August 29, 2011 at 11:14The practice of radio as it is
Every day we are faced with different types of radio communications and wireless data transmission. But what are we encountering there: we are practically penetrated by radio waves of different frequencies, modulations, and intensities (with the exception, perhaps, of the case if we are not inside the "Faraday cage"). Here, on the hub, due to its IT orientation, there are a lot of articles about types of communication and data transfer, about various telecoms, about highways and “last miles”, and much more about what has a direct or indirect relation to communication, like to wired or wireless.
Also, for sure, almost all the residents of the schools, in physics classes, were told about the oscillatory circuits, the propagation and wavelength, and other processes that underlie the foundations of any technology of radio and wireless communications.
However, after searching by the Habr, I never found a single article that would talk about radio communications from a household and amateur point of view. But if you approach radio communication with just such an everyday look - for some it can become a convenient and sometimes irreplaceable assistant in many matters, and for others it can turn into an interesting hobby or hobby. It is with these 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 to face and learn about.
Quite a bit of theory in a free presentation.
For starters, ranges. Consider the ranges of radio waves and choose those that will interest us from a practical point of view. Wikipedia gives GOST, in which radio waves are divided into the following ranges, based on wavelength:
- 3 kHz - 30 kHz - Extra-long waves.
- 30 kHz - 300 kHz - Long waves.
- 300 kHz - 3 MHz - Medium waves.
- 3 MHz - 30 MHz - Shortwave.
- 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 on Wikipedia, but I will only write a simple and understandable thesis - the shorter the wavelength - the less it is subject to noise and attenuation, penetration 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 path for propagation, but at the same time, to increase the communication range in open space, an increase in the transmitter power is required. And a wave with a length of, for example, 70 cm (433 MHz) will practically not bend around trees, but will propagate solely due to the gaps between the trees, its penetrating ability and the possibility of reflection. However, due to its noise immunity and low attenuation,
True, it’s worth adding a small disclaimer here: on the shortwave ranges, the effects of radio waves are observed due to multiple reflections from the Earth’s atmosphere, and sometimes situations arise where you can absolutely safely establish contact with a correspondent who is many thousands of kilometers away, and a friend who’s in a couple of kilometers - not to hear at all. But, this phenomenon is closely related to natural factors, inconsistent and little predictable, therefore, for domestic use this effect is extremely unreliable.
I will say right away: we will touch a little on short waves, and take a close look at meter and decimeter waves. We will discard the rest due to the complexity of the equipment, antenna management, difficulties of use, and simply inconvenience in everyday life. Someone will argue with me that in many cases only centimeter waves are acceptable for data transmission, someone will say that only short waves are well suited for communication over long distances, and these people will be right. But now we are considering the simplest and most affordable species, from the point of view of a simple layman.
We proceed smoothly to the specifics.
By virtue of the theoretical knowledge discussed above, let us summarize the intermediate result: we are interested in the ranges of decimeter, meter, and a small part of the range of short radio waves. Briefly, theses, on the selected ranges:
-Short waves : 3 MHz - 30 MHz. Both professional radio amateurs (beginning of the range, from 3 MHz), using expensive equipment, huge antennas with professional skills and knowledge, and serious structures that require communication over extremely long distances, such as Arctic expeditions, work in this range. 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 ¼ the length of the radio wave, that is, about 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 engaged in private transport chose this range, due to the relative availability and affordable price of equipment, as well as the lack of the need to obtain a ham status to use these frequencies. For use in the city is 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 subbands, including LowBand (30-50 MHz, which was used almost everywhere in Soviet times for utilities, ambulances, etc., and is still used in the regions) and the so-called “2 meters” range ( 136-174 MHz), which is so named for its wavelength. In the “2 meters” range, city and federal services operate, such as fire brigades, the Ministry of Emergencies and others. There are also free frequencies that are issued on a commercial basis to organizations and enterprises. In my city, one of the taxi companies operates in this range, they are very pleased with the quality of communication, compared to CB (27 MHz), which is used by other taxi fleets as free. Also in the "2 meters" range there is a small piece allocated for radio amateurs (144-146 MHz). These frequencies can legally be used by any person who has received an amateur radio category and callsign, adhering to the rules of amateur communication. Using directional antennas with a high installation point, even with a small radiated power, it is possible to establish communications for tens, and in good conditions, for hundreds of kilometers. It is also worth mentioning the air band (118-136 MHz), everything is serious here, great responsibility and reliable communication.
- decimeter waves: 300 - 3000 MHz. Many different radio stations and communication equipment work in this range, we will only consider the part of the range that is of interest to us, namely 400-470 MHz, which has received the name “70 centimeters” due to its wavelength. Due to the optimal characteristics for use in a large industrial city (good noise immunity, long-distance distribution in conditions of radio visibility at low power), many large services in large cities are switching or switched to this frequency range. Here you can’t do without the use of “repeaters” - special signal transceivers installed at the highest points, with high-quality and sensitive antennas, and accordingly capable of receiving and transmitting a signal over long distances (do not forget: in the presence of direct radio visibility for these frequencies, the signal propagates far and without attenuation, even at low power). But repeaters are a separate conversation, I would not want to touch on them in today's article, because this is a very interesting topic, and it should be described separately.
We came to the most interesting part of the article: in the “70 centimeters” range there are allocated frequency bands, both for official radio amateurs and for free use by everyone (on a non-commercial basis). Frequencies of 430-440 MHz are allocated for hams, 433.075 MHz - 434.775 MHz (a grid of 69 channels with a step of 25 kHz, LPD) and 446.00625 - 446.09375 MHz a grid of 8 channels with a step of 12.5 kHz, PMR) are allocated. It was with a set of simple radio stations, bought in one of the mobile phone stores, that my closer acquaintance began, therefore we will consider the LPD and PMR standards.
Household Communication
LPD- stands for Low Power Device, that is, "devices with low radiation power." That is exactly so - according to the standard, the power radiated 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 for communication at a distance of several kilometers, in direct visibility conditions. In fact, most of the semi-toy sets of radio stations on sale have significantly more power, although they are certified as LPD. As the saying goes, “the rigor of our laws is compensated by the non-bindingness of their enforcement”, which is what suppliers use for certification: radio stations exhibit a low level of power through the menu, the product passes certification, and then, in the same way through the standard menu, normal power returns, usually 2-4 watts.
PMR - stands for Private Mobile Radio, that is, radio communications for private use. By standard, the permitted radiation power here is already greater than that of LPD, namely 0.5 watts. However, unlike LPD, this power is usually honest, a rare PMR has a power of more than 1 Watt, since this standard is allowed in many European countries, and certification takes place more seriously. 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 rather, with a set of the simplest radio stations from a mobile phone store) that my more intimate acquaintance with radio communications began. But soon there was a disappointment from the rather poor quality of the devices, they were more likely “toys” rather than something relatively serious. However, I was interested in radio communications, and I ordered from a store well-known among amateur radio enthusiasts, a good portable radio station, already 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 assessment - 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.
For half a year of using the radio station, I managed to get tired of communicating only on “civilian frequencies” (LPD and PMR, all channels of these two grids are easily tuned in the “70 centimeters” range), it was decided to receive the amateur radio category, call sign, and registration of the radio station. Now I am an official radio amateur, it has become my hobby. The technologies do not stand still, and with the help of a handheld portable radio station I can make communications with a range of several thousand kilometers (via artificial Earth satellites), communicate with the ISS crew, and other amateur radio enthusiasts (at frequencies allocated for this).
And of course - it’s convenient and easy! My family is equipped with simple, small (less than a mobile phone), inexpensive Chinese radio stations that are flashed to free channels of the LPD range, and depending on whether we go to the forest for mushrooms or to the store for shopping, we are always in touch.
The plans include the creation of a single citywide information communication channel for car owners, tourists, and just residents of the city, which will be available even to people with inexpensive sets of radio stations from mobile phone 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. It does not pretend to be encyclopedic.
Also, for sure, almost all the residents of the schools, in physics classes, were told about the oscillatory circuits, the propagation and wavelength, and other processes that underlie the foundations of any technology of radio and wireless communications.
However, after searching by the Habr, I never found a single article that would talk about radio communications from a household and amateur point of view. But if you approach radio communication with just such an everyday look - for some it can become a convenient and sometimes irreplaceable assistant in many matters, and for others it can turn into an interesting hobby or hobby. It is with these 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 to face and learn about.
Quite a bit of theory in a free presentation.
For starters, ranges. Consider the ranges of radio waves and choose those that will interest us from a practical point of view. Wikipedia gives GOST, in which radio waves are divided into the following ranges, based on wavelength:
- 3 kHz - 30 kHz - Extra-long waves.
- 30 kHz - 300 kHz - Long waves.
- 300 kHz - 3 MHz - Medium waves.
- 3 MHz - 30 MHz - Shortwave.
- 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 on Wikipedia, but I will only write a simple and understandable thesis - the shorter the wavelength - the less it is subject to noise and attenuation, penetration 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 path for propagation, but at the same time, to increase the communication range in open space, an increase in the transmitter power is required. And a wave with a length of, for example, 70 cm (433 MHz) will practically not bend around trees, but will propagate solely due to the gaps between the trees, its penetrating ability and the possibility of reflection. However, due to its noise immunity and low attenuation,
True, it’s worth adding a small disclaimer here: on the shortwave ranges, the effects of radio waves are observed due to multiple reflections from the Earth’s atmosphere, and sometimes situations arise where you can absolutely safely establish contact with a correspondent who is many thousands of kilometers away, and a friend who’s in a couple of kilometers - not to hear at all. But, this phenomenon is closely related to natural factors, inconsistent and little predictable, therefore, for domestic use this effect is extremely unreliable.
I will say right away: we will touch a little on short waves, and take a close look at meter and decimeter waves. We will discard the rest due to the complexity of the equipment, antenna management, difficulties of use, and simply inconvenience in everyday life. Someone will argue with me that in many cases only centimeter waves are acceptable for data transmission, someone will say that only short waves are well suited for communication over long distances, and these people will be right. But now we are considering the simplest and most affordable species, from the point of view of a simple layman.
We proceed smoothly to the specifics.
By virtue of the theoretical knowledge discussed above, let us summarize the intermediate result: we are interested in the ranges of decimeter, meter, and a small part of the range of short radio waves. Briefly, theses, on the selected ranges:
-Short waves : 3 MHz - 30 MHz. Both professional radio amateurs (beginning of the range, from 3 MHz), using expensive equipment, huge antennas with professional skills and knowledge, and serious structures that require communication over extremely long distances, such as Arctic expeditions, work in this range. 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 ¼ the length of the radio wave, that is, about 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 engaged in private transport chose this range, due to the relative availability and affordable price of equipment, as well as the lack of the need to obtain a ham status to use these frequencies. For use in the city is 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 subbands, including LowBand (30-50 MHz, which was used almost everywhere in Soviet times for utilities, ambulances, etc., and is still used in the regions) and the so-called “2 meters” range ( 136-174 MHz), which is so named for its wavelength. In the “2 meters” range, city and federal services operate, such as fire brigades, the Ministry of Emergencies and others. There are also free frequencies that are issued on a commercial basis to organizations and enterprises. In my city, one of the taxi companies operates in this range, they are very pleased with the quality of communication, compared to CB (27 MHz), which is used by other taxi fleets as free. Also in the "2 meters" range there is a small piece allocated for radio amateurs (144-146 MHz). These frequencies can legally be used by any person who has received an amateur radio category and callsign, adhering to the rules of amateur communication. Using directional antennas with a high installation point, even with a small radiated power, it is possible to establish communications for tens, and in good conditions, for hundreds of kilometers. It is also worth mentioning the air band (118-136 MHz), everything is serious here, great responsibility and reliable communication.
- decimeter waves: 300 - 3000 MHz. Many different radio stations and communication equipment work in this range, we will only consider the part of the range that is of interest to us, namely 400-470 MHz, which has received the name “70 centimeters” due to its wavelength. Due to the optimal characteristics for use in a large industrial city (good noise immunity, long-distance distribution in conditions of radio visibility at low power), many large services in large cities are switching or switched to this frequency range. Here you can’t do without the use of “repeaters” - special signal transceivers installed at the highest points, with high-quality and sensitive antennas, and accordingly capable of receiving and transmitting a signal over long distances (do not forget: in the presence of direct radio visibility for these frequencies, the signal propagates far and without attenuation, even at low power). But repeaters are a separate conversation, I would not want to touch on them in today's article, because this is a very interesting topic, and it should be described separately.
We came to the most interesting part of the article: in the “70 centimeters” range there are allocated frequency bands, both for official radio amateurs and for free use by everyone (on a non-commercial basis). Frequencies of 430-440 MHz are allocated for hams, 433.075 MHz - 434.775 MHz (a grid of 69 channels with a step of 25 kHz, LPD) and 446.00625 - 446.09375 MHz a grid of 8 channels with a step of 12.5 kHz, PMR) are allocated. It was with a set of simple radio stations, bought in one of the mobile phone stores, that my closer acquaintance began, therefore we will consider the LPD and PMR standards.
Household Communication
LPD- stands for Low Power Device, that is, "devices with low radiation power." That is exactly so - according to the standard, the power radiated 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 for communication at a distance of several kilometers, in direct visibility conditions. In fact, most of the semi-toy sets of radio stations on sale have significantly more power, although they are certified as LPD. As the saying goes, “the rigor of our laws is compensated by the non-bindingness of their enforcement”, which is what suppliers use for certification: radio stations exhibit a low level of power through the menu, the product passes certification, and then, in the same way through the standard menu, normal power returns, usually 2-4 watts.
PMR - stands for Private Mobile Radio, that is, radio communications for private use. By standard, the permitted radiation power here is already greater than that of LPD, namely 0.5 watts. However, unlike LPD, this power is usually honest, a rare PMR has a power of more than 1 Watt, since this standard is allowed in many European countries, and certification takes place more seriously. 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 rather, with a set of the simplest radio stations from a mobile phone store) that my more intimate acquaintance with radio communications began. But soon there was a disappointment from the rather poor quality of the devices, they were more likely “toys” rather than something relatively serious. However, I was interested in radio communications, and I ordered from a store well-known among amateur radio enthusiasts, a good portable radio station, already 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 assessment - 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.
For half a year of using the radio station, I managed to get tired of communicating only on “civilian frequencies” (LPD and PMR, all channels of these two grids are easily tuned in the “70 centimeters” range), it was decided to receive the amateur radio category, call sign, and registration of the radio station. Now I am an official radio amateur, it has become my hobby. The technologies do not stand still, and with the help of a handheld portable radio station I can make communications with a range of several thousand kilometers (via artificial Earth satellites), communicate with the ISS crew, and other amateur radio enthusiasts (at frequencies allocated for this).
And of course - it’s convenient and easy! My family is equipped with simple, small (less than a mobile phone), inexpensive Chinese radio stations that are flashed to free channels of the LPD range, and depending on whether we go to the forest for mushrooms or to the store for shopping, we are always in touch.
The plans include the creation of a single citywide information communication channel for car owners, tourists, and just residents of the city, which will be available even to people with inexpensive sets of radio stations from mobile phone 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. It does not pretend to be encyclopedic.