Walking receiver. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Walking receiver. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Such a receiver should be compact, lightweight, not require frequent replacement of batteries, and so that a novice radio amateur can quickly make it, it should also be simple. The listed requirements correspond to the design, the description of which is given below.

The direct amplification receiver, the circuit of which is shown in fig. 1 is made according to the reflex scheme using only one microcircuit - K118UN1B. Although it is old, it is not rare in amateur radio laboratories. Yes, it is still for sale. The microcircuit is a two-stage video amplifier, and therefore, for the intended purpose, it has good frequency and amplifying properties. The reflex (double) use of the microcircuit allows saving the number of necessary elements, energy consumption from the current source, simplifying the design and at the same time obtaining a fairly good amplification at high and low frequencies. The receiver, made according to the proposed scheme, satisfactorily receives on the internal magnetic antenna of radio stations remote at a distance of 200 ... 300 km, and when an external antenna is connected - up to 700 ... 800 km.

walk receiver

The signals of radio stations are distinguished by the oscillatory circuit L1 C1 of the magnetic antenna WA1 and through the communication coil L2 are fed to the radio frequency amplifier - chip DA1 (pin 3). The load of the radio frequency amplifier is a matching high-frequency transformer with windings L3, L4. Diode VD1 detects the signal and the low-frequency component is fed back to the microcircuit.

For a low-frequency signal, the microcircuit serves as an audio frequency amplifier, which is loaded through a separating capacitor C6 to a sound emitter with a resistance of 50 ... 300 Ohms - telephone capsules of types TA-56m, TK-67-NT or headphones TM-2m, TON-2.

The receiver does not have a volume control, since even at its maximum value it is quite comfortable for normal listening to programs. If you need to reduce it, you just need to slightly rotate the receiver body relative to its axis (when receiving a signal with a magnetic antenna) or move the headphones relative to the auricle. If the volume control is still required (when reception is carried out in the immediate vicinity of radio stations), then it is necessary to replace the resistor R1 with a variable resistor with the specified resistance value and connect the capacitor C8 to the engine of this resistor.

The receiver is powered by a built-in battery (galvanic cells or batteries) with a voltage of 4,5 ... 6 V, it consumes only 3 ... 4 mA, which allows you to use even watch batteries such as STs-32 and the like.

Since the author did not set miniaturization as the ultimate goal, he proposes a variant of the receiver printed circuit board (Fig. 2) for a somewhat unusual case - a case from an audio compact cassette.

walk receiver

The location of the elements for the proposed version of the board is shown in Fig.3.

walk receiver

The magnetic antenna is made on a ferrite rod 400НН or 600НН, 65 mm long. The coils of the magnetic antenna are wound with PEV-1 wire 0,12 mm directly on the rod. To operate in the long wave range, the L1 coil must have 210 turns, and L2 - 10. For the medium wave range, the number of turns, respectively, is 70 and 4, the PEV-1 wire is 0,15. It is desirable to place the L2 coil on a movable cuff to select the optimal connection. The high-frequency transformer is made on a K7x4x2 ring magnetic circuit made of 1000NN grade ferrite. Coil L3 has 80, and L4 - 70 turns, wire PEV-1 0,12.

This design is not critical to the choice of types of resistor and capacitors. In the absence of a microcircuit of the specified type, you can use its analogue - K122UN1B. True, she has a completely different case design and pinout. This should be taken into account when manufacturing a printed circuit board.

Setting up the receiver is easy. Check the supply voltage and, when receiving radio signals, adjust the position of the coupling coil to obtain the required selectivity and sensitivity. In case self-excitation occurs, it is necessary to place the high-frequency transformer as far away (as far as possible) from the magnetic antenna or use a shield for the transformer.

If self-excitation cannot be eliminated, following the recommendations of the author, it is advisable to swap the connection of the leads of one of the windings of the high-frequency transformer. If this does not give positive results, then in addition to the measures taken, a resistor with a resistance of 8 ... 2 k3m must be connected in series with the capacitor C0, and the left (according to the diagram) output of the communication coil should be connected to a common wire through a capacitor with a capacity of 0,01 .0,022 uF.

Author: O. Smirnykh, Birofeld village, Birobidzhan district

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