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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Amateur angler's radio. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur Various designs of radio receivers for anglers have been repeatedly published in amateur radio literature, but all of them were designed to use monophonic headphones such as TM-1, TM-2 or the like. Currently, such headphones can rarely be found on store shelves, since stereo headphones for players and modern pocket radios are most common. The described receivers for anglers are quite laborious to manufacture and cannot always be repeated by inexperienced radio amateurs. In this regard, the requirements for the creation of a radio receiver for the fisherman were formulated, and then a simple circuit design of the receiver was found, the manufacture of which is within the power of everyone. When designing a radio receiver for anglers, the following requirements are imposed. The receiver should be small enough to fit in a jacket or shirt pocket. Its sensitivity should allow receiving on a magnetic antenna radio stations located at a distance of up to 200 km from the place of reception, and even further when an external antenna is connected. The operating frequency range, medium or long waves, since you have to fish far from cities, where the reception of VHF stations is in many cases impossible, and reception on HF is unstable. The circuit of the receiver should be simple enough so that anyone who has little soldering skills with an electric soldering iron can assemble it. In this case, it is better to mount parts on a mounting plate, since the manufacture of a printed circuit board is a rather complicated process for inexperienced amateurs. The fisherman's receiver should be powered from a source with a constant voltage of 1,5-3 V. It can be one or two galvanic cells of type 316. Listening to radio stations on such a receiver should be done on the most common types of headphones, in particular, electrodynamic or isodynamic stereo headphones with resistance of voice coils from 28-300 Ohm.
Fig. 1 A schematic diagram of an angler's receiver that meets the above requirements is shown in fig. 1. The receiver is assembled on a single transistor VT1 according to a reflex circuit. Transistor VT1 simultaneously performs two functions, a radio frequency amplifier and an audio frequency amplifier. Tuning to the radio station is carried out by a variable capacitor C2, which, together with the inductor L1, forms an oscillatory circuit. Through the communication coil L2, inductively coupled with the coil L1, the radio signal is fed to the base of the transistor VT1, which operates as a radio frequency amplification stage. The load of the cascade is the voice coils of the stereo headphones. The high-frequency signal amplified by the transistor from the voice coils is fed to the diode detector VD1 and is detected. The detected signal (audio frequency) enters the base of the transistor VT1. In this case, the transistor VT1 already works as an audio frequency amplifier. The audio frequency load of the cascade is the resistance of the windings of the stereo headphone coils. The required mode of operation of the transistor VT1 is provided by the bias voltage that is supplied to its base through the diode VD1. The receiver does not have a volume control. To change the sound volume, the directional properties of the magnetic antenna, which is located in the case, are used. The volume of the stereo headphones sound will decrease or increase if you turn the receiver case in one direction or another. The receiver also does not have a separate power switch, it turns on when the stereo headphone plug is inserted into the XS2 jack. Turning off the receiver corresponds to the case when the plug is removed from the socket. The radio receiver is powered by a single element of type 316. In silent mode, the receiver consumes a current of 2,2 mA. One of the features of the radio receiver is the use of a transistor of the KT3102G type, which has a higher current transfer coefficient in the small signal mode in a circuit with a common emitter h21e = 400-1000, while for widely used transistors, for example, KT315 B, this figure is much less and is h21e=50-350. Due to the properties of the KT3102G transistor, it was possible to build a receiver with good sensitivity, on just one transistor, otherwise, this would require 2-3 KT315 type transistors. The second feature of the receiver is as follows. In reflex amplifying stages there is always a high-frequency transformer or choke, which serves to separate the high-frequency signal from the audio frequency signal and transfer it to the detector. In this design, this problem is solved using the windings of the stereo headphone coils, due to their large inductance. In other words, the role of the choke is performed by the windings of the stereo headphone coils. This made it possible to save space on the circuit board, but most importantly, the removal of the inductive element outside the receiver housing made it possible to eliminate the possible danger of self-excitation of the device. In the receiver, you can use transistors of the KT3102 type with any letter index. Instead of the type of diode indicated on the diagram, you can use diodes of the D9 or D18 type. Fixed capacitors C1, C3 type K10-7, and variable capacitor C2 type KPE-5 from the Selga-404 receiver. The XS2 jack is industrial-grade, for connecting stereo headphones with a 3,5 mm plug. Coils L1 and L2 are wound on plastic or paper frames, which can move freely along a flat ferrite rod of the 400HN or 600HN brand and with dimensions of 100x20x3 mm. For medium waves, coil L1 contains 68 turns of LESHO wire 7x0,7 wound round to turn, and L2 - 6 turns of PEV-1 0,15-0,2. In the case of long waves, L1 should have 55x4 turns of PEV-1 0,08-0,1 wire wound on the frame in bulk in four sections, and L2 - 20 turns of PEV-1 0,1-0,12. You can also use suitable ready-made contour coils from industrial pocket radios. The receiver is assembled in a plastic box with external dimensions 120x68x20 mm. In the author's version, the "Angler's Box" is used as the receiver's body. Work begins with the fact that holes are drilled in the case for mounting a variable capacitor, contacts of a galvanic cell, a small mounting plate and a headphone jack. After that, the main overall parts of the receiver are fastened with screws and nuts. A ferrite rod with inductors is fixed in the protrusions of small plastic corners glued with dichloroethane to the inner side of the case. The passive elements and electronic components of the receiver are mounted on a mounting plate, to which, according to the circuit diagram, the leads of the wires in plastic insulation coming from the variable capacitor, the contacts of the galvanic cell, the headphone jack and the leads of the inductors are soldered, fig. 2.
A properly soldered receiver does not require special adjustment. Laying the boundaries of the received wave range is carried out by moving the frames of the contour coils along the ferrite rod. When installing a galvanic cell and connecting headphones, the receiver starts working immediately. Tuning on the radio station is carried out by rotating the control knob, which is a plastic disk with a diameter of 45 mm and a thickness of 3 mm, which is fixed on the axis of rotation of the variable capacitor rotor with a screw. For ease of rotation of the tuning disk, notches are made on its end. Any other plastic handle suitable for this purpose can be used as a tuning organ. To increase the range of the radio while fishing outside the city, you need to connect an external antenna to the XS1 antenna jack, and when you are in a city apartment, it is enough to place its magnetic antenna near a water pipe or steam heating pipe, orienting it perpendicular to their major axis. Author: V.M. Pestrikov, St. Petersburg; Publication: cxem.net
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