Direct gain receiver on a logic chip. Scheme, description

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Direct gain receiver on a logic chip. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / radio reception

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By using logic elements of the CMOS series (in other words, series made on complementary pairs of MOS transistors) as amplifying stages, it is possible to assemble a receiver of small dimensions with interesting abilities. Firstly, it does not require any adjustment even when installing parts with denominations that differ from those indicated in the diagram (Fig. 1) by 2..3 times. In addition, the receiver remains operational when the supply voltage drops to 3 V. This is explained by the introduction of deep negative feedbacks in the amplification stages.

Direct Gain Receiver on Logic Chip
Rice. 1. Scheme of the receiver. D1 - K176LE5 or K176LA7

Consider the operation of the receiver. The radio station signal received by the magnetic antenna W1 and selected by the L1C1 circuit is fed to the RF amplifier. assembled on element D1.1. A resistor R1 is connected between the output and the input of the element, which provides negative feedback but a constant voltage. Capacitor C2 eliminates the same AC voltage coupling. The receiver is tuned to a particular radio station with a tuning capacitor C1.

From the output of the element D1.1, the signal goes to the detector, made on the diodes V1, V2 according to the voltage doubling scheme. The audio frequency signal from the detector load is fed to the amplifier, in which the elements D1.2 - D1.4 work. In the cascade, assembled on the element D1.2, a negative DC voltage feedback is introduced through resistors R3, R4. Due to this, a voltage equal to half the voltage of the power source is set at the output of the element. This voltage is stable, so such feedback chains can be omitted in subsequent stages. On the alternating voltage of the audio frequency, the feedback is removed by connecting the capacitor C6. The load, which is used as a miniature headphone TM-4, is connected to the amplifier via connector X1.

To prevent possible self-excitation of the amplifier both at low and high frequencies, the power supply (it is connected with the phone plug inserted into the X1 connector) is shunted by capacitors C8, C9.

The K176LE5 chip can be replaced with the K176LA7 without changing the circuit. Adjusted capacitor C1 - KPK-M, electrolytic capacitors - K50-6). the rest of the permanent capacitors - K10-7V or other small ones. Under these parts, a printed circuit board (Fig. 2), made of foil material, is designed.

Direct Gain Receiver on Logic Chip
Rice. 2. PCB

The coil L1 of the magnetic antenna is wound on a rod with a diameter of 8 mm from 600NN ferrite. The length of the rod is taken as long as possible with the selected receiver housing. For the DV range, in which the authors work with the receiver, the coil contains about 900 turns of PEV-1 0,07 wire, evenly wound in sections along the entire length of the rod (50 ... 100 turns per section). For the CB range, the number of turns of the coil must be reduced accordingly. It should be remembered that the sensitivity of the receiver at a frequency of more than 1 MHz (wavelength less than 300 m) will decrease due to the drop in the gain of the cascade on element D1.1.

Socket X1 - converted (Fig. 3). Another spring plate is added to it, removed from the same socket to turn on the TM-4 phone. The power source can be a Krona battery or a 7D-0.1 battery.

Direct Gain Receiver on Logic Chip
Rice. 3. Headphone jack combined with power switch

As mentioned earlier, the receiver does not require adjustment, it will only be necessary to more accurately select the number of turns of the L1 coil, depending on the frequency of the received radio stations. If powerful radio stations are operating near the receiving location, the receiver stages will be overloaded due to the high level of the received signal and the sound will become distorted. In this case, we recommend redoing the output stage (Fig. 4) - and the receiver will turn out to be loud-speaking (power will have to be supplied through the switch).

Direct Gain Receiver on Logic Chip
Rice. 4. UZCH on logical elements

Transformer T1 can be an output transformer from any transistor receiver (one half of the primary winding is used), and dynamic head B1 can be any small head with a power of 0,05 ... 0,5 W.

Authors: N.Smirnov, V.Stryukov

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