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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Radio receiver Super-Test. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / radio reception The receiver allows you to receive signals from amateur radio stations operating CW and SSB in the ranges of 1,8; 3,5; 7; 10; 14; 18; 21; 24 and 28 MHz. Technical specifications
Power can be supplied from AC 220 V or from a DC source with a voltage of 12...24 V. The receiver circuit is shown in fig. 1. It is a superheterodyne with one frequency conversion. The RF signal through the antenna socket XW1 and the capacitor C1 is fed through the switch SA1.1 to a part of the coil L1, which together with the variable capacitor (KPI) C3 forms the input circuit. The restructuring of the receiver from range to range is carried out by closing the corresponding part of the turns of the coil with the SA1.2 range switch section. The SA1.1 switch section on any of the ranges connects only a part of the turns (about half) of the input circuit coil to the antenna, thereby providing an acceptable match with the antenna.
In the range of 1,8 MHz, capacitor C3 is connected in parallel to KPI C2, which makes it possible to tune in this frequency range while reducing the frequency overlap ratio. The RF signal from the input circuit through C4 is fed to the first gates of field-effect transistors VT1 and VT2, on which a switchable balanced mixer is made. The gain of this receiver stage is about 8. The signal of the GPA (smooth range generator) made on the transistor VT1 according to the Wakar scheme is fed to the second gates of the transistors through the transformer T9 in antiphase. The generator according to this scheme has increased frequency stability. The SA1.3 switch connects various capacitors to the GPA circuit on the appropriate ranges, ensuring the generation of the necessary frequencies with the necessary frequency overlap. The power supply voltage of the GPA is stabilized by a parametric stabilizer VD15R45. The GPA signal amplifier is assembled on the VT10 transistor. An elliptical low-pass filter of the seventh order with a cutoff frequency of 12,65 MHz is connected to its output. On the 10, 21, 24 and 28 MHz bands, the GPA generates a frequency half that required to obtain the desired IF (5,5 MHz). The required doubling occurs in the mixer (VT1, VT2) when the contacts of relay K1.1 are switched to the left (according to the diagram) position. The second group of relay contacts K1.2 provides the connection of the resistor R2 in parallel with R3 to ensure the best conversion mode on the indicated ranges. The switch section SA1 controls the switching on of the relay K1.4. On the other ranges, the frequency doubling of the GPA in the mixer does not occur. On the ranges of 21, 24 and 28 MHz, only half of the input winding of the transformer T2 is turned on at the mixer output, which increases the transformation ratio on these ranges. As a result, the sensitivity of the receiver is also improved. The output winding of transformer T2 and capacitors C8, C9 form an IF circuit tuned to a frequency of 5,5 MHz. The signal taken from this circuit is amplified by the first IF stage, which is made on a VT3 field effect transistor. The AGC voltage is supplied to the second gate of this transistor through resistor R9. The IF circuit is included in the drain circuit. The main selection is carried out by a quartz eight-crystal ladder-type filter (ZQ1-ZQ8). The bandwidth of the filter in SSB mode is 2,4 kHz (Fig. 2).
When the relay contacts K2.1 and K2.2 are closed, the band narrows to 1 kHz (CW mode - Fig. 3).
The filtered IF signal is amplified by the second IF stage (VT4 transistor). The second gate of this transistor is also connected to the AGC circuits through resistor R15. From the output VT4, the IF signal through the phase-inverting stage on the transistor VT5 is fed to the ring balanced mixer VD1-VD4 (SSB signal detector). A signal with a frequency of 5,5 MHz is supplied to the other arm of the mixer, which is generated by a quartz local oscillator on a VT11 transistor. Trimmer resistor R20 can be used to adjust the transfer coefficient of the cascade on the transistor VT5. An emitter follower of a quartz local oscillator signal is made on the VT12 transistor. From the output of the ring balanced mixer, the audio frequency signal through the C39R24C40 RC filter goes to a low-frequency pre-amplifier made on the DA1 chip, and from it through the volume control resistor R31 to the final ULF (transistors VT6, VT7, VT8). Switch SA2 can turn off the dynamic head BA1. Connector XS1 is designed to connect headphones. From the output of the DA1 microcircuit, the low-frequency signal also goes to the AGC signal rectifier, assembled on diodes VD7 and VD8. The response time of the AGC system is determined by the capacitance of the capacitor C94. The AGC signal amplifier is made on the VT13 transistor. The emitter circuit of this transistor includes a RA1 microammeter with a total deflection current of 100 μA (S-meter). Resistor R58 serves to limit the maximum voltage supplied to the second gates of transistors VT3, VT4 (it should be no more than 5 V). Variable resistor R59 adjust the IF gain manually. The AGC threshold is selected by resistor R64. The applied circuit allows you to read the S-meter readings regardless of the position of the R31 resistor slider or the position of the SA2 switch. In addition, as the IF gain decreases, the S-meter readings decrease, which corresponds to the logic, in contrast to the AGC scheme used in the "TURBO-TEST" radio receiver. The power supply of the receiver consists of a transformer TZ, a rectifier bridge VD11 and a voltage regulator +12 V on the op amp DA2 and transistors VT14, VT15. The collector of the VT15 transistor is connected to the device case, which made it possible not only to do without an additional heat sink, but also to use a negative voltage (present on the VT15 emitter relative to the case) to lock the idle stages of the transmitting set-top box in the receive mode. The collector of the transistor VT8 is also connected to the case, and the transistor VT7 has thermal contact with the receiver chassis through a mica gasket. This made it possible to avoid the use of separate heat sinks. The frequencies generated by the receiver's GPA are shown in Table. 1, and winding data of circuits and transformers - in table. 2. Transformer T1 is wound in three, and T2 - in four wires twisted together (twisting pitch - 3 mm). Winding lead coil to coil.
The design of the coils L1, L7 and their winding data are the same as in the "TURBO-TEST" receiver [1, 2]. The receiver case, the outlines of the printed circuit board, the vernier, the capacitors of the GPA and the input circuit, as well as the power transformer, are used the same as and in the "TURBO-TEST" receiver. The IF and elliptical filter coils are enclosed in aluminum screens. The frames of the L1 and L7 coils are ceramic, the rest of the coils are polystyrene. A sketch of the coil L1 is shown in fig. 4. Sectioned winding. The sections are separated by cheeks made of getinax 1 mm thick. They are tightly put on the frame and glued to it with Moment glue. The length of the coil frame L7 is 46 mm.
The receiver uses resistors MLT, SPZ-9a, SPZ-386. Capacitors - KT-1, KD-1, KM, KLS, K50-6, K53-1. To tune the receiver in frequency, the so-called differential KPI ("butterfly") YaD4.652.007 from the radio station R-821 (822) was used. To increase the maximum capacity, their stators are connected to each other, and the rotors are connected to a common wire. In terms of the dependence of the capacitance on the angle of rotation of the rotor, these capacitors are direct-capacitive, therefore, without any special tricks, it was possible to obtain a sufficiently large stretching of the scale in the telegraph sections. Relays K1 and K2 - RES60 version RS4.569.437 (operating current - 12,4 mA, and winding resistance - 675 ... E25 Ohm). Switch SA1 - ha-flight PGZ-11P4N. The SA1.4 biscuit is located between the SA1.3 biscuit (located closer to the printed circuit board) and the SA1.1, SA1.2 biscuits (located closer to the front panel of the receiver); SA2 - microtumbler MT-1; SA3 - push-button P2K with fixation in the pressed position; SA4 - microtumbler MT-3. Measuring head RA1 - microammeter M476/3 with a total deflection current of the arrow 100 μA (from the tape recorder "Romantic-3"). In the quartz filter and the quartz oscillator, quartz resonators from the set "Quartz resonators for radio amateurs" No. 1 (passport IG2.940.006 PS), manufactured by the Omsk Instrument-Making Plant named after. Kozitsky. Network transformer TK - TVK from a black and white tube TV. To improve reliability, it is desirable to modify it, as described in [3] (disassemble the plates of the magnetic circuit and assemble them with an overlap, thereby removing the gap between the plates). Before installation in the receiver, the transformer must be placed in a box-shaped screen made of mild steel with a thickness of 0,5 ... 0,8 mm. Most of the receiver parts are mounted on a 1,5 mm thick foil fiberglass printed circuit board. The L1 coil is installed on the front panel, the L7 coil is on the printed circuit board, the axes of their projections intersect at an angle of 90°. The GPA is separated from the reference oscillator and the rest of the receiver stages by a screen - a partition 46 mm high, bent from sheet brass 1 mm thick. The quartz filter is also separated by a similar brass baffle. The screens of the coils L8, L9, L10 form a kind of screen for the mixer VT1, VT2, separating it from the rest of the cascades. Establishing the receiver begins with checking the absence of a short circuit in the power circuits. Then, by adjusting the resistor R68, the supply voltage is set at the output of the stabilizer (at the cathode of the VD9 diode relative to the case) +12 V. Next, the modes of the transistors VT1-VT4 are set for direct current by selecting the resistors in the gate circuits (R1, R7, R13) so that at their sources a constant voltage of about +0,9 V was established. The mode of the transistor VT10 is selected by resistor R43. The specified operation must be performed with the antenna turned off, the range switch in the "14 MHz" position, the sliders of the resistors R31 and R59 in the positions corresponding to the maximum gain. Resistor R58 is selected according to the maximum gain with an undistorted signal in the IF stages, while the constant voltage on the collector of the transistor VT13 must be within +3 ... 5 V. In any case, it should not exceed +5 V. The establishment of the terminal ULF consists in selecting the resistor R33 in order to set the quiescent current of the output transistors VT7, VT8, equal to 9 mA, and selecting R35 to set the supply voltage of these transistors, equal to half the supply voltage. By selecting the resistor R27, the supply voltage at pin 5 of the DA1 chip is set, equal to half the supply voltage. By selecting the resistor R29, you can achieve a change in the gain of the cascade in one direction or another (in this case, its frequency response changes somewhat). The quartz filter is tuned by selecting capacitors according to the method described in [4]. When the contacts of relay K2 are closed, the bandwidth should narrow to 1 kHz. If the bandwidth differs from the specified one, capacitors C16, C18 should be selected. GPA frequencies are set in accordance with Table. 1 by adjusting capacitors C56-C63. After that, thermal compensation is performed by replacing capacitors C52, C66, C64, C67, C68 on the 18 MHz band with capacitors equal in nominal value, but with different TKE (temperature coefficient of capacitance). Similarly, replace the capacitors C49-C51, C53-C55, C105 on the remaining ranges. By tuning the L8-L10 coils, an elliptical filter is tuned, achieving a cutoff frequency of 12,65 MHz and the absence of noticeable frequency response dips. The frequency of the VT11 quartz local oscillator is set by adjusting the L13 coil on the lower slope of the quartz filter characteristic. By adjusting the L11 coil, they achieve the maximum signal at the emitter of the VT12 transistor. By applying a signal from the GSS with a frequency corresponding to the selected range, C3, L2, L4 are adjusted to the maximum output signal. The selection of the resistor R2 achieves the highest conversion ratio on the HF bands. By adjusting the resistor R23, the mixer is balanced for the best suppression of the quartz local oscillator signal. The selection of the resistor R55 ensures the absence of distortion of the sinusoidal signal of the local oscillator at maximum amplitude. By selecting the resistor R64, an acceptable level of AGC operation is set. The AGC time constant is adjusted by selecting capacitor C94. For stable operation, it is desirable to shunt the base-emitter junction of the VT15 transistor with a 1 ... 3 kOhm resistor. Literature
Author: Vladimir Rubtsov (UN7BV)
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