"Radio waves" transmit music, conversations, photos and data invisibly through the air, often over millions of miles - this happens every day in thousands of different ways! Even though radio waves are invisible and completely undetectable by humans, they have completely changed society. Whether we're talking about a cell phone, a baby monitor, a cordless phone, or any of the thousands of other wireless technologies, they all use radio waves to communicate.
Here are just a few everyday technologies that rely heavily on radio waves:
The funny thing is that, at its core, radio is an incredibly simple technology. With just a few electronic components that cost no more than a dollar or two, you can create simple radio transmitters and receivers. The story of how something so simple became the core technology of the modern world is fascinating. In today's article, we will look at a technology called radio, so that you can fully understand how invisible radio waves make so many things and make our lives easier.
Radio can be incredibly simple, and by the turn of the century this simplicity made early experimentation possible for just about anyone. How easy is it to get a radio? One example is described below:
In the early days, radio transmitters were called spark coils, and in addition they produced a continuous stream of sparks at much higher voltages (e.g. 20,000 volts). The high voltage consequently contributed to the creation of large sparks, such as you see in a spark plug, for example. Today a transmitter like this is illegal because it spams the entire radio frequency spectrum, but in the early days it worked great and was very common because there weren't many people using radio waves.
Any radio installation has two parts: transmitter(transmitter) and receiver(receiver). The transmitter intercepts some kind of message (this could be the sound of someone's voice, the image of a TV screen, data for a radio modem, or any other thing), encodes it into a sine wave and transmits it with radio waves. The receiver, of course, receives radio waves and decrypts the message from the sine wave that it receives. Both the transmitter and receiver use antennas to radiate and capture the radio signal.
A baby monitor is about as simple as the resulting radio technology. There is a transmitter that “sits” in the child’s room and a receiver that parents use to listen to their child. Here are some of the important features of a typical baby monitor:
A typical baby monitor with a transmitter on the left and a receiver on the right. The transmitter is located directly in the child’s room and serves as a kind of mini-radio station. Parents take a receiver with them and use it to listen to the child’s actions. Communication range is limited to 200 feet (61 meters)
Don't worry if terms like "modulation" and "frequency" don't make sense to you now - we'll get to them in a while and I'll explain what they mean.
A mobile phone contains both a receiver and a transmitter, and both operate simultaneously on different frequencies. A cell phone communicates with a cell tower and is capable of transmitting signals over a distance of 2 or 3 miles (3-5 kilometers)
A cell phone is also a radio and is a much more complex device. A cell phone contains both a transmitter and a receiver, and you can use both at the same time—so you'll use hundreds of different frequencies and be able to switch between them automatically. Here are some of the important characteristics of a typical analog cell phone:
You can get an idea of how a radio transmitter works by starting with a battery and a piece of wire. As you know, a battery sends electricity (a flow of electrons) through a wire when it is connected between two terminals. The moving electrons create a magnetic field surrounding the wire, and the field is strong enough to affect the compass.
Let's say you take another wire and place it parallel to the battery wire by a few inches (5 centimeters). When you connect a very sensitive voltmeter to a wire, the following will happen: Each time you connect or disconnect the first wire from the battery, you will feel a very small voltage and current in the second wire; any change in the magnetic field can cause an electric field in the conductor - this is the basic principle underlying any electrical generator. So:
One important thing to note is that electrons only flow in the second wire when you connect or disconnect the battery. A magnetic field does not cause electrons to flow in a wire unless the magnetic field changes. Connecting and disconnecting a battery changes the magnetic field (connecting a battery to a wire creates a magnetic field, while disconnecting it destroys it). Thus, the flow of electrons flows in the second wire at those two moments.
If you have a sine wave and a transmitter that sends the sine wave into space with an antenna, you have a radio station. The only problem is that the sine wave contains no information. You have to modulate the wave in some way to encode information on it. There are three common ways to modulate a sine wave:
Pulse Modulation- in PM you simply turn the sine wave on and off. This is an easy way to send Morse code. PM is not that common, but one good example of it is the radio communication system that sends signals to radio-controlled watches in the United States. One PM transmitter can cover the entire United States of America!
Amplitude modulation- Both AM radio stations and part of the television signal signal amplitude modulation to encode information. In amplitude modulation, the amplitude of a sine wave (its voltage from peak to peak) changes. So, for example, the sine wave produced by a person's voice is superimposed on the transmitter's sine wave to change its amplitude.
Frequency modulation- FM radio stations and hundreds of other wireless technologies (including the audio portion of television signals, cordless phones, cell phones, and so on) use frequency modulation. The advantage of FM is that it is largely immune to static. In FM, the change in frequency of the transmitter's sine wave is very loosely based on the information signal. Once you have modulated a sine wave with information, you can transmit it!
Frequency
One feature of a sine wave is its frequency. The frequency of a sine wave is the number of times it oscillates up and down per second. When you listen to an AM radio broadcast, your radio is tuned to a sine wave at a frequency of approximately 1,000,000 cycles per second (cycles per second are also known as Hertz). For example, 680 on the AM dial is 680,000 cycles per second. FM radio signals operate in the range of 100,000,000 hertz. Thus, 101.5 in the FM dial will be listed as 101500000 cycles per second.
Here's a real world example. When tuning your AM car radio to a station such as 680 on the AM dial, the transmitter's sine wave is transmitting 680,000 hertz (the sine wave repeats 680,000 times per second). The DJ's voice is modulated on this carrier wave by changing the amplitude of the transmitter's sine wave. The amplifier boosts the signal to something like 50,000 watts for a large AM station. The antenna then transmits radio waves into space.
So how does your car's AM radio - the receiver - receive the 680,000 hertz signal that is sent by the transmitter and extract information (the DJ's voice) from it? Next, I will list the steps of this process for you:
You've probably noticed that almost every radio, be it a cell phone, a car radio, or more, has an antenna. Antennas come in all shapes and sizes, depending on the frequency the antenna is trying to receive. Radio transmitters also use extremely tall antenna towers to transmit their signals.
The idea of an antenna in a radio transmitter involves launching a radio wave into space. At the receiver, the idea is to take as much data from the transmitter as possible and supply it to the tuner. For satellites that are millions of miles away, NASA uses huge satellite dishes up to 200 feet (60 meters) in diameter - just imagine an oil painting like that.
The size of the optimal radio antenna is related to the frequency of the signal the antenna is attempting to transmit or receive. The reason for this relationship has to do with the speed of light, which can send electrons over long distances. The speed of light is 186,000 miles per second (300,000 kilometers per second).
Let's assume you are trying to build a radio tower for a 680 AM radio station. It transmits a sine wave with a frequency of 680,000 hertz. In one sine wave cycle, the transmitter will move electrons into the antenna in one direction, switch and hold them, switch again and expose them, and then switch again and bring them back. In other words, the electrons will change direction four times during one sine wave cycle. If the transmitter operates at 680000 hertz, this means that each cycle is completed in (1/680000) 0.00000147 seconds. One quarter of this is 0.0000003675 seconds. At the speed of light, electrons can travel 0.0684 miles (0.11 kilometers) in 0.0000003675 seconds. This means that the optimal antenna size for a 680,000 hertz transmitter is 361 feet (110 meters). Thus, AM radios need very tall towers. For a mobile phone operating on the 900000000 (900 MHz) frequency, on the other hand, the optimal antenna size is around 8.3 centimeters or 3 inches - which is why mobile phones can have such short antennas.
You might wonder why when a radio transmitter transmits something, the radio waves want to propagate through space far from the antenna at the speed of light. Why can radio waves travel millions of miles? It turns out that in space the magnetic field created by the antenna induces an electric field in space. This electric field, in turn, induces another magnetic field in space, which induces another magnetic field, which induces another magnetic field, and so on. These electric and magnetic fields (electromagnetic fields) force each other through space at the speed of light, thus traveling far from the antenna. That's all for today. I hope that the article was very interesting, informative, useful and that you learned a lot about everyday technology.
Currently, the electronic equipment market offers hundreds of models of radio broadcast receivers from dozens of manufacturers. How to choose the right radio receiver? This review discusses aspects of choosing the device that best suits your goals and objectives. To do this, we analyzed the technical parameters that must be taken into account when selecting the best radio receiver with good reception in your conditions.
Radio receiver - This is a device that is capable of selectively receiving radio waves modulated by sound from the air, and isolating and reproducing this sound signal. In English, the name of such devices sounds like receiver. In addition, devices have now appeared that receive broadcasts from radio stations broadcasting not on the air, but on the Internet. They are called Internet radios.
Household terrestrial radio receivers can be classified according to several criteria:
Internet radio Sangean WFR-27C:
Based on wavelength, radio broadcasting ranges are divided into:
Modulation is a method by which sound is superimposed on a radio wave, which carries information over a distance. The wave itself is called “carrier”. Modulation is named according to the wave parameter that changes when sound is superimposed. For radio broadcasting, two types of modulation are used:
There are two types of tuners used in household radio receivers:
Example of an analog device: Sangean PR-D6.
Example of a digital radio: Tecsun PL-380.
The circuitry of analog radio receivers is usually built according to two principles:
Manufacturers of radio receivers currently prefer not to indicate by what scheme the receiving part is assembled. And it is impossible to say with certainty about a specific device without seeing its diagram that it is a superheterodyne, direct amplification or direct conversion. However, you can be sure that inexpensive receiving devices are not superheterodynes.
The main technical characteristics of radio receivers include:
Since household radio broadcast receivers are not currently subject to mandatory certification, manufacturers of these radio receivers, at best, indicate only the sensitivity, output power and current consumption of radio receivers.
The presence of a processor in digital radios allows for additional advantages:
For example, a radio with RDS - Eton Traveler III.
Radio receivers are divided into several groups according to the place of use:
According to the method of power supply, broadcast receivers are divided into:
In the photo there is a radio with mains power - BZRP RP-301.
Example - model with built-in battery Lira RP-260-1:
Often the manufacturer produces radio receivers with combined power supply:
Internet radios occupy a separate niche because:
For devices of this class, the main method of connecting to the Internet is Wi-Fi:
For example, Sangean WFR-29C stereo internet radio:
In the photo - an Internet radio receiver with a USB input Sangean WFR-28C:
Currently, broadcast receivers from dozens of different manufacturers are offered on the electronics market. Let's consider brands of manufacturers offering products at affordable prices and with good quality.
The Taiwanese company Sangean was founded in 1974 and has headquarters in New Taipei and offices in the Netherlands and the USA. Production is located in China. Sangean offers the widest range of radio receivers with excellent quality. Let's look at the most interesting models:
The domestic manufacturer Izhevsk Radio Plant (IRZ) produces radio receivers under the Lear brand. Russian radios are distinguished by good quality, compliance with GOST standards and low price. The most successful examples:
The Chinese company Tecsun, founded in 1994, focuses on the production of VHF, HF and MF radio broadcast receivers. Some manufactured models are borrowed from Eton. The most interesting examples of products:
Another Chinese manufacturer, Onyx International, specializes in producing e-books under the Onyx brand. Radio receivers for sale in Russia are produced under delusion
Characteristic signs and causes of malfunctions of receivers and radios
Characteristic symptoms of a malfunction | Possible reasons |
Network receiver power supply |
|
The radio does not turn on. There is voltage in the lighting network | Check the fuse, power cord with plug, power switch, primary winding of the power transformer |
When you turn on the radio, the fuse blows | Short circuit in the winding circuits of the power transformer; the kenote, ron or selenium rectifier type ABC is faulty; The mains voltage switch is set to a voltage position lower than the mains voltage |
The power transformer heats up excessively even when the lamps are removed. The voltage on all windings is below rated | Short-circuited turns in the power transformer winding and insulation breakdown between the transformer winding and the chassis |
The fuse blows, the power transformer blows, ABC heats up quickly; sparking and a strong blue glow are observed in the kenotron | Breakdown and short circuit of one of the electrolytic capacitors of the smoothing filter, most often the first one. Short circuit of rectified voltage on the body and any circuit circuit |
The power transformer gets very hot, the receiver lamps do not light There is no rectified voltage at the output capacitor of the smoothing filter | Short circuit in the power supply circuit of the receiver lamps Failure of the kenotron or ABC. Broken choke or filter resistor. Break in the step-up circuit of the power transformer |
Rectified anode voltage below normal | Emission losses by kenotron. ABC is wrong. Break in the step-up winding of the power transformer (in a full-wave rectification circuit) |
The rectified anode voltage is low. The anodes of the kenotron become very hot (until a white glow) Reception on all bands is accompanied by an alternating current background. The same thing happens when playing a record. | High leakage current in electrolytic capacitors, short circuit in the radio receiver circuit A decrease in the capacity of the electrolytic capacitors of the smoothing filter due to their drying out, an open circuit of the filter capacitors, a part of the turns of the filter choke winding is shorted |
LF amplifier output stage |
|
Complete absence of sound. The screen grid in the output lamp becomes very hot (noticeable to the eye in glass lamps) | Break in the primary winding of the audio output transformer |
There is no reception, the output transformer gets very hot. No voltage at output tube anode There are no low sound frequencies | Short circuit of the primary winding of the output transformer to the housing or to the secondary winding Short circuit of part of the turns in the primary winding of the output audio transformer |
No sound. A voltmeter connected between the lamp anode and the chassis shows the full voltage of the power source | The bias resistor in the cathode circuit of the output lamp is broken or burned out |
There is no sound, the voltage at the anode of the output lamp is zero | The capacitor connected between the anode of the output lamp and the receiver chassis is broken |
The output sound is greatly distorted; on the control grid of the output lamp - positive voltage instead of negative | Breakdown or large leakage in the transition capacitor in the control grid circuit of the output lamp |
After a short period of operation of the radio receiver, the sound is distorted (wheezing) | The output lamp (or one of the lamps) is faulty |
At high volume of the received signal, rattling is observed | The voice coil or speaker cone is damaged. Poor voice coil alignment. One of the receiver parts is poorly secured |
The loudspeaker produces a noise reminiscent of a motor boat. After turning on the receiver, after a while an alternating current background is heard | Open resistor in the control grid circuit of the output lamp One of the tubes in the low-frequency amplifier is faulty, most often the output tube |
LF pre-amplification cascade |
|
No sound. There is no voltage at the lamp anode | Burnout or breakage of the load resistor or decoupling filter in the anode circuit of the lamp |
No sound. The quenching resistor heats up excessively; the voltage on the shielding grid is very small or equal to zero | Short circuit of the blocking capacitor in the shielding grid circuit |
No sound. The voltage at the anode of the lamp is equal to the voltage of the power source | Break or burnout of the bias resistor in the lamp cathode circuit |
The radio station being received and the recording being played are faintly audible, the voltage at the lamp electrodes is normal | Loss of capacitance of a capacitor connected in parallel with a bias resistor |
Distortion and weakening of sound when receiving radio stations and when listening to recordings | Break or burnout of the quenching resistor in the lamp shielding grid circuit |
Adjusting the volume is accompanied by a strong crackling sound | Poor contact between the slider and the conductive layer of the volume potentiometer, wear or contamination of the conductive layer |
Detector, AGC circuit and tuning indicator |
|
There is no signal reception. Bass amplifier works fine | Break or breakdown of the semiconductor diode. Break in the transition capacitor or load resistor of the detector. Open circuit or short circuit on the chassis of the secondary winding of the IF filter |
Reception of powerful radio stations occurs at high volume, accompanied by strong distortion. Hardly audible radio stations are received without distortion. Bass amplifier works fine | The AGC of the radio receiver does not work. Short circuit of the AGC filter capacitor or open circuit in the AGC circuit |
Reception of radio stations is accompanied by stuttering. Bass amplifier works fine | Break in the decoupling filter resistor in the AGC circuit |
The radio or radio works normally on all bands, but the optical indicator does not work | The optical indicator lamp is faulty |
Intermediate frequency amplifier |
|
There is no signal reception. Lamp operating mode is normal | Short circuit in the capacitor or coil of the IF filter |
There is no signal reception. No voltage at the lamp anode | Breakage of the anode coil of the IF filter. Breakdown of the capacitor or breakage of the decoupling filter resistor in the lamp anode circuit |
Reception with reduced volume. The voltage at the lamp electrodes is normal | IF filter is out of tune |
Whistling when tuning to a radio station, especially when tuning to a hard-of-hearing station. The pitch of the whistle depends on the receiver setting and varies from very high to low tones | |
Poor selectivity of the radio receiver | RF circuits or IF filters are detuned |
High frequency block |
|
There is no signal reception on all bands | Radio tube 6A7 or 6I1P is faulty |
Radio stations can only be heard on some bands | Partial (at some points) short circuit of the plates of a variable capacitor |
There is no signal reception on all bands; the voltage at the anode of the heterodyne is zero in all positions of the range switch | Capacitor breakdown or resistor break in the local oscillator anode circuit. One of the local oscillator feedback coils may break if they are connected in series |
An intermediate frequency signal fed to the signal grid passes well, but signals corresponding in frequency to the tested ranges do not pass through | The local oscillator does not generate oscillations |
The receiver does not work only at the end of the short-wave range or at the very short-wave extended sub-band | Partial loss of frequency converter lamp emission |
Radio stations are difficult to hear, but when you connect the antenna directly to the signal grid of the mixer, the signals are heard much better | There is no pairing of input and heterodyne circuits |
Tuning into a radio station is accompanied by a strong crackling sound on all bands | Poor contact of range switches; poor contact in the rotor current collector of the variable capacitor unit |
Switching from range to range is accompanied by a strong crash | The range switch is faulty or dirty |
Radio stations are not received on one of the receiver bands, but on the others they can be heard normally | There is a break in any of the UHF circuits operating on this band; the band switch is faulty |
The received radio stations do not correspond to the scale graduation | The local oscillator circuits are incorrectly configured. It is necessary to lay the range boundaries |
A ringing howl when receiving loud shortwave stations, changing when you tap on the radio body | Acoustic influence of a loudspeaker on local oscillator parts. By successively tapping the parts, wires and local oscillator lamp with a rubber hammer, find the vibrating part and secure it |
When the adjustment knob is rotated evenly, the needle moves along the scale jerkily or does not move at all | The vernier cable is loose or broken. Tighten the cable or rub it with rosin |
By periodically connecting the antenna to the control grids of the lamps of the amplifier, converter and UHF cascades (if the lamps in the cascades are working), rustling and clicking noises will be heard in the receiver's loudspeaker. For example, if, when connecting the antenna to the control grid of the lamp of the second stage of the amplifier, rustling or crackling is heard in the loudspeaker, then all cascades, starting from the control grid of this stage up to and including the loudspeaker, are working properly. If, when connecting the antenna to the control grid, no clicks are heard from the lamp of the first stage of the amplifier, then this indicates a malfunction of the first stage of the amplifier.
This test is simple; it allows only a very rough assessment of the quality of operation of the high-frequency stages of the receiver. It is possible to more accurately check the passage of signals through these cascades using measuring equipment. A standard signal generator of the G4-1A or TR-0608 type is used as a voltage source for testing the high-frequency stages of the AM circuit. With the same generator you can check and tune the intermediate frequency amplifier and the fractional detector of the FM path. To test the VHF unit, a G4-6 type signal generator is used as a signal source.
After finding a cascade in which the signal does not pass, they begin a detailed check of its circuits and parts. It should be remembered that during repairs it is especially important to establish the reason that caused the damage to the part. For example, when replacing a burnt-out resistor in an anode decoupling filter, it is necessary to check whether the decoupling capacitor is broken, which caused the failure of the resistor. If the cause of the resistor failure is not determined, when the receiver is turned on, the newly installed resistor may also burn out. The procedure for finding faults is given in more detail in Table. 3-1.
Broadcast tube receivers and radios have a variety of circuits. However, despite this, the faults in them are approximately the same, because they all have components that are common in purpose. The list of the most common malfunctions and their characteristic symptoms is given in table. 3-2.
3-6. Transistor
broadcast receivers
The use of transistors, small-sized parts and printed wiring has made it possible to design a large number of different small-sized radio receivers. They are assembled mainly using a superheterodyne circuit, only some miniature ones are assembled using a direct amplification circuit.
The circuit diagrams of dual-band receivers have a lot in common. So, the mixer and local oscillator are made on the same transistor. The load of the frequency converter is a lumped selection filter (FSS). The intermediate frequency amplifier is a two-stage amplifier: one stage is performed as an aperiodic amplifier, and the second as a resonant amplifier with neutralization. A low-frequency amplifier usually consists of three stages and contains four transistors. The final stage is performed according to a push-pull circuit. All large receiver units, such as a variable capacitor (VCA), loudspeakers, band switches, are similar in design, and some of them are even of the same type.
A characteristic feature of the circuit diagrams of all-wave transistor receivers is that in them the local oscillator and mixer are assembled on separate transistors, the IF amplifier consists of three stages and there is a power supply voltage stabilization circuit.
Circuits with a separate local oscillator and mixer provide higher stability of the frequency converter. Increasing the number of IF amplifier cascades increases the sensitivity and selectivity of the receiver. The power supply voltage stabilization circuit increases the stability of the local oscillator when the supply voltage changes, and also maintains the high sensitivity of the receiver when the batteries are discharged. The circuit is assembled using one transistor of type P40, P41 and a silicon diode of type D101, D220, etc. Some receivers, for example “Ocean”, use a more complex circuit using two transistors of type MP41, MP37 and a zener diode of type 7GE2A-S. Stabilized voltage powers the collector and base circuits of the frequency converter and local oscillator, as well as the bias circuits of the amplifier transistors.
Transistor receivers are equipped with an internal magnetic antenna designed to receive radio broadcasting stations in the DV and SV bands. Some models have a socket for connecting an external antenna. us, which slightly increases the sensitivity of the receiver. All-wave receivers for receiving radio broadcasting stations in the HF and VHF ranges have a whip telescopic antenna.
Some receivers have a socket for connecting a small-sized telephone-headphone of the TM-4 type. When you connect a phone, the speakerphone is automatically turned off. The receiver housings are made of impact-resistant plastics in a variety of colors, and the front grille that covers the loudspeaker is made of plastic or metal with a silver or gold finish. For carrying, some receivers are supplied with leather cases with a strap.
In high-frequency cascades of receivers, transistors such as P401, P402, P403, P422, P423, GT309 (A - E), GT310 (A - E), GT313 (A, B), GT322 (A - B), KT315 (A - D) are used ). Detection is carried out by semiconductor diodes: in AM detector circuits - germanium point diodes of types D1, D2 and D9; in the FM detector circuits - germanium point diodes of types D9, D18 and D20; in the AGC circuit and amplitude limiters of the signal - diodes of types D9, D18, silicon DYuZ, D104 and germanium planar D7; in the supply voltage stabilizer circuits of the basic circuits of the IF and local oscillator amplification path - silicon point diodes of types D101 and D220, selenium zener diodes of types 7GE1A-S, 7GE2A-S and silicon zener diodes of types D809, D814 and D815; in the circuits of stabilizers of power supplies and rectifiers of chargers - germanium planar diodes of type D7 and silicon zener diodes of types KS156A, KS168A; The following transistors are used in LF amplifier circuits: P13(A, B), P14(A, B) P15(A B) P25(A, B), P37(A, B), P38A, P201, P202, P203, P213( A, B), P216GA B), MP25(A, B), MP37(A, B), MP38A, MP39(A, B), MP40(A, B) MP41A. GT108(A - E), GT109(A - E), GT402(A, B), GT403, GT404(A, B).
For portable transistor radios, issues of reducing weight and dimensions are of no small importance. This problem is solved by using small-sized components and parts. However, the most effective solution is achieved by using integrated circuits, in which resistors, capacitors, and transistors are made in a thin slab of single-crystal semiconductor. Hybrid integrated circuits of the K224 and K237 series are used in transistor broadcast receivers. Microcircuits have a relatively low cost, high noise immunity and can operate in difficult temperature conditions. More details about integrated circuits are described in the seventh chapter.
Based on these microcircuits, portable radio receivers of class III “Ural-301”, “Ural-302”, “Orion-301”, radio receivers of class II “Ukraine-201”, “Meridian-201”, “Meridian-202”, “Geologist” are produced " and etc.
reference publications. M., Book. 1981. 114 p.pdf Bakhturina... V.A. Analog integrated circuits for domesticradio equipment. Directory. M., Publishing house... M., 2005. html Joseph Brodsky. Nobel lecture. Library...
Informationbook Household receiving and amplifying radio equipment Householdradio equipment (Brodsky M.A.) Householdradio equipment And...
Elements and parts of amateur radio receivers ( Informationbook) (Enyutin V.V.) Subways (... A.-Y.K.) Household receiving and amplifying radio equipment. Directory (Alekseev Yu. P.) Householdradio equipment (Brodsky M.A.) Householdradio equipment And...
60) M 1971 Brodsky, M.A. Color televisions... 1980 Gromov, N.V. TVs: Informationbook L 1979 Gruev, I.D. ... Lepaev, D.A. Repair household electrical appliances, electric players and..., V.D. Inspection and testing radio equipment M 1970 Manovtsev, A.P. ...
Electric current, flowing in any conductor, generates an electromagnetic field that spreads in the space surrounding it.
If this current is alternating, then the electromagnetic field is capable of inducing (inducing) E.M.F. in another conductor located at some distance - electrical energy is transferred over a distance.
This method of energy transfer has not yet received widespread use - losses are very high.
But to transmit information, it has been used for more than a hundred years, and very successfully.
For radio communication, electromagnetic oscillations are used, the so-called radio frequency range, directed into space - radio waves. For the most effective radiation into space, antennas of various configurations are used.
The simplest antenna is a half-wave vibrator, consisting of two pieces of wire directed in opposite directions, in the same plane.
Their total length is half the wavelength, and the length of an individual segment is a quarter. If one end of the vibrator is directed vertically, the ground can be used instead of the second, or even the common conductor of the transmitter circuit.
For example, if the length of a vertical antenna is 1 meter, then for a radio wave 4 meters long (VHF band) it will present the greatest resistance. Accordingly, the efficiency of such an antenna will be maximum - precisely for radio waves of this length, both during reception and transmission.
To tell the truth, in the VHF range, the most reliable reception should be observed when the antenna is positioned horizontally. This is due to the fact that transmission in this range is, in fact, most often carried out using horizontally located half-wave vibrators. Therefore, a half-wave vibrator (and not a quarter-wave vibrator) will be a more efficient receiving antenna.
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Despite the abundance of mobile devices capable of receiving signals from FM radio stations and playing audio and video, radios are still popular. A musical background in the house, in the country, in nature or on a trip is good, but if it is also diluted with news releases and the voices of DJs, then this is generally wonderful.
And for those who remain fans of radio and, in addition to music content, like to listen to more serious stations, they cannot do without a receiver. To do this, it’s worth understanding a little and remembering some of the subtleties of how to choose a radio receiver so that it best suits your needs.
Today, the rare tape recorder, player, radio tape recorder or cell phone is not equipped with a built-in radio. But for some, the capabilities of the proposed FM band are not enough, but for others, the compactness, ease of operation and affordable price of the device are much more important. Modern radios have high-quality stereo sound and allow you to listen to radio stations from all over the world, continuously broadcasting news and music. They still remain in demand among summer residents, motorists, housewives and office workers who do not have time to track news and replace songs in their favorite player.
What is important to know about how to choose the best quality radio without resorting to the services of a sales consultant. Before you go to the store to buy a radio, you need to answer the question, where exactly will it be used? In a city apartment, in a country house, or do you plan to constantly take it on trips or car trips? By answering this question, you can understand the appearance and functionality of the device. Then it’s worth determining in what range it should work. After this, it is enough to compare the technical characteristics of the selected models to determine the most suitable one.
You should not write off the appearance of the device, because it is purchased for personal use. If you are choosing a radio for your home, it is better if the model can fit into the design of the room, and the variety of cases and colors of portable models will allow you to choose the best option that will easily fit into any image.
All radios are divided into stationary models and portable.
Stationary radios have fairly substantial dimensions and weight, which are compensated by excellent sound and high-quality signal. Most often, radio amateurs choose such receivers for use at home.
Portable models are divided into portable and camping and are compact in size, light weight and self-powered. They are easy to transport and therefore portable models are most often chosen for traveling or trips out of town. The miniature size of camping radio models costs a little more money, but this is more than compensated by the ability to conveniently carry the device in a small backpack, around the neck or even on the wrist (using a special loop strap). Portable models are usually a little larger and more powerful, which is why they are often chosen for a summer house or country house.
A high-quality radio receiver is made of impact-resistant plastic. And when choosing a portable model, it is better to choose one with a moisture-resistant and waterproof case, and ideally also with a protective case included.
One of the most important factors when choosing a radio is the range of frequencies it receives.
If mobile phones are only able to pick up short FM waves, which are where all the popular domestic music radio stations are located (87.5-108 MHz), then most inexpensive radios can also pick up mid-range AM signals.
To listen to foreign radio stations, you must choose a radio receiver designed to receive both the FM band and long- and medium-wave signals (LW and MW).
The serious radio listener needs an all-wave receiver capable of receiving signals in all broadcast bands, including long wave and VHF (65-74 MHz). If the radio receiver will mostly be used outside the city, then only VHF will help there (the reception radius of the FM range is limited to 20 km from the radio point).
Fans of listening to conversations between dispatchers and pilots should think about an all-wave receiver that supports operation in the aviation range, but this is already in the category of professional radio equipment.
How high-quality a radio signal a radio receiver will receive depends on the type of antenna installed in it, as well as two important characteristics - sensitivity and selectivity.
Antennas can be built-in or external. When choosing a stationary model equipped with a built-in internal antenna, you don’t have to worry - it will provide the owner with high-quality and reliable signal reception.
The small size of portable receivers does not allow them to be equipped with internal antennas; either metal telescopic antennas or wired ones (for example, headphones in a mobile phone that act as an antenna) are responsible for receiving the signal. Most often they work only with the FM range and are not able to provide reliable signal reception. When choosing between portable models with a telescopic or wired antenna, preference should be given to the second option, which is characterized by greater durability and quality of work. By purchasing a radio receiver in a store (this method will not work via the Internet), you can check the quality of the antenna (it is better if it is in the form of a thin metal tube rather than a wire). To do this, just turn on the device and move it. If everything is in order, the radio broadcast will be clear of the rustling and crackling of the swinging antenna. The performance of a telescopic antenna can be significantly improved by attaching a piece of insulated copper wire (2-3 meters long) to it. True, this can only be done if the receiver is used indoors.
Depending on the adjustment method, radios are divided into digital and analog. Analog models have a mechanical tuning scale, and the selection of the desired radio station is done the old-fashioned way, by rotating the tuning wheel or slider. Such a receiver is cheaper and is an excellent option for those who listen to the same wave all the time and rarely change radio stations. The disadvantage of analog models is inaccuracy in determining the range and lack of memory.
But for those who like to surf the radio waves in search of their favorite songs or news, a digital receiver with automatic frequency search will be more convenient and useful. To turn on the desired radio station, just press a button and the only thing the owner will have to worry about is that there may not be enough memory cells for everyone (depending on the model, there can be from ten to several hundred). Unlike analog models, digital radios are equipped with LCD monitors, which display information about the frequency of the selected radio station, date, time, etc. In addition, they usually have a set of additional functions, the most common of which are: alarm clock (with the ability to program the signal), timer, search and charge indicator.
Modern digital radios support MP3 and may have USB, SD/MMC and Aux connections. Depending on the design, a radio receiver can not only receive a signal, but also filter it by frequency, amplify it, and even digitize it, converting the signal into analog form.
Sound quality is one of the most important characteristics of any radio. It depends on the size of the speakers, as well as the type of sound of the receiver. Like any other speaker system, a radio can produce both simple mono sound and more advanced stereo sound. It can be created either through two external speakers or through headphones (a standard 3.5 mm jack for connecting which is available on all receivers without exception). At the same time, do not forget that the sound quality (as well as the price of the receiver) depends on the size of the speakers; the larger they are, the better the sound and the more expensive the radio. If simple and unpretentious mono sound is enough for you, then you shouldn’t overpay for a more expensive stereo model.
If, when purchasing a stationary radio, the ability to use both mains power and batteries is not very important, then for portable models, the presence of an autonomous operating mode is very important. It can be provided by both a built-in battery and a set of batteries. In terms of reliability, standard alkaline batteries can be placed in first place, built-in batteries in second place, and the use of solar panels in third place. The number and size of batteries used directly depends on the power consumption of the receiver; the higher it is, the more and larger they are. On average, a set of batteries is enough to ensure uninterrupted operation of the radio for 15-35 hours. In this case, the most expensive mode of operation is in the FM frequency range.
When choosing a portable radio, it is best to give preference to models with dual power supply: those that can be powered from the network (have a connector for connecting an AC adapter) and from batteries/rechargeable batteries. Thus, while in the house you can save energy from autonomous power sources and listen to music by connecting the radio to the mains.
Having familiarized yourself with the important selection criteria in the article, it is easier to navigate how to choose a radio receiver of a suitable model. It is important to determine for yourself which technical characteristics of the radio receiver are the most preferred and most important, and which are of secondary importance. This will allow you to select the optimal radio model without errors. For some, the best will be a rare (or not so rare) model with analog mechanical control. Some will prefer an electronic receiver with a display, a variety of control buttons and a decent set of additional functions, and for some, the ideal solution would be the simplest, field-resistant, cheap Chinese receiver, capable of picking up just a couple of nearby radio stations and capable of working for a long time without replacing batteries. .
