycles to produce an intermediate frequency range of 2.5 to 30.5 megacycles, beating the intermediate frequency energy so produced with local oscillations varying in frequency from 4.15 to 32.15 megacycles to produce a second intermediate frequency energy of 1650 kc., and demodulating the second intermediate frequency energy.

2. In a triple detection superheterodyne receiver, the combination of a first detector circuit including a highly selective input circuit resonant to signal frequencies in a range above 30 megacycles, a local oscillator operating at a fixed frequency which is of a value such that its oscillations heterodyne with the signals impressed on said iirst detector to produce a range of intermediate frequency values below 30 megacycles to above 2 megacycles, an adjustable converter network constructed and arranged to convert energy in said intermediate frequency range to a second intermediate frequency energy of a frequency value of less than 2 megacycles, and means for detecting the second intermediate frequency energy.

3. In a triple detection superheterodyne receiver, the combination of a first detector circuit including a highly selective input circuit resonant to signal frequencies in a range above 30 megacycles, a local oscillator operating at a fixed frequency which is of a value such that its oscillations heterodyne with the signals impressed on said first detector to produce a range of intermediate frequency values below 30 megacycles to above 2 megacycles, an adjustable converter network constructed and arranged to convert energy in said intermediate frequency range to a second intermediate frequency energy of a frequency value of less than 2 megacycles, means for detecting the second intermediate frequency energy, and means for controlling the tuning of said first detector and converter network in unison through their respective frequency ranges.

4. In a superheterodyne receiver, a first detector having a highly selective input circuit resonant to signal frequencies in the signal range of 32 to 60 megacycles, a frequency controlled local oscillator, coupled to said first detector, constructed to operate at an accurately fixed fre- ,quency value of 29.5 megacycles, a first intermediate frequency amplifier having means for tuning it through a frequency range of 2.5 to 30.5 megacycles, a second detector having means for tuning it through a frequency range equal to the frequency range of said intermediate frequency amplifier, a second local oscillator having means for tuning it through a frequency range which differs from the frequency range of said second detector by a substantially constant second intermediate frequency value of 1650 kc., and means for detecting the second intermediate frequency energy.

5. Apparatus for adapting a short wave receiver of the superheterodyne type designed to receive signals in a certain frequency range to one capable of receiving signals in a higher frequency range, comprising a detector circuit having a highly selective input circuit tunable through said range of higher frequencies, a fixed frequency local oscillator coupled to said detector circuit to produce an intermediate frequency which varies depending upon the tuning of the detector input circuit, said variable intermediate frequencies lying in the range of frequencies for which the receiver is designed, and an output circuit for feeding said Variable intermediate frequencies to the input of the receiver proper.

6. Apparatus for adapting a short wave receiver of the superheterodyne type designed to receive eiciently signals in the frequency range between 2.5 to 30.5 megacycles tc one capable of efficiently receiving signals in the frequency range between 32 to 60 megacycles, comprising a detector circuit having a highly selective input circuit tunable through said last mentioned range of frequencies, a local heterodyne oscillator producing oscillations at the fixed frequency of 29.5 megacycles coupled to said detector circuit to produce an intermediate frequency which varies depending upon the tuning of the detector input circuit, said range of intermediate frequencies lying in the range of frequencies for which the receiver is designed, and an output circuit for feed-V ing said variable intermediate frequencies to the input of the receiver proper.

RUDOLPH H. SIEMENS.

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