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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Range 160 meters in Radio-76. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Civil radio communications Using the scheme of the "Radio-76" transceiver (B. Stepanov. G. Shulgin. "Radio-76" transceiver .- "Radio", 1976, No. 6. p. 17; No. 7, p. 19), it is easy to make a single-band transceiver for operation in the range of 160 m (1850...1950 kHz). The sensitivity of the receiving path of such a transceiver will be no worse than 1 μV with a signal-to-noise ratio of 10 dB, the output power of the transmitting path will be about 2 W at an active 75-ohm load. The rest, the parameters of the transceiver are the same as those of the Radio-76 transceiver. From the "Radio-76" transceiver, the new device will differ only in the data of the elements of the band-pass filters of the receiver and transmitter, the contour of the smooth range generator, as well as the circuits of the pre-terminal and final power amplifiers of the transmitting path. The new bandpass filters have a bandwidth of 0,7 around 120kHz. In this case, the mirror channel in the receiver is suppressed by at least 60 dB. The filter coils (L1 and L2 in Fig. 3 and 4 in the mentioned article) are wound in the SB-12a armor core with PEV-2 0,33 wire and contain 20 turns each (the tap is made from the 5th turn, counting from the grounded output). Coil L3 (Fig. 4) of the smooth range generator circuit is wound in the same core and with the same wire, but contains 28 turns. To ensure the required frequency overlap in the local oscillator, a KV104G varicap should be used. The loop capacitors in the bandpass filters of the receiver and transmitter (C1 and C2 - in Fig. 3, as well as C1 and C3 - in Fig. 4) must have a capacitance of 1000 pF, and the coupling capacitors (C3 - in Fig. 3 and C2 - in Fig. 4 30) - XNUMX pf. Coils L3-L5 (Fig. 3) in the terminal stage of the transmitter are wound on a ring core made of M20VCh2 ferrite (size K12x6x4) with PEV-2 0.33 wire. They contain 3, 22 and 3 turns, respectively. The retraction of the L5 coil is made from the middle. Coils L6-L8 in the terminal stage are wound on a ring core made of M50VCh2 ferrite (size K20x10x5) with the same wire as the previous ones, and contain 3, 22 and 4 turns. Before winding the coils, the cores must be wrapped with one or two layers of varnished cloth or fluoroplastic tape. Capacitors C8 and C14 in the power amplifier (Fig. 3) - 240 and 300 pF, respectively. Because of. that the relative frequency overlap in the range of 160 m is large enough, for a uniform power gain in different parts of the range, it becomes necessary to adjust the contours of the transmitter's pre-terminal and final stages. To do this, the tuning capacitors in these circuits are replaced by variables. As variable capacitors C7 and C13 (Fig. 3), you can use tuning KPV-140 or variable capacitors from any small-sized transistor radio. They are installed on the front panel of the transceiver between the tuning scale and the measuring device and are connected to the L4 and L7 coils with short lengths of any type of coaxial cable. Capacitors must be separated by a partition made of foil fiberglass. It is useful to place the same screen between the main board and the stages of the local oscillator and power amplifier. The boundary frequencies of the smooth range generator are set equal to 2340 and 2460 kHz (i.e., with a margin of 10 kHz at the edges). To do this, first achieve a generation frequency of 2400 kHz by rotating the core of the L3 coil (Fig. 4). The handle of the variable resistor R6 (Fig. 4) should be approximately in the middle position. Then check the upper and lower limits of the range. If the "Setting" knob fails to cover the entire range, then resistors R5 and R7 should be installed with a lower resistance. After "laying" the frequency boundaries of the smooth range generator, the receiving path of the transceiver is adjusted. By applying a signal with a frequency of 1900 kHz and a level of 100 μV through the equivalent of the antenna to the input of the transceiver. tuned to the frequency of the generator. In this case, the "Gain" knob should be in the position corresponding to the maximum gain. The low frequency output voltage is controlled by an oscilloscope or an output meter. By rotating the trimmers of the bandpass filter coils and gradually reducing the level of the signal supplied from the generator, the maximum sensitivity of the receiver is achieved. The next step is to set up the transmitter. First, the input band-pass filter of the power amplifier is temporarily disconnected from the main board, and a signal with a frequency of 1900 kHz with a level of 100 mV is applied to the filter input from the generator. An antenna equivalent is connected to the antenna socket - an MLT-2 resistor with a resistance of 75 ohms. The transver is switched on for transmission and, observing the readings of the measuring device that measures the current of the output stage, the trimmers of the band-pass filter coils are rotated, achieving the maximum deflection of the arrow. The contour of the pre-terminal cascade is tuned by the capacitor C7. If the generator is rebuilt within ± 30 kHz, the current should fall off smoothly. If this does not happen, then the power amplifier is excited. Self-excitation can be eliminated by connecting resistors with a resistance of 7 ... 13 kOhm in parallel with capacitors C10 and C15. The output circuit of the final stage is tuned by capacitor C13. by controlling the collector current of the output transistor (it should be 5...10% less than the maximum value) or the voltage at the transmitter load (it should be 12...15 V). Then the power amplifier is connected to the main board and the operation of the transceiver as a whole is checked, controlling the signal quality with the communication receiver. In conclusion, it should be noted that the transceiver is designed to work with a low-impedance antenna (75 ohms). The high-impedance antenna should only be connected through a matching device. Author: G. Shulgin (UA3ACM), Moscow; Publication: N. Bolshakov, rf.atnn.ru
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