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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING 10m direct conversion CW-SSB transceiver. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Civil radio communications The transceiver is designed to transmit and receive SSB and CW in the range of 28...29,7 MHz. The device is built according to the direct conversion scheme with a common mixer - modulator for reception and transmission. Transceiver Specifications: 1. Sensitivity in the reception mode with a signal-to-noise ratio of 10 dB, not worse than ........ 1 μV.
A schematic diagram of the transceiver (without a telegraph node) is shown in Figure 1. The transceiver has separate high-frequency and low-frequency paths for receiving and transmitting, common to both modes are a mixer-modulator and a smooth range generator.
The smooth range generator (GPA) is made on two field-effect transistors VT5 and VT6 with source connection. It operates at a frequency equal to half the frequency of the received or transmitted signal. When working for reception and transmission, the output circuits of the GPA are not switched, and the load on the GPA does not change. As a result, when switching from reception to transmission or vice versa, the VPA frequency does not deviate. Tuning within the range is performed using a variable capacitor with an air dielectric C10, which is part of the GPA circuit. In the SSB transmission mode, the signal from the microphone is amplified by the operational amplifier A2 and fed to the phase shifter on the elements L10, L11, C13, C14, R6, R7, which in the frequency range of 300 ... 3000 Hz provides a phase shift of 90 °. In the circuit L4 C5, which serves as a common load of mixers on diodes VD1-VD8, an upper sideband signal is allocated in the range of 28-29,7 MHz. The high-frequency broadband phase shifter L8 R5 C9 in this range provides a phase shift of 90 °. The selected single-sideband signal through the capacitor C6 is fed to a three-stage power amplifier based on transistors VT7-VT9. The cascade of pre-amplification and decoupling of the output circuit of the mixer-modulator is made on the transistor VT9. The high input impedance, combined with the low capacitance of C6, ensures that the effect of the power amplifier on the circuit is minimal. The VT9 collector circuit includes a circuit tuned to the middle of the range. The intermediate stage on the field-effect transistor VT8 operates in class "B" mode, and the output stage in class "C" mode. The "P"-shaped low-pass filter on L12 C25 and C26 cleans the output signal from high-frequency harmonics and ensures that the output impedance of the output stage matches the characteristic impedance of the antenna. Ammeter PA1 is used to measure the drain current of the output transistor and indicates the correct setting of the "P" filter. The telegraph mode is provided by replacing amplifier A2 with a sinusoidal signal generator with a frequency of 600 Hz (Figure 2). Switching CW-SSB is done using switch S1. The telegraph key controls the VT11 offset of the oscillator preamplifier, and consequently, the supply of a low-frequency signal to the modulator.
In receive mode, 42 V power is not supplied to the transmitter stages and the power amplifier and microphone amplifier are turned off. At this time, a voltage of 12V is applied to the cascades of the receiving path. The signal from the antenna is fed to the input circuit L2 C3 through the coupling coil L1, it matches the resistance of the circuit with the resistance of the antenna. On the transistor VT1 is made URC. The stage gain is determined by the bias voltage at its second gate (the divider across resistors R1 and R2). The load of the cascade is the circuit L4C5, the connection of the cascade of the RF with this circuit is carried out by means of the coupling coil L3. From the coupling coil L5, the signal is fed to a diode demodulator on diodes VD1-VD8. Coils L8, L9 and a phase shifter on L10 and L11 emit an AF signal in the frequency band of 300 ... 3000 Hz, which is fed through the capacitor C15 to the input of the operational amplifier A1. The gain of this microcircuit determines the main sensitivity of the transceiver in the receive mode. This is followed by an AF amplifier on transistors VT2-VT4, from the output of which the AF signal is fed to a small-sized speaker B1. The reception volume is controlled using a variable resistor R15. In order to eliminate loud clicks when switching the "RX-TX" modes, power is supplied to the UMZCH on transistors VT2-VT4 both during reception and transmission. Most of the transceiver parts are installed on three printed circuit boards, the designs of which are shown in Figures 3-5. On the first board there are details of the input URF of the receiving path (on the transistor VT1), details of the mixer - modulator with phase-shifting circuits, as well as details of the local oscillator. On the second board - low-frequency stages on microcircuits A1 and A2 and transistors VT2-VT4. On the third board the power amplifier of the transmitting path is located. The board with the mixer-modulator, URCH and GPA is shielded. The transceiver chassis is 350mm wide and 310mm deep. All control knobs and a socket for a microphone and a telegraph key are displayed on the front panel. The speaker is also installed on the front panel, it is screwed with M3 bolts through rubber gaskets Switching of the "RX-TX" modes is done by a pedal that turns off and on the voltage of 42 V and controls two electromagnetic relays, one of which switches the antenna, and the second voltage 12 V to the receiving tract. The relay windings are powered by 42 V, and in the de-energized state they turn on the receive mode (RX). Sockets for connecting the antenna, pedal and 12 V source are located on the rear panel. To power the transceiver, a basic stationary power supply is used, from which a constant stabilized voltage of 12V with a current of up to 200 mA and a constant unstabilized voltage of 42 V with a current of up to 1 A are supplied. The transceiver uses MLT fixed resistors for the power indicated in the diagrams. Trimmer resistor SPZ-4a. Loop capacitors are necessarily ceramic, tuning KPK-M. Electrolytic capacitors type K50-35 or similar imported ones. Variable capacitors of the local oscillator and the output circuit - with an air dielectric. For winding the URF loop coils, the mixer and the transmitter, ceramic frames with a diameter of 9 mm with tuning cores SCR-1 are used (plastic frames from the UPCH paths of old tube TVs are also possible, but their thermal stability is much worse than that of ceramic ones). The low-frequency coils of the mixer-modulator L8 and L9 are wound on K16x8xb ring cores made of ferrite 100NN or higher frequency (100VCh, 50VCh). Coils L10 and L11 are wound on OB-30 frames made of ferrite 2000IM1. Coils of erasing and magnetizing generators of semiconductor reel-to-reel tape recorders were wound on such cores. Transistors KP303G can be replaced with KP303 with any letter index or KP302. The KP350A transistor can be replaced with KP350B, KP350V or KP306. Transistor KP325 - on KT3102. Powerful field-effect transistors KP901 and KP902 can be with any letter indices. Any silicon and germanium (respectively) transistors of the corresponding structure are suitable for UMZCH. Diodes KD503 can be replaced with KD514, diode D9 with D18. The establishment of the transceiver begins with the GPA. By adjusting the L7 core and turning on additional capacitors (by 5-30 pF) in parallel with C10, it is necessary to achieve overlapping by the generator at a frequency of 14,0 ... 14,85 MHz. Table 1
The operation of the local oscillator can be checked using a frequency meter and an RF voltmeter, the voltage on each of the halves of the L6 coil should be 1,6 ... 1,8 V. If it is not within these limits, you need to select the number of turns L6. Now you need to move on to setting up the microphone amplifier and mixer - modulator. Without connecting the 42 V power supply, apply a voltage of 12 V to pin 7 A2 and check the operation of the amplifier. You can adjust its sensitivity by selecting the value of R31. To set up the mixer - modulator, you will need an oscilloscope, a millivoltmeter and an audio frequency generator (GZCH). Using a millivoltmeter and a generator, tune the L11 C 14 circuit to a frequency of 480 Hz, then the L10 C13 circuit to a frequency of 1880 Hz. The phase shifter input is disconnected from the capacitors C1S and C41, and the outputs from the coils L8 and L9. The input "X" of the oscilloscope and the output of the AF generator are connected to the connection point of the coils L10 and L11. The connection point L10 SI is connected to the oscilloscope input "V. A signal with a frequency of 480 Hz is supplied from the generator. There should be a straight inclined line on the oscilloscope screen. If it is an ellipse instead, you need to more accurately adjust the L11 C14 circuit. Then the connection point is connected to the input "Y" L11 C12 and, in the same way, check the setting of L10 C13 to a frequency of 1880 Hz. After that, a free output of the phase shifter is connected to the input of the oscilloscope "X" instead of the input of the phase shifter. Equal gains are set in the channels of the oscilloscope. The GZCH is tuned to a frequency of 1880 Hz. Resistors R6 and R7 is temporarily replaced by variables of 1 kOhm. By rotating the slider R6, a circle appears on the screen. Then, by setting the GZCH to 480 Hz, the resistance of the resistor R7 is similarly selected. The setting will be correct if, when the frequency changes at the output of the GZCH within 300 ... 3000 Hz, a circle will remain on the oscilloscope screen. Resistor R5 achieves the best suppression of the lower sideband. The input circuit and the L4C5 circuit are tuned to the middle frequency of the range. Then, sequentially supplying power to the stages of the power amplifier, the circuits L16 C34 and L15 C32 are tuned to the middle of the range. The output stage is tuned in the connected equivalent of the antenna - a 75 Ohm 10 W resistor (you can solder a battery of four 2 W 300 Ohm resistors connected in parallel). Setting the UMZCH comes down to setting the voltage at the emitters VT16 and VT4 equal to half the supply voltage by selecting the resistance of the resistor R3. Author: Bortkov V.; Publication: N. Bolshakov, rf.atnn.ru
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