Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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The article describes a simple transceiver with a self-made quartz filter made from identical resonators at a frequency of 8,867238 MHz. Such resonators are not in short supply - they are used in PAL-SECAM television decoders. The main board of the transceiver, having made minimal changes to it, can be used in a multi-band device.

The main parameters of the transceiver: sensitivity at a signal-to-noise ratio of 12 dB - no worse than 1 μV; selectivity for adjacent and other side reception channels - no worse than 60 dB; adjustment depth of the AGC system - not less than 60 dB; peak output power of the transmitter at a load of 50 ohms - at least 5 W; suppression of spurious emissions in the transmission mode - no worse than 40 dB; current consumption in transmission mode - no more than 0,6 A at a supply voltage of 12 V.

Thanks to the use of integrated circuits, it became possible to create a compact transceiver that does not have scarce components and is easy to configure. Of course, such a device does not have very high parameters, but it can be recommended either as a transceiver for a beginner shortwave radio amateur, or as a mobile auxiliary transceiver.

The reversible path of the transceiver is implemented on two K174XA2 microcircuits [1]. Of the composition of the microcircuits, only adjustable URCH, mixers and UPTs of the AGC UPCH system were used. Adjustable IF circuits themselves are not used, since they have a large noise figure and are not designed to operate at frequencies above 1 MHz.

Structurally, the transceiver is divided into three nodes: the main board (Fig. 1),

(click to enlarge)

smooth range generator (Fig. 2)

and power amplifier (Fig. 3).

The scheme of interblock connections of the transceiver is shown in fig. 4.

In the receive mode, the signal from the antenna input through the KZ.2 contacts of the K3 relay located in the PA unit is fed to pin 3 of the main board. On the elements of L1C4C6C8L4, a two-loop bandpass filter (DFT) is assembled. The radio frequency signal, passing through the DFT, is fed to the input of the DA1 chip. This microcircuit amplifies the signal and converts it to the IF frequency. The GPA signal is fed to pin 6 of the main board and through contacts K 1.1 of relay K1, transformer T1 is fed to the DA1 chip. The L5C19 circuit, connected to the output of the IC converter, is tuned to the IF frequency. The six-resonator crystal filter Z1 is connected to the tap of the inductor L5, which ensures optimal matching.

The filter circuit is shown in fig. 5.

From the output of the quartz filter, the IF signal is fed to the DA2 chip. The reference oscillator signal comes to this chip through contacts K2.1 of relay K2 and transformer T2. Resistor R15 emits an audio frequency signal. The low pass filter C27R19C28 attenuates the high frequency components of the detected signal. The audio frequency amplifier is assembled on an integrated circuit K174UN14 in a typical inclusion. Its gain is 40 dB. From output 11 of the main board, the 3H signal through the volume control R1 (see Fig. 4) enters the headphones.

The receiving path is covered by the AGC system. The signal for the operation of the AGC system is taken from the output of the ultrasonic frequency converter and, through the resistor R23, is fed to the VD7VD8 detector. The speed of the system is determined by the capacitance of the capacitor C29. From the output of the emitter follower VT3, the AGC voltage is supplied to the DC amplifier (UCA) of the S-meter (pin 9 of the DA2 microcircuit) and through the VD4 diode to the control inputs of the DA1 and DA2 microcircuits. The diode is installed so that the control voltage does not affect the S-meter in transmit mode.

Voltage is supplied to the S-meter from pin 13 of the main board through a trimmer resistor R22 and a diode VD9 connected to pin 10 of the DA2 chip.

The reference frequency generator is assembled on a field-effect transistor KP303G (VT1). The frequency of the resonator ZQ1 is 8,867238 MHz. By adjusting the inductor 12, it is possible to shift the oscillation frequency of the generator relative to the passband of the quartz filter within a small range. The source follower on the transistor VT2 eliminates the influence of the load on the oscillation frequency of the generator.

The transceiver is switched to transmission mode by pressing the SB1 ("Control") button connected to the XS3 connector. In this case, the short circuit relay in the UM unit is activated. This relay, depending on the mode of operation, connects the antenna either to the input of the receiving path or to the output of the transmitter with its contacts KZ.2 and at the same time switches the necessary supply voltages of the transceiver nodes with contacts K3.1. A voltage of +12 V (TX) is applied to terminals 4 and 12 of the main board, relays K1, K2 are activated and the signals of the GPA and the reference oscillator are switched. From pin 12, the voltage is supplied to the inverse input of the UZCH DA3 microcircuit and blocks it. The supply voltage is also supplied to the BM1 electret microphone (see Fig. 4).

The signal from the microphone is fed to the DA1 chip through the C5L3C10 low-pass filter, which prevents high-frequency interference from entering the microphone amplifier input. In transmission mode, the DA1 chip operates as a balanced modulator. The reference oscillator signal is fed through transformer T1. At the output of the modulator, a two-sideband signal with a suppressed carrier (DSB) is formed. Maximum carrier suppression occurs when the modulator is precisely balanced by the trimmer resistor R10. From the output of the DSB modulator, the signal is fed to a quartz filter, which selects the lower sideband. The DA2 chip converts the IF signal into a 160 meters amateur band signal. The load DA2 at high frequency is a broadband transformer TK, which matches the high output impedance of the mixer with a low load resistance. The RF signal from pin 9 of the main board goes to the power amplifier. Adjustment of the transmission coefficient of the path is made by the resistor R3 "LEV.TH". The maximum transmission coefficient corresponds to the minimum voltage at pin 8 of the main board.

In the PA unit, the signal passes through a two-circuit band-pass filter L7C53C54C55L8, is amplified by the pre-terminal amplifier on transistors VT6, VT7 and the final stage on VT8.

Imported 2SC2078 is selected as the output transistor. This transistor is commonly used in the final stages of CB radio stations in the 27 MHz band and develops a power of at least 4 watts at a supply voltage of 12 V. As it turned out, it is not difficult to obtain it on the radio markets in large cities. In the range of 160 meters from this transistor, you can easily get 5 watts of peak power. The R37VD11R38 chain sets the initial bias current of the transistor in transmit mode so that it operates in linear mode. The amplified signal through the KZ.2 contacts enters the antenna. From the R39R40 divider, part of the output signal voltage goes to the level detector. The voltage rectified by the detector is applied to the RA1 indicator.

GPA transceiver (see Fig. 2) - two-cascade. On the transistor VT4, a master oscillator is assembled according to the capacitive three-point scheme, on VT5 - a buffer stage. Frequency tuning is performed by KPE C1 with an air dielectric. When using resonators at a frequency of 8,867238 MHz in a quartz filter, the GPA tuning range will be 10698 ... 10867 kHz (plus the required margin of several kilohertz at the edges of the range).

To power the transceiver, a stabilized +12 V voltage source is required. The VD1 zener diode (Fig. 4) is used for protective purposes. When the polarity is reversed or the supply voltage is exceeded, the current through the zener diode increases significantly and the FU1 fuse blows.

The transceiver uses fixed resistors such as C1-4, C2-23, MLT; rigged - SPZ-38b; variable resistors - SP4-1a. All permanent capacitors - K10-17, KM; tuned capacitors - KT4-23, and oxide capacitors - K50-35. Tuning capacitor C1 - KPI from a tube radio.

Inductors L1, L2, L4, L5, L7, L8 are wound on polystyrene frames with a diameter of 5 mm with tuned cores PR No. 2 (carbonyl from R-20 grade material, M4 thread). The author used frames from the Len VHF radio station. Coils L1 and L7 contain 10 + 40 turns (counting from the grounded terminal), L2 and L8 - 50 turns, L4 - 25 + 25 turns of wire PEV-2 0,15, and coil L5 - 8 + 8 turns of wire PEV-2 0,25 ,6. The GPA L12 coil is wound on a frame with a diameter of 12 mm and contains 2 turns of PEV-0,45 4 wire (trimming core - PR No. 20, carbonyl - R-7, thread - M0,75x1). Broadband transformers Т7-ТЗ are wound on ring ferrite magnetic cores of size К4х2х600 mm, grade 1000-1НН. T2 and T2 contain 20x2 turns of wire PEV-0,25 3, TK contains 20x4 turns of the same wire. The T600 transformer is wound on an annular ferrite magnetic circuit of the 10NN brand, size K6x3x20 mm. The primary winding contains 2 turns of wire PEV-0,25 5, the secondary - 9 turns of the same wire. Coils L11-L50 are wound on an annular ferrite magnetic circuit of brand 2VCh-25, size K12x7x9 mm. L3 contains 10 turns, L25 - 11 turns, L5 - 2 turns of PEV-0,6 3 wire. Before winding, all ferrite rings must be wrapped with one layer of varnished cloth. L0,1 - standard choke DM-100-12 μH, L0,6 - D-20-1 μH. Relays K2 and K49 - RES270 with a winding resistance of 9 ohms. Short circuit relay - RES500 type with winding resistance 1 Ohm. ВМ1 - imported two-output electret microphone. RA50 - microammeter with a total deflection current of 100-1 μA. Quartz resonators ZQ7-ZQ174 - in small-sized cases. Instead of K2XA440 microcircuits, if possible, it is advisable to use imported TCA174, the K14UN2003 microcircuit can be replaced with TDAXNUMX.

Loop capacitors C4, C8, C19, C53, C55 are soldered directly to the terminals of the respective coils. Cases of quartz resonators ZQ1-ZQ7 are soldered along one of the ends to the upper metallization layer.

The main board and the PA board of the transceiver are made of double-sided foil fiberglass. The foil on the part installation side serves as a common wire and at the same time a screen. Around the conclusions of the parts that should not have contact with the common wire, the holes are countersunk. The GPA board is made of one-sided foil fiberglass. Drawings of printed circuit boards and the arrangement of elements on them are shown in fig. 6 - 8.

The transceiver is assembled in a case measuring 210x210x110 mm, made of two U-shaped duralumin plates. The approximate layout of the transceiver is shown in fig. 9. The compartment in which the PA is located is separated from the rest of the transceiver nodes by a shielding partition. The PA block is attached to the rear wall of the case. The VT8 transistor is isolated from the case with a mica spacer.

Setting up the transceiver begins with laying the frequencies of the GPA. The nominal supply voltage is supplied to the GPA board, a frequency meter is connected to the output (pins 4, 5). With the KPE C1 rotor fully inserted, by rotating the trimmer of the L6 coil, the lower limit of the local oscillator tuning (10690 kHz) is set, after which the KPI rotor is set to the minimum capacitance position and the upper limit (10870 kHz) is checked. If the tuning range is insufficient, a capacitor C2 with a larger capacitance is installed; if the tuning range is large, the value of C2 is reduced.

When setting up the main board, first of all, the operation of the UZCH is checked. After that, the operation of the reference generator is checked. By connecting the frequency meter to the right (according to the diagram) output of the capacitor C18, they make sure that the generator is working and adjusting the coil L2 sets the generator frequency to 200 ... 300 Hz lower than the frequency value at the point with a level of -6 dB on the frequency response of the quartz filter Z1.

Then the AGC system is turned off by unsoldering one of the terminals of the resistor R23. In the receive mode, an unmodulated signal from the GSS is fed to the input of the transceiver with a level of about 100 μV in the operating range, achieving the appearance of a sound signal in the telephones.

By rotating the coil trimmer L5, the IF circuit is tuned to the maximum receive volume.

To adjust the input DFT, it is convenient to use the frequency response meter (if available). You can also tune the DFT using the GSS. A signal with a level of about 10 μV is fed to the input of the transceiver. Rebuilding the GSS in the operating frequency range, control the level of the output 3H signal. By rotating the trimmers of the coils L1 and L4, the maximum volume of the received signal is achieved. The AGC system must be disabled. In an extreme case, the DFT can be adjusted according to the volume of the received signals from amateur stations.

Further settings are made by switching the transceiver to transmit mode. An RF millivoltmeter is connected to output 9 of the main board and, without applying an audio signal to the input of the transceiver, by adjusting the resistor R10, a minimum of readings is achieved. After that, one of the terminals of the resistor R6 is soldered to turn off the microphone supply voltage. A 3H generator signal with an amplitude of 5 ... 10 mV is fed to the microphone input of the transceiver. The generator is tuned in frequency in steps of 100 ... 200 Hz. In this mode, it is convenient to take the frequency response of the quartz filter and adjust its parameters. By selecting filter capacitors and, possibly, resonators, minimal passband ripple is achieved. The output signal level is controlled by a millivoltmeter at pin 9 of the main board. The "TX Level" control is set to the middle position in order to prevent overloading of the transmitting path. The lower limit of transmitted frequencies should be within 300...500 Hz, the upper limit - 2900...3100 Hz. The shift of the band of transmitted frequencies upwards or downwards is carried out by adjusting the frequency of the reference oscillator.

The UM block is configured separately from the main board. Without applying the supply voltage to the terminal transistor VT8, tune the DFT of the transmitter. The tuning technique is similar to the receiver DFT tuning technique described above. The output level control signal can be taken from the terminal transistor base. After that, a matched load (50 Ohm) is connected to the output of the block and the supply voltage is applied to the transistor VT8. In the absence of a signal, the quiescent current of the final stage is set. A milliammeter can be connected to a break in the power supply circuit of the terminal transistor, for example, by unsoldering one of the terminals of the L12 inductor. The quiescent current must be within 200...220 mA. Its value can be adjusted by selecting the resistor R37. When the GSS signal is applied to the input of the PA block, the output stage circuit is adjusted so that the maximum transmission is in the center of the operating range - approximately at a frequency of 1915 kHz. The setting is carried out by selecting the capacitor C62. The final stage of setup is to connect all the nodes of the transceiver and check the output power. When a signal with a frequency of 400 ... 1000 Hz at a level of 10 mV is applied to the microphone input of the transceiver, the output power of the transceiver at a load of 50 Ohms must be at least 2 W. The resistance R4 is selected so that the transmission path is not overloaded at the maximum gain. By selecting the resistor R41, they ensure that at the transmission peaks the arrow of the output level indicator does not go beyond the scale.

How to set up the S-meter of the transceiver in receive mode is described in detail in [2].

The output stage of the transceiver is designed to operate on a load of 50 ohms. When working on an antenna with an unknown input impedance (an oblique beam of unknown length, an L-shaped antenna, etc.), it is necessary to select the number of turns of the L11 coil according to the maximum of the emitted signal, controlling it with an indicator. In order for the main board of the Amator-KF-160 transceiver to be used in a multi-band transceiver, it must be modified. The elements of the input DFT are removed, and a notch filter tuned to the IF frequency is installed in their place (Fig. 10).

This filter is designed to attenuate IF frequency noise that enters the input path. The effect of these interferences is more noticeable on those bands whose frequency is close to Fp (7, 10, 14 MHz). L' contains 16 turns of wire PEV-2 0,25 on a frame with a diameter of 5 mm (trimmer, as in previous versions).

Literature

1. Ataev D. I., Bolotnikov V. A. Analog integrated circuits for household equipment. Directory. - M.: MPEI Publishing House, 1991, p. 135-150.
2. Lapovok Ya. S. I am building a KB radio station. - M.: Patriot, 1992, p. 73, 74.

Author: A. Temerev (UR5VUL)

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