AM broadcast receiver. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

AM broadcast receiver. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / radio reception

Comments on the article

Figure 1 shows a diagram of a simple broadcast receiver operating on medium or long wavelengths. In his circuit, the very minimum of details is two transistors, three capacitors, a resistor, a magnetic antenna, a power source.

The receiver works on headphones B1. Since power is supplied to the circuit through them, turning off the phones is tantamount to turning off the power.

AM broadcast receiver
Rice. 1. Schematic diagram of the receiver

The supply voltage is 1,5V, - only one "finger" element of the "AAA" type (as from a TV remote control).

The receiver works on a magnetic (ferrite) antenna.

The composite transistor VT1-VT2 is connected according to a common emitter circuit, this further increases its input resistance. Due to the large input impedance, the oscillatory circuit can be connected directly to the input of the amplifier without the use of coupling coils or autotransformer circuits.

Tuning to the station is carried out by a variable capacitor C1, it changes the resonant frequency of the circuit L1-C1.

The bias voltage to the base VT1 is supplied through the resistor R1 and the coil L1. Resistor R1 creates the necessary operating point of the cascade, and capacitor C2 transmits a signal from the circuit to the base of the transistor bypassing this resistor (so that the resistance R1 does not weaken the signal).

The cascade on VT1-VT2 is interesting in that, in addition to amplifying the radio frequency signal by current, it also performs the functions of an amplitude detector. The amplitude modulated signal is detected at the emitter junction VT2, and the capacitor C3 is a filter that suppresses the RF component.

Power is supplied to the emitter VT2 through the resistance of headphones B1. When the phones are turned off, the power circuit is broken and the receiver turns off. The telephones serve as the load of the cascade.

Most of the details are located on the printed circuit board, the diagram of which is shown in Figure 2. On the same board there is a power source - a galvanic cell of the "AAA" type. It is installed between two homemade springy contacts cut from brass. The contacts are soldered to the printed circuit board. You can also use ready-made contacts, for example, from battery compartments of remote controls.

AM broadcast receiver
Rice. 2. PCB

The basis of the magnetic antenna is a ferrite rod with a diameter of 8 mm and a length of at least 80 mm. (the longer the better). One layer of paper is wound around the rod, so that a sleeve 60 mm long is obtained. A coil is wound on this sleeve. To work in the long-wave range, the L1 coil must contain 250 turns of PEV winding wire with a cross section of 0,1-0,2 mm. For the medium wave range - 70 turns of PEV wire with a cross section of 0,2-0,5 mm. Winding - turn to turn. The ends of the winding must be secured with threads impregnated with paraffin or BF glue. It is impossible to tie the ends of the coil with knots, or twist them together.

Variable capacitor C1 - from a pocket receiver. Headphones are connected via a jack. It is advisable to use high-impedance headphones such as TON-1, TON-2, but you can also use low-impedance headphones from an audio player, although in this case the receiver will work worse (and quieter).

Capacitor C2 can be from 50 to 200 pF, capacitor C3 - from 1500 to 4700 pF.

All these circuits use KT315G transistors. You can determine the terminals of the KT315 transistor (as well as the KT815) as follows - turn it towards you with the marking and the pins up, - the base terminal will be on the left, in the middle - the collector, and on the right - the emitter.

Literature

V.Polyakov. Radio receiver powered by a multimeter. Radio, No. 8, 2004.
E. Mukhutdinov. Touch switch for backlight, Radio, No. 4, 2004.

Author: R. Lyzhin

See other articles Section radio reception.

Read and write useful comments on this article.

<< 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

Cosmic rays - a threat to the colonists of Mars 13.11.2014

The Sun's magnetic field acts as a barrier to high-energy cosmic rays that are produced outside the Solar System in supernova explosions. The more active the Sun, the stronger the magnetic field, and the more dangerous radiation it delays. However, scientists believe that solar activity will continue to wane, which is more bad news for future space travelers.

A new NASA study shows that a 30-year-old man who flies to Mars during a period of low solar activity will reach the radiation safety limit in less than 400 days, which is barely enough time to get to the Red Planet and back. The woman will reach the limit even faster - in 300 days. If solar activity continues to decline, the limit for males will be reached in 320 days and for females in less than 240 days.

To estimate how long a person can withstand cosmic radiation in outer space, NASA experts used the automatic interplanetary station Lunar Reconnaissance Orbiter. It is equipped with a device for measuring cosmic rays and solar radiation CRaTER, which has in its arsenal a special plastic equivalent to the tissues of the human body. It shows how a person's muscles will react to radiation.

However, it should be taken into account that the limit of radiation safety depends not only on solar activity, but also on the age of the space traveler.

Other interesting news:

▪ Prosthesis that senses touch

▪ Air powered generator

▪ There are lees to every wine

▪ Phone for Chinese

▪ Xiaomi USB-C Multi-Function Adapter

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Palindromes. Article selection

▪ article Praises are tempting - how not to wish them! Popular expression

▪ article Why is a computer program update called a patch? Detailed answer

▪ article Sausage tree. Legends, cultivation, methods of application