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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING High frequency signal generator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology The high-frequency signal generator is designed to test and adjust high-frequency electronic devices. The main parameters
The generator consists of the RF generator itself (transistor V3), an emitter follower (transistor, V4), an output amplifier (transistor V6) and an amplitude modulator (transistor V5).
The required subrange of generated frequencies is selected by switch S1, the generator is rebuilt with a double block of capacitors of variable capacitance C6 (both sections are connected in parallel). Diode VI in the gate circuit of transistor V3 acts as a limiter, which increases the stability of the output signal amplitude when the generator is tuned (within the subrange). Resistors R1*-R4* attenuate positive feedback, improving the waveform. The supply voltage of this stage is stabilized by the Zener diode V2. From the source of the transistor V3, the high-frequency oscillation voltage is supplied to the emitter follower, which provides decoupling between the generator and the load. The voltage developed by the generator (transistor V3) is significantly greater than that required for the normal operation of subsequent stages. Therefore, the signal is supplied to the output amplifier from the divider formed by resistors R9 and R10 in the emitter circuit of transistor V4. The output broadband amplifier (transistor V6) is made on a circuit with a common emitter. Its load is a variable resistor R15, from the engine of which the signal is fed to the output coaxial connector K2. In order to provide a sufficiently wide output amplifier bandwidth, the resistance of this resistor should be no more than 150 ohms. Then, with a capacitive load of about 50 pF (capacitance of a coaxial cable about 0,7 m long), the bandwidth of the amplifier is 20 .. 30 MHz. In this case, a relatively large current (about 10 mA) must be passed through the transistors. the voltage drop across the resistor R15 should be about 2 times the amplitude of the output signal. Amplitude modulation is carried out in the output stage. Transistor V5 of the modulator is connected in direct current in series with transistor V6, and the modulating voltage from connector X1 is supplied simultaneously to the bases of both transistors (on V6 - through resistor R13 *). The result is a mixed (collector-base) modulation of the output signal. Using such modulation, by simply increasing the AF voltage, you can get almost 100% modulation of a high-frequency signal with low non-linear distortion. Turn on the modulation switch S2. The generator uses a small-sized dual block (its sections are connected in parallel during installation) of variable capacitors with a solid dielectric KPTM-4 (from Neiva, Etyud, Signal, Orbita transistor radios). The axis of the block is lengthened with a piece of brass rod with a diameter of 4 and a length of 18 mm. At one end, an axial hole 8 mm deep was drilled in it, in which an M2 thread was then cut. For the connection, a steel pin M2 X 8 was used, which is screwed on BF-2 glue into a threaded hole in the axis of the KPE block, and an extension rod is screwed onto the protruding end on the same glue to failure. To adjust the output voltage, a variable wire resistor PPB-1V was used, but another resistor could be used, the resistance of which would not exceed 150 ohms. The generator uses capacitors KT-1a (C1-C4), K50-6 (C13), KM (C15) and KLS (the rest). All fixed resistors, except for R10-VS-0,125 (MLT-0,125, MLT-0,25, etc.). Resistor R10 - MON-0,5, if necessary, it can be made independently by winding, for example, a piece of PEV-2 wire with a diameter of 0,06 mm on the body of the MLT-0,5 resistor with a resistance of at least 100 ohms. A piece of wire 790 mm long is folded in half and the loop is fixed on the resistor with a drop of molten rosin. After winding, the ends are soldered to the terminals of the resistors. The device can use any field-effect transistor of the KP303 series and any low-power silicon high-frequency transistors. The static current transfer coefficient of transistors V4 and V6 must be at least 60, transistor V5 - at least 30. Diode V1 - any high-frequency silicon. The generator coils L1 and L2 are wound on M1000NM-A-K10 X 6X 4,5 ferrite rings (outer diameter 10, inner diameter 6, height 4,5 mm, ferrite grade 1000NM). The first of them contains 25 + 50 turns of PEV-2 wire with a diameter of 0,15 mm, the second - 7 + 14 turns of PEV-2 wire with a diameter of 0,41 mm. Coils L3 and L4 are wound respectively on ferrite rods M600NN-2-CC3, 5 X 20 (diameter 3,5, length 20 mm) and M600NN-3-CC2,8 x 12 (diameter 2,8, length 12 mm). Coil L3 consists of 10 + 20 turns of PEV-2 wire with a diameter of 0,25 mm, L4 - 4 + 8 turns of PEV-2 wire with a diameter of 0,5 mm.
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