I think everyone twisted the handle of the radio, switching between "VHF", "DV", "SV" and heard hiss from the speakers.
But besides deciphering cuts, not everyone understands that it hides behind these letters.
Let's get closer with radio wave theory.
Radio wave
The wavelength (λ) is the distance between adjacent crests of the waves.
Amplitude (A) is the maximum deviation from the average value with the oscillatory movement.
Period (T) - time of one complete oscillatory movement
Frequency (V) - the number of total periods per second
There is a formula that allows determining the wavelength in frequency:
Where: The wavelength (M) is equal to the ratio of the speed of light (km / h) to the frequency (kHz)
"VHF", "DV", "SV"
Super long waves - V \u003d 3-30 kHz (λ \u003d 10-100 km).They have the property to penetrate the thickness of water to 20 m and in connection with this are used to communicate with submarines, and the boat is not necessary to pop up to this depth, it is enough to throw the radio buoy to this level.
These waves can spread up to the edge of the Earth, the distance between the earth's surface and the ionosphere, represents the "waveguide" for them, along which they differ freely.
Long waves(DV) V \u003d 150-450 kHz (λ \u003d 2000-670 m). 
This type of radio wave has the properties to overeat obstacles, is used to communicate over long distances. Also has a weak penetrating ability, so if you do not have a remote antenna, you can hardly catch any radio station.
Medium waves (SV) V \u003d 500-1600 kHz (λ \u003d 600-190 m). 
These radio waves are well reflected from the ionosphere, located at a distance of 100-450 km above the surface of the Earth. The possibility of these waves is that during the daytime they are absorbed by the ionosphere and the reflection effect does not occur. This effect is used practically for communication, usually several hundred kilometers at night.
Short waves(KV) V \u003d 3-30 MHz (λ \u003d 100-10 m). 
Like medium waves, they are well reflected from the ionosphere, but in contrast to them, regardless of the time of day. They may be distributed over long distances (several thousand km) due to the reflections from the ionosphere and the surface of the Earth, such distribution is called Skachkov. Light power transmitters for this is not required.
Ultrashort waves(VHF) V \u003d 30 MHz - 300 MHz (λ \u003d 10-1 m). 
These waves can overtake obstacles in a size of several meters, and also have a good penetrating ability. Due to such properties, this range is widely used for broadcast radio. The disadvantage is their relatively fast attenuation when meeting with obstacles.
There is a formula that allows you to calculate the range of communication in the VHF range:
So for example, when radio broadcasts with the Ostankino TV bashing, a height of 500 m on a receiving antenna with a height of 10 m, a distance of communication under the condition of direct visibility will be about 100 km.
High Frequencies (HF Santimeter Range) V \u003d 300 MHz - 3 GHz (λ \u003d 1-0.1 m).
Do not envelop obstacles and have a good penetrating ability. Used in cellular networks and Wi-Fi networks.
Another interesting feature of the waves of this range is that water molecules are capable of absorbing their energy as much as possible and transform it into thermal. This effect is used in microwave ovens.
As you can see, Wi-Fi equipment and microwave ovens operate in the same range and can affect water, so sleeping in an embrace with a Wi-Fi router is not worth a long time.
Extremely high frequencies (EHF-millimeter range) V \u003d 3 GHz - 30 GHz (λ \u003d 0.1-0.01 m).
Reflected by almost all obstacles, freely penetrate through the ionosphere. At the expense of its properties are used in space communication.
AM - FM.
Often, the receiving devices have the positions of the AM-FM switches, what is it:AM. - amplitude modulation
This change in the amplitude of the carrier frequency under the action of coding oscillations, for example, the voice from the microphone.
AM is the first type of modulation invented by man. Of the disadvantages, as well as any analog type of modulation, has low noise immunity.
FM. - frequency modulation 
This is a change in the carrier frequency under the influence of coding oscillations.
Although, this is also an analog modulation type, but it has a higher noise immunity than AM and therefore is widely used in the sound of TV broadcasts and VHF broadcasting.
In fact, there are subspecies in the modulation species described, but their description is not included in the material of this article.
More Terms
Interference - As a result of reflections of waves from various obstacles, the waves fold. In the case of addition in the same phases, the amplitude of the initial wave may increase, when adding in opposite phases, the amplitude can decrease up to zero.This phenomenon is mostly manifested when receiving VHF CM and TV signal.
Therefore, for example inside the room, the quality of reception on the room antenna TV strongly "floats".
Diffraction - The phenomenon that occurs when a radio wave is met with obstacles, as a result of which the wave can change the amplitude, phase and direction.
This phenomenon explains the connection on the KV and SV through the ionosphere, when the wave is reflected from various inhomogeneities and charged particles and thereby changes the direction of distribution.
The same phenomenon explains the ability of radio waves to propagate without direct visibility, the rich earth surface. For this, the wavelength must be opposed to the obstacle.
PS:
I hope the information described by me will be useful and will bring some understanding on this topic.Analog television signal has a width of several megahertz, so the ranges of long, medium and short waves are too narrow for it. To transmit such signals, at least ultra-screwed waves are used. This situation has not changed and with the transition to digital television.
Instruction
Wave ranges allocated for television broadcast differ in different countries. In Russia, standard D is adopted for analog broadcasting on meter waves, providing 12 channels. The first of them corresponds to the frequency in 49.75 MHz to transmit the image signal and in 56.25 MHz - to transmit the sound signal. In the last one, the image and sound are transmitted, respectively, at frequencies in 223.25 and 229.75 MHz. The transmission on decimeter waves was not in all cities, but today - almost every one. Channel frequencies in this range are set by the standard K. On the first of them, carrying number 21, the frequencies in 471.25 and 477.75 MHz are provided for image signals and sound. The last channel of the range was first 41 (631.25 and 637.75 MHz), then 60 (783.25 and 789.75 MHz), and today it is a channel with number 69 (855.25 and 861.75 MHz). Image signal modulation amplitude, sound - frequency. The attentive reader considers that in all cases the difference between the frequencies for transmitting the image and sound is 6.5 MHz. In other countries, this difference may differ, which, for example, 5.5 MHz (standards B and G).
Between channels 5 and 6, as well as 12 and 21 there are large gaps. It is impossible to organize the television broadcasting on these gaps on the air - it can prevent radio broadcasting and other types of communication. But they can be broadcast on the cable, which is often practiced today. At first, televisions were unable to operate in these ranges - consoles were required. Now take these channels that received numbers from S1 to S40, almost all TVs can independently. The frequency differences for the transmission of signals of the image and sound on these channels also correspond to the standards adopted in the country.
Digital television broadcast is conducted at frequencies within an existing decimeter range, so the antennas can be used already available. Only between the antenna and the TV, it is necessary to place a decoder console, or use a TV with a built-in decoder. But thanks to the compression in digital broadcasting, the introduction of so-called cartoons is possible when several television broadcast is broadcast on one frequency channel. In the DVB-T2 standard, the compression is even more efficient than in DVB-T. For broadcasting over the cable, DVB-C and DVB-C2 standards are used.
In satellite television broadcasts used frequency ranges corresponding to units and dozens of Gigahertz. Previously, it was also analog, but frequency modulation was used to transmit image signals. Now satellite broadcast is conducted in the same ranges, but using digital standards, in particular, DVB-S and DVB-S2.
ATTENTION, only today!
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Radio waves with a frequency in the range from 3 kHz to 300 GHz belong to the electromagnetic spectrum. Other facts about radio waves are presented in this article.
Transmission of waves!
A significant discovery in the field of communications, radio waves were opened in 1867 by the Scottish physicist James Maxwell.
You ever noticed most of the devices that we use in our lives are based on the concept of data transmission through radio waves.
The television antenna takes electromagnetic waves from the television station and in turn transmits different channels. Microwave or telephone, almost all of our devices require radio waves to work or transmit data. Radio waves are used mainly to transfer information in space. Their main function is to transmit data through modulation. They have an advantage over many other types of signals due to the fact that their speed is equal to the speed of light when driving in vacuo. High transmission rates make the transfer process very efficient.
How do radio wave work?
Telecommunications in a wireless medium mainly use electromagnetic signals. The carrier signal is one of such electromagnetic signals used to transmit information in space. The bearing signal is modulated to perform various types of data. AM and FM are examples of such modulations used to broadcast radio waves. Let's consider an example to understand this concept better. The radio antenna is mandatory for receiving signals from AM and FM stations. This makes the radio capable of catching a number of signals. The radio tuner is then used to configure the required frequency. The radio transforms the received signals into the sound for the listener.
Some facts about radio waves.
◾ The length of radio waves refers to the distance from one vertex to another in the electric field of the wave. Hesitated from 1 mm to 100 kilometers.
◾ Radio frequency is the degree of proximity of these waves. The frequency of these types of waves in the range from 3 kHz to 300 GHz. The amplitude determines the height of radio waves.
◾ Length and frequency of radio waves are inversely proportional.
◾ The erroneous view is that radio waves are sound waves, they are electromagnetic waves.
◾ Radio waves can spread over long distances with minimal energy costs.
◾ Radovalna will be held from the ground to the Sun in 8 minutes.
◾ FM has a higher sound quality compared to AM.
◾ AM is cheaper than FM and can be transmitted over long distances, unchanged.
◾ Radio wave almost 100,000 times longer than the visible light wave.
◾ Radio waves can be distributed at different frequencies.
◾ Radio waves can be generated, naturally, due to the use of astronomical bodies or lightning.
◾ The use of radio waves is governed by various laws. This is carried out in order to avoid mutual interference between different frequencies.
◾ Radio waves are used in telescopes, radio, x-ray devices, cell phones, and radio-controlled toys.
◾ Astronauts, use radio waves to communicate with Earth.
◾ Airplanes and large vessels use radio compasses, during the navigation process.
◾ Antennas and telescopes also use radio waves for transmitting and receiving data.
Analog television signal has a width of several megahertz, so the ranges of long, medium and short waves are too narrow for it. To transmit such signals, at least ultra-screwed waves are used. This situation has not changed and with the transition to digital television.
Instruction
Wave ranges allocated for television broadcast differ in different countries. In Russia, standard D is adopted for analog broadcasting on meter waves, providing 12 channels. The first of them corresponds to the frequency in 49.75 MHz to transmit the image signal and in 56.25 MHz - to transmit the sound signal. In the last one, the image and sound are transmitted, respectively, at frequencies in 223.25 and 229.75 MHz. The transmission on decimeter waves was not in all cities, but today - almost every one. Channel frequencies in this range are set by the standard K. On the first of them, carrying number 21, the frequencies in 471.25 and 477.75 MHz are provided for image signals and sound. The last channel of the range was first 41 (631.25 and 637.75 MHz), then 60 (783.25 and 789.75 MHz), and today it is a channel with number 69 (855.25 and 861.75 MHz). Image signal modulation amplitude, sound - frequency. The attentive reader considers that in all cases the difference between the frequencies for transmitting the image and sound is 6.5 MHz. In other countries, this difference may differ, which, for example, 5.5 MHz (standards B and G).
Between channels 5 and 6, as well as 12 and 21 there are large gaps. It is impossible to organize the television broadcasting on these gaps on the air - it can prevent radio broadcasting and other types of communication. But they can be broadcast on the cable, which is often practiced today. At first, televisions were unable to operate in these ranges - consoles were required. Now take these channels that received numbers from S1 to S40, almost all TVs can independently. The frequency differences for the transmission of signals of the image and sound on these channels also correspond to the standards adopted in the country.
Digital television broadcast is conducted at frequencies within an existing decimeter range, so the antennas can be used already available. Only between the antenna and the TV, it is necessary to place a decoder console, or use a TV with a built-in decoder. But thanks to the compression in digital broadcasting, the introduction of so-called cartoons is possible when several television broadcast is broadcast on one frequency channel. In the DVB-T2 standard, the compression is even more efficient than in DVB-T. For broadcasting over the cable, DVB-C and DVB-C2 standards are used.
In satellite television broadcasts used frequency ranges corresponding to units and dozens of Gigahertz. Previously, it was also analog, but frequency modulation was used to transmit image signals. Now satellite broadcast is conducted in the same ranges, but using digital standards, in particular, DVB-S and DVB-S2.
Analog television signal has a width of several megahertz, so the ranges of long, medium and short waves are too narrow for it. To transmit such signals, at least ultra-screwed waves are used. This situation has not changed and with the transition to digital television.
