Practice radio as it is
All of us are daily confronted with different types of radio communications and wireless data transmission. What are we facing there: we are practically riddled with radio waves of different frequencies, modulations and tensions (except, perhaps, for a case if we are not inside the “Faraday cage”). Here, in Habré, by virtue of IT orientation, there are a lot of articles about types of communication and data transmission, about various telecoms, about highways and “last miles”, and there is a lot more about what is directly or indirectly related to communication both wired and wireless.
Also, for sure, almost all habravchanam in schools, physics lessons, talked about oscillatory circuits, the propagation and wavelength, and other processes underlying the technologies of any radio and wireless communications.
However, having searched by Habra, I still have not found a single article that would tell about radio communications from a household and amateur point of view. But if you approach the radio communication with just such a domestic outlook, for some it can become a convenient, and sometimes even an indispensable assistant in many matters, and for others it can turn into an interesting hobby or hobby. It is with such intentions that I want to try today to simply and easily talk about radio communications, about how it is in life, about what I myself had a place to face and learn about.
Quite a bit of theory in free presentation.
')
To begin with - ranges. Consider the ranges of radio waves and choose those that will interest us from a practical point of view. Wikipedia leads GOST, in which radio waves are divided into the following ranges, based on the wavelength:
- 3 kHz - 30 kHz - Ultra-long waves.
- 30 kHz - 300 kHz - Long waves.
- 300 kHz - 3 MHz - Medium waves.
- 3 MHz - 30 MHz - Short waves.
- 30 MHz - 300 MHz - Meter waves.
- 300 MHz - 3 GHz - Decimeter waves.
- 3 GHz - 300 GHz - Centimeter waves.
The definition of the wavelength can be read in Wikipedia, and I will only write a simple and understandable thesis - the shorter the wavelength - the less it is susceptible to interference and decay, the penetrating power increases, the envelope decreases. That is, if the wavelength is 11 meters (27 MHz), then this wave easily bends around dense clusters of trees in the forest and finds a way for propagation, but to increase the communication range in open space, an increase in transmitter power is required. And a wave length of, for example, 70 cm (433 MHz) will practically not bend around trees, but will be propagated solely due to the gaps between the trees, its penetrating ability and the possibility of multiple reflections. However, due to its noise immunity and low attenuation, in open space, the communication range will be limited only to the line of sight, with low transmitter power.
It is worth adding, however, a small caveat: the effects of radio waves passing through the short wave bands are due to multiple reflections from the Earth’s atmosphere, and sometimes there are situations where you can absolutely calmly establish a connection with a correspondent located many thousands of kilometers away. in a couple of kilometers - not to hear at all. However, this phenomenon is closely related to natural factors, it is not constant and little predictable, therefore, for household use this effect is extremely unreliable to use.
I will say right away: we will touch on short waves a bit, and closely consider meter and decimeter waves. We will reject the rest due to the complexity of the equipment, antenna farming, difficulties of use, and simply inconvenience in everyday life. Some will argue with me that in many cases only centimeter waves are acceptable for data transmission, someone will say that only short waves are good for communication over long distances, and these people will be right. But now we are considering the most simple and affordable species, from the point of view of a simple man in the street.
Smoothly go to the specifics
By virtue of the theoretical knowledge discussed above, we summarize the intermediate result: we are interested in the UHF, meter, and a small part of the range of short radio waves. Briefly, by theses, on the selected ranges:
- Short waves : 3 MHz - 30 MHz. In this range, there are professional radio amateurs (the beginning of the range, from 3 MHz), using expensive equipment, huge antennas with professional skills and knowledge, and serious structures that require communication at ultra-long distances, such as Arctic expeditions. At the end of this range, frequencies are allocated for domestic and civil use.
- CB 27 MHz. Here, the wavelength reaches 11 meters (the effective antenna has a physical length equal to the length of the radio wave, that is, approximately 2.7 meters). Surely, many of you have seen taxi cars with a long whip on the roof - this is the antenna for this range. In the nineties, many taxi companies and people involved in private carriage, chose this range, due to the relative availability and reasonable price of equipment, as well as the lack of need to get the status of amateur radio to use these frequencies. For use in the city - not the best choice, because we remember that this range is extremely susceptible to interference, which in the city is very much from the mass of electrical devices and power lines.
- Meter waves : 30 MHz - 300 MHz. This range is divided into several subranges, including LowBand (30-50 MHz, used in Soviet times almost everywhere for public services, ambulance services, etc., in areas used to this day) and the so-called "2 meter" range ( 136-174 MHz), which is so named for its wavelength. In the 2 meter range, there are city and federal services, such as fire brigade, emergency ministry and other. There are also free frequencies that are issued on a commercial basis to organizations and enterprises. In my city, one of the taxi companies works in this range, very pleased with the quality of communication, compared to CB (27 MHz), which is used by the rest of the taxi fleets, as free. Also in the range of "2 meters" there is a small piece, dedicated to radio amateurs (144-146 MHz). These frequencies can legally be used by any person who has received a radio amateur category and call sign signal, adhering to the rules of amateur communication. Using directional antennas with a high installation point, even with a small radiated power, you can establish communications for dozens and, under favorable conditions, even hundreds of kilometers. It is also worth mentioning the air band (118-136 MHz), everything is serious here, a great responsibility and reliable communication.
- Decimeter waves : 300 - 3000 MHz. In this range, there are many different radio stations and communications equipment, we consider only the part of the band that is interesting for us, namely, 400-470 MHz, which was called “70 centimeters” due to its wavelength. Due to the optimal characteristics for use in a large industrial city (good noise immunity, long-range distribution in radio visibility conditions at low power), many large services in large cities are switching to or switching to this frequency range. Here we can’t do without the use of “repeaters” - special signal transceivers installed at the highest points, having high-quality and sensitive antennas, and accordingly capable of receiving and transmitting a signal over long distances (remember: in the presence of direct radio visibility for these frequencies, the signal extends far and without attenuation, even at low power). But repeaters are a separate conversation, I would not want to touch them in today's article, because this is a very interesting topic, and it should be described separately.
We have come to the most interesting part of the article: in the range of “70 centimeters” there are dedicated frequency bands, both for official radio amateurs and for free use by everyone (on a non-commercial basis). For radio amateurs, frequencies of 430-440 MHz are set aside, 433.075 MHz - 434.775 MHz (grid of 69 channels with a 25 kHz step, LPD) and 446.00625 - 446.09375 MHz of a grid of 8 channels with a step of 12.5 kHz, PMR for residential use. It was with a set of unpretentious radio stations, bought in one of the shops of cellular communication and began my closer acquaintance, therefore, we consider the standards LPD and PMR.
Household communications
LPD - stands for Low Power Device, that is, "devices with low radiation power." This is exactly the case - according to the standard, the power emitted by the transmitter of a radio station of the LPD standard should not exceed 10 mW, which is extremely small, although even this is enough to communicate at a distance of several kilometers, under direct visibility conditions. In fact, most of the semi-toy radio sets on sale have much more power, although they are certified as LPD. As the saying goes, “the severity of our laws is compensated for by the non-necessity of their execution”, which is what suppliers use for certification: radio stations have a low power level through the menu, the product is certified, and then, just as well, through the standard menu, the normal power returns, as a rule 2-4 watts. This power is enough to communicate for 10-12 kilometers in good conditions, for example, over a lake, or from a hill (do not forget about the poor envelope of obstacles at a given wavelength).
PMR - stands for Private Mobile Radio, that is, radio communications for private use. According to the standard, the allowed radiation power here is already greater than that of the LPD, namely 0.5 Watt. However, unlike LPD, this power is usually honest, a rare PMR radio station has a capacity of more than 1 Watt, since this standard is permitted in many European countries, and certification is more serious there. Also, the PMR frequency range is narrower, and only 8 channels are “placed” in it (against 69 channels for LPD).
It was with these standards (or more precisely, the set of the simplest radio stations from the cellular communications store) that began my more intimate acquaintance with radio communications. But soon the disappointment of a rather poor quality of devices came, they were more like “toys” than something relatively serious. However, I was interested in radio communication, and I ordered from one store that was not well-known in radio amateur circles, a good portable radio station of an amateur level, in which there were two bands at once, namely “2 meters” (136-174 MHz) and “70 centimeters” ( 400-470 MHz). In my humble estimate, these are currently the most popular and accessible to a wide range of users ranges. The equipment is relatively affordable (especially Chinese, the price is low, the quality is high), which has serious functionality and has a pleasant appearance. I also can not help but notice that on the indicated ranges the antenna can actually be portable (unlike, for example, from CB, we recall the wavelength).
For half a year of using the radio station, I managed to get bored to communicate only on “civil frequencies” (LPD and PMR, all channels of these two grids are easily tuned in the range of “70 centimeters”), it was decided to receive the amateur radio category, call sign, registration of the radio station. Now I am an official radio amateur, it has become my hobby. Technologies do not stand still, and with the help of a pocket portable radio station I can carry out communications with a range of several thousand kilometers (via artificial Earth satellites), communicate with the crew of the ISS, and other radio amateurs (at the allocated frequencies).
And of course - it is convenient and easy! My family is equipped with simple, small (less mobile phone), inexpensive Chinese radio stations that are broadcasted on free LPD channels of the range, and depending on whether we go to the forest for mushrooms, or to shop for shopping - we are always in touch.
The plans include the creation of a single city-wide information channel of communication for car owners, tourists, and just residents of the city, which will be available even to people with inexpensive radio stations from cellular stores. But this is a separate conversation, there is a whole concept.
Thank you for attention!
PS The article is presented in free form and using simplifications in some concepts and details. For encyclopedic accuracy does not claim.
Also, for sure, almost all habravchanam in schools, physics lessons, talked about oscillatory circuits, the propagation and wavelength, and other processes underlying the technologies of any radio and wireless communications.
However, having searched by Habra, I still have not found a single article that would tell about radio communications from a household and amateur point of view. But if you approach the radio communication with just such a domestic outlook, for some it can become a convenient, and sometimes even an indispensable assistant in many matters, and for others it can turn into an interesting hobby or hobby. It is with such intentions that I want to try today to simply and easily talk about radio communications, about how it is in life, about what I myself had a place to face and learn about.
Quite a bit of theory in free presentation.
')
To begin with - ranges. Consider the ranges of radio waves and choose those that will interest us from a practical point of view. Wikipedia leads GOST, in which radio waves are divided into the following ranges, based on the wavelength:
- 3 kHz - 30 kHz - Ultra-long waves.
- 30 kHz - 300 kHz - Long waves.
- 300 kHz - 3 MHz - Medium waves.
- 3 MHz - 30 MHz - Short waves.
- 30 MHz - 300 MHz - Meter waves.
- 300 MHz - 3 GHz - Decimeter waves.
- 3 GHz - 300 GHz - Centimeter waves.
The definition of the wavelength can be read in Wikipedia, and I will only write a simple and understandable thesis - the shorter the wavelength - the less it is susceptible to interference and decay, the penetrating power increases, the envelope decreases. That is, if the wavelength is 11 meters (27 MHz), then this wave easily bends around dense clusters of trees in the forest and finds a way for propagation, but to increase the communication range in open space, an increase in transmitter power is required. And a wave length of, for example, 70 cm (433 MHz) will practically not bend around trees, but will be propagated solely due to the gaps between the trees, its penetrating ability and the possibility of multiple reflections. However, due to its noise immunity and low attenuation, in open space, the communication range will be limited only to the line of sight, with low transmitter power.
It is worth adding, however, a small caveat: the effects of radio waves passing through the short wave bands are due to multiple reflections from the Earth’s atmosphere, and sometimes there are situations where you can absolutely calmly establish a connection with a correspondent located many thousands of kilometers away. in a couple of kilometers - not to hear at all. However, this phenomenon is closely related to natural factors, it is not constant and little predictable, therefore, for household use this effect is extremely unreliable to use.
I will say right away: we will touch on short waves a bit, and closely consider meter and decimeter waves. We will reject the rest due to the complexity of the equipment, antenna farming, difficulties of use, and simply inconvenience in everyday life. Some will argue with me that in many cases only centimeter waves are acceptable for data transmission, someone will say that only short waves are good for communication over long distances, and these people will be right. But now we are considering the most simple and affordable species, from the point of view of a simple man in the street.
Smoothly go to the specifics
By virtue of the theoretical knowledge discussed above, we summarize the intermediate result: we are interested in the UHF, meter, and a small part of the range of short radio waves. Briefly, by theses, on the selected ranges:
- Short waves : 3 MHz - 30 MHz. In this range, there are professional radio amateurs (the beginning of the range, from 3 MHz), using expensive equipment, huge antennas with professional skills and knowledge, and serious structures that require communication at ultra-long distances, such as Arctic expeditions. At the end of this range, frequencies are allocated for domestic and civil use.
- CB 27 MHz. Here, the wavelength reaches 11 meters (the effective antenna has a physical length equal to the length of the radio wave, that is, approximately 2.7 meters). Surely, many of you have seen taxi cars with a long whip on the roof - this is the antenna for this range. In the nineties, many taxi companies and people involved in private carriage, chose this range, due to the relative availability and reasonable price of equipment, as well as the lack of need to get the status of amateur radio to use these frequencies. For use in the city - not the best choice, because we remember that this range is extremely susceptible to interference, which in the city is very much from the mass of electrical devices and power lines.
- Meter waves : 30 MHz - 300 MHz. This range is divided into several subranges, including LowBand (30-50 MHz, used in Soviet times almost everywhere for public services, ambulance services, etc., in areas used to this day) and the so-called "2 meter" range ( 136-174 MHz), which is so named for its wavelength. In the 2 meter range, there are city and federal services, such as fire brigade, emergency ministry and other. There are also free frequencies that are issued on a commercial basis to organizations and enterprises. In my city, one of the taxi companies works in this range, very pleased with the quality of communication, compared to CB (27 MHz), which is used by the rest of the taxi fleets, as free. Also in the range of "2 meters" there is a small piece, dedicated to radio amateurs (144-146 MHz). These frequencies can legally be used by any person who has received a radio amateur category and call sign signal, adhering to the rules of amateur communication. Using directional antennas with a high installation point, even with a small radiated power, you can establish communications for dozens and, under favorable conditions, even hundreds of kilometers. It is also worth mentioning the air band (118-136 MHz), everything is serious here, a great responsibility and reliable communication.
- Decimeter waves : 300 - 3000 MHz. In this range, there are many different radio stations and communications equipment, we consider only the part of the band that is interesting for us, namely, 400-470 MHz, which was called “70 centimeters” due to its wavelength. Due to the optimal characteristics for use in a large industrial city (good noise immunity, long-range distribution in radio visibility conditions at low power), many large services in large cities are switching to or switching to this frequency range. Here we can’t do without the use of “repeaters” - special signal transceivers installed at the highest points, having high-quality and sensitive antennas, and accordingly capable of receiving and transmitting a signal over long distances (remember: in the presence of direct radio visibility for these frequencies, the signal extends far and without attenuation, even at low power). But repeaters are a separate conversation, I would not want to touch them in today's article, because this is a very interesting topic, and it should be described separately.
We have come to the most interesting part of the article: in the range of “70 centimeters” there are dedicated frequency bands, both for official radio amateurs and for free use by everyone (on a non-commercial basis). For radio amateurs, frequencies of 430-440 MHz are set aside, 433.075 MHz - 434.775 MHz (grid of 69 channels with a 25 kHz step, LPD) and 446.00625 - 446.09375 MHz of a grid of 8 channels with a step of 12.5 kHz, PMR for residential use. It was with a set of unpretentious radio stations, bought in one of the shops of cellular communication and began my closer acquaintance, therefore, we consider the standards LPD and PMR.
Household communications
LPD - stands for Low Power Device, that is, "devices with low radiation power." This is exactly the case - according to the standard, the power emitted by the transmitter of a radio station of the LPD standard should not exceed 10 mW, which is extremely small, although even this is enough to communicate at a distance of several kilometers, under direct visibility conditions. In fact, most of the semi-toy radio sets on sale have much more power, although they are certified as LPD. As the saying goes, “the severity of our laws is compensated for by the non-necessity of their execution”, which is what suppliers use for certification: radio stations have a low power level through the menu, the product is certified, and then, just as well, through the standard menu, the normal power returns, as a rule 2-4 watts. This power is enough to communicate for 10-12 kilometers in good conditions, for example, over a lake, or from a hill (do not forget about the poor envelope of obstacles at a given wavelength).
PMR - stands for Private Mobile Radio, that is, radio communications for private use. According to the standard, the allowed radiation power here is already greater than that of the LPD, namely 0.5 Watt. However, unlike LPD, this power is usually honest, a rare PMR radio station has a capacity of more than 1 Watt, since this standard is permitted in many European countries, and certification is more serious there. Also, the PMR frequency range is narrower, and only 8 channels are “placed” in it (against 69 channels for LPD).
It was with these standards (or more precisely, the set of the simplest radio stations from the cellular communications store) that began my more intimate acquaintance with radio communications. But soon the disappointment of a rather poor quality of devices came, they were more like “toys” than something relatively serious. However, I was interested in radio communication, and I ordered from one store that was not well-known in radio amateur circles, a good portable radio station of an amateur level, in which there were two bands at once, namely “2 meters” (136-174 MHz) and “70 centimeters” ( 400-470 MHz). In my humble estimate, these are currently the most popular and accessible to a wide range of users ranges. The equipment is relatively affordable (especially Chinese, the price is low, the quality is high), which has serious functionality and has a pleasant appearance. I also can not help but notice that on the indicated ranges the antenna can actually be portable (unlike, for example, from CB, we recall the wavelength).
For half a year of using the radio station, I managed to get bored to communicate only on “civil frequencies” (LPD and PMR, all channels of these two grids are easily tuned in the range of “70 centimeters”), it was decided to receive the amateur radio category, call sign, registration of the radio station. Now I am an official radio amateur, it has become my hobby. Technologies do not stand still, and with the help of a pocket portable radio station I can carry out communications with a range of several thousand kilometers (via artificial Earth satellites), communicate with the crew of the ISS, and other radio amateurs (at the allocated frequencies).
And of course - it is convenient and easy! My family is equipped with simple, small (less mobile phone), inexpensive Chinese radio stations that are broadcasted on free LPD channels of the range, and depending on whether we go to the forest for mushrooms, or to shop for shopping - we are always in touch.
The plans include the creation of a single city-wide information channel of communication for car owners, tourists, and just residents of the city, which will be available even to people with inexpensive radio stations from cellular stores. But this is a separate conversation, there is a whole concept.
Thank you for attention!
PS The article is presented in free form and using simplifications in some concepts and details. For encyclopedic accuracy does not claim.
Source: https://habr.com/ru/post/127235/
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