A simple radio path of the transceiver. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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A simple radio path of the transceiver. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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Radio amateurs do not lose interest in simple designs that can become the first devices for beginners and the second for experienced shortwavers (for example, as mobile or "dacha" devices). A variant of the base unit of such a device is proposed in this article.

The creation of the proposed radio path was preceded by the desire of the author to minimize the number of radio elements in the device, while maintaining high electrical performance. It uses the widely used K174XA2 chip, the idea of its effective use was proposed in [1]. The sensitivity of the radio path at the input is 1 μV. Selectivity is determined by the type of main selection filter applied and the value of the intermediate frequency. Clogging dynamic range - 75...80 dB. The output voltage of the generated SSB signal during transmission is 0,5 ... 1 V.

The diagram of the radio path is shown in fig. 1. In the receive mode, the input signal from the lumped selection band filter (FSS) through the capacitor C1 is fed to the gate of the transistor VT1. The use of a field-effect transistor makes it possible to use the full inclusion of the FSS circuit, and the "paraphase" output of this cascade "matches" well with the symmetrical input of the URF of the DA1 microcircuit. This has a positive effect on the sensitivity and dynamics of the radio path. From the UHF output, the signal through capacitors C2, C3 and normally closed contacts of relay K1 is fed to the inputs of the UHF microcircuit (pins 1 and 2). A local oscillator signal is supplied to the mixer of the microcircuit (pins 4 and 5) through a balun transformer T1.

(click to enlarge)

The load of the DA1 chip mixer is the L2C11 circuit. The intermediate frequency signal isolated by the circuit through the coupling coil L3 is fed to the main selection filter (FOS) ZQ1 and then through the capacitor C12 to the input of the IF of the microcircuit (pin 12).

The filter of the main selection ZQ1 is made according to the ladder scheme on the same resonators at a frequency of 8,86 MHz (Fig. 2). The K174XA2 microcircuit is recommended to be used with an IF not higher than 5 MHz, but, as experiments show, it also works at higher frequencies with acceptable quality.

A simple radio path of the transceiver

At the output of the IF (pin 7), the transformer T2 is turned on, which together with the capacitor C15 forms a resonant circuit. At the same time, it is also a balancing transformer of a ring balanced mixer on VD3-VD6 diodes. The signal from the reference frequency generator (KG) is fed to the primary winding of the T3 transformer, according to the recommendations in [2].

Usually (for example, [3]), the signal to the second mixer is supplied from the coupling coil of the IF output circuit, and the number of turns of the coupling coil is 5...10% of the number of turns of the contour coil. Accordingly, the same signal level comes from the circuit to the mixer. In the Niva industrial radio station, the output circuit of the IF is also the input coil of the mixer. Such a solution allows, in addition to increasing the sensitivity of the device, to reduce the number of winding units. In the proposed scheme, this circuit is formed by the capacitor C15 and the primary winding of the transformer T2.

From the output of the second mixer, through the filter L4C17R10C18L5C19, a low-frequency signal is fed to the input of the ultrasonic frequency converter.

In the transmission mode, the supply voltage is applied to the relay winding K1. The signal from the dynamic microphone is fed through the C7L1C8 low-pass filter to the input of the URF microcircuit, which now serves as a microphone amplifier. A KG signal is sent to the mixer of the microcircuit. A two-way signal is fed to ZQ1. After the SSB filter, the signal through the IF amplifier of the microcircuit, the second mixer and the capacitor C16 is fed to the band FSS transmitter. The signal voltage from the GPA is applied to the primary winding of the transformer TZ.

The gain adjustment of the URF microcircuit was performed in accordance with the recommendations given in [4]. The K174XA2 gain is regulated by applying a voltage from 0 to +2 V to pin 9 of the microcircuit. The author used the AGC scheme for the "Radio-76" transceiver in [5]. In transmission mode, you can use the ALC system.

The printed circuit board of the radio path with the arrangement of elements on it is shown in Fig. 3.

A simple radio path of the transceiver

On the "unwired" section of the board, you can assemble an AGC or UZCH circuit. The dimensions of the board are 105x145 mm, which allows using the path instead of the main board of the Radio-76 transceiver. When wiring the board, the possibility of installing both a home-made quartz filter and an electromechanical type FEM2-018-500-ZV-1 (shown by a dotted line) was taken into account. The radio path was tested in two versions: with an IF of 8,86 MHz and a self-made quartz filter, as well as with an IF of 500 kHz and an EMF as a FOS.

In the quartz filter (see Fig. 2) there are resonators ZQ1.1-ZQ1.8, the so-called "television" resonators at a frequency of 8,86 MHz. Filter bandwidth (at -3 dB level) - 2,3 kHz with 1,5 dB unevenness (tnx RZ6FN!). Filter dimensions - 40x30x15 mm.

If an EMF is installed in the path, in addition to replacing the winding units, capacitors C11 and C15 should be installed with a capacity of 1000 pF. To tune the EMF converters into resonance, the capacitor C12 must have a capacitance of about 100 pF [6]. In addition, it is advisable to introduce an appropriate capacitor between L3 and the EMF input.

Relay K1 - RES 47 (passport RF4.500.408). Trimmer resistors - SPZ-19a, SPZ-22b, the rest - MLT 0,25. Permanent capacitors - KLS, KM, oxide - K50-16, K50-35.

Winding data of coils and transformers for IF 8,86 MHz are given in Table. one.

A simple radio path of the transceiver

Choke L4 - DO,2 200 uH. For an IF of 500 kHz, the winding data of the nodes are given in Table. 2. For L1, L4, L5 they are the same as in the 8 MHz IF option (see Table 86).

A simple radio path of the transceiver

Setting up the device is easy. After checking the installation, the GPA and KG are connected to the path. Having applied the supply voltage, in the receive mode, the L2C11 circuit and the T2C15 transformer circuit are tuned with interlineators, achieving maximum sensitivity. Then the path is switched to transmission mode and the circuit is balanced with resistor R6 at the minimum carrier level (controlled by a receiver or an RF millivoltmeter). The required signal level from the microphone is set by resistor R8. The level of the output SSB signal is determined by the control voltage at pin 9 of the microcircuit.

If, on the basis of this scheme, a transceiver will be manufactured only for the low frequency ranges, the elements R1 - R4, C2, C3, VT1, K1.1 can be excluded. The first leg of the K174XA2 chip is connected directly to the connection point R5 and C5, and C1 is connected to the contacts K1.2. This slightly reduces the sensitivity of the tract.

In the author's version, the schemes published in [7] were used as GPA and CG.

Literature

Shulgin G. Speech signal compressor. - Radio, 1988, No. 5, p. 22, 23.
Menshov V., Bulatov A. Improvement of mixers in "Radio-76" and "Radio-76M2". - Radio, 1988, No. 12, p. 23, 24.
Stepanov B., Shulgin G. Transceiver "Radio-76". - Radio, 1976, No. 6, 7.
Solovyov V. Increasing the sensitivity of the receiver on the IC K174XA2. - Radio, 1986, No. 4, p. 16.
Bepple V. ARU for "Radio-76". - Radio, 1982, No. 9, p. 19.
Shulgin K. The main parameters of disk EMF at a frequency of 500 kHz. - Radio, 2002, No. 5, p. 59-61.
Stepanov B., Lapovok Ya., Lyapin G. Amateur radio communication on HF. - M.: Radio and communication, 1991, p. 30-35.

Author: A.Vorontsov (RW6HRM)

See other articles Section Civil radio communications.

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