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March 13, 1962 .J March 13, 1962 .J. E. DURKEE 3,025,394 'SUPER-REGENERATIVE TRANSISTOR DETECTOR Filed May 15, 1958 |n INVENTOR. JOHN E. DURKEE BY - amass nited States Patented Mar. 13, 1%32 1 2 3,025,394 pacitance of the transistor is used to provide the re SUPER-REGENERATIVE TRANSISTOR DETECTQR generative feedback path, but the strength of the signal John E. Durkee, Conesus, N.Y., assignor to General Dy is maintained ‘below the oscillatory level by the external namics Corporation, Rochester, N.Y., a corporation of capacitance which ‘bleeds off a portion of the feedback Delaware signal. Filed May 15, 1958, Ser. No. 735,611 In accordance with another aspect of the invention, 2 Claims. (Cl. 250-20) the regenerative detector circuit is made super-regenera tive by incorporating therein a relaxation type oscillator The present invention relates to radio receivers and it circuit to provide the quench frequency signal which relates more particularly to a new and improved detector 10 periodically causes the detector circuit to oscillate. Op circuit which is both ef?cient and reliable in operation eration of the detector in this manner thus greatly in and which utilizes relatively few components so as to be creases its gain and reduces the number of additional small in size, simple in construction, and inexpensive to stages of audio ampli?cation which are required for driv manufacture. - ing the speaker. Radio‘ receivers which are sufficiently small to ?t in 15 Many other objects and advantages of the present in one’s pocket or, perhaps, to be strapped to the wrist, have vention will become apparent from a consideration of many important uses such, for example, as a primary the following detailed description when taken in conjunc component in paging systems of the type presently used tion with the following drawing which is a schematic in industrial plants, hospitals and the like. Moreover, circuit diagram of a radio receiver embodying the present such receivers can be carried by ?remen during the ?ght 20 invention. ing of a ?re to provide direct communication between Referring now to the drawing, a radio receiver Jiii a number of ?remen and a central station from which comprises an antenna coil 11 which intercepts an ampli ?re ?ghting directions are given to the individual ?re tude modulated radio signal to develop therein a current men. In this latter application the receivers must be varying in accordance with the radio signal. A ?xed so small in size and light in weight as not to interfere, 25 capacitor 12 and an adjustable trimmer capacitor 13 are in any appreciable way, with the activities of the ?re connected in parallel across the antenna coil 11 to pro men, but they must also be extremely reliable in oper vide the usual tank circuit which is adjustably tunable ation to insure that the communication links between the to select a desired signal from the various radio frequency central station and the individual ?remen is maintained at all times. signals which are intercepted by the antenna coil 11. 30 Where the radio receiver 10 is designed for operation at In order to minimize the number and size of the circuit a single frequency, the capacitor 13 is not ordinarily ad~ components used in the receiver, it would be desirable justed during normal use of the receiver but should be to employ a super-regenerative detector circuit using a adjusted at the factory. transistor. The advantage of a super-regenerative de The receiver v10 is energized by a battery 14 having tector circuit is that a maximum gain is achieved with 35 the positive pole thereof connected to ground through a the smallest number of components, and the provision receiver on-otf switch 15. The switch 15 is a simple, of the transistor reduces the size of the receiver because single throw, single pole switch which is shown in the a transistor is considerably smaller than a comparable “off” position. Therefore, with the switch 15 in the tube, and a very small battery may be employed because “on” position, the antenna circuit is connected between of the relatively low power drain of the transistor. 40 the negative pole of the'battery 14 and the collector of Therefore, an object of the present invention is to pro a PNP junction transistor 16 whose base is connected to vide a new and improved radio receiver. the positive pole of the battery 14 through the ground Another object of the present invention is to provide connection. As shown, the antenna coil 11 is connected a new and improved radio'receiver which is operable in the UHF frequency band. 45 to the negative pole of the battery 14 through the primary winding of an audio frequency coupling transformer 17 A further object of the present invention is to pro and the base of the transistor 16 is connected to ground vide a new and improved super-regenerative detector cir cuit. through the parallel circuit comprising a capacitor 13 and 'a pair of resistors ‘19 and 20. If the receiver 10 is A further object of the present invention is to pro 50 to be used in a system employed in ?ghting ?res, it is vide a new and improved super-regenerative detector cir desirable that it operate in the UHF frequency range cuit using a transistor as the nonlinear impedance ele such as, for example, at a frequency of 41.6 megacycles ment. I which is the frequency'allotted by the Federal Com Another object of the present invention is to provide munications Commission ‘for this purpose. Accordingly, a new and improved quench circuit for use in conjunc it is necessary to select a transistor 16 which may be tion with a radio receiver employing a super-regenerative 55 detector. operated at this high frequency and it has been found that certain types of transistors such, for example, as Brie?y, the above and further objects are realized in the surface barrier transistors satisfy this requirement, accordance with the present invention by operating a but the internal capacitance between the collector and transistor detector at a su?iciently high frequency that 60 the emitter thereof, which is designated in the drawing the internal capacitance between the electrodes of the by the number 22, provides suf?cient feedback to cause transistor provides su?icient regenerative feedback to oscillation of the transistor 16. For voice transmission cause the transistor circuit to oscillate, and reducing the purposes, this is, of course, undesirable, and therefore, amplitude ofthe feedback‘ signal below the oscillatory it is necessary to prevent the transistor 16 and its as level by means of a capacitor connected between one of 65 sociated circuit components from continuously oscillat the electrodes and ground. In this way the internal ca ing at these high UHF frequencies. Consequently, and 3,025,894 4 3 components are very small in size and provide a low cur in accordance with the present invention, the variable rent drain on the battery. Consequently, a small, reli capacitor 24 is connected between ground and the emit able, and inexpensive radio receiver may be designed in ter of the transistor 16 thereby to bleed off an adjustable corporating the detector and quench circuit of the pres portion of the signal which is fed back from the collector ent invention. to the emitter through the internal capacitance 22. That By way of illustration only, and not by way of limiting is, capacitances 22 and 24 constitute a voltage divider this application thereto, the following component values and the carrier potential across capacitance 22, and hence have been found to give ef?cient operation in a particu the degree of carrier feedback, may be controlled by lar construction of the disclosed radio receiver. properly selecting the value of capacitance 24. A direct current path around the capacitor 24 is provided prefer 10 Transistor 16 ______________ __ SBl03. ably by a high inductance coil 24a. Continuous oscilla Transistor 30 ______________ __ 2N l 32. tion of the detector circuit may thus be prevented by Resistor 19 ________________ _. 2700 ohms. properly adjusting the capacitor 24. If it were desired Variable resistor ___________ __ 1200 ohms maximum. to operate the detector circuit including the transistor Resistor 29 ________________ _. 1 kilohm maximum. 16 as a regenerative detector, the value of the capacitor 15 Capacitor 12 _______________ _. 62 micrornicrofarads. 24 would be adjusted such that the gain of the feedback Capacitor 13 ___________ __»__-_ 5—25 micrornicrofarads. loop including the internal capacitance 22 were slightly Capacitor 18 _______________ _. .005 microfarad. less than unity thereby to provide maximum gain without Capacitor 24 ______________ __ 5-25 micromicrofarads. any oscillation. Capacitor 3‘1 ______________ __ .01 microfarad. While a substantial amount of ampli?cation may be 20 Capacitor 33 ______________ __ 25 microfarads. provided by the detector 16 when it is operated regenera Capacitor in trap 28 _________ _. .01 rnicrofarad. tively in this manner, it would be desirable to further Conductor ‘in trap 28 ________ __ 10 millihenries. increase the ampli?cation thereof if such would reduce While there has been described what is at present the required number of audio stage ampli?cation. Con 25 considered to be a preferred embodiment of the inven sequen-tly, in accordance with the present invention the tion, it Will be understood that various modifications gain of the detector is substantially increased by operat may be made therein which are within the true spirit ing the transistor 16 super-regeneratively. and scope of the invention as de?ned in the appended In order to periodically render the detector circuit claims.
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