A simple radio circuit: a description. Old radios
For a long time, radio receivers headed the listthe most significant inventions of mankind. The first such devices are now reconstructed and changed to a modern mode, however, in the circuit of their assembly, little has changed - the same antenna, the same grounding and the oscillatory circuit for screening out an unnecessary signal. Undoubtedly, the schemes have become much more complicated since the time of the creator of the radio, Popov. His followers developed transistors and microcircuits for the reproduction of a better quality and energy-consuming signal.
Why it is better to start with simple schemes?
If you understand the simple scheme of the radio, thenyou can be sure that most of the way to achieve success in the field of assembly and operation has already been mastered. In this article, we will analyze several schemes of such devices, the history of their occurrence and the main characteristics: frequency, range, etc.
May 7, 1895 is considered the birthday of the radio. On this day the Russian scientist AS Popov demonstrated his apparatus at a meeting of the Russian Physico-Chemical Society.
In 1899 the first line was builta 45 km long radio link between the island of Hogland and the city of Kotka. During the First World War, a direct amplification receiver and electronic tubes were distributed. During the war, the availability of radio was strategically necessary.
In 1918, simultaneously in France, Germany andUSA scientists L. Levvy, L. Schottky and E. Armstrong have developed a method for superheterodyne reception, but because of weak electron tubes, this principle was widely adopted only in the 1930s.
Transistor devices appeared and developedin the 50's and 60's. The first widely used radio receiver on four Transistors Regency TR-1 was created by the German physicist Herbert Matara with the support of the industrialist Jacob Michael. He went on sale in the US in 1954. All the old radios worked on transistors.
In the 1970s, the study and implementation of integrated circuits began. Now the receivers are developing with the help of a large integration of nodes and digital signal processing.
Both old radios and modern ones have certain characteristics:
- Sensitivity is the ability to receive weak signals.
- The dynamic range is measured in Hertz.
- Noise immunity.
- Selectivity (selectivity) is the ability to suppress extraneous signals.
- Own noise level.
These characteristics do not change in new generations of receivers and determine their operability and ease of operation.
Principle of operation of radio receivers
In the most general form, the radio receivers of the USSR worked according to the following scheme:
- Due to fluctuations in the electromagnetic field, an alternating current appears in the antenna.
- Oscillations are filtered (selectivity) to separate information from interference, that is, an important component is extracted from the signal.
- The received signal is converted into sound (in the case of radio receivers).
By a similar principle, an image appears on the TV, digital data is transmitted, radio-controlled equipment (children's helicopters, cars) works.
The first receiver was more like a glass receiverA tube with two electrodes and sawdust inside. The work was carried out according to the principle of the action of charges on metal powder. The receiver had a huge resistance (up to 1000 ohms) due to the fact that the sawdust was in poor contact with each other, and a part of the charge slipped into the air space where it dispersed. Over time, these sawdust were replaced by an oscillatory circuit and transistors for conservation and transmission of energy.
Depending on the individual receiver circuitrythe signal in it can pass additional filtering by amplitude and frequency, amplification, digitization for further program processing, etc. A simple radio circuit scheme provides for a single signal processing.
The oscillatory contour in the simplest formThe coil and the capacitor closed in a chain are called. With the help of them, out of all the incoming signals, it is possible to isolate the necessary circuit due to the natural frequency of the oscillations. Radio receivers of the USSR, as well as modern devices, are based on this segment. How does all this work?
As a rule, the radio receivers are powereddue to the batteries, the number of which varies from 1 to 9. For transistor devices, 7D-0.1 and Krona batteries with voltage up to 9 V are widely used. The more batteries a simple radio circuit requires, the longer it will work.
By frequency of received signals, the devices are divided into the following types:
- Long-wave (DV) - from 150 to 450 kHz (easily scattered in the ionosphere). Significance has ground waves, the intensity of which decreases with distance.
- Medium-wave (CB) - from 500 to 1500 kHz (easily scattered in the ionosphere during the day, but at night reflected). During the daytime, the radius of action is determined by the ground waves, at night - reflected.
- Shortwave (HF) - from 3 to 30 MHz (notthey land, are exclusively reflected by the ionosphere, so there is a radio silence zone around the receiver). At low transmitter power, short waves can propagate over long distances.
- Ultra-shortwave (VHF) - from 30 to 300 MHz (have a high penetrating ability, usually reflected by the ionosphere and easily envelop obstacles).
- High-frequency (HF) - from 300 MHz to 3 GHz (used in cellular communications and Wi-Fi, operate within sight, do not go around obstacles and spread rectilinearly).
- Extremely high frequency (EHF) - from 3 to 30 GHz (used for satellite communications, reflected from obstacles and operate within the line of sight).
- Hyperfrequency (GHG) - from 30 GHz to 300 GHz (do not skip obstacles and are reflected as light, they are used extremely limitedly).
When using HF, SW and DV, broadcasting can bekeep away from the station. The VHF band receives signals more specifically, but if the station only supports it, then it will not work at other frequencies. The receiver can be embedded player for listening to music, a projector for displaying on remote surfaces, a clock and an alarm clock. The description of the radio circuit with such additions will become more complicated.
The introduction of the microcircuit into the radio enabledsignificantly increase the receiving radius and the frequency of the signals. Their main advantage in the relatively low energy consumption and small size, which is convenient for carrying. The chip contains all the necessary parameters to reduce the signal sampling and the convenience of reading the output data. Digital signal processing dominates in modern devices. Radio receivers of the USSR were intended only for the transmission of audio signals, only in the last decades the arrangement of receivers has evolved and become more complicated.
Schemes of the simplest receivers
The scheme of the simplest radio for building a housewas developed back in Soviet times. Then, as now, the devices were divided into detector, direct amplification, direct conversion, superheterodyne type, reflex, regenerative and super-regenerative. The most simple in perception and assembly are the detector receivers, from which, we can assume, the development of radio began in the early 20th century. The most complex in the construction of steel devices on microcircuits and several transistors. However, if you understand in one scheme, others will not be a problem anymore.
Simple detector receiver
The circuit of the simplest radio receiver containstwo parts: a germanium diode (D8 and D9 are suitable) and a main phone with high resistance (TON1 or TON2). Since there is no oscillatory circuit in the circuit, it will not be able to catch the signals of a certain radio station broadcasting in a given locality, but with its main task to cope.
To work, you need a good antenna, whichcan be thrown on a tree, and a ground wire. To be faithful, it is enough to attach it to a massive metal debris (for example, to a bucket) and bury it a few centimeters into the ground.
Variant with oscillatory circuit
In the past scheme for introducing selectivityYou can add an inductor and a capacitor by creating an oscillatory circuit. Now, if you want, you can catch the signal of a particular radio station and even amplify it.
Lamp regenerative shortwave receiver
Lamp radios, whose scheme is prettysimple, are made for reception of signals of amateur stations on small distances - on ranges from VHF (ultra-shortwave) to DV (long-wave). In this scheme, finger battery lamps operate. They are best generated on VHF. And the resistance of the anode load is removed by a low frequency. All the details are shown in the diagram, only the coils and the throttle can be considered self-made. If you want to receive television signals, then the L2 coil (EBF11) is made up of 7 turns with a diameter of 15 mm and a wire of 1.5 mm. For the amateur receiver, 5 turns are suitable.
Direct amplification radio receiver on two transistors
The circuit contains a magnetic antenna and a two-stageThe low-frequency amplifier is a tunable input circuit of the radio receiver. The first stage is an RF modulated signal detector. The coil of the inductance is wound in 80 turns by a PEV-0.25 wire (from the sixth turn, a bend is taken from the bottom according to the scheme) on a ferrite rod 10 mm in diameter and 40 in length.
Such a simple scheme of the radio receiver is designed to recognize powerful signals from nearby stations.
Super-power device on FM-bands
FM-receiver, collected by model E. Solodovnikov, uncomplicated in the assembly, but has a high sensitivity (up to 1 μV). Such devices are used for high-frequency signals (more than 1 MHz) with amplitude modulation. Due to strong positive feedback, the cascade gain increases to infinity, and the circuit goes into the generation mode. For this reason, self-excitation occurs. To avoid it and use the receiver as a high-frequency amplifier, set the coefficient level and, when it reaches this value, drastically reduce to a minimum. To continuously monitor the gain, you can use a sawtooth pulse generator, or you can make it easier.
In practice, often as a generatorthe amplifier itself appears. With the help of filters (R6C7), which allocate low frequency signals, the ultrasonic oscillation path is limited to the input of the next stage of the VLF. For FM signals 100-108 MHz, the L1 coil is converted into a half-twig with a cross section of 30 mm and a linear part of 20 mm with a wire diameter of 1 mm. A coil L2 contains 2-3 turns with a diameter of 15 mm and a wire with a cross section of 0.7 mm inside the half-wool. It is possible to amplify the receiver for signals from 87.5 MHz.
Device on the chip
HF radio receiver, the circuit of which was developedin the 70's, now considered a prototype of the Internet. Short-wave signals (3-30 MHz) travel for huge distances. It is not difficult to set up the receiver to listen to the broadcast in another country. For this prototype was called the world radio.
Simple HF receiver
A simpler radio circuit is devoid ofmicrocircuit. Overlaps the range from 4 to 13 MHz in frequency and up to 75 meters in length. Power - 9 V from the battery "Crohn". An antenna can be a mounting wire. The receiver works on the headphones from the player. The high-frequency tract is built on transistors VT1 and VT2. Due to the capacitor C3, there is a positive reverse charge, regulated by the resistor R5.
Modern radio receivers
Modern machines are very similar toradio receivers of the USSR: they use the same antenna on which weak electromagnetic oscillations arise. In the antenna there are high-frequency oscillations from different radio stations. They are not used directly for signal transmission, but the subsequent circuit is operating. Now this effect is achieved with the help of semiconductor devices.
Wide development receivers have received in the middle of the 20th century and since then have been continuously improving, despite the replacement of their mobile phones, tablets and televisions.
General device of radio receivers since Popovhas changed slightly. We can say that the circuits are much more complicated, the chips and transistors were added, it became possible to take not only the audio signal, but also to embed the projector. So the receivers evolved into TVs. Now, if you want, you can embed everything that your heart desires.