Encyclopedia of radio electronics and electrical engineering / radio reception

 Comments on the article

German shortwaves have developed a regenerative receiver that is easy to repeat for beginner radio amateurs (Sieghard Scheffczyk "Einmal um die Welt fur 5 Euro". - CQ DL, 2004, No. 10, S. 720). Its peculiarity lies in the fact that it is possible to receive radio stations immediately after the manufacture of the structure, since it does not need an external antenna. A frame consisting of several turns of wire is both an antenna and an inductor of the regenerative detector circuit. The receiver (Fig. 1) allows you to receive at frequencies of 5 ... 22 MHz the signals of amateur radio stations operating by telegraph (CW) and single-sideband modulation (SSB), as well as signals from broadcasting stations using amplitude modulation (AM).

The receiver circuit is shown in fig. 2. The reception frequency is determined by the loop inductance WA1 and the capacitance of the variable capacitor C1. The regenerative detector is assembled on a field-effect transistor VT1 according to a capacitive feedback circuit. By changing the voltage at the source of the transistor VT4 with a variable resistor R1, the degree of feedback is regulated. At the threshold of excitation, this stage will work as a detector of AM signals, and beyond the threshold - as a detector of CW and SSB signals.

Rice. 2 (click to enlarge)

The detected signal from the source of the transistor VT1 is fed to a three-stage low-frequency amplifier. The last stage of the ULF is an emitter follower, made on a conventional low-power transistor. It allows you to connect headphones with a resistance of about 100 ohms. Such phones are not very common, but the developers of the receiver found an easy way out.

They proposed to use with this receiver the widely used "ear" phones, which are used with pocket receivers, players, etc.

The emitters of such headphones usually have an impedance of 32 ohms. If they are connected in series, then phones are obtained in which the resistance will be 64 ohms - a completely acceptable value for this receiver. When desoldering the emitters, you only need to remember the need for their correct phasing. It is easily determined by ear by the more natural sounding of signals.

The receiver is mounted on support contact pads cut out on foil-coated fiberglass - a modern version of the once popular mounting "on racks". The rest of the metal foil is not removed, but is used as a common wire for the device. This method is very convenient for the manufacture of simple structures by novice radio amateurs, since the placement of parts on a conditional "printed circuit board" can be close to the electrical circuit of the device.

The contact pads are cut out with a cutter, but it is best to make a special device for this (Fig. 3), which consists of a needle, a miniature cutter and a fastener. The needle and cutter are made from used dental burs. To sharpen them, you can use an abrasive stone or a diamond file. Fastener - steel sleeve with a diameter of 6 mm. The needle and cutter are inserted into the holes drilled in the sleeve and secured with two M3 screws. For reliable fastening on the side surfaces of the needle and cutter facing the screws, it is desirable to chamfer. As shown in fig. 3, the shank of the needle must be longer than the shank of the cutter so that it can be fixed in the drill.

Fig. 3

It is expedient to pre-mark the centers of future "patch patches" so that during the manufacture of the contact pads, due to the possible slippage of the needle, their positions on the board do not shift. When working, you should not make great efforts so as not to create "seizures" of the fiberglass. The groove width of such a device is approximately 0,8 mm, and the diameter of the support circle is 5 mm (Fig. 4).

To give the entire structure the necessary rigidity, the board is attached to a base made of thick plywood (see Fig. 1). The front panel of the receiver is also made of foil fiberglass and soldered at an angle of 90 degrees to the board on which the parts are placed.

A frameless inductor of the input circuit - a loop antenna - is made of a wire with a diameter of 1,3 ... 1,5 mm. It contains four turns, which are wound on a frame with a diameter of 90 mm (turn to turn). They are fastened at several points along the circumference with epoxy glue. The frame must first be wrapped with a layer of thin paper so that the coil can be removed from it after the glue has hardened.

Variable capacitor C1 - from a broadcasting transistor receiver. Since the manufactured receiver has a relatively large frequency overlap, this capacitor must have a vernier.

A view of the installation of the high-frequency part of the receiver is shown in fig. 5.

Fig. 5

Transistor VT1 can be replaced with a field-effect transistor of the KP303 type (preferably with the letter index E - its characteristics are closest to those of the BF256C). Transistors BC547C (VT2-VT4) can be replaced by transistors KT3102G or KT3102E, as well as transistors KT342V. They, like the BC547C transistor, have a large static current transfer coefficient - at least 400. As VTZ-VT4, you can use the same transistors with any letter indices, but you may have to select a resistor R8 with such a value that the voltage at the VT3 collector is about 2,2 V, and resistor R10 so that the voltage at the emitter of transistor VT4 is approximately 4,2 V. For transistor VT2, such a replacement is not desirable. It operates in low collector current mode. At the same time, the value of the static current transfer coefficient is noticeably reduced, therefore, a transistor with a large initial value of at least 400 is needed here. Note that the KT3102 transistors (except for transistors with letter indices A and Zh), as well as the KT342B and KT342D transistors, have an upper value possible values ​​​​of the static current transfer coefficient - 500, therefore, a replacement for the transistor VT2 can also be selected from transistors with such letter indices.

When repeating the design, in order to increase the stability of its operation, it is advisable to additionally include a capacitor with a capacity of 0,01 ... 0,1 microns between the drain of the transistor VT1 and the common wire. In addition, it is advisable to increase the capacitance value for capacitor C6 to 470 pF. This will improve the filtering of the high frequency (above 5 kHz) components of the detected signal.

Author: B.Stepanov

See other articles Section radio reception.

Read and write useful comments on this article.

<< Back

<< Back

Latest news of science and technology, new electronics:

Artificial leather for touch emulation 15.04.2024

In a modern technology world where distance is becoming increasingly commonplace, maintaining connection and a sense of closeness is important. Recent developments in artificial skin by German scientists from Saarland University represent a new era in virtual interactions. German researchers from Saarland University have developed ultra-thin films that can transmit the sensation of touch over a distance. This cutting-edge technology provides new opportunities for virtual communication, especially for those who find themselves far from their loved ones. The ultra-thin films developed by the researchers, just 50 micrometers thick, can be integrated into textiles and worn like a second skin. These films act as sensors that recognize tactile signals from mom or dad, and as actuators that transmit these movements to the baby. Parents' touch to the fabric activates sensors that react to pressure and deform the ultra-thin film. This ... >>

Petgugu Global cat litter 15.04.2024

Taking care of pets can often be a challenge, especially when it comes to keeping your home clean. A new interesting solution from the Petgugu Global startup has been presented, which will make life easier for cat owners and help them keep their home perfectly clean and tidy. Startup Petgugu Global has unveiled a unique cat toilet that can automatically flush feces, keeping your home clean and fresh. This innovative device is equipped with various smart sensors that monitor your pet's toilet activity and activate to automatically clean after use. The device connects to the sewer system and ensures efficient waste removal without the need for intervention from the owner. Additionally, the toilet has a large flushable storage capacity, making it ideal for multi-cat households. The Petgugu cat litter bowl is designed for use with water-soluble litters and offers a range of additional ... >>

The attractiveness of caring men 14.04.2024

The stereotype that women prefer "bad boys" has long been widespread. However, recent research conducted by British scientists from Monash University offers a new perspective on this issue. They looked at how women responded to men's emotional responsibility and willingness to help others. The study's findings could change our understanding of what makes men attractive to women. A study conducted by scientists from Monash University leads to new findings about men's attractiveness to women. In the experiment, women were shown photographs of men with brief stories about their behavior in various situations, including their reaction to an encounter with a homeless person. Some of the men ignored the homeless man, while others helped him, such as buying him food. A study found that men who showed empathy and kindness were more attractive to women compared to men who showed empathy and kindness. ... >>

Random news from the Archive Unraveled the reason for the fresh smell of the forest after the rain 25.01.2015 We begin to smell when molecules of a smelling substance reach the receptors in our nose. If the substance itself is liquid or solid, then the fastest way to smell is to spray tiny drops of liquid containing the desired substance into the air. Air fresheners work according to this principle - gas from a canister under pressure sprays an aerosol into the air, and the room is instantly filled with the desired aroma. However, in the forest, no one runs around with a can of air freshener. It turns out that there is some other, natural method for obtaining an aerosol. If the source of the forest smell is on the ground, and the only thing that distinguishes a wet forest from a dry one is falling drops of water, then the key to the puzzle is most likely in them. Armed with high-speed video cameras, a team of MIT researchers set out to see what happens when a raindrop hits a porous surface. It turned out that at the moment of impact, microscopic air bubbles form at the boundary between the fallen drop and the surface. These bubbles, like in a glass of champagne, begin to rise up and, having come to the surface, throw microdrops of water into the air. An aerosol cloud forms over a fallen raindrop, containing substances that the water carried away from the soil surface. And a light breeze will already spread the smell of geosmin throughout the forest. Naturally, the researchers did not limit themselves to discovering the very fact of aerosol formation by falling drops, but carried out a detailed study of this mechanism. After conducting about 600 experiments in various conditions, they found that the most aerosol is formed with moderate rainfall and average soil moisture. During a heavy downpour, the bubbles inside the droplets simply do not have time to form, and sandy and clay soils contribute to the best aerosol formation. In addition to forest odors from the ground, aerosols can lift bacteria or spores into the air, which can spread over long distances. And if in the forest the probability of inhaling something very dangerous and poisonous is very small, then in large cities a walk after a little summer rain may not be as useful as it seems.

Other interesting news:

▪ K70 RGB Pro Mechanical Keyboard

▪ Flying over Venus

▪ Television through socket

▪ 88-inch OLED 8K display from LG

▪ Voice will betray depression

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the website Electrotechnical materials. Article selection

▪ article Anchor, another anchor! Popular expression

▪ article Why is the marathon distance 42 km 195 m? Detailed answer

▪ article Programmer of trade enterprise. Job description

▪ article Scheme of power supply of high-voltage fluorescent lamps from a rechargeable battery. Encyclopedia of radio electronics and electrical engineering

▪ article Timer for periodic switching on of the load. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024