US2283106A - Carrier-signal selector network - Google Patents

Description

May 12, 1942. B. F. T'YSON 2,283,106

CARRIER-SIGNAL SELECTOR NETWORK Y 1111@ oct. 8, 1940 Patented May i2, 1942 UNITED STATES PATENT OFFICE4 2,283,1os I CARRIER-SIGNAL sELEcron NE'rwonx Benjamin F. Tyson, Bayside, N. Y., assignor to llazeltine Corporation, a corporation of Del- Application October 8, 1940, Serial No. 360,249 7^Claims. (Cl. 178-44) The present invention relates to an improved selector network adapted to translate a plurality of carrier signals and, particularly, to a selector network having a plurality of predetermineddistinct band-pass characteristics any one oi which may be selected substantially to the exclusion of the others. Whilev the invention is of general application, it has particular utility as a selector network between successive stages of intermediate-frequency amplification of a superhetero-V dyne receiver andwill, therefore, be described in that connection.

Conventional carrier-signal receivers adapted to operate over a plurality of carrier-signal frequency bands generally employ a single xed intermediate frequency usually between 170 and 470 kilocycles. This intermediate frequency provides satisfactory image rejection when the receiver is operating yin the low-frequency carriersignal bands, but does not provide entirely satisfactory image rejection in the higher-frequency bands, the image rejection becoming increasingly poor as the signal frequency increases.

In order that the image-'rejection characteristic of the receiver shall be more nearly uniform overl the entire frequency range of the receiver, it is desirable that different intermediate frequencies be employed for diierent ones of the frequency bands. The selection of a particular intermediate frequency is preferably accomplished by a' switching arrangement operated simultaneously with the radio-frequency band selector of the receiver. `In general, an intermediate frequency of 465 kilocycles is satisfactory for frequency bands up to 20 megacycles and an intermediate frequency of 2,250 kilocycles is satisfactory for the frequency bands extending from 20 megacycles up-to 100 megacycles. The use of a plurality of intermediate frequencies has the ,additional important advantages that tuning of the receiver is greatly facilitated, the detrimental effect of frequency drift of the local oscillator is minimized,and the larger separation of oscillator frequency and signal frequency in the higherf-frequency bands makes for greater ease in aligning the receiver by decreasing the drag of' have individual and different band-pass'characteristics suitable to provide the desired over-all band-pass characteristic for each of the several intermediate frequencies. Any one of the several intermediate-'frequency selectors is selectively chosen byan appropriateswitching arrangement. The switching systems heretofore employed for this purpose have been unduly complex and,l

therefore, relatively expensive 'or have not been altogether satisfactory in enabling the attainment of the required plurality of intermediatefrequency amplifier band-pass characteristics.

It is an object of the present invention, therefore, to provide a new and improved selector network which, while of general application, is especially suitable for use in coupling successive stages of intermediate-frequency amplification and onewhich avoids one or more of the abovementioned disadvantages and limitations of the prior art devices.

It is a further object of the invention to provide an improved selector network having a plurality of predetermined distinct frequency bandpass characteristics any one of which is eflectivev. I

ly selected substantially to the exclusion of the others by the selective operation of a simplified and improved switching system.

In accordance with one embodiment of the invention, aselector network adapted to translate a plurality of carrier signals comprises a pairof I input terminals and a pairl of output terminals,

and a plurality of transformers permanently connected in series and coupled between the input and output terminals. The selector network also includesy means for imparting to each of the transformers a predetermined different Acarrierthe oscillator-tuned circuit on the radio-frequency circuits o f the receiver, o'r vice versa, due to incidental coupling between these circuits.

AFor the purpose of ensuring that the gain of the receiver shall be uniformly high at each intermediate frequency employed, it is desirable that an individual intermediate-frequency selector be provided for each one of the several intermediate frequencies. Each selector thus may 5.5;

^ drawing, and its scope will be pointed out in the appended claims. Y

Referring now to the drawing, Fig. 1 is acircuit diagram, partly schematic, of a complete carrier-signal yreceiver embodying the invention;

and`Flg. 2 is a circuit diagram representing a modiiied form of the invention.

Referring now more particularly to Fig. 1, thereV is represented schematically a complete carrier-signal receiver of a conventional design embodying the present invention in a preferred form. In general, the receiver includes a radiofrequency amplier I9 having its input circuit connected to an antenna system I2 and having its output circuit connected to an oscillatormodulator I3. Connected in cascade with the oscillator-modulator I3, in the order named, are an intermediate-frequency amplier |4 more fully described hereinafter, a detector and automatic amplification control or A. V. C. supply I5, an audio-frequency amplifier |'1 of one or more stages, and a sound reproducer I3. The radiofrequency amplier III and oscillator-modulator I3 are adapted to operate over a plurality of frequencybands any one of which may be selected by operation of wave band switches conventionally represented at I9 and 23. The A. V. C. bias derived bythe unit I3 is applied to the input circuit of the radio-frequency ampliner |3, the oscillator-modulator I3, and the intermediatefrequency ampliiler lI4 in conventional manner.

It will be understood that the various units just described may, with the exception of the intermediate-frequency amplifier I4, be of a conventional construction, the details of which are well known in the art, rendering detailed description thereof unnecessary. Considering briefly the operation of the receiver as a whole, and neglecting for the moment the: operation of the intermediate-frequency amplifier I4 presently to be described, a desired carrier signal in one of the frequency bands selected by the band-change switches I9, 29 is received and amplied by the radio-frequency amplifier III, converted to an intermediate-frequency carrier signal in the oscillator-modulator |3, amplified in the intermediate-frequency amplifier |4, and detected by the detector IS thereby to derive the audio-frequency modulation components. The audio-frequency components are, in turn, amplied in the audiofrequency amplier I1 and are reproduced by the sound reproducer I8 in a conventional manner.

. The automatic amplification control supply of unit I operates in a conventional manner to maintain the signal input to the detector within relatively narrow limits for a wide range of received signal intensities.

Referring now more particularly to the portion of the system embodying the present invention, the intermediate-frequency amplifier |4 includes an input selector network 2| and an output selector network22 each adapted to translate a plurality of intermediate-frequency carrier signals. These selector networks are essentially similar in construction and operation and only one, therefore, will be considered in detail; similar circuit elements of each network are desisnated by similar reference numerals except that elements of the network 22 are distinguished from those of the network 2| by prime numerals. The selector network 2| has a pair of input terminals 23, 24 and a pair of output terminals 25,

terminals. In order selectively to short-circuit either of the primary windings 2.9 or 39 thus effectively to short-circuit all but one of the transformers. there is provided means comprising a single-pole switch 33 having a switch blade connected to the junction of the primary windt ings 29, 30 and having switch contacts individually connected to opposite terminalsvof the transformer primary windings. There are connected across the input terminals 23, 24 and the output terminals 25, 26 respective condensers 31 and 33. Upon operation of the switch 33 to close its lower contact, condenser 31 tunes the primary winding 29 of transformer 21 to a ilrst intermediate frequency while the condenser 33, together with the capacitive effect of the transformer secondary winding 32 and a condenser 4| connected in parallel thereto, tunes the secondary winding 3| of transformer 21 to the same intermediate frequency. The condensers 31 and 33 thus comprise capacitive means individually connected across the input and output terminals effectively to tune one of the' transformers, speciilcally the transformer 21, to the frequency of a predetermined one of the carrier signals applied to the selector network 2| upon the selection of such one trans-.- former by the switching means 33. A resistor 33 may be connected across the primary winding of transformer 21 fto aid in imparting to this transformer a predetermined carrier-frequency band-pass characteristic. Permanently connected across the primary winding 39 and secondary winding 32 of transformer 23 are respective condensers 43 and 4|. Upon closure of the switch 33 to its upper contact, the condenser 49 aids the condenser 31 in tuning the primary winding 33 of transformer 23 to its own individual intermediate frequency. while the condenser 4I, together with the capacitive effect of the transformer secondary winding 3| and condenser 38. tunes the secondary winding 32 of transformer 23 to the same intermediate frequency. The

condensers 43 and 4I thus comprise means individual to the transformer 23 and effective with the aforementioned capacitive means comprising condensers 31 and 33 to tune the latter transformer to the frequency of an individual one of the applied carrier signals upon selection by the short-circuiting or switching means 33 of such latter transformer. The condensers 31. 33, 40 and 4| and the resistor 39 comprise means for imparting to each of the transformers 21, 23 a predetermined different carrier-frequency bandpass characteristic for translating a different one of the plurality of carrier signals applied to the selector network 2|.

'Ihe intermediate-frequency amplifier I4 includes 'a vacuum-tube repeater 42 having input electrodes coupled to the output terminals 23, 23 of the input selector network 2| and output electrodes coupled to the input terminals 23',v 24 of the output selector network 22. The repeater 42 is suitably energized from 'sources of operating potential +B and +Sc. The switches 3'3 and 33' of the respective networks 2| and 22 are connected for unicontrol operation with the wave band switches I3 and 23 of the radio-frequency 23. A plurality of intermediate-frequency transformers 21, 23 have their respective primary windings 23, 33 permanently connected in series acro the input terminals 23, 24 and their respective secondary windings 3|, 32 permanently connected in series across the outputterminals 29, 23 and thus are permanently connected in amplifier I3 and oscillator-modulator I3, as indicated by the broken line 43.

In considering the operation of the circuit just described, it will be-assumed that the wave band switches I3 and 23 of the radio-frequency ampliiler |3 and oscillator-modulator |3 are positioned for operation of the receiver over la lower-freseries and coupled between the input and output quency 110111101' example. the broadcast band .if frequencies from 500 to 1,500 kilocycles, and that the transformers 28 and 28' are connected in circuit by operation of their respective switches 33 and 33' to close their upper contacts. It will further be assumed that the output of the oscillator-modulator I3 has a relatively low intermediate frequency, for example, 456 kilocycles, to which the transformers 28 and 28 are tuned. The switches 33 and 33 now short-circuit the respective transformer primary windings 28, 23', whereby the intermediate-frequency transformers 21, 21' are effectively short-circuited and removed from circuit. The intermediate-frequency amplifier I4 consequently operates in conventional manner to translate intermediatefrequency carrier signals within the pass band of the transformers 28, 28' and effectively to 31 and 40, the'condensers 38 and 4I may arbisuppress all other intermediate-frequency carrier signals. The over-all transmission band-pass characteristic of the amplifier I4* is, under the assumed conditions, determined solely by the.

band-pass characteristics of the transformers 28, 28.

Upon movement of the wave band switches I8 and 20 to select a higher-frequency band over which the receiver is to be operated, as, for example, a frequency band above megacycles, the switches 33, 33' are simultaneously moved,

by virtue of their mechanical connection with the wave band switches, to close their lower'contacts. The transformer primary windings 38, 3U

are thereupon short-circuited, whereby the transformers 28, 28' are effectively removed from circuit, and the transformers 21, 21 are connected in circuit in the intermediate-frequency amplifier I4. At the same time, the operation of the switch 20 to its new position has the result that the intermediate frequency now produced'in the output of the oscillator-modulator I3 has a relatively high frequency, for example, 2,250 kilocycles, to which the transformers 21, 21' are tuned. The operation of the intermediate-frequency amplier I4 is again conventional in every respect except that it translates intermediate-frequency carrier signals of the new intermediate frequency and effectively suppresses the transmission of all other intermediate-frequency signals. The over-all transmission characteristic of the intermediate-frequency amplier I4 is now determined solely by the individual band-pass characteristics of the transformers 21, 21'.

The selector network of the invention thus comprises -two tuned transformers having primary windings, selected by switches, which are resonant at either of two carrier-signal frequencies and a secondary circuit which is simultaneously resonant at both these frequencies, thereby to provide two selectable band-pass characteristics having maximum transmission at two carrier-signal frequencies. The network also has a minimum transmission characteristic at a carrier-signal frequency lying between the two frequencies of maximum transmission. In selecting the values of the circuit constants of the selector network, the values of the transformer primary windings 28 and 30 and the condensers 31 and 40 are computed in conventional manner,

'the value of the condenser 31 preferably being made as small as possible consistent with permissible small changes of capacitance resulting from tube replacements, temperature variations, etc., in order that the voltage-transfer ratio of the transformers 21 and 21' should be high.

l Having chosen suitable values for the condensers trarily be given the same respective values and the values Vof inductances of the transformer secondary windings 3l and 32, and the minimum transmission frequency, are given by the following equations:

4- 412f12f3202 I where,

`Ca='the capacitance of ,condenser 4I,

C1=the capacitance of condenser 38,

L3=theinductance of the transformer secondary winding 3l,

L4=the inductance of the transformer secondary winding 32,

f1=the carrier-signal frequency to former 28 is tuned,

fz--the-'frequency of minimum response of the selector network, and

'fa=the carrier-signal frequency to which the transformer 21 is tuned.

Fig. 2 isaJ circuit diagram representing a modiwhich trans- 'fied form of the invention essentially similar to that of the Fig. 1 embodiment except that the selector network of this modification is adapted to translate more than two intermediate-frequency carrier signals. Circuit elements of the' Fig. 2 arrangement corresponding to similar circuit elements of the Fig. l arrangement arc designated by similar reference characters and analogous circuit elements by the same reference numerals double-primed. 'In this modification, a transformer 44 has a primary winding 45 l which is permanently connected in series with the primary windings 28 and 38 of the respective transformers 21 and 28 across the input terminals 23, 24 and has a secondary winding 46 which is permanently connected in series with the secondary windings 3I and 32 across 'the output terminals 25, 26 of the selector network. 'I'he transformer 44 is tuned by a condenser 41 and by a condenserv 48 with other of the capacitive effects of the secondary circuit elements tov an intermediate frequency different from those to which the transformers 21 and 28 are tuned. A resistor 49 is connected "across the primary winding toaid in imparting to transformer 44 a predetermined carrier-frequency band-passv characteristic. The switch 33" is slightly different from the corresponding switch of the Fig., 1 arrangement in that it'has a pair of segments 5I), 5I which rotate together, each of the segments being of sufficient length to engage any three adjacent .switch contacts. The switch has four equally-spaced contacts 52-55,

`contacts 52 and 55 vbeing individually connected across the input terminals 23, 24, contact 53 being connected to the junction ofthe primary windings'of transformers 21 and 4,4,.and contact 54 being connected to the junction of the primary windings of transformers 44 and .28. The switch 33" is uni-controlled with the wave band switch of the receiver as indicatedby the broken line 43. Y

The operation of this modification of1 the invention is essentially similar to that of the Fig. 1 embodiment, the switch 33" short-circuiting all but a selected one of the transformer primary to translate and effectively suppresses the transmission o'f all other carrier signals. From the foregoing description of the invention, it will be evident that a selector network embodying the invention has a plurality of predetermined distinct frequency band-pass characteristics any one of which is eflectively selected substantially to the exclusion` ofthe others by the selective operation of a single switch of simple and inexpensive construction comprising a minimum of switch contacts. Each of the frequencyband-pass characteristics of the `vselector network may be adjusted and shaped quite independently ofA other of the kband-pass characteristics since individual groups of elements provide a given Aband-pass characteristic andA operate quite independently of other groups of elements of the vselector network.

While the switches 33, 33' and 33" are arranged to short-circuit selected ones of the transformer primary windings, it will be evident to one skilled in the art that, as an alternative andequivalent arrangement, the switches could equally well be arranged to short-circuit selected ones of the transformer secondary windings.

While there have been described what are at present considered to be the preferred embodiments of this inventiomitwill be obvious to those Askilled in the art that various; changes and modia plurality of transformers having primary windings permanently connected in series across said input terminals and secondary'windings permanently connected, in series across said output terminals, means for imparting to each of said transformers a predetermined different carrierfrequency band-pass characteristic for translating a different one of said carrier signals, and a single switch for short-circuiting all but a selected one of said transformer primary windings effectively to short-circuit all but oneof said transformers to suppress the transmission between the said input and output terminals of all of said carrier signals except the carrier signal which said one transformer is' adapted to translate.

4. A selector network adapted to translate a plurality of carrier signals comprising, a pair of input terminals anda pair of output terminals, a pair of transformers having primary windings permanently connected in series across said input terminals and secondary windings permanently connected in series across said output terminals, means for imparting to each of -said transformers a predetermined different carrier-frequency band-pass characteristic for translating a different one of said carrier signals, and a singlepole switch having a switch blade'connected to the junction of one of said pairs of series-concations mayl be made therein without departing from the'invention, and it is, therefore,'aim'ed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. Av selector network adapted to translate a plurality'of carrier signals comprising, a pair of input terminals and a pair of output terminals, a plurality of transformers permanently connected in series and, coupled between said input and'output terminals, means for `imparting to each of said transformers a predetermined different carrier-frequency band-pass characteristic for translating a different one of said carrier signals, and a single switch foreffectively shortcircuiting all but a selected one of said transformers effectively to suppress the transmission between the said input and output terminals of all'of said applied carrier signals except the carrier signal which said one transformer is adapted to translate. ,A

2. A selector network adapted to translate a plurality of carrier signals comprising, a pair of 'input terminals and a pair` of output terminals, a plurality of transformers having pri'- mary windings permanently connected in` series across said input terminals and secondary windings permanently connected lin series across said output terminals, means for imparting to each of said `transformers a predetermined different carrier-frequency band-pass characteristic for Cil translating a different one of said carrier signals,

and a single switch for effectively short-circuiting all but a selected one of said transformers efthe said input and output terminals of all of said carrier signals except the carrier signal which fectively' to suppress the transmissionbetween nected windings and switch contacts individually connected to opposite terminals thereof, whereby either of said one transformer windings may be selectively l'short-circuited effectively to short? circuit one of saidetransformersto suppress the transmission between the said input and output `terminals of all of. said applied carrier signals except the carrier signal which the otherof said transformers is adapted to translate.

5. A selector network adapted to translate a plurality of carrier signals comprising, a pair of input terminals and a pair of output terminals, -a pair of transformers having primary windings permanently connected in series across said input terminals and secondary windings permanently connected in series across said output terminals, means for imparting to each of said transformers a predetermineddifferent carrierfrequency band-pass characteristic for translating al different one of said carrier signals, and a single switch having a switch blade connected to the junction of .said primary windings and switch contacts individually connected to the op- Y posite terminals thereof, whereby either of said primary windings may be short-circuited effectively to short-circuit one lof said transformers to suppress the transmission between the said linput and output terminals of all of said carrier signals except the carrier signal which said other transformer is adapted to translate.

6. A selector network adapted to translate a plurality of carrier signals comprising, a pair of input terminals and a pair of output terminals, a plurality of transformers having primary windings permanently connected in series across said input terminals and secondary windings permanently connected in series across said output terminals, means for effectively short-circuiting all but one of said transformers, capacitive means individually connected across said input and output terminals effectively to tune one of said transformers to the frequency of a predetermined one of said carrier signals upon the selection of said y named capacitive means to tune each of said other transformers to the frequency of a dif- -ferent one of said carrier signals upon the selection by said short-circuiting means'of others of said transformers.

7. A selector network adapted to translate a plurality of carrier signals comprising, a pair of input terminals and a pair of output terminals, a. plurality of transformers having primary windings permanently connected in series across said input terminals and secondary windings permanently connected in series across said output terminals, means for eiectively short-circuiting all but a selected one of said primary windings, ca-

pacitive means individually connected across said input and output terminals effectively to tune one of said transformers to the frequency of a predetermined one of 1said carrier signals upon the selection of said one transformer by said lastnamed means, and capacitive means individual toeach of the other of said transformers and effec-v tive with said rst-named capacitive means to tune each of said other transformers to the frequencyV of a different one of said carriersignalsupon the selection by said short-circuiting means of others of said transformers.

BENJAMIN F. rTYSON.

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