Improvement of the receiver with PLL. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Improvement of the receiver with PLL. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / radio reception

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VHF receiver with PLL, the description of which was published two years ago in the journal "Radio" (see V. Polyakov's article "VHF receiver with PLL" in Radio, 1979, No. 9, pp. 33, 34), aroused keen interest radio amateurs involved in the design of radio receiving equipment. Along with excellent operational parameters, designers were attracted by its simplicity and high reliability in operation. However, this generally very good device has one unfortunate drawback: low temperature stability caused by . using a hybrid microcircuit without temperature stabilization elements. To eliminate this shortcoming, it is proposed to replace the hybrid microcircuit with a transistor assembly, using one of its transistors as a temperature-compensating diode.

A schematic diagram of a receiver improved in this way is shown in the figure. The new receiver is supplemented with a V9 field-effect transistor LF pre-amplifier, which matches its output with the input of a stereo decoder. In addition, to eliminate the mutual influence of the tuning circuits and the PLL, it uses various types of varicaps. So the functions of the PLL are performed, as in a slow-moving receiver, by the varicap matrix KVS111A, and the tuning functions are performed by two back-to-back diodes D223 (their capacitance at zero bias should be 20 ... 25 pF). This technical solution allows you to set the boundaries of the received range using a single resistor R8. By the way, for the convenience of carrying out this operation, it can be replaced by two series-connected resistors: a constant and a tuned one.

Receiver PLL Improvement

Setting up the receiver begins with checking the modes of the transistors, which should not differ from those indicated in the diagram by more than 20%. Further, by connecting the antenna, the boundaries of the received frequency range are set, first roughly - using the L2 coil, and then accurately - using the resistor R8. It should be borne in mind that with a zero bias on the tuning diodes V7, V8, radio stations operating in the low-frequency range should be received. In conclusion, the input circuit is adjusted according to the maximum holding band and the optimal signal level in the antenna is selected.

Author: V. Korshunov, Moscow; Publication: N. Bolshakov, rf.atnn.ru

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