About frequency stabilization GPA
However, this method is not the only one. If the oscillating circuit includes a variable capacitor, the frequency stabilization can be accomplished through the filing of the varicap control voltage, which depends, among other things, and temperature. This control voltage is supplied to thermostability the resistive divider, and with him already on the varicap. Hot shoulder termosaving divider is a resistor with a positive temperature coefficient of resistance (TCR), and cold - with a negative TCR. In this way, in combination with the generally accepted was carried out frequency stabilization GPA transceiver . In Fig. 1, which shows the schema fragment GPA is given to the inclusion of such divider .
The designations in the figure are the same as in . As the hot shoulder divider RA is used, the resistance between the bases B1 and B2 (emitter remains free) unijunction transistor Ckts any letter index. The gap between the bases B1 and B2 of the transistor QT is a silicon resistance with a large positive TCR - up to 0.5 to 0.9%/°C [2, 3]. The value of cross-database resistance of transistors CT lies in the range from 4 to 12 ohms, used RA=10 kω. As the cold shoulder divider RB applied semiconductor thermistor KMT-10 a resistance of 80 ohms at 20°C, a negative TCR of which at 20°C is 4.2%/°C[4,5]. When overcompensation, i.e. when the frequency of the GPA will begin to change in the opposite direction, you shall be shorted hot shoulder divider RA conventional resistor, such as MLT, the value of which is chosen according to the degree of frequency stabilization of the GPA. The stabilization of the frequency of the GPA should start with a 10-meter range .
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Author: V. Kulgavchuk (RA3TIB), Russia, Sarov, Nizhny Novgorod region; Publication: N. Bolshakov, rf.atnn.ru