Radio electronics, or how I began to comprehend it
Good afternoon, dear community.
I was surprised all the time by people who understand radio electronics. I always considered them to be a kind of shamans: how can one understand this abundance of elements, tracks and documentation? How can you just look at the board, “poke” a couple of times with the oscilloscope in only one clear place for him and with the words “a, it’s clear” take a soldering iron in your hands and resurrect, sort of like a deceased favorite toy. Otherwise, as magic it can not be called.
The heyday of electronics in our country came in the 80s, when there was nothing and everything had to be done by hand. Since then, many years have passed. Now I have the impression that, along with the generation of the 70s, knowledge with skill is also going away. I was unlucky: my parents planned half of the heyday of me, and I spent the second half playing with cubes and other machines. When at the age of 12 I went to the “Young Technician” Circle - these were not the most prosperous times, and due to circumstances six months later I had to be “tied up” with the circle, but the dream remained.
')
For current activities I am a programmer. I realize that finding an error in a large code is exactly the same thing as finding a “bad” capacitor on the board. No sooner said than done. Since by nature I like to study on my own - I went to look for literature. There were several attempts to start, but every time I started reading books, I rested against the fact that I could not figure out basic things, for example, “what is voltage and amperage.” Requests to the great and terrible Google also gave sample answers copied from textbooks. I tried to find a place in Moscow where you can learn this skill - the search did not end with the result.
So, welcome to the beginner radio amateur circle.
I love to learn and learn something new, but just knowledge is not enough for me. At school, I was taught the skill “The theorem cannot be learned - it can only be understood” and now I carry this rule through life. Surrounding people, of course, look puzzled when, instead of taking ready-made solutions and putting them together quickly, I begin to reinvent my bikes. The second reason for writing an article is the thought "if you understand the subject, you can easily explain it to another." Well, I'll try to understand myself and explain to others.
My first goal, just like in books, is an analogue radio receiver, and then we’ll go into numbers.
I just want to warn you - the article is written by an amateur in radio electronics and physics and is rather a reasoning. All amendments will be glad to hear in the comments.
So, what is voltage, current and other resistance? In most cases, an analogy with water is given to understand electrical processes. We will not deviate from this rule, but with minor deviations.
Imagine a pipe. To monitor some indicators, we will include several water meters, pressure gauges, and elements that interfere with the flow of water.
In electrical equivalent, the circuit would look something like this:
A physics course tells us that voltage is the potential difference between two points. If we put the definition on our pipe with water, then the potential is pressure, i.e. voltage is the pressure difference between two points. This explains the principle of its measurement with a voltmeter. It turns out that if we try to measure the voltage at two adjacent points of the pipe, where there are no resistances to the movement of water (there are no taps and restrictions, we still neglect internal friction of water against the pipe walls) and the pressure does not change - then the pressure difference at these two points will be zero . If the resistance is present, there is a decrease in pressure (in electrical equivalent voltage drop), then we get the voltage value. The sum of the voltages on all elements is equal to the voltage on the source. Those. If we add up the readings of all voltmeters on our circuit, we get the battery voltage.
For example, we assume that our battery provides a voltage of 5 volts and resistors have a resistance of 100 and 150 ohms. Then, according to Ohm's law U = IR, or I = U / R, we find that a current with a strength I = 5/250 = 20 mA flows through the circuit. Since the current strength in the whole circuit is the same (explained a little further), it follows from the same Ohm’s law that the first voltmeter will show U = 0.02 * 100 = 2V, and the second U = 0.02 * 150 = 3V.
From the same physics course, it is known that this is the amount of charge per unit of time. In water equivalent, it is water itself, and its meter, ammeter is a water meter. Again, it becomes clear why the ammeter is connected to the open circuit. If you connect it into place, for example, a voltmeter V1, then a new circuit is formed, from which resistance R1 will be excluded, which means at least we will get incorrect values ​​(which will be “at most” will become clear a little later). Let us return to our water - connecting an ammeter in parallel with any of the elements means that part of the water goes through the main pipe, and the other part goes through the counter - and just this counter will lie.
Oh yes, about the chain. In most of the literature, I came across a phrase that batteries are only a source of voltage, and only resistances are a source of current. How so? How can resistance be the source of something other than the source of resistance (heat is not counted for the time being)? That's right, if you rely on Ohm's law I = U / R, however, how much do not apply resistance, the current will not appear until there is a voltage source and a closed circuit (just like if you plug our pipe to the right with a stopper that do not do - the water meters will be silent) !
The resistance in the circuit just needs to be present, because if it is zero, the current will rush to infinity. We see such a situation when “closing” - sparks this is a very large current, or, more precisely, heat, equal to Q = (I ^ 2) Rt (the formula is valid at a constant current and resistance).
Another important note - when considering the calculation of voltage and current, I did not find any clarifications that in a closed circuit in all parts of the current will be the same. Those. All counters will spin at the same speed and show the same values. In fact, the amount of current that passed through the circuit is similar to the amount of "water" that came out of the pipe.
Perhaps the simplest phenomenon to explain. Returning to our pipe, resistance is all possible restrictions and taps. According to what we have disassembled above, as the resistance increases, the current in the entire circuit decreases and lowers the voltage at the ends of the resistance. Or again, in watery realities - the closure of our tap for half a turn will cause a decrease in water consumption at all meters and a proportional (depending on resistance) pressure drop on the gauges.
So where does everything fall and fall? Here, the analogy with water is ambiguous, since in the case of electricity, the “surplus” is converted into heat and dissipates. The amount of heat that is released in this case can again be calculated by the formula Q = (ΔI ^ 2) Rt (again with constant resistance). If we divide the amount of heat by time, we get the power that needs to be applied when choosing the resistor P = Q / t = (ΔI ^ 2) R.
Alternating current, as such, is rarely used in electronics. It is at least made permanent and in most cases reduced. Apparently because of this in the literature I came across about him almost does not say.
What is its difference? From the philistine point of view, in the small - the direction of the current in it changes. Here the analogy with the pipe is not quite appropriate, the first thing that comes to mind is a cocktail shaker (liquid when mixed in it walks back and forth). In radio electronics, we need to know how current flows in our circuit in order to get from it what we want.
The next thing I went to figure out was semiconductors. Holes? Electrons? Key mode? Cascades? Field transistor, then the one that is found in the field? Nothing is clear yet ...
I was surprised all the time by people who understand radio electronics. I always considered them to be a kind of shamans: how can one understand this abundance of elements, tracks and documentation? How can you just look at the board, “poke” a couple of times with the oscilloscope in only one clear place for him and with the words “a, it’s clear” take a soldering iron in your hands and resurrect, sort of like a deceased favorite toy. Otherwise, as magic it can not be called.
The heyday of electronics in our country came in the 80s, when there was nothing and everything had to be done by hand. Since then, many years have passed. Now I have the impression that, along with the generation of the 70s, knowledge with skill is also going away. I was unlucky: my parents planned half of the heyday of me, and I spent the second half playing with cubes and other machines. When at the age of 12 I went to the “Young Technician” Circle - these were not the most prosperous times, and due to circumstances six months later I had to be “tied up” with the circle, but the dream remained.
')
For current activities I am a programmer. I realize that finding an error in a large code is exactly the same thing as finding a “bad” capacitor on the board. No sooner said than done. Since by nature I like to study on my own - I went to look for literature. There were several attempts to start, but every time I started reading books, I rested against the fact that I could not figure out basic things, for example, “what is voltage and amperage.” Requests to the great and terrible Google also gave sample answers copied from textbooks. I tried to find a place in Moscow where you can learn this skill - the search did not end with the result.
So, welcome to the beginner radio amateur circle.
I love to learn and learn something new, but just knowledge is not enough for me. At school, I was taught the skill “The theorem cannot be learned - it can only be understood” and now I carry this rule through life. Surrounding people, of course, look puzzled when, instead of taking ready-made solutions and putting them together quickly, I begin to reinvent my bikes. The second reason for writing an article is the thought "if you understand the subject, you can easily explain it to another." Well, I'll try to understand myself and explain to others.
My first goal, just like in books, is an analogue radio receiver, and then we’ll go into numbers.
I just want to warn you - the article is written by an amateur in radio electronics and physics and is rather a reasoning. All amendments will be glad to hear in the comments.
So, what is voltage, current and other resistance? In most cases, an analogy with water is given to understand electrical processes. We will not deviate from this rule, but with minor deviations.
Imagine a pipe. To monitor some indicators, we will include several water meters, pressure gauges, and elements that interfere with the flow of water.
In electrical equivalent, the circuit would look something like this:
Voltage
A physics course tells us that voltage is the potential difference between two points. If we put the definition on our pipe with water, then the potential is pressure, i.e. voltage is the pressure difference between two points. This explains the principle of its measurement with a voltmeter. It turns out that if we try to measure the voltage at two adjacent points of the pipe, where there are no resistances to the movement of water (there are no taps and restrictions, we still neglect internal friction of water against the pipe walls) and the pressure does not change - then the pressure difference at these two points will be zero . If the resistance is present, there is a decrease in pressure (in electrical equivalent voltage drop), then we get the voltage value. The sum of the voltages on all elements is equal to the voltage on the source. Those. If we add up the readings of all voltmeters on our circuit, we get the battery voltage.
For example, we assume that our battery provides a voltage of 5 volts and resistors have a resistance of 100 and 150 ohms. Then, according to Ohm's law U = IR, or I = U / R, we find that a current with a strength I = 5/250 = 20 mA flows through the circuit. Since the current strength in the whole circuit is the same (explained a little further), it follows from the same Ohm’s law that the first voltmeter will show U = 0.02 * 100 = 2V, and the second U = 0.02 * 150 = 3V.
Current strength
From the same physics course, it is known that this is the amount of charge per unit of time. In water equivalent, it is water itself, and its meter, ammeter is a water meter. Again, it becomes clear why the ammeter is connected to the open circuit. If you connect it into place, for example, a voltmeter V1, then a new circuit is formed, from which resistance R1 will be excluded, which means at least we will get incorrect values ​​(which will be “at most” will become clear a little later). Let us return to our water - connecting an ammeter in parallel with any of the elements means that part of the water goes through the main pipe, and the other part goes through the counter - and just this counter will lie.
Oh yes, about the chain. In most of the literature, I came across a phrase that batteries are only a source of voltage, and only resistances are a source of current. How so? How can resistance be the source of something other than the source of resistance (heat is not counted for the time being)? That's right, if you rely on Ohm's law I = U / R, however, how much do not apply resistance, the current will not appear until there is a voltage source and a closed circuit (just like if you plug our pipe to the right with a stopper that do not do - the water meters will be silent) !
The resistance in the circuit just needs to be present, because if it is zero, the current will rush to infinity. We see such a situation when “closing” - sparks this is a very large current, or, more precisely, heat, equal to Q = (I ^ 2) Rt (the formula is valid at a constant current and resistance).
Another important note - when considering the calculation of voltage and current, I did not find any clarifications that in a closed circuit in all parts of the current will be the same. Those. All counters will spin at the same speed and show the same values. In fact, the amount of current that passed through the circuit is similar to the amount of "water" that came out of the pipe.
Resistance
Perhaps the simplest phenomenon to explain. Returning to our pipe, resistance is all possible restrictions and taps. According to what we have disassembled above, as the resistance increases, the current in the entire circuit decreases and lowers the voltage at the ends of the resistance. Or again, in watery realities - the closure of our tap for half a turn will cause a decrease in water consumption at all meters and a proportional (depending on resistance) pressure drop on the gauges.
So where does everything fall and fall? Here, the analogy with water is ambiguous, since in the case of electricity, the “surplus” is converted into heat and dissipates. The amount of heat that is released in this case can again be calculated by the formula Q = (ΔI ^ 2) Rt (again with constant resistance). If we divide the amount of heat by time, we get the power that needs to be applied when choosing the resistor P = Q / t = (ΔI ^ 2) R.
Smoking is not cool!
When I went to the Young Technician circle, the older comrades carried out “experiments” with electric lighting. To do this, they took the power supply, connected low-power resistors to it and increased the voltage. Raised until he red-hot, like a car cigarette lighter. After that, almost instantly, the resistor “burned out” and went into the trash.
With direct current, everything is clear, but variable?
Alternating current, as such, is rarely used in electronics. It is at least made permanent and in most cases reduced. Apparently because of this in the literature I came across about him almost does not say.
What is its difference? From the philistine point of view, in the small - the direction of the current in it changes. Here the analogy with the pipe is not quite appropriate, the first thing that comes to mind is a cocktail shaker (liquid when mixed in it walks back and forth). In radio electronics, we need to know how current flows in our circuit in order to get from it what we want.
The next thing I went to figure out was semiconductors. Holes? Electrons? Key mode? Cascades? Field transistor, then the one that is found in the field? Nothing is clear yet ...
Source: https://habr.com/ru/post/249923/
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