|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING How to increase the selectivity of the receiver. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / radio reception The VHF FM receiver with PLL [1] developed at the time by A. Zakharov still attracts the attention of radio amateurs. As noted in later publications of the Radio magazine [2, 3], one of the significant drawbacks of this type of receivers is their low selectivity in the adjacent channel. The reason for this is the direct detection of powerful signals at the emitter junctions of transistors connected in parallel with alternating current.
In radio engineering, to combat direct signal detection, it is recommended to use the back-to-back switching of frequency converter diodes both in voltage (Fig. 1) and in current (Fig. 2). If you use this method to eliminate direct detection in A. Zakharov's receiver, then in parallel with the base-emitter junction of the converter transistor, you will need to turn on the diode in the opposite direction (Fig. 3). However, this cannot be done, since in this case the diode will be closed by the voltage at the base-emitter junction. To get out of this difficulty, I propose to turn on the diode in series with this transition in direct current and in anti-parallel in alternating current (Fig. 4). The retention band of the receiver modified in this way is somewhat wider than that of the previously described ones. It is useful to reduce the quality factor of the L2C7 circuit. To do this, either wind the L2 coil with a thinner wire (0,2 ... 0,3 mm), or introduce an additional resistor R5 into the circuit circuit.
The converted receiver uses inductors similar to those used in [1]. The coil L1 is frameless, the winding diameter is 5 mm, the winding pitch is 1 mm, it contains 6 turns of PEL 0,5 wire. Coil L2 is wound on the coil frame of the shortwave range of the Ocean receiver, the winding pitch is 1 mm. The winding consists of nine turns of wire PEV-2 0,27. The trimmer of this coil is an aluminum tube with an outer diameter of 5 mm and a length of 20 mm. The receiver settings for the standard VHF range are achieved by selecting capacitors C2 and C7, and its highest sensitivity is achieved by selecting resistor R1. To avoid self-excitation of the receiver at audio frequencies, the capacitance of the diode VD1 must be significantly less than the capacitance of the emitter junction of the transistor VT1. This condition is fully satisfied by the KD521 and KD522 diodes with any letter indices. The capacitance of capacitor C6 depends on the intended mode of operation of the receiver (mono or stereo). On the circuit diagram shown in fig. 4 shows the capacity for the mono version. In the stereo version, it should be five times less. The operating experience of the receiver [1] showed that in Minsk it confidently received all four VHF radio stations without mutual interference, however, during pauses, interference from the sound accompaniment of television broadcasts of the first and third channels was heard. After altering the receiver, these interferences ceased to be heard. To this it should be added that the anti-parallel connection of the limiting diode and the base-emitter junction of the transistor made it possible to limit the level of signals from powerful radio stations.
In several receivers made by me, an electronic tuning device works reliably (Fig. 5), in which a KT315 transistor is used instead of a varicap (it is possible with any letter index). This device with a supply voltage of 3V allows you to cover the entire standard VHF band (65.8-.73 MHz). Literature 1. A. Zakharov. VHF FM receivers with PLL. - Radio, 1985, No. 12, p. 28-30.
Author: M. Sapozhnikov, Minsk; Publication: N. Bolshakov, rf.atnn.ru
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ Power supply Ecosol Powerstick ▪ Cypress CYFB0072 4,8Gb/s video buffer chip ▪ $7 Hyundai A80 Tablet: 1,5GHz, Android 4.0
▪ section of the site Protection of electrical equipment. Article selection ▪ article by Helen Adams Keller. Famous aphorisms ▪ article What kind of load can a woman's braid withstand? Detailed answer ▪ article Orientation on the seas and oceans. Travel Tips ▪ article Note to the student. Directory ▪ article Hindu basket. Focus Secret
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page