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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Six receivers on one transistor. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / radio reception Perhaps, the promise in the title will raise doubts among many. In fact, is it possible to do something workable on one transistor. It turns out that quite a lot is possible. Let us recall the "radio pills" produced by the industry, designed to examine the human stomach. On one transistor, you can assemble a "beeper" for teaching amateur radio code, a switch for an electronic-mechanical clock, a toy musical instrument, a transmitter, a photoexposure meter, a measuring device with a high input impedance ... And, of course, a variety of radio receivers. About them and will be discussed further. It is clear that the capabilities of such radios are modest - they are designed mainly for listening to local or not too distant stations using headphones. And if this satisfies you, you will immediately discover the advantages of such devices - small costs of funds, effort and time for construction, small dimensions and weight. Figure 1 shows the simplest radio installation, which includes an oscillating circuit L1C2, a diode detector VD1, an audio amplifier based on a low-frequency transistor VT1 and a telephone BF1. Such a receiver, together with a small external antenna and grounding, will allow you to become a listener to a nearby powerful radio station. Coil L1 is placed on a round or rectangular ferrite rod about 100 mm long, designed for magnetic antennas.
For the range of long waves, the winding should have about 220 turns of PELSHO 0,15-0,2 wire; the turns are laid in bulk on a paper sleeve 30-35 mm long put on the rod. The tap is made from about the 50th turn, counting from the grounded end. Connecting the detector circuit to a part of the turns of the coil allows you to match their resistance and thereby improve the operation of the circuit. For the medium wave range, a coil of 75 turns of the same wire is wound in one layer turn to turn, with a tap from 20 turns. The phone should be taken sensitive, high-resistance, with a resistance of 1,5-2 kiloohms. Instead of the diode VD1 indicated on the diagram, you can use D9, D2 with any letter index. Replace the transistor with any low-power one; for the npn structure, you will need to reverse the polarity of GB1 and C3. The quiescent current of the transistor, close to that indicated in the figure, is set by selecting the value of the resistor R2. If the location of the radio installation is not supposed to be changed and only one radio station is working nearby, the smooth tuning by the capacitor can be replaced with a cheaper, fixed one, which will be discussed later. After assembling the circuit, compare its operation with and without capacitor C4. Leave the best option. Suitable permanent capacitors KLS, oxide K50-6, etc .; resistors ML T, MT up to 0,5 W power. The circuit shown in Figure 2 was very widespread in the "era" of radio tubes. This is the so-called regenerative receiver with adjustable positive feedback. The oscillatory circuit L2C2 here is similar to that described above, only the tap from the coil is made from 25 turns for the DV range and from 8 turns for the CB. The high-frequency transistor VT1 amplifies and detects the signal received by the circuit. The increased RF signal delivery, flowing through the feedback coil L1, induces an additional EMF in the loop coil, which significantly increases the sensitivity and selectivity of the receiver. The feedback is regulated by the resistor R2. The low frequency component of the collector current makes the phone BF1 sound. It should be taken high-resistance. Under favorable conditions, the receiver will work without an external antenna, although with it the results are much better and even remote radio stations can be received.
The circuits we have considered are designed to be powered from a source with a voltage of 4,5 V, for which the Planet battery, three 316 cells or four D-0,1 disk batteries are suitable. If necessary, you can switch to a lower voltage from two cells or two or three batteries, or to an increased voltage up to 9V (from a Korund battery). But this will require an appropriate selection of resistor values in the base transistor circuits in order to maintain the current values \uXNUMXb\uXNUMXbspecified on the circuits. Figure 3 shows a diagram of a reflex receiver, in which the transistor VT1 combines the functions of amplifying radio frequency and sound vibrations. The tuned circuit of the magnetic antenna L1C2 can be the same as that of the previous receiver, only its connection with the base of the transistor is provided by the coil L2. It is placed on a ferrite rod next to the contour, the number of its turns is about 25 for the LW and 8-10 for the SW. It is better to wind the communication coil on a paper ring, which moves along the rod with friction. This will improve the detuning of radio stations operating at close frequencies. Of course, the improvement in selectivity comes at the price of some signal level reduction. One feature of the circuit is interesting: the BF1 phone here acts in two roles - a high-frequency choke - the load of the radio frequency amplifier and the load - the sound emitter in the bass amplifier.
The signal received by the L1C2 circuit is amplified by the transistor VT1 and fed to the detector, assembled according to the doubling circuit on VD2 diodes, from where the low-frequency component is returned through the C5R2L2 circuit to the base of the transistor, where it is amplified and drives the telephone BF1. To avoid self-excitation of the receiver, the capacitance C4 should be selected according to the maximum volume of undistorted transmission. The DC transistor mode is set by resistor R1. The phone of our design, unlike the above-considered miniature, low-resistance, type TM-2M or TM-4. The receiver can operate in the supply voltage range from 3 to 9 V, for which it is enough just to adjust the value of the resistance R1. You can assemble it in a miniature case, and to improve reception, it is better to resort to an external antenna. For those who spend a lot of time in nature, it makes sense to "draw energy" to power the transistor from the "earth's bowels". The simplest receiver developed many years ago (Fig. 4), which resembles the first scheme, is designed for this. It is designed to listen to nearby long-wave radio stations. An external antenna with a length of 20 m or more, with a suspension height of 10-15 m, is desirable for it. Telephone - TM-2A or TON-2. The coil is wound on a paper sleeve, into which a piece of an antenna ferrite rod 30-50 mm long is inserted. About 300 turns of wire, PEV-2-0,2, are wound on the frame. The electrodes of the "earth" battery are a copper tube ("+") and an aluminum sheet ("-") the size of a notebook sheet. The electrodes are buried in moist soil to a depth of about 1 m, at a distance of 0,3-0,5 m from one another. The output of the "negative" electrode must be isolated from the ground.
Another amateur receiver is able, in addition to the radio program, to extract free energy from the electromagnetic field of a powerful radio station in close proximity. With a high field strength, reception is possible on one internal magnetic antenna; in other cases, you should use an external one (Fig. 5). The receiver circuit again has much in common with the circuit of the first receiver that we have analyzed. Its difference is a fixed tuning to the station. It is achieved by selecting the capacitance of the capacitor C3, which must have a tolerance of at least 10%; the tuned capacitor C2 of the PDA-2 allows you to tune the circuit exactly to the desired frequency. For a magnetic antenna, a ferrite rod 140-160 mm long is required, the phone can be TM-2A or high-resistance. The coil of circuit L1 is wound in one layer turn to turn in the middle of the rod. The number of turns is -180 with a tap from the middle, PEV wire, PELSHO 0,15-0,3.
For all the cases mentioned, an external antenna for a summer cottage can be built from an insulated plastic wire stretched between poles on the roof of a house or nearby trees. During a thunderstorm, radio reception must be abandoned, and the antenna lowering must be securely connected to the grounding input - a metal sheet or pipe buried in the ground. In urban conditions, stretch the antenna between sticks fixed on the sides of the balcony. Here, a heating or water pipe will serve as grounding, on which the paint has been removed at the point of contact. The receiver shown in Figure 6 is a super-regenerative detector with very high sensitivity to weak signals and allows you to break into the vastness of the VHF band. Reception is carried out on a telescopic antenna or a piece of wire 0,5-1 m long. The antenna is inductively connected to the circuit L1, C2 using a coil L2. The super-regeneration mode is set by a tuning capacitor C1 of the KPK-M, KPK-1 type. Its characteristic feature is the noise in the F1 phone, reminiscent of the hiss of a primus stove when the receiver is not tuned to the station. When finely tuned with capacitor C2, the noise disappears.
Coils LI, L2 are placed on a common plastic frame without a core with a diameter of 6,5 mm. Antenna L1 has 9 turns, contour L2-6 turns of PEV-2-0,44 wire. Choke L3 is wound on the same frame with PEV-2-0,25 wire and has 25 turns. Capacitor C2 is better to get a trimmer with an air dielectric, but you can get by with a not very durable ceramic KPK-1 by soldering a copper tube to the rotor turn, which will serve as the axis for the tuning knob. Permanent capacitors can be of the KLS type. The phone is high-resistance, with a resistance of about 2 kOhm. The boundaries of the received VHF range may cover the frequencies of the sound accompaniment of channels I and III of television and the VHF-FM range between them. With such a significant overlap, detuning at the latter can be difficult. If it is this frequency band that is of interest, the overlap should be reduced by selecting fixed capacitors connected in series and in parallel with C2. Adjustment of the range limits is provided by moving the turns of the coil L2. To obtain a satisfactory result from the receiver, careful installation and configuration is required. Since the operator's hands can also affect the setting, you should not chase after the minimum dimensions - it is better if they are commensurate with the telescopic antenna. One more note that applies to all schemes. When setting up receivers in an urban environment, keep in mind that many modern buildings have walls heavily reinforced with steel, which can greatly reduce the radio signal level. Author: Yu.Georgiev
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