Bugs, transmitters and receivers: basic terms. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Bugs, transmitters and receivers: basic terms. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Brief glossary on transceiver technology

Transmitter - a device that transmits a signal.

Receiver - a device that receives a signal

Antenna - an element of the electrical circuit that converts the received electromagnetic oscillations into an electrical signal (receiving antenna), or vice versa - an electrical signal into electromagnetic oscillations (transmitting antenna). The same antenna can be both transmitting and receiving, and even at the same time.

Antenna impedance - a value, roughly speaking, indicating how "hard" the energy leaves the antenna on the air. Knowing this resistance is necessary for the correct calculation of the radiated power: the higher the resistance of the antenna, the greater the voltage of the signal supplied to it must be to obtain the same power.

In receiving antennas, knowledge of the resistance is necessary for the correct calculation of the receiver front end.

Feeder - a line through which high-frequency energy is transmitted. Most often, a coaxial cable is used as a feeder.

Wave resistance - the value determined by the ratio of the linear capacitance and linear inductance of the cable. Depends on the type of cable - usually indicated in the name. Standard VS values: 50 ohms, 75 ohms, 300 ohms. It must be known for the correct matching of devices connected by this cable (for example, a transmitter and an antenna).

output impedance - the amount of resistance that must be connected to the output of the device to obtain the rated power.

Input impedance - the resistance that the input of the device has.

Device matching - alignment of input/output impedances of two connected devices. For efficient power transfer between two devices, the output impedance of the transmitter must be equal to the input impedance of the receiver.

Antenna resonant frequency is the frequency at which the antenna has the least impedance.

Broadband/narrowband antenna - a term that talks about how the antenna relates to frequencies that are greater and less than resonant. That is, how sharply its effectiveness decreases when moving away from the resonant frequency in one direction or another. That is, what is its bandwidth.

Bugs, transmitters and receivers: basic terms. radiation pattern

Antenna pattern - a curve showing the spatial distribution of the radiated power / sensitivity of the antenna for various angles relative to the main axis. Typically, pie charts are used, which look something like the one shown in the figure. The curve thus turns out in the form of "petals". Therefore, you can often hear the term "directivity lobe"

Sensitivity receiver - a value that characterizes the ability to receive weak electrical signals. The lower the signal voltage that the receiver can still receive, the better the sensitivity. It is expressed in microvolts (µV) - if the input signal is electrical, or microvolts per meter (µV / m) - if the input signal is electromagnetic oscillations (in this case, not voltage is measured, but the strength of the electromagnetic field).

Modulation - this, I hope, is clear - a method of packing an informative low-frequency modulating signal (for example, sound) into a high-frequency carrier (signal broadcast). Modulation can be amplitude (AM), frequency (FM or FM), phase, pulse width or some other. We are interested in the first two. With amplitude modulation, the low-frequency signal controls the amplitude of the carrier, with frequency modulation, the frequency (within small limits).

Deviation - threshold deviation of the carrier frequency from the state of rest with frequency modulation. The rest state is when the modulating (low frequency) signal is 0.

Harmonics - frequency components of the signal, multiples of its fundamental frequency. Usually, harmonics are higher than the fundamental frequency. How many times the harmonic is greater than the fundamental frequency is its number. That is, if it is three times larger, then its name is "3rd harmonica", if it is five times larger - "5th harmonica", etc. Harmonics are the result of non-linear distortion of the signal, they can be separated from the signal using band-pass filters or oscillatory circuits.

Harmonics are widely used in radio engineering, both in transmitters and receivers.

In transmitters, they are used to obtain large frequencies from small ones. For example, there is a quartz at 20,57 MHz, and we need to receive a signal with a stable frequency of 144 MHz. What are we doing? We make an oscillator at 20,57 MHz, then select the 7th harmonic of its signal and amplify it. So much for 144MHz!

Harmonics are also used to build heterodyne receivers.

However, harmonics are also harmful. For example, a signal containing many harmonics should not be broadcast because the harmonics will clog multiple frequencies and may interfere with other radio stations.

Linear distortion - signal distortions, which allow you to subsequently restore the original signal from the distorted one. These include adjusting the amplitude (power), frequency spectrum, phase angle, etc.

Nonlinear distortion - signal distortions, after which it is impossible to restore the original signal. These include, for example, overmodulation - a distortion that occurs when the signal amplitude is excessive: the signal "tops are cut off".

Oscillating circuit - a circuit consisting of a capacitor and an inductor connected in parallel or in series. With shock excitation, damped sinusoidal (harmonic) oscillations of a certain frequency appear in the CC, which is called the "resonant frequency", is determined by the capacitance of the capacitor and the inductance of the coil and is calculated by the formula:

$Bugs, transmitters and receivers: basic terms. Fres \u1d 2/XNUMXp (square (LC))$

QC is used in the transmitter generator to obtain the required frequency, in the receiver - to isolate a certain frequency from the received radio signal.

frequency filter - a circuit that allows you to attenuate or amplify a certain range of frequencies.

Publication: radiokot.ru

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