On the stabilization of the GPA frequency. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Generators, heterodynes
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Almost all radio amateurs who manufacture KB equipment face work on stabilizing the GPA frequency. To obtain a stable frequency, it is usually recommended to select capacitors with a positive (or) negative capacitance coefficient in the GPA and the oscillatory circuit. In some cases, this is either impossible to do for various reasons, or the effect obtained is insufficient.
However, this method is not the only one. If a varicap is included in the oscillatory circuit, frequency stabilization can be carried out by applying a control voltage to the varicap, which depends, among other reasons, on temperature. To do this, the control voltage is first applied to the temperature-dependent resistive divider, and from there to the varicap. The hot arm of the temperature-dependent divider is a resistor with a positive temperature coefficient of resistance (TCS), and the cold arm is a negative TCR. In this way, in combination with the generally accepted one, the frequency stabilization of the GPA transceiver was carried out [1]. On fig. 1, where a fragment of the GPA circuit is shown, a circuit for switching on such a divider is given [1].
Ris.1
The designations in the figure are the same as in [1]. As the hot arm of the RA divider, the resistance between the bases B1 and B2 (the emitter remains free) of the KT117 unijunction transistor with any letter index is used. The gap between the bases B1 and B2 of the transistor KT117 is a silicon resistance with a large positive TCR - up to 0,5 to 0,9% / ° C [2, 3]. The value of the interbase resistance of transistors KT117 lies in the range from 4 to 12 kOhm, RA=10 kOhm was used. As the cold arm of the RB divider, a KMT-10 semiconductor thermistor with a resistance of 80 kΩ at 20°C is used, the negative TCR of which at 20°C is 4.2%/°C [4,5]. When overcompensating, i.e. when the GPA frequency starts to change in the opposite direction, it is necessary to shunt the hot arm of the RA divider with a conventional resistor, for example, an MLT, the value of which is selected according to the degree of stabilization of the GPA frequency. Stabilization of the GPA frequency should start from the 10-meter range [1].
Literature
1. Lapovok Ya. I am building a KB station. - M.: DOSAAF. - 1983.
2. Nedoluzhko I. Unijunction transistors. - M.: Enerpm. - 1974. - p.27.
3. Olsevich A. Two-base diodes in automation. - M.: Energy, - 1972. - p.17.
4. Zaitsev Yu. Semiconductor resistors in radio circuits. - M.: Energy. - 1971.-p.9.
5. Neznaiko A. Capacitors and resistors. MRB, issue 861. - M.: Energy, - 1974.-c.l08.
Author: V.Kulgavchuk (RA3TIB), Russia, Sarov, Nizhny Novgorod region; Publication: N. Bolshakov, rf.atnn.ru
See other articles Section Knots of amateur radio equipment. Generators, heterodynes.
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