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“Varactor” diode used in radio receiver
Feb., I96O.]
CURRENT TOPICS
The geometrical optics of the tube are good enough for details in the pattern on the cathode about one fifteenth of a millimeter in diameter to be reproduced clearly on the screen. The present area of the dynodes is small--just smaller than a dime. It is planned to enlarge them in future instruments. Even with these small pictures, detail is on a par with a 250-line scanning T V system. With bigger dynodes, performance approximating a 600-700 line scanner could probably be achieved.
"Varactor" Diode Used in Radio Receiver.--An ultra-high frequency mobile telephone radio receiver designed around solid-state devices was described by L. G. Schimpf of Bell Telephone Laboratories at the annual meeting of the Professional Group on Vehicular Communications of the Institute of Radio Engineers. Mr. Schimpf told how new devices such as the " v a r a c t o r " diode can be used in a solid-state radio receiver designed to operate at around 900 mc. The receiver is of the double-conversion superheterodyne type with a first i.f. centered at 63 me. and the second at 10.7 me. It has a sensitivity of about one microvolt for 13 db of quieting. All amplification, conversion, and frequency generation operations are fulfilled by using solid-state devices. T o provide the high local oscillator frequency necessary for the first conversion, a three-step chain is employed, consisting of a crystal-controlled transistor oscillator, a transistor doubler and a frequency tripler. It is in this frequency tripler stage that the special characteristics of the varactor diode are employed to advantage. The " v a r a c t o r " diode, or variable-
I57
capacitance diode, was developed recently at Bell Laboratories. It consists of a p-n junction whose capacitance varies as the reverse voltage across the junction is varied. Thus, if a sine wave is impressed on the diode, the o u t p u t will be very rich in harmonics. The varactor diode is, therefore, a very efficient harmonic generator and in the multiplier chain functions as a frequency tripler. A silicone diode is used as the first mixer, and the first i.f. consists of a two-stage transistor amplifier with a gain of about 35 db. The second oscillator is transistorized and crystalcontrolled, providing a frequency of 73.7 mc. This frequency, when mixed with the first i.f. of 63 me., gives the second i.f. of 10.7 me. This second i.f., which is also transistorized, serves as a limiter when FM signals are being received. The varactor diode used in this receiver is a versatile device. It has been employed extensively as the variable reactance element in parametric amplifiers to provide extremely low-noise radio-frequency amplification.
TV Optical System for Dental, Medical U s e . - - A new instrument that permits a dentist to view any part of a patient's mouth, highly magnified, on a T V screen has been successfully demonstrated at the U.S. N a v y Dental School, Bethesda, Md., according to a joint announcement by the N a v y and Avco Corporation. The device, which is a new optical fiber probe linked to a closed-circuit T V system, can eventually be adapted for medical probes to explore inside the human body. It has been developed under a feasibility study sponsored by the Office of Naval Research and carried out at Wilmington,
CURRENT TOPICS
The geometrical optics of the tube are good enough for details in the pattern on the cathode about one fifteenth of a millimeter in diameter to be reproduced clearly on the screen. The present area of the dynodes is small--just smaller than a dime. It is planned to enlarge them in future instruments. Even with these small pictures, detail is on a par with a 250-line scanning T V system. With bigger dynodes, performance approximating a 600-700 line scanner could probably be achieved.
"Varactor" Diode Used in Radio Receiver.--An ultra-high frequency mobile telephone radio receiver designed around solid-state devices was described by L. G. Schimpf of Bell Telephone Laboratories at the annual meeting of the Professional Group on Vehicular Communications of the Institute of Radio Engineers. Mr. Schimpf told how new devices such as the " v a r a c t o r " diode can be used in a solid-state radio receiver designed to operate at around 900 mc. The receiver is of the double-conversion superheterodyne type with a first i.f. centered at 63 me. and the second at 10.7 me. It has a sensitivity of about one microvolt for 13 db of quieting. All amplification, conversion, and frequency generation operations are fulfilled by using solid-state devices. T o provide the high local oscillator frequency necessary for the first conversion, a three-step chain is employed, consisting of a crystal-controlled transistor oscillator, a transistor doubler and a frequency tripler. It is in this frequency tripler stage that the special characteristics of the varactor diode are employed to advantage. The " v a r a c t o r " diode, or variable-
I57
capacitance diode, was developed recently at Bell Laboratories. It consists of a p-n junction whose capacitance varies as the reverse voltage across the junction is varied. Thus, if a sine wave is impressed on the diode, the o u t p u t will be very rich in harmonics. The varactor diode is, therefore, a very efficient harmonic generator and in the multiplier chain functions as a frequency tripler. A silicone diode is used as the first mixer, and the first i.f. consists of a two-stage transistor amplifier with a gain of about 35 db. The second oscillator is transistorized and crystalcontrolled, providing a frequency of 73.7 mc. This frequency, when mixed with the first i.f. of 63 me., gives the second i.f. of 10.7 me. This second i.f., which is also transistorized, serves as a limiter when FM signals are being received. The varactor diode used in this receiver is a versatile device. It has been employed extensively as the variable reactance element in parametric amplifiers to provide extremely low-noise radio-frequency amplification.
TV Optical System for Dental, Medical U s e . - - A new instrument that permits a dentist to view any part of a patient's mouth, highly magnified, on a T V screen has been successfully demonstrated at the U.S. N a v y Dental School, Bethesda, Md., according to a joint announcement by the N a v y and Avco Corporation. The device, which is a new optical fiber probe linked to a closed-circuit T V system, can eventually be adapted for medical probes to explore inside the human body. It has been developed under a feasibility study sponsored by the Office of Naval Research and carried out at Wilmington,