We deliver voice to the mobile network: step 1 - how the voice turns into an electrical signal
We all use mobile communications, and do not think about how difficult the path is for our voice to be heard by our interlocutor, hundreds and thousands of kilometers away. A huge amount of tasks is performed by the simplest handset, even while waiting for a call (when it is on your desk), and, of course, you get into respect for those who developed all this, first in theory, and then implemented it in real equipment.
For the usual actions: take the phone, dial the number, and hear the voice in the handset, there are so many technical details, fundamental discoveries and technological transformations that we need to break the description into several stages, and consider each of them separately.
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It all started simple .
The first thing that comes to mind when we are trying to communicate at a great distance is to increase the volume of the sound source, for example, using a horn as in the figure above, and receiver sensitivity:
However, if it is necessary to transmit sound between rooms, horns become useless, and an inquisitive engineering mind has developed options for "air ducts" along which a message can be passed from one point to another.
For example, intercoms, which can still be found on large ships:
All these tricks allow us to transmit sound vibrations (of which our speech actually consists) for a little more distance than what nature intended. But we need to provide voice transmission for almost an unlimited distance, through any obstacles!
So the idea is not to transmit the original sound waves, but to carry out an intermediate conversion to another transmission medium, which will save the necessary information without data loss, and allow it to be restored on the receiving side. As an intermediate medium, various materials or physical phenomena can be used.
In childhood, probably, many were engaged in the manufacture of "phones" from improvised means, for example, a pair of boxes and a regular thread:
With all the simplicity of the solution, the sound from one box, through the elastic vibrations of the thread, is perfectly transmitted to the second, where it can be clearly heard. However, the minuses in this solution are much more pluses: to transfer elastic vibrations from the box along the thread, it is required to tighten the thread and ensure that it does not touch anything; the maximum distance to which a voice can be transmitted using such elastic vibrations is only tens of meters, etc. All this excludes the possibility of using this, and similar to it, transformations, as a real intercom.
The above-described search for options for voice transmission leads us to the need to choose a suitable intermediate medium, and methods for the qualitative transformation of sound vibrations - into the parameters of the new medium and vice versa. Of all the variety of physical phenomena and materials, the electrical signal best meets these requirements, and here, finally, one can begin the description of the first transformation, which is carried out in modern wireless networks:
To perform the conversion "Sound vibrations - Electrical signal", a device called "Microphone" is used, from the Greek micros it is small, the background is sound.
Let's try to describe the main milestones in the development of sound-to-electrical signal conversion technology.
1. Alexander Bella's liquid transmitter “liquid transmitter”
It is believed that the development of sound-to-electricity converters began with it. Alexander Bell conducted experiments in 1876, and even managed to pass his voice over the wires for a short distance.
In the horn located at the top it was necessary to speak, a thin needle (or wire) was attached to the bottom of the diaphragm attached to the horn, and moved under the influence of sound vibrations. In the lower container there was a solution of water with a small amount of acid (to improve electrical conductivity), the needle, when moving with the diaphragm, was more or less immersed in the liquid, and the resistance of the system changed, which was monitored on the device with a coil and magnet.
The disadvantages of the solution are visible to the naked eye - a bulky device, the presence of liquids, low conversion accuracy. All this did not allow the use of an experimental device for commercial projects, but a start was made.
An inquisitive reader may try to reproduce such a device, for example, according to recommendations from this site: Step-by-step recommendations for the manufacture of a “Bell liquid transmitter”
2. David Hughes' carbon (rod) microphone
A few years later, David Hughes introduced another version of the microphone, in which a carbon rod was used as a sound-to-electricity transducer. Under the influence of sound vibrations, the area of contact of the carbon rod with the metal platform changed, and the resistance of the rod proportionally changed. This device has already been used for practical purposes, for real voice transmission. But an era of advanced carbon-based solutions was coming (the same coal that Hughes used in his rod).
3. Edison carbon (powder) microphone
The primacy in the development of this microphone was disputed for a long time, between American engineers Bell, Berliner and Edison, there is also evidence that the Russian engineer Michalsky, at about the same time, manufactured a similar device.
According to the generally accepted version, Edison is considered the inventor, and Bell's laboratory (which bought Berliner's early patent and took the inventor to work, but then Edison proved his first priority in court) is the main developer and popularizer. The principle of operation of this microphone is based on the fact that coal crushed into fine powder changes the electrical resistance, depending on its density. Thus, the membrane under the influence of sound waves changes the density of the coal powder, which leads to a change in the characteristics of the electric current passing through it. The microphone was so successful that it was used from the end of the 19th century up to the beginning of the 21st, in devices using analogue voice transmission (we will talk about Digital-to-Analog Transformations in the next section).
4. Dynamic and condenser microphones
Further development of technologies led to the development of condenser and dynamic microphones, approximately in the 20-30s of the 20th century. In a condenser microphone, the change in the parameters of the electric current occurs due to a change in the capacitance of the capacitor, one of the conductive plates of which is made in the form of a membrane moving under the influence of sound waves.
A dynamic microphone consists of a stationary magnet, and a winding that moves along with the membrane, thus creating an electric current.
Both versions of microphones have their own advantages and disadvantages, and now both condenser and dynamic designs are used. These microphones allow us to catch such frequencies of sound vibrations that are inaccessible for perception by the human ear, thus, for our purposes - converting a voice into an electrical signal, their capabilities are more than enough. It is only necessary to fit this design into the body of a mobile phone. To do this, the engineers had to break my head a little more.
5. Electret microphones
The main requirement for microphones, for use in a cell phone - the minimum size, and an acceptable quality conversion. For such purposes, one of the condenser microphone options is the best: the electret microphone. In it one lining is made of electret material, which is able to maintain a polarized state for a long time, after the removal of external influence.
The first models of electret microphones were made in the form of caps, and could already be used in the handsets of cell phones:
Microelectromechanical systems - MEMS and surface mounting - SMD
Further miniaturization leads us to a new class of components - MEMS, where mechanical and electronic devices are combined on a single printed circuit board. Later, with the advent and development of surface-mounted printed circuit boards (SMD), miniaturization of microphones reached maximum values, and we finally can fit our microphone in a phone less than 10 mm thick.
So, thanks to technical progress and engineering, we have a miniature and high-quality device that converts sound vibrations into an electrical signal:
This is only the first transformation of our voice in the process of its transmission over the cellular network, and each next step will require more and more complex technical devices and an advanced mathematical apparatus. The next part is the necessary transformations of the received electrical signal, still inside the phone, in order to prepare it for transmission to the radio broadcast, with brief historical excursions - how our understanding of these processes developed.
For the usual actions: take the phone, dial the number, and hear the voice in the handset, there are so many technical details, fundamental discoveries and technological transformations that we need to break the description into several stages, and consider each of them separately.
')
It all started simple .
The first thing that comes to mind when we are trying to communicate at a great distance is to increase the volume of the sound source, for example, using a horn as in the figure above, and receiver sensitivity:
However, if it is necessary to transmit sound between rooms, horns become useless, and an inquisitive engineering mind has developed options for "air ducts" along which a message can be passed from one point to another.
For example, intercoms, which can still be found on large ships:
All these tricks allow us to transmit sound vibrations (of which our speech actually consists) for a little more distance than what nature intended. But we need to provide voice transmission for almost an unlimited distance, through any obstacles!
So the idea is not to transmit the original sound waves, but to carry out an intermediate conversion to another transmission medium, which will save the necessary information without data loss, and allow it to be restored on the receiving side. As an intermediate medium, various materials or physical phenomena can be used.
In childhood, probably, many were engaged in the manufacture of "phones" from improvised means, for example, a pair of boxes and a regular thread:
With all the simplicity of the solution, the sound from one box, through the elastic vibrations of the thread, is perfectly transmitted to the second, where it can be clearly heard. However, the minuses in this solution are much more pluses: to transfer elastic vibrations from the box along the thread, it is required to tighten the thread and ensure that it does not touch anything; the maximum distance to which a voice can be transmitted using such elastic vibrations is only tens of meters, etc. All this excludes the possibility of using this, and similar to it, transformations, as a real intercom.
The above-described search for options for voice transmission leads us to the need to choose a suitable intermediate medium, and methods for the qualitative transformation of sound vibrations - into the parameters of the new medium and vice versa. Of all the variety of physical phenomena and materials, the electrical signal best meets these requirements, and here, finally, one can begin the description of the first transformation, which is carried out in modern wireless networks:
First transformation: Voice - Electrical signal
To perform the conversion "Sound vibrations - Electrical signal", a device called "Microphone" is used, from the Greek micros it is small, the background is sound.
Let's try to describe the main milestones in the development of sound-to-electrical signal conversion technology.
1. Alexander Bella's liquid transmitter “liquid transmitter”
It is believed that the development of sound-to-electricity converters began with it. Alexander Bell conducted experiments in 1876, and even managed to pass his voice over the wires for a short distance.
In the horn located at the top it was necessary to speak, a thin needle (or wire) was attached to the bottom of the diaphragm attached to the horn, and moved under the influence of sound vibrations. In the lower container there was a solution of water with a small amount of acid (to improve electrical conductivity), the needle, when moving with the diaphragm, was more or less immersed in the liquid, and the resistance of the system changed, which was monitored on the device with a coil and magnet.
The disadvantages of the solution are visible to the naked eye - a bulky device, the presence of liquids, low conversion accuracy. All this did not allow the use of an experimental device for commercial projects, but a start was made.
An inquisitive reader may try to reproduce such a device, for example, according to recommendations from this site: Step-by-step recommendations for the manufacture of a “Bell liquid transmitter”
2. David Hughes' carbon (rod) microphone
A few years later, David Hughes introduced another version of the microphone, in which a carbon rod was used as a sound-to-electricity transducer. Under the influence of sound vibrations, the area of contact of the carbon rod with the metal platform changed, and the resistance of the rod proportionally changed. This device has already been used for practical purposes, for real voice transmission. But an era of advanced carbon-based solutions was coming (the same coal that Hughes used in his rod).
3. Edison carbon (powder) microphone
The primacy in the development of this microphone was disputed for a long time, between American engineers Bell, Berliner and Edison, there is also evidence that the Russian engineer Michalsky, at about the same time, manufactured a similar device.
According to the generally accepted version, Edison is considered the inventor, and Bell's laboratory (which bought Berliner's early patent and took the inventor to work, but then Edison proved his first priority in court) is the main developer and popularizer. The principle of operation of this microphone is based on the fact that coal crushed into fine powder changes the electrical resistance, depending on its density. Thus, the membrane under the influence of sound waves changes the density of the coal powder, which leads to a change in the characteristics of the electric current passing through it. The microphone was so successful that it was used from the end of the 19th century up to the beginning of the 21st, in devices using analogue voice transmission (we will talk about Digital-to-Analog Transformations in the next section).
4. Dynamic and condenser microphones
Further development of technologies led to the development of condenser and dynamic microphones, approximately in the 20-30s of the 20th century. In a condenser microphone, the change in the parameters of the electric current occurs due to a change in the capacitance of the capacitor, one of the conductive plates of which is made in the form of a membrane moving under the influence of sound waves.
A dynamic microphone consists of a stationary magnet, and a winding that moves along with the membrane, thus creating an electric current.
Both versions of microphones have their own advantages and disadvantages, and now both condenser and dynamic designs are used. These microphones allow us to catch such frequencies of sound vibrations that are inaccessible for perception by the human ear, thus, for our purposes - converting a voice into an electrical signal, their capabilities are more than enough. It is only necessary to fit this design into the body of a mobile phone. To do this, the engineers had to break my head a little more.
5. Electret microphones
The main requirement for microphones, for use in a cell phone - the minimum size, and an acceptable quality conversion. For such purposes, one of the condenser microphone options is the best: the electret microphone. In it one lining is made of electret material, which is able to maintain a polarized state for a long time, after the removal of external influence.
The first models of electret microphones were made in the form of caps, and could already be used in the handsets of cell phones:
Microelectromechanical systems - MEMS and surface mounting - SMD
Further miniaturization leads us to a new class of components - MEMS, where mechanical and electronic devices are combined on a single printed circuit board. Later, with the advent and development of surface-mounted printed circuit boards (SMD), miniaturization of microphones reached maximum values, and we finally can fit our microphone in a phone less than 10 mm thick.
So, thanks to technical progress and engineering, we have a miniature and high-quality device that converts sound vibrations into an electrical signal:
This is only the first transformation of our voice in the process of its transmission over the cellular network, and each next step will require more and more complex technical devices and an advanced mathematical apparatus. The next part is the necessary transformations of the received electrical signal, still inside the phone, in order to prepare it for transmission to the radio broadcast, with brief historical excursions - how our understanding of these processes developed.
Source: https://habr.com/ru/post/248807/
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