For a long time, radios topped the list of the most significant inventions of mankind. The first such devices have now been reconstructed and changed in a modern way, however, little has changed in their assembly scheme - the same antenna, the same grounding and an oscillatory circuit to filter 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 to reproduce a better and more energy-intensive signal.
Why is it better to start with simple patterns?
If you understand a simple radio circuit, you can be sure that most of the way to 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.
Historical background
May 7, 1895 is considered the birthday of the radio. On this day, the Russian scientist A. S. Popov demonstrated his apparatus at a meeting of the Russian Physical and Chemicalsociety.
In 1899, the first 45 km long radio communication line was built between the island of Hogland and the city of Kotka. During the First World War, the direct amplification receiver and vacuum tubes became widespread. During the hostilities, the presence of a radio proved to be strategically necessary.
In 1918, simultaneously in France, Germany and the USA, scientists L. Levvy, L. Schottky and E. Armstrong developed the method of superheterodyne reception, but due to weak vacuum tubes, this principle was widely used only in the 1930s years.
Transistor devices appeared and developed in the 50s and 60s. The first widely used four-transistor radio receiver, the Regency TR-1, was created by German physicist Herbert Matare with the support of industrialist Jacob Michael. It went on sale in the US in 1954. All old radios used transistors.
In the 70s, the study and implementation of integrated circuits began. Receivers are now evolving with great node integration and digital signal processing.
Instrument specifications
Both old and modern radios have certain characteristics:
- Sensitivity - the ability to receive weak signals.
- Dynamic range - measured in Hertz.
- Noise immunity.
- Selectivity (selectivity) - the ability to suppress extraneous signals.
- Internal noise level.
- Stability.
These characteristics are notchange in new generations of receivers and determine their performance and ease of use.
How radios work
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 noise, i.e., its important component is extracted from the signal.
- The received signal is converted into sound (in the case of radios).
According to a similar principle, an image appears on a TV, digital data is transmitted, radio-controlled equipment works (children's helicopters, cars).
The first receiver was more like a glass 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 by modern standards (up to 1000 ohms) due to the fact that the sawdust had poor contact with each other, and part of the charge slipped into the airspace, where it dissipated. Over time, these sawdust were replaced by an oscillatory circuit and transistors to store and transfer energy.
Depending on the individual circuit of the receiver, the signal in it can undergo additional filtering by amplitude and frequency, amplification, digitization for further software processing, etc. A simple radio receiver circuit provides for a single signal processing.
Terminology
An oscillatory circuit in its simplest form is called a coil andcapacitor closed in a circuit. With the help of them, from all incoming signals, it is possible to select the desired one due to the natural frequency of oscillations of the circuit. USSR radios, as well as modern devices, are based on this segment. How does it all work?
As a rule, radio receivers are powered by 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 receiver circuit requires, the longer it will work.
According to the frequency of received signals, devices are divided into the following types:
- Longwave (LW) - from 150 to 450 kHz (easily scattered in the ionosphere). Significant are ground waves, the intensity of which decreases with distance.
- Medium wave (MW) - from 500 to 1500 kHz (easily scattered in the ionosphere during the day, but reflected at night). During daylight hours, the range is determined by ground waves, at night - by reflected waves.
- Shortwave (HF) - from 3 to 30 MHz (they do not land, they are exclusively reflected by the ionosphere, so there is a radio silence zone around the receiver). With low transmitter power, short waves can travel long distances.
- Ultra shortwave (VHF) - from 30 to 300 MHz (have a high penetrating ability, as a rule, are reflected by the ionosphere and easily go around 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 andpropagate rectilinearly).
- Extreme high frequency (EHF) - from 3 to 30 GHz (used for satellite communications, reflected from obstacles and operate within line of sight).
- Hyper high frequency (HHF) - from 30 GHz to 300 GHz (do not go around obstacles and are reflected like light, are used very limitedly).
When using HF, MW and LW, broadcasting can be carried out while being far from the station. The VHF band receives signals more specifically, but if the station supports only it, then listening to other frequencies will not work. The receiver can be equipped with a player for listening to music, a projector for displaying on remote surfaces, a clock and an alarm clock. The description of the radio receiver circuit with such additions will become more complicated.
The introduction of a microchip into radio receivers made it possible to significantly increase the reception radius and frequency of signals. Their main advantage is relatively low energy consumption and small size, which is convenient for carrying. The microcircuit contains all the necessary parameters for signal downsampling and readability of the output data. Digital signal processing dominates modern devices. Radio receivers of the USSR were intended only for transmitting an audio signal, only in recent decades the device of receivers has developed and become more complicated.
Schemes of the simplest receivers
The scheme of the simplest radio receiver for assembling a house was developed back in the days of the USSR. Then, as now, devices were divided into detector, direct amplification, direct conversion,superheterodyne type, reflex, regenerative and superregenerative. The simplest in perception and assembly are detector receivers, from which, it can be considered, the development of radio began at the beginning of the 20th century. The most difficult to build were devices based on microcircuits and several transistors. However, if you understand one scheme, others will no longer be a problem.
Simple detector receiver
The circuit of the simplest radio receiver contains two parts: a germanium diode (D8 and D9 will do) and a main telephone 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 broadcast in a given area, but it will cope with its main task.
To work, you will need a good antenna that can be thrown on a tree, and a ground wire. To be sure, it is enough to attach it to a massive metal fragment (for example, to a bucket) and bury it a few centimeters into the ground.
Oscillatory circuit option
In the previous circuit to introduce selectivity, you can add an inductor and a capacitor, creating an oscillatory circuit. Now, if desired, you can catch the signal of a specific radio station and even amplify it.
Valve regenerative shortwave receiver
Valve radios, the circuit of which is quite simple, are made to receive signals from amateur stations at short distances - on the ranges from VHF(ultrashortwave) to LW (longwave). In this circuit, finger-type battery lamps work. They generate best on VHF. And the resistance of the anode load is removed by low frequency. All details are shown in the diagram, only coils and a choke can be considered homemade. 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 an amateur receiver, 5 turns will do.
Direct amplification radio with two transistors
The circuit contains a magnetic antenna and a two-stage bass amplifier - this is a tuned input oscillatory circuit of the radio receiver. The first stage is the RF modulated signal detector. The inductor is wound in 80 turns with PEV-0, 25 wire (from the sixth turn there is a tap from the bottom according to the diagram) on a ferrite rod with a diameter of 10 mm and a length of 40.
Such a simple radio circuit is designed to recognize strong signals from nearby stations.
Super-generative FM device
FM-receiver, assembled according to the model of E. Solodovnikov, is easy to assemble, but has high sensitivity (up to 1 μV). Such devices are used for high-frequency signals (more than 1 MHz) with amplitude modulation. Due to the strong positive feedback, the gain of the stage increases to infinity, and the circuit enters the generation mode. For this reason, self-excitation occurs. To avoid it and use the receiver as a high-frequency amplifier, set the levelcoefficient and, when it reaches this value, sharply reduce to a minimum. A sawtooth pulse generator can be used to constantly monitor the gain, or it can be made simpler.
In practice, the amplifier itself often acts as a generator. With the help of filters (R6C7), which highlight low-frequency signals, the passage of ultrasonic vibrations to the input of the subsequent ULF cascade is limited. For FM signals 100-108 MHz, the L1 coil is converted into a half-turn with a cross section of 30 mm and a linear part of 20 mm with a wire diameter of 1 mm. And the L2 coil contains 2-3 turns with a diameter of 15 mm and a wire with a cross section of 0.7 mm inside the half-turn. Receiver gain available for signals from 87.5 MHz.
Device on a chip
The HF radio, which was designed in the 70s, is now considered the prototype of the Internet. Shortwave signals (3-30 MHz) travel great distances. It is easy to set up the receiver to listen to a broadcast in another country. For this, the prototype received the name of world radio.
Simple HF receiver
A simpler radio receiver circuit is devoid of a microcircuit. Covers the range from 4 to 13 MHz in frequency and up to 75 meters in length. Food - 9 V from the Krona battery. A wire can serve as an antenna. The receiver works on headphones from the player. The high-frequency treatise is built on transistors VT1 and VT2. Due to the capacitor C3, a positive reverse charge arises, regulated by the resistor R5.
Modernradios
Modern devices are very similar to the radio receivers of the USSR: they use the same antenna, on which weak electromagnetic oscillations occur. High-frequency vibrations from different radio stations appear in the antenna. They are not used directly for signal transmission, but carry out the work of the subsequent chain. Now this effect is achieved with the help of semiconductor devices.
Receivers were widely developed in the middle of the 20th century and have been continuously improved since then, despite their replacement by mobile phones, tablets and TVs.
The general arrangement of radio receivers has changed slightly since the time of Popov. We can say that the circuits have become much more complicated, microcircuits and transistors have been added, it has become possible to receive not only an audio signal, but also to embed a projector. So receivers evolved into televisions. Now, if you wish, you can build whatever your heart desires into the device.
