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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Receiver design. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur Possible designs of the described variants of the detector receiver are shown in fig. 35. In any of them, diode D, which acts as a detector, type D9 or D2, The capacitance of the blocking capacitor can be in the range from 2200 to 6800 pF, the antenna - from 47 to 100 pF.
Mount the receiver of the first option (Fig. 35, a) on a plywood panel measuring approximately 60 x 100 mm. From below, along the edges, nail bars 10-15 mm high, which will serve as racks. On top of the panel there will be a coil, a switch, jacks for turning on telephones, antenna and ground clamps, under the panel - diode D (detector), blocking capacitor C and all connections of parts. Glue the coil to the panel. Pass the taps, the beginning and the end of the coil through the holes for the panel, and connect their stripped ends to the switch contacts and the antenna clamp. After completing the installation, check the strength of all connections and their correctness according to the circuit diagram (Fig. 34, a), turn on the phones, connect the antenna and ground, and proceed to test the receiver. It may happen that the longest radio station will be faintly audible even when all the turns of the coil are included in the circuit. In this case, an additional capacitor with a capacity of 100-270 pF will have to be connected between the antenna and Ground terminals. Mount it on the receiver. You can make changes to the design of the receiver. If, for example, you want to make it in a box, fix the coil under the panel, from the installation side. In this case, the panel will serve as the lid of the box. And if the transmissions of two radio stations are simultaneously listened to, then to improve the selectivity of the receiver, turn on a capacitor in the antenna circuit. For the receiver of the second option (Fig. 35, 6), you can use the same coil as in the receiver of the first option. Its mid-wave part will be the first two (counting from the beginning) sections. Other coil taps are not used. It is desirable that the largest capacitance of the tuning capacitor C2 be 450-470 pF. Connect a group of movable capacitor plates to a grounded conductor, and a fixed group to an antenna conductor. The end of the axis of the movable plates will protrude from the front side of the panel. Put a pen with an arrow on it, and against the arrow stick a paper semicircle with divisions on the panel - the tuning scale. Determine the dimensions of the panel on which you will mount the receiver, based on the dimensions of the available parts. This panel will simultaneously serve as a cover for the receiver box. In the design shown in Fig. 35, in, you should find out the third option for an experienced receiver - with a ferrite rod tuning. During the experiments, the coil lay on the table and you connected its leads to the antenna and ground terminals on the detector attachment, here the coil is glued with the ends of the frame into the holes of the same attachment. Tuning is carried out only with a ferrite rod, on which marks are made corresponding to stations that can be received on a detector receiver. Install a coil in the receiver of the range, the radio stations of which are well audible in your area. In the event that in your area the transmissions of only one radio station are clearly audible, say, only local, and the transmissions of others are weak, you can make a simpler detector receiver - with a fixed setting, for example, according to the circuit shown in Fig. 36. A receiver built according to this scheme does not have tuning knobs. It is tuned in once to the selected station and is always ready to receive that station.
You can tune the receiver to a local station with a ferrite tuning core of the coil L and the selection of the capacitance of the capacitor C1 from 100 to 300 pF. In the diagram, the tuning core is symbolized by a short bold line intersecting with a "hammer". If the capacitor needs to be selected, then an asterisk is placed next to its letter designation, as in fig. 36. For such a receiver, you can use the coil with a ferrite core that you already have. In this case, the rod will be called a trimmer core. But, of course, you can wind a new, shorter coil, and use a piece of a ferrite rod as a core along the length of the coil frame. Strengthen the core on the receiver panel motionlessly, and you will adjust the circuit by moving the coil along the core. Having adjusted the circuit in this way, fix the coil frame on the core with a drop of glue. You can, however, do otherwise: use a coil with taps and adjust the circuit by selecting the number of its turns and the capacitance of the capacitor. But still, a receiver with a fixed setting of the first option will work better. This is explained by the fact that the electrical properties of a coil with a ferromagnetic core are higher than those of a coil without a core. As for the design of the receiver, then, I believe, you will decide this issue yourself. When using such a receiver, remember that its circuit includes the capacitance and inductance of the antenna. Therefore, when connecting another antenna to it, the circuit will have to be adjusted again. Publication: N. Bolshakov, rf.atnn.ru
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