A quantum mechanical state has a physical meaning of the energy of this state, and therefore the system of units is often chosen in such a way that frequency and energy are expressed in the same units (in other words, the conversion factor between frequency and energy is Planck’s constant in the formula E = hν - is chosen equal to 1).
The human eye is sensitive to electromagnetic waves with frequencies from 4⋅10 14 to 8⋅10 14 Hz (visible light); The frequency of vibration determines the color of the observed light. The human auditory analyzer perceives acoustic waves with frequencies from 20 Hz to 20 kHz. Different animals have different frequency ranges of sensitivity to optical and acoustic vibrations.
The ratios of the frequencies of sound vibrations are expressed using musical intervals, such as octave, fifth, third, etc. An interval of one octave between the frequencies of sounds means that these frequencies differ by 2 times, an interval of a perfect fifth means the ratio of frequencies 3 ⁄ 2 . In addition, to describe frequency intervals, a decade is used - the interval between frequencies that differ by a factor of 10. Thus, the range of human sound sensitivity is 3 decades (20 Hz - 20,000 Hz). To measure the ratio of very close audio frequencies, units such as the cent (frequency ratio of 2 1/1200) and millioctave (frequency ratio of 2 1/1000) are used.
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Instantaneous frequency and frequencies of spectral components
A periodic signal is characterized by an instantaneous frequency, which is (up to a coefficient) the rate of change of phase, but the same signal can be represented as a sum of harmonic spectral components that have their own (constant) frequencies. The properties of the instantaneous frequency and the frequency of the spectral component are different.
Cyclic frequency
If the unit of angular frequency is used as degrees per second, the relationship with ordinary frequency will be as follows: ω = 360°ν.
Numerically, the cyclic frequency is equal to the number of cycles (oscillations, revolutions) in 2π seconds. The introduction of cyclic frequency (in its main dimension - radians per second) allows us to simplify many formulas in theoretical physics and electronics. Thus, the resonant cyclic frequency of an oscillatory LC circuit is equal to ω L C = 1 / L C , (\displaystyle \omega _(LC)=1/(\sqrt (LC)),) whereas the usual resonant frequency ν L C = 1 / (2 π L C) . (\displaystyle \nu _(LC)=1/(2\pi (\sqrt (LC))).) At the same time, a number of other formulas become more complicated. The decisive consideration in favor of cyclic frequency was that the factors 2π and 1/(2π), which appear in many formulas when using radians to measure angles and phases, disappear when cyclic frequency is introduced.
In mechanics, when considering rotational motion, an analogue of cyclic frequency is angular velocity.
Discrete event rate
The frequency of discrete events (pulse frequency) is a physical quantity equal to the number of discrete events occurring per unit of time. The unit of frequency of discrete events is a second to the minus first power (Russian designation: s −1; international: s−1). The frequency 1 s −1 is equal to the frequency of discrete events at which one event occurs in 1 s.
Rotation frequency
Rotation frequency is a physical quantity equal to the number of full revolutions per unit of time. The unit of rotation speed is the second minus the first power ( s −1, s−1), revolutions per second. Units often used are revolutions per minute, revolutions per hour, etc.
Other quantities related to frequency
Units
The SI unit of measurement is the hertz. The unit was originally introduced in 1930 by the International Electrotechnical Commission, and in 1960 adopted for general use by the 11th General Conference of Weights and Measures as the SI unit. Previously, the unit of frequency was used cycle per second(1 cycle per second = 1 Hz) and derivatives (kilocycle per second, megacycle per second, kilomegacycle per second, equal to kilohertz, megahertz and gigahertz, respectively).
Metrological aspects
To measure frequency, different types of frequency meters are used, including: to measure the frequency of pulses - electronic counting and capacitor ones, to determine the frequencies of spectral components - resonant and heterodyne frequency meters, as well as spectrum analyzers. To reproduce the frequency with a given accuracy, various measures are used - frequency standards (high accuracy), frequency synthesizers, signal generators, etc. The frequencies are compared with a frequency comparator or using an oscilloscope using Lissajous figures.
Standards
National frequency standards are used to verify frequency measuring instruments. In Russia, national frequency standards include:
- The state primary standard of units of time, frequency and national time scale GET 1-98 is located in VNIIFTRI.
- Secondary standard of the unit of time and frequency VET 1-10-82- located in SNIIM (Novosibirsk).
Computations
Calculating the frequency of a recurring event is done by taking into account the number of occurrences of that event during a given period of time. The resulting amount is divided by the duration of the corresponding time period. For example, if 71 homogeneous events occurred within 15 seconds, then the frequency will be
ν = 71 15 s ≈ 4.7 Hz (\displaystyle \nu =(\frac (71)(15\,(\mbox(s))))\approx 4.7\,(\mbox(Hz)))If the number of samples obtained is small, then a more accurate technique is to measure the time interval for a given number of occurrences of the event in question, rather than finding the number of events within a given period of time. Using the latter method introduces a random error between zero and first readings, averaging half a reading; this can lead to an average error in the calculated frequency Δν = 1/(2 T m) , or relative error Δ ν /ν = 1/(2v T m ) , Where T m is the time interval, and ν is the measured frequency. The error decreases as frequency increases, so this problem is most significant at low frequencies, where the number of samples N few.
Measurement methods
Stroboscopic method
The use of a special device - a strobe - is one of the historically early methods of measuring the rotational speed or vibration of various objects. The measurement process uses a stroboscopic light source (usually a bright lamp that periodically produces short flashes of light), the frequency of which is adjusted using a pre-calibrated timing circuit. A light source is directed at a rotating object, and then the frequency of flashes is gradually changed. When the frequency of the flashes is equalized with the frequency of rotation or vibration of the object, the latter has time to complete a complete oscillatory cycle and return to its original position in the interval between two flashes, so that when illuminated by a strobe lamp, this object will appear motionless. This method, however, has a drawback: if the rotation speed of the object ( x) is not equal to the strobe frequency ( y), but is proportional to it with an integer coefficient (2 x , 3x etc.), then the object will still look motionless when illuminated.
The stroboscopic method is also used to fine-tune the rotational speed (oscillations). In this case, the frequency of the flashes is fixed, and the frequency of the periodic movement of the object changes until it begins to appear motionless.
Beat method
All of these waves, from the lowest frequencies of radio waves to the high frequencies of gamma rays, are fundamentally the same, and they are all called electromagnetic radiation. They all propagate in a vacuum at the speed of light.
Another characteristic of electromagnetic waves is wavelength. Wavelength is inversely proportional to frequency, so electromagnetic waves with a higher frequency have a shorter wavelength, and vice versa. In a vacuum the wavelength
λ = c / ν , (\displaystyle \lambda =c/\nu ,)Where With- speed of light in vacuum. In an environment in which the phase velocity of propagation of an electromagnetic wave c′ differs from the speed of light in vacuum ( c′ = c/n, Where n- refractive index), the relationship between wavelength and frequency will be as follows:
λ = c n ν . (\displaystyle \lambda =(\frac (c)(n\nu )).)Another frequently used characteristic of a wave is the wave number (spatial frequency), equal to the number of waves per unit length: k= 1/λ . Sometimes this quantity is used with a coefficient of 2π, by analogy with the ordinary and circular frequency k s = 2π/λ. In the case of an electromagnetic wave in a medium
k = 1 / λ = n ν c . (\displaystyle k=1/\lambda =(\frac (n\nu )(c)).) k s = 2 π / λ = 2 π n ν c = n ω c . (\displaystyle k_(s)=2\pi /\lambda =(\frac (2\pi n\nu )(c))=(\frac (n\omega )(c)).)Sound
The properties of sound (mechanical elastic vibrations of the medium) depend on frequency. A person can hear vibrations with frequencies ranging from 20 Hz falls within the range of the note 50 Hz. In North America (USA, Canada, Mexico), Central and some countries in the northern part of South America (Brazil, Venezuela, Colombia, Peru), as well as in some Asian countries (southwestern Japan, South Korea, Saudi Arabia , Philippines and Taiwan) uses a frequency of 60 Hz. See Standards for connectors, voltages and frequencies in different countries. Almost all household electrical appliances work equally well in networks with a frequency of 50 and 60 Hz, provided the network voltage is the same. At the end of the 19th - first half of the 20th centuries, before standardization, frequencies from 16 were used in various isolated networks , although it increases losses when transmitting over long distances - due to capacitive losses, an increase in the inductive reactance of the line and losses on
A characteristic of a periodic process, equal to the number of complete cycles of the process completed per unit of time. Standard notations in formulas are , , or . The unit of frequency in the International System of Units (SI) is generally the hertz ( Hz, Hz). The reciprocal of frequency is called period. Frequency, like time, is one of the most accurately measured physical quantities: up to a relative accuracy of 10 −17.
Periodic processes are known in nature with frequencies from ~10 −16 Hz (the frequency of the Sun's revolution around the center of the Galaxy) to ~10 35 Hz (the frequency of field oscillations characteristic of the most high-energy cosmic rays).
Cyclic frequency
Discrete event rate
The frequency of discrete events (pulse frequency) is a physical quantity equal to the number of discrete events occurring per unit of time. The unit of frequency of discrete events is the second to the minus first power ( s −1, s−1), however in practice the hertz is usually used to express the pulse frequency.
Rotation frequency
Rotation frequency is a physical quantity equal to the number of full revolutions per unit of time. The unit of rotation speed is the second minus the first power ( s −1, s−1), revolutions per second. Units often used are revolutions per minute, revolutions per hour, etc.
Other quantities related to frequency
Metrological aspects
Measurements
- To measure frequency, different types of frequency meters are used, including: to measure the frequency of pulses - electronic counting and capacitor ones, to determine the frequencies of spectral components - resonant and heterodyne frequency meters, as well as spectrum analyzers.
- To reproduce the frequency with a given accuracy, various measures are used - frequency standards (high accuracy), frequency synthesizers, signal generators, etc.
- Compare frequencies using a frequency comparator or using an oscilloscope using Lissajous patterns.
Standards
- State primary standard of units of time, frequency and national time scale GET 1-98 - located at VNIIFTRI
- Secondary standard of the unit of time and frequency VET 1-10-82- located in SNIIM (Novosibirsk)
see also
Notes
Literature
- Fink L. M. Signals, interference, errors... - M.: Radio and Communications, 1984
- Units of physical quantities. Burdun G. D., Bazakutsa V. A. - Kharkov: Vishcha school,
- Physics Handbook. Yavorsky B. M., Detlaf A. A. - M.: Science,
Links
Wikimedia Foundation. 2010.
Synonyms:- Authorization
- Chemical physics
See what “Frequency” is in other dictionaries:
FREQUENCY- (1) the number of repetitions of a periodic phenomenon per unit of time; (2) Ch. side frequency, greater or less than the carrier frequency of the high-frequency generator, occurring when (see); (3) Number of rotations is a value equal to the ratio of the number of revolutions... ... Big Polytechnic Encyclopedia
Frequency- ion plasma frequency - the frequency of electrostatic oscillations that can be observed in a plasma whose electron temperature significantly exceeds the temperature of the ions; this frequency depends on the concentration, charge and mass of plasma ions.... ... Nuclear energy terms
FREQUENCY- FREQUENCY, frequencies, plural. (special) frequencies, frequencies, women. (book). 1. units only distracted noun to frequent. Frequency of cases. Rhythm frequency. Increased heart rate. Current frequency. 2. A quantity expressing one or another degree of some frequent movement... Ushakov's Explanatory Dictionary
frequency- s; frequencies; and. 1. to Frequent (1 digit). Monitor the frequency of repetition of moves. Required part of planting potatoes. Pay attention to your pulse rate. 2. The number of repetitions of identical movements, oscillations in what direction. unit of time. Hours of wheel rotation. H... encyclopedic Dictionary
FREQUENCY- (Frequency) number of periods per second. Frequency is the reciprocal of the oscillation period; eg if the alternating current frequency f = 50 oscillations per second. (50 N), then the period T = 1/50 sec. Frequency is measured in hertz. When characterizing radiation... ... Marine Dictionary
frequency- harmonic, vibration Dictionary of Russian synonyms. frequency noun density density (about vegetation)) Dictionary of Russian synonyms. Context 5.0 Informatics. 2012… Synonym dictionary
frequency- occurrence of a random event is the ratio m/n of the number m occurrences of this event in a given sequence of tests (its occurrence) to the total number n of tests. The term frequency is also used to mean occurrence. In an old book... ... Dictionary of Sociological Statistics
Frequency- oscillations, the number of complete periods (cycles) of the oscillatory process occurring per unit of time. The unit of frequency is the hertz (Hz), corresponding to one complete cycle in 1 s. Frequency f=1/T, where T is the oscillation period, however often... ... Illustrated Encyclopedic Dictionary
Electromagnetic radiation exists exactly as long as our Universe lives. It played a key role in the evolution of life on Earth. In fact, this disturbance is the state of an electromagnetic field distributed in space.
Characteristics of electromagnetic radiation
Any electromagnetic wave is described using three characteristics.
1. Frequency.
2. Polarization.
Polarization– one of the main wave attributes. Describes the transverse anisotropy of electromagnetic waves. Radiation is considered polarized when all wave oscillations occur in the same plane.
This phenomenon is actively used in practice. For example, in cinemas when showing 3D films.
Using polarization, IMAX glasses separate the image that is intended for different eyes. 
Frequency– the number of wave crests that pass by the observer (in this case, the detector) in one second. It is measured in hertz.
Wavelength– a specific distance between the nearest points of electromagnetic radiation, the oscillations of which occur in the same phase.
Electromagnetic radiation can propagate in almost any medium: from dense matter to vacuum.
The speed of propagation in a vacuum is 300 thousand km per second.
For an interesting video about the nature and properties of EM waves, watch the video below:
Types of electromagnetic waves
All electromagnetic radiation is divided by frequency. 
1. Radio waves. There are short, ultra-short, extra-long, long, medium.
The length of radio waves ranges from 10 km to 1 mm, and from 30 kHz to 300 GHz.
Their sources can be both human activity and various natural atmospheric phenomena.
2. . The wavelength ranges from 1mm to 780nm, and can reach up to 429 THz. Infrared radiation is also called thermal radiation. The basis of all life on our planet.
3. Visible light. Length 400 - 760/780 nm. Accordingly, it fluctuates between 790-385 THz. This includes the entire spectrum of radiation that can be seen by the human eye.
4. . The wavelength is shorter than that of infrared radiation.
Can reach up to 10 nm. such waves are very large - about 3x10^16 Hz.
5. X-rays. waves are 6x10^19 Hz, and the length is about 10 nm - 5 pm.
6. Gamma waves. This includes any radiation that is greater than X-rays, and the length is shorter. The source of such electromagnetic waves is cosmic, nuclear processes.
Scope of application
Somewhere since the end of the 19th century, all human progress has been associated with the practical use of electromagnetic waves.
The first thing worth mentioning is radio communication. It gave people the opportunity to communicate, even if they were far from each other.
Satellite broadcasting and telecommunications are a further development of primitive radio communications.
It is these technologies that have shaped the information image of modern society.
Sources of electromagnetic radiation should be considered both large industrial facilities and various power lines.
Electromagnetic waves are actively used in military affairs (radars, complex electrical devices). Also, medicine could not do without their use. Infrared radiation can be used to treat many diseases.
X-rays help determine damage to a person's internal tissues.
Lasers are used to perform a number of operations that require pinpoint precision. 
The importance of electromagnetic radiation in human practical life is difficult to overestimate.
Soviet video about the electromagnetic field:
Possible negative impact on humans
Although useful, strong sources of electromagnetic radiation can cause symptoms such as:
Fatigue;
Headache;
Nausea.
Excessive exposure to certain types of waves causes damage to internal organs, the central nervous system, and the brain. Changes in the human psyche are possible.
An interesting video about the effect of EM waves on humans:
To avoid such consequences, almost all countries in the world have standards governing electromagnetic safety. Each type of radiation has its own regulatory documents (hygienic standards, radiation safety standards). The effect of electromagnetic waves on humans has not been fully studied, so WHO recommends minimizing their exposure.
Comfort of life is provided by various devices and installations that emit waves that affect health in high concentrations. Therefore, every person should know how to measure electromagnetic radiation in order to protect themselves from negative effects.
Definition of the concept
Electromagnetic radiation is defined as an altered state of the electromagnetic field. It is generated by the movement of electrical charges and is capable of affecting a person far from the source, reducing its impact with increasing distance.
Radiation consists of waves, which are divided into the following types:
- radio emission;
- infrared;
- terahertz;
- ultraviolet;
- visible light;
- X-ray.
Any space is exposed to different frequencies, wavelengths and polarizations. In this case, radiation can have a negative impact on the operation of electrical appliances and living organisms.
The first sign of an increase in the level of electromagnetic radiation in an apartment or industrial premises is the incorrect operation of household appliances (their breakdowns and malfunctions), interference when reproducing images and sounds on a TV, improper operation of personal computers, and interference in radio communications.
How harmful is electromagnetic radiation?
The human body and domestic animals depend on environmental conditions. Every day a person is faced with the operation of numerous devices that can influence the electromagnetic background. At elevated levels of this background, protective measures must be taken.
A person in a room can be negatively affected by electrical wiring and electrical appliances, nearby power lines, transformer substations, transmitting television and radio stations. A greater impact can be caused by EMR that has high rates when located at a close distance.
Exposure to sources that generate radiation has a detrimental effect on:
- heart and blood vessels;
- immune system;
- female and male sexual health;
- nervous and endocrine system.
Increased electromagnetic background causes fatigue in the body, causes blood diseases and malignant tumors. Therefore, every person should know how to measure electromagnetic radiation.
Example of electromagnetic background
You can clearly imagine the level of electromagnetic radiation using the following example. For this purpose, the interior space of an office is suitable, in which there are the following devices: a personal computer with WI-FI, a cell phone, a WI-FI router, a Yota WiMax device, a microwave oven, a household fan.
Each of the devices generates electromagnetic radiation. When the state of the device changes, it also changes. The ATT-2592 meter will show the maximum numbers when the device is working and located next to the meter. Accordingly, the minimum will be for a switched off device located at a distant distance and emitting radiation away from the meter.
For example, the highest voltage of electrical radiation located next to a cell phone meter with a sensor directed towards the antenna will be 24.52 V/m, with an omnidirectional one - 11.44 V/m. If the transmitting device is 0.3 m away from the sensor and the antenna is turned to the side, the highest voltage value will be 10.65 V/m. The example clearly shows how electromagnetic background can be reduced.
Manual Radiation Measurement Instructions
In order to measure electromagnetic radiation in an apartment, you first need to prepare the necessary tools and instruments. To work, you will need a screwdriver with an indicator, a simple radio receiver, and a hand-held analyzer for measuring radiation.
The process of measuring radiation using a receiver includes the following steps:
- Pull the antenna out of the receiver and screw a wire loop with a diameter of 40 cm to it.
- Tune the radio to an empty frequency.
- Slowly walk around the room, listening to the sounds of the receiver.
- Draw a conclusion: the place where distinct sounds are heard is a source of radiation.
The measurement of electromagnetic radiation can be visually carried out using an indicator screwdriver with an LED. You can buy it in the store. If you bring the device close to the switched on device, the indicator will light up red, the intensity of which will indicate the strength of the radiation. These methods will not allow you to determine radiation in numbers.
Diagnostics with a special device
A special device – a handheld analyzer – will help you measure electromagnetic radiation in numbers. It operates at different frequencies and allows you to capture the level of electromagnetic field strength. The device is available to employees of the State Sanitary and Epidemiological Supervision services, labor protection and certification organizations.
This electromagnetic radiation meter is adjusted to the desired frequency mode. Then the units of measurement are selected. These can be volts/meter or microwatts/cm². The device monitors the selected frequency, the results are displayed on the computer.
Device Description
There are many instruments with which electromagnetic radiation is measured. The optimal solution is the ATT-2592 electromagnetic radiation level meter. The device is portable, has a 3-channel sensor, a backlit LCD display, a memory capacity of 99 measurements, powered by a Krona battery (9 V), dimensions 60/60/237, weighs 200 g.
Measurements are performed isotropically in the frequency range from 50 MHz to 3.5 GHz, sampling frequency is 2 times per second, turns off automatically after 15 minutes. The device allows you to measure voltage in the following units: mV/m, V/m, µA/m, mA/m, µW/m², mW/m², µW/cm².
EMR measurement procedure
In any room there is a danger of excess electromagnetic background. If this is a production facility, then there is strict monitoring of indicators. In residential premises, the owner himself must take care of how to measure electromagnetic radiation and minimize its harmful effects.
Only specialists can give an accurate picture of EMR in a private home. They operate within the law according to the following scheme. When the SES service receives a corresponding application, workers go to the site with special equipment to assess the state of the electromagnetic background in the room.
The devices allow you to obtain accurate data, which is then processed. In the case of a normal background, no measures are taken. If the indicators are overestimated, then a set of measures is developed that can lead to a decrease in the background. First of all, the reason for this situation is clarified. These could be errors in design and construction, violation of the rules of operation of the facility.
Electromagnetic radiation examination
The electromagnetic field is formed by the interaction of opposite charges of physical bodies with each other, is formed next to the generation source and is divided into three types (far, intermediate, near).
The amount of electromagnetic radiation is calculated using two components: electrical (volt/meter) and magnetic (tesla). Both of them are divided into low and high frequency waves, which have different origins and conditions of occurrence. The second component has a harmful effect on living beings.
An electric field above normal is typical for places where faxes, televisions, printers, stoves, and copiers are installed, emitting electromagnetic waves that move in space. The level of the magnetic field is increased near electrical wires, transformers, and antennas, as it arises due to the movement of current through the wires.
As part of the work of the Sanitary and Epidemiological Service of the Russian Federation, a Federal Law was adopted, on the basis of which representatives of the service carry out an examination of premises using special equipment. The objects of inspection are household electrical appliances, radio communication systems, transformer substations, radar installations, and power lines.
Sanitary standards
The law establishes standards for electromagnetic radiation. The maximum permissible rate of the emitted magnetic component is from 0.2 to 10 µT. An increased level of the magnetic field is recorded when the radiation frequency reaches 50 Hz. A properly installed power supply system will help prevent magnetic radiation from exceeding the norm.
The standards for the electric field contain the following indicators enshrined in the law:
- residential premises (up to 0.5 kV/m);
- residential zone (up to 1 kW/m);
- outside the residential area (up to 5 kV/m);
- at the intersection of high-voltage power lines with class I-IV highways (up to 10 kV/m);
- in uninhabited areas (up to 20 kV/m).
If officials violate these norms, administrative liability is provided. These indicators are important for summer residents, since the plots are often located in the area of high-voltage power lines.
It is very important to remember that a person is often unconsciously exposed to EMR, since he simply does not have the ability to independently measure the level of emitted waves. In addition, the norms are conditional in nature, since it is still necessary to take into account the individual characteristics of the body.
Methods of protection against exposure
In the event that it is established that the exposure to electric current on a person exceeds the norm, it is necessary to reduce the stay in the danger zone to a minimum. Increasing the possible distance from a harmful source in many cases makes it possible to reduce undesirable effects on the body.
Another method of protection is the installation of special structures that will prevent the spread of dangerous waves. Do not neglect personal protective equipment (shoes, clothing, glasses, masks, etc.). These items are used by specialists during work and can reduce harmful indicators.
There are so-called organizational means of protection. They are used from time to time in relation to the entire team (working, living in areas of possible increased background). Such means include routine medical examinations and vacations, which help protect human health.
Electricity is a significant invention of mankind. It is impossible to imagine our life without it today. But at the same time, EMR generated when electricity is used for human needs can have a negative impact on life and health.
Pulmonologist, Therapist, Cardiologist, Functional Diagnostics Doctor. Doctor of the highest category. Work experience: 9 years. Graduated from Khabarovsk State Medical Institute, clinical residency in therapy. I am engaged in the diagnosis, treatment and prevention of diseases of internal organs, and also conduct medical examinations. I treat diseases of the respiratory system, gastrointestinal tract, and cardiovascular system.
Ministry of General and Professional
education of the Russian Federation.
Orsk Humanitarian-Technological Institute
Department of General Physics.
COURSE WORK
Measurements of parameters of electromagnetic waves at ultrahigh frequencies.
Completed by: student of the Faculty of Physics and Mathematics, group 4B
Bessonov Pavel Alexandrovich .
Scientific supervisor: Ph.D. n. assistant professor Abramov Sergey Mikhailovich .
Orsk. 1998
1. Basic concepts 3
2. §1. Power measurement 3
3. 1. General information 3
4. 2. Calorimetric power meters 3
5. §2. Frequency measurement 8
6. 1. Main characteristics of frequency meters 8
7. 2. Resonant frequency meters 8
8. 3. Heteroid frequency meters 13
9. §3. Impedance measurement 15
10. 1. General information 15
11. 2. Polarization impedance meters 51
12. 3. Panoramic SWR and impedance meters 17
BASIC CONCEPTS
In the microwave range, as a rule, the power, frequency and impedance of devices are measured. Also important are measurements of the phase shift, field strength, quality factor, wave power attenuation, amplitude-frequency spectrum, etc. To determine these quantities in wide ranges of their variation, it is necessary to use various methods and radio measuring instruments.
There are direct and indirect measurements. Direct measurements are used in cases where the measured quantity can be directly compared with a measure or can be measured with instruments calibrated in selected units. Direct measurements are carried out either by the method of direct assessment, when the measured value is determined by the readings of a calibrated instrument, or by the comparison method, when the measured value is determined by comparing it with the measure of a given value. Indirect measurements consist of replacing measurements of a given quantity with others related to the desired known relationship.
The main characteristics of radio measuring instruments are: range of measured values; frequency range in which the device can be used; sensitivity for the measured parameter, which is the ratio of the increment in the instrument readings to the increment in the measured value that caused it; resolution, defined as the minimum difference between two measured values that the device can distinguish; error; power consumption.
§1. POWER MEASUREMENT.
1. General information
The power levels to be measured vary by more than twenty orders of magnitude. Naturally, the methods and instruments used for such measurements are very diverse. The operating principle of the vast majority of microwave power meters, called wattmeters, is based on measuring changes in temperature or resistance of elements in which the energy of the electromagnetic oscillations being studied is dissipated. Instruments based on this phenomenon include calorimetric and thermistor power meters. Wattmeters using ponderomotive phenomena (electromechanical forces) and wattmeters operating on the Hall effect have become widespread. The peculiarity of the first of them is the possibility of absolute power measurements, and the second - power measurement regardless of the coordination of the RF path.
Based on the method of inclusion in the transmitting path, wattmeters are divided into transmitting type and absorbing type. The transmitted type wattmeter is a four-terminal device in which only a small part of the total power is absorbed. An absorption-type wattmeter, which is a two-terminal network, is connected at the end of the transmission line, and ideally, all the power of the incident wave is absorbed in it. A transmitted-type wattmeter is often based on an absorption-type meter connected to the path through a directional coupler.
2. Calorimetric power meters
Calorimetric methods for measuring power are based on the conversion of electromagnetic energy into thermal energy in the resistance of the load, which is an integral part of the meter. The amount of heat generated is determined by the temperature changes in the load or in the environment to which the heat is transferred. There are static (adiabatic) and flow (non-adiabatic) calorimeters. In the first, the microwave power is dissipated in a thermally insulated load, and in the second, a continuous flow of calorimetric liquid is provided. Calorimetric meters allow you to measure power from a few milliwatts to hundreds of kilowatts. Static calorimeters measure low and medium power levels, while flow calorimeters measure medium and high power levels.
The heat balance condition in the calorimetric load has the form
where P is the microwave power dissipated in the load; T And T 0- load and ambient temperature, respectively; With , m- specific heat capacity and mass of the calorimetric body; k-thermal dissipation coefficient. The solution to the equation is represented in the form
(2)
Where τ =c m / k- thermal time constant.
In the case of a static calorimeter, the measurement time is much less than the constant τ and microwave power in accordance with the formula 1 will:
(3,a)
Here the rate of temperature change in the load is measured in degrees s -1, m-in g, c- in J (g deg) -1, R- in W.
If With has the dimension cal (g deg) -1, then
(3,b)
The main elements of static calorimeters are a thermally insulated load and a temperature measuring device. It is easy to calculate the absorbed microwave power from the measured rate of temperature rise and the known heat capacity of the load.
The instruments use a variety of high-frequency terminations made of solid or liquid lossy dielectric material, or in the form of a high-resistance plate or film. Thermocouples and various thermometers are used to determine temperature changes.
Let's consider a static calorimeter, in which the requirements for thermal insulation are reduced and there is no need to determine the heat capacity T c calorimetric attachment (Fig. 1 ). This circuit uses the substitution method. In it for calibrating the device 4 , measuring the temperature increase as the measured power supplied to the arm is dissipated 1 , a known direct current or low frequency current power is used, supplied to the arm 2. It is assumed that the temperature of the nozzle 3 changes equally when dissipating equal values of microwave power and direct current. Static calorimeters can measure power of several milliwatts with an error of less than ±1%.
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Rice. 1 |
The main elements of a flow calorimeter are: a load, where the energy of electromagnetic vibrations is converted into heat, a fluid circulation system, and a means for measuring the temperature difference between the incoming and outgoing fluid flowing through the load. By measuring this temperature difference at steady state, the average power can be calculated using the formula
(4)
Where υ - flow rate of calorimetric liquid, cm 3 s -1; d- liquid density, g cm -3; Δ T - temperature difference, K; With, cal (g deg) -1 .
Flow calorimeters are distinguished by the type of circulation system (open and closed), by the type of heating (direct and indirect) and by the measurement method (true calorimetric and replacement).
In open-type calorimeters, water is usually used, which from the water supply network first enters the tank to stabilize the pressure, and then into the calorimeter. In closed-type calorimeters, the calorimetric liquid circulates in a closed system. It is constantly inflated by a pump and cooled to ambient temperature before entering the calorimeter again. In this system, in addition to distilled water, a solution of sodium chloride, a mixture of water with ethylene glycol or glycerin are used as coolants.
With direct heating, RF power is absorbed directly by the circulating fluid. With indirect heating, the circulating fluid is used only to remove heat from the load. Indirect heating allows operation over a wider range of frequencies and powers, since the functions of heat transfer are separated from the functions of RF energy absorption and load matching.
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Rice. 2 . |
The diagram of the true calorimetric method is shown in (Fig. 2 .). The measured RF power is dissipated in load 1 and directly or indirectly transfers energy to the flowing fluid. The temperature difference between the liquid entering and exiting the load is measured using thermoblocks 2. The amount of liquid flowing in the system per unit time is measured with a flow meter 3. Naturally, the flow of liquid during such measurements must be constant.
RF power measurement errors in the considered circuit are associated with a number of factors. First of all the formula 4 does not take into account the heat transfer existing between different parts of the calorimeter and the heat loss in the RF load and piping. Various design techniques can reduce the influence of these factors. The unevenness of the flow rate of the calorimetric liquid and the appearance of air bubbles lead to an error in determining the flow rate of the liquid and a change in its effective heat capacity. To reduce this error, air bubble traps are used and uniform fluid flow is achieved using a flow regulator and other means.
The measurement circuit that implements the substitution method differs from the one considered in that an additional heating element is introduced in series with the microwave load, dissipating the power of the low-frequency current source. Note that with indirect heating, the power of the microwave signal and the power of the low-frequency current are introduced into the same load and the need for an additional heating element disappears.
There are two possible measurement methods using the substitution method - calibration and balance. The first of them is to measure the low frequency power supplied to the heating element at which the difference in temperature of the liquid at the inlet and outlet is the same as when applying microwave power. With the balanced method, a certain temperature difference in the liquid is first established when low-frequency power P 1 is supplied, then the measured RF power P is supplied, and the low-frequency power is reduced to such a value P 2 that the temperature difference remains the same. In this case, P=P 1 -P 2.
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Rice. 3 . |
Measurement errors associated with the variability of the fluid flow rate during the measurement cycle can be avoided if there is load 1 at the input and output (Fig. 3 ) and heating element 2, provide temperature-sensitive resistors R 1, R 2, R 3, R 4 connected via a bridge circuit. Provided that the temperature-sensitive elements are identical, the balance of the bridge will be observed for any fluid flow rate. Measurements are carried out in a balanced manner.
The considered flow calorimeters are used for absolute measurements, primarily at high power levels. In combination with calibrated directional couplers, they serve for calibration of medium and low power meters. There are designs of flow calorimeters for direct measurements of medium and low powers. The measurement time does not exceed several minutes, and the measurement error can be reduced to 1-2%
Among the calorimetric wattmeters for measuring the power of continuous oscillations, as well as the average power of pulse-modulated oscillations, we note the devices MZ-11A, MZ-13 and MZ-13/1, which cover the range of measured powers from 2 kW to 3 MW at frequencies up to 37. 5 GHz.
§2. FREQUENCY MEASUREMENT
1. Main characteristics of frequency meters
One of the most important tasks of measuring technology is to measure the frequency or wavelength of vibrations. Frequency is related to wavelength as follows: (5)
The measurements of frequency and wavelength are different in nature: the first is based on the measurement of time, and the second is based on the measurement of length. Typically, frequency is chosen as the main quantity, since its value does not depend on propagation conditions and, just as important, there are high-precision frequency standards with which the measured frequencies can be compared.
The main characteristics of instruments used to measure frequency and wavelength are: relative error, sensitivity, range of measured frequencies and operational reliability.
The relative error of a device is understood as the ratio of the difference between the measured and reference frequencies to the value of the reference frequency. According to accuracy, all devices are divided into three groups: low accuracy with a relative error of more than 0.1%, medium accuracy with an error of (0.01-0.1)% and high accuracy with an error of less than 0.01%. The sensitivity of the device is characterized by the minimum signal power supplied to the frequency meter at which frequency reading is possible.
2. Resonant frequency meters
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Rice. 4 .
Rice. 5 . |
Resonant frequency meters usually contain the following elements (Fig. 4 ): volumetric resonator 2, communication elements 1, tuning element 3, indicator 5 with or without amplifier 4. The connection between the input line and the indicator device with the resonator is selected based on a compromise between the value of the loaded quality factor of the resonator and the sensitivity of the device. The frequency meter is tuned to a specific frequency of measured oscillations by measuring the geometric dimensions of the resonator. In this case, the dimensions of the resonant wavelength or frequency are determined by the position of the tuning elements at the moment of resonance, which is determined by the indicator device. As indicators, a direct current microparameter is most often used, and when the frequency of modulated oscillations changes, an oscilloscope or measuring amplifier is used. There are two ways to turn on the frequency meter - with indication of the setting according to the maximum current of the device (pass-through circuit) and the minimum current (absorption or absorption circuit). The first scheme, which has become most widespread, is shown in (Fig. 5) . A resonator with coupling elements and a frequency tuning device is shown in (Fig. 5.a), its equivalent circuit is shown in (Fig. 5 B). When the resonance of the frequency meter is detuned, the reading of the indicator device is zero. At the moment of resonance, maximum current flows through the device (see Fig. 5.c).
In some cases, a second circuit for switching on a resonant frequency meter is useful - with an indication of the minimum current at. resonance. The structure of such a resonator is shown in (Fig. 6a), the equivalent circuit is shown in (Fig. 6b). At frequencies other than resonant, the input impedance of a parallel-connected circuit is small and, being transformed into a circuit. detector through a segment of length λ/4, does not introduce noticeable changes into the main circuit. As a result, through the indicator device of the frequency meter, the corresponding frequency of the measured oscillations is carried out by changing the geometric dimensions of the resonator. In this case, the value of the resonant wavelength or frequency is determined by the position of the tuning elements at the moment of resonance, which is noted by the indicator device. A DC microammeter is most often used as indicators, and when measuring the frequency of modulated oscillations, an oscilloscope or measuring amplifier is used. There are two ways to turn on the frequency meter - with indication of the setting according to the maximum current of the device (pass-through circuit) and the minimum current (absorption, or absorption, circuit). The first scheme, which has become most widespread, is shown in (Fig. 2 ). A resonator with coupling elements and a frequency retuning device is shown in (Fig. 2a), its equivalent circuit is shown in (Fig. 26 ). When the frequency meter resonator is detuned, the reading of the indicator device is zero. At the moment of resonance, maximum current flows through the device (see Fig. 2v).
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Rice. 6 . |
Let's consider the design features of resonant frequency meters. They mainly differ in the type of oscillatory systems.
On (Fig. 7 ) shows resonator devices with communication and tuning elements, most often used in resonant frequency meters. On (Fig. 7a) the design of a resonator in the form of a quarter-wave section of a coaxial line is shown. The resonator is connected to the RF generator and the measuring device through loops located in the side wall. The resonator is adjusted by changing the length of the central conductor. The scale of the micrometer connected to the central conductor is graduated in wavelengths or provided with a calibration curve. The RF contact between the inner conductor and the end wall of the resonator is formed using a capacitor. The opposite end of the resonator is closed with a metal cover. Due to the capacitive edge effect, the resonant length at the free end of the central conductor is slightly less than λ/4.
Coaxial type frequency meters are used primarily in the wavelength range 3-300 cm. The adjustment range of frequency meters with a moving central conductor is 2:1. The error of frequency meters of coaxial design is (0.05-0.1)% and depends on the design features of the device and the accuracy of calibration.
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Rice. 7 . |
At higher frequencies in the microwave range, resonant frequency meters in the form of cylindrical volumetric resonators are used. Resonators excited by vibrations of the type H O 011 and H O 111 have greater broadband and high quality factor.
In the case of resonators based on vibrations of the type H O 011, a non-contact end plate can be used to change the length of the cylinder (see Fig. 7, b), since the current lines of vibrations of this type have the form of circles in the cross section of the cylinder. The presence of a gap is necessary to eliminate other types of vibrations whose current lines pass through the gap. The field of these vibrations, excited in the space behind the plate, is absorbed in a special absorbing layer. The most dangerous are vibrations of the type E O 111, which have the same resonant frequency as H O 011. To suppress it, in addition to the measures listed above, the choice and arrangement of coupling elements are of great importance, taking into account the difference in the configuration of oscillation fields of the form H O 011 and E O 111. In the case under consideration, the coupling element is a narrow slot cut along the generatrix of the cylinder and along the narrow wall of the supply waveguide. Increased demands are placed on the careful manufacturing of the resonator, since even a slight asymmetry can lead to the excitation of vibrations of the E O 111 type and to a decrease in the quality factor of the resonator, reaching 50,000 in the 10-cm wavelength range.
The error in measuring frequency with a resonant frequency meter depends on the accuracy of its adjustment to resonance, on the perfection of the mechanical system and calibration, as well as on the influence of humidity and ambient temperature.
The accuracy of tuning to resonance depends on the loaded quality factor of the resonator Q and the error of the indicator device:
(6)
Where Δ f-frequency detuning at which the current amplitude in A times less than the current amplitude at resonance. To decrease Δ f / f 0 , you need to choose A as close as possible to unity, i.e. it is necessary to have an accurate indicator device that marks small changes in current. So, if A= 1.02, then Δ f / f 0 = 1/ 10 Q n and at Q n=5000 turns out Δ f / f 0 =2·10 -5.
In resonant frequency meters with a high quality factor, a certain error is introduced by mechanical inaccuracy of adjustment due to backlash in the drive, unreliable contacts between the moving parts of the resonator, etc.
The larger the frequency range the frequency meters are designed for, the greater the measurement error associated with the inaccuracy of reading readings. This error can be calculated using the formula
Where Δl- error in determining the position of the tuning element, usually corresponding to the price of one division and equal to 0.5-10 microns. In order for this error to be the same throughout the entire operating frequency range, it is necessary to have df / dl proportional f 0 .
Resonant frequency meters are usually calibrated by comparing their readings with the readings of a reference device at different frequencies. Acceptable accuracy is obtained if the error of the standard frequency meter, together with the error of the method, is five times less than the error of the calibrated device.
A change in the dielectric constant of air, caused by the variability of its temperature and humidity, leads to a change in the resonant frequency of the frequency meter, and consequently to a measurement error. Under normal conditions, this error reaches 5 10 -5.
When the ambient temperature changes, the geometric dimensions of the resonator change, and this, in turn, leads to an error in frequency measurement. The error from this cause is calculated using the formula
Δ f / f 0 =- αkΔT (8)
where α is the linear temperature expansion coefficient of the resonator material; k-coefficient depending on the design of the resonator. For cylindrical resonators ( k=1), made of copper, a temperature change of 1°C gives an error in frequency of 2 10 -5.
The table shows the main parameters of some resonant frequency meters in continuous generation (CW) and pulse modulation (PM) modes. The measurement error for all given devices is 0.05%. The last column gives the resistance of the coaxial input element or the cross-section of the rectangular waveguide.
The devices discussed in the table consist of a resonator, a 10 dB variable attenuator, an amplifier and an indicator. In frequency counters Ch2-31-Ch2-33, cylindrical resonators are used as a resonant system, excited by vibrations of the type H O 112, and in other frequency counters, coaxial-type resonators are used. The resonators are connected in a pass-through circuit.
Parameters of resonant frequency meters
3. Heterodyne frequency meters.
The most accurate frequency meters are devices based on comparing the frequency of the signal under study with the frequency of a highly stable source. There are different methods for comparing frequencies: zero beats, interpolation generator and sequential frequency reduction.
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Rice. 8 . Rice. 9 . |
On the linear mixing element (Fig. 8 ) an RF signal with an unknown frequency is supplied f x and a signal with frequency f op from the reference source. The output of the mixer produces signals with the same frequencies, as well as their harmonics and signals with beat frequencies. Since the amplitudes of the harmonic components are small, and therefore the signals of their difference frequency are also small, it is convenient to use a signal with a beat frequency for indication f b = f X – f op =0 . Hence the name of the method - the zero beat method. At the output of the nonlinear element, an indicator is turned on, for example a telephone, transmitting only audio frequency signals. If you smoothly change the frequency of the reference oscillator, then when f X - f op <15000 Гц в телефоне появляется тон разностной частоты, который понижается три сближении f X And f op .
On (Fig. 9 ) shows the nature of the change f b at a fixed unknown frequency f X and tunable frequency f op. At f b <16 Hz the human ear ceases to perceive low frequencies, and as a result the error can reach 32 Hz. To reduce the error, you should use a “fork” count: remember by ear a certain beat tone, for example, corresponding to the frequency f op1. Then note the frequency f op2, in which the same beating tone is heard on the phone. Search frequency f X is the arithmetic mean of the marked frequencies.
In real conditions, the harmonic components of the main signals are simultaneously generated in the mixer, therefore zero beats are noted when the harmonic frequencies are equal nf X=m f op, Where n , t=1,2,3... To eliminate the error in choosing a harmonic in this case, you must first approximately measure the unknown frequency using some method, for example, a resonant one.
If the measured frequency lies outside the frequency range of the reference oscillator, then it is measured by the beat method between the harmonic components and the fundamental frequency signal. So, if f X << f op, then alternately tune the reference oscillator to zero beats with any two adjacent harmonic components of the measured frequency: f op1 =p f X and f op2 =(n±1) f X .
. (9)
If f x 1 >>f oа, then tune the reference oscillator to such two frequencies f op1 and f op2 so that f x =m f op1 and f x =(m±1)f op2. Then
(
10
)
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Since it is difficult to make a reference oscillator with smooth tuning and high frequency stability, they resort to the interpolation method. In this case, in the diagram 1 Along with the intertulation generator, the frequency of which can be smoothly changed, a standard generator with a fixed frequency grid is introduced. The measurement procedure is as follows. The interpolation generator is sequentially adjusted to zero beats with the measured frequency signal f x and with adjacent harmonic components of the reference frequency of the reference generator T f x and (m+1)f op on both sides of the frequency f x . The readings on the scale of the interpolation generator will be α X,α 1, α 2. In this case
(11)
The accuracy of measurements is higher, the smaller the frequency difference between adjacent harmonics of the reference generator, the linear the tuning scale of the interpolation generator and the higher its resolution.
When the frequency difference f X - f op greater than the limiting frequency of the audio frequency meter, double heterodyning can be applied using the circuit 2 . Measurements using this scheme are more accurate, since it is easier to create a frequency meter with high stability and increased measurement accuracy using an interpolation generator with a small frequency tuning range.
The errors of heterodyne frequency meters are determined primarily by the errors of the quartz and interpolation oscillators. Thus, quartz oscillators have a relative frequency error of ±10 -8 –10 -9. The interpolation generator introduces an additional error due to the change in the frequency of the generator during the measurements, the inaccuracy of the scale calibration and the reading error. As a result, the error of such frequency meters is ±5 10 -6. It should be noted that the indicated error value is obtained only after prolonged warming up of the device (up to 1–1.5 hours).
§3. Impedance measurement
1. General information
Issues of measuring the impedance of nodes or elements of the RF path arise whenever they have to be solved. matching problems, finding the parameters of equivalent circuits or calculating the frequency characteristics of microwave devices.
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Rice. 10 . |
The basis for determining the load impedance is its connection with the standing wave coefficient and the position of the minimum voltage in the line. The most widespread is the determination of impedance based on SWR measurements and the position of the minimum of the standing wave using a measuring line. The corresponding functional diagram is presented in (Fig. 10 ). The device whose impedance needs to be measured is connected to the microwave generator through the measuring line. The industry produces measuring lines that cover the frequency range from 0.5 to 37.5 GHz.
Portable instruments for determining impedances based on SWR and phase measurements are polarization type meters. These devices are characterized by broadband and high accuracy. The frequency range they cover extends from 0.02 to 16.67 GHz.
There are devices that provide semi-automatic panoramic measurement of SWR as a function of frequency. These devices can significantly reduce the time for matching devices, as well as observe and measure the amplitude-frequency characteristics of quadripoles. They cover the frequency range from 0.02 to 16.67 GHz.
This chapter discusses the principle of operation of the device, which allows one to determine the impedance values of the devices under study as a function of frequency directly from a circular diagram of the impedances plotted on the screen of the cathode ray tube. Devices of this type cover the frequency range from 0.11 to 7 Hz.
2. Polarization impedance meters
The polarization impedance meter consists of rectangular 7 and cylindrical segments 6 waveguides, and the cylindrical waveguide is located at right angles to the wide wall of the rectangular waveguide (Fig. 11 ). Communication between waveguides is carried out through three slits 8 of the same size, located at an equal distance from the center of the cylindrical waveguide.
The operating principle of the polarization meter is as follows. Electromagnetic N □ 10 - a wave propagating from the generator towards the load excites a circularly polarized HO 11 wave in the cylindrical waveguide. This is achieved by choosing the location and size of the slits: two slits located across the wide wall of the waveguide are located at the maximum of the field component H x , and the third gap is at the maximum of the field component H z. These slits excite two H O 11 waves in a cylindrical waveguide, mutually perpendicular in space and shifted in phase by an angle π/2. The latter is a consequence of the time shift by π/2 of the field components X x and H z in a rectangular waveguide. Since by choosing the size of the slits it is possible to achieve equality in the amplitudes of the excited waves, the wave in a cylindrical waveguide will have circular polarization.
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Rice. 11 . |
If you change the direction of wave propagation in a rectangular waveguide, then a wave with the opposite direction of field rotation is excited in a cylindrical waveguide. Obviously, if there is a reflected wave in a rectangular waveguide, in a cylindrical waveguide there will be two H O 11 waves with opposite directions of circular polarization. As a result of the superposition of these waves, a wave with elliptical polarization is formed, which carries the necessary information about the magnitude of the SWR and the position of the minimum of the standing wave in a rectangular waveguide. SWR is equal to the ratio of the main axes of the ellipse, the values of which correspond to the sum and difference in the amplitudes of the incident and reflected waves.
Table 1
Measuring Line Parameters
3begins, a diode chamber rotating around the waveguide 2 with probe 1 reproduces the distribution of field strength in a rectangular waveguide, and a full revolution of the camera corresponds to the movement of the probe in the rectangular waveguide at wavelength λv. The position of the smaller axes of the ellipse is uniquely related to the position of the field minimum in the rectangular waveguide, i.e., to the phase of the reflection coefficient.
Measuring the phase of the reflection coefficient consists of reading along the dial 5 the position of the diode chamber at which the indicator device shows the minimum value. The diode chamber is rotated using a rotating joint 3. The “phase” reading scale is a semicircle divided by marks into 180 equal parts, so that the value of each scale division corresponds to 2° of the measured phase angle. The accuracy of the reflection coefficient phase reading using a vernier is ±20.
For initial calibration of the device in phase relative to the measuring flange, there is no need to use a short circuit, but rather use the “frequency” scale 4, which is rigidly connected to the diode chamber and can be rotated relative to the “phase” scale. The “frequency” scale is calculated as follows. that when setting the operating frequency, the diode chamber is rotated by an angle equal to the corresponding change in the phase of the wave between the measuring flange and the plane of symmetry of the device.
table 2
Parameters of polarization meters
| Device type |
Frequency range, GHz |
Measurement limits |
Measurement error |
Dimensions of the RF section section, mm |
||
| Phases, degrees |
SWR. % (SWR=1.05÷2) |
phase, rad (SWR=2) |
||||
| 0,15-1 8,24-2,05 |
4.1 (at SWR=1.2) 4.1 |
|||||
| Diameters of the outer and inner conductors of the coaxial * 2 Wide and narrow waveguide walls, |
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The polarization meter allows you to determine the impedance even at high microwave power levels. To do this, the device provides for replacing the diode with a diode plug, which has the same dimensions. A variable attenuator is placed between the polarization meter and the external diode chamber, by adjusting which the power level on the diode is achieved within the limits corresponding to the quadratic portion of the characteristic.
It is preferable to use measuring amplifiers as an indicator device when working with polarization meters. The parameters of polarization meters are given in Table. 2 .
3. Panoramic SWR and impedance meters
A panoramic SWR meter consists of a sweep generator, a voltage ratio meter with a directional coupler, and an oscilloscope instrument (Fig. 12 ). The principle of operation of the device is to isolate a signal proportional to the power of the reflected wave and subsequently measure the ratio of the powers of the reflected and incident waves, which is equal to the square of the modulus of the reflection coefficient.
After amplification, this voltage enters the vertical deflection channel of the oscilloscope. The horizontal plates of the oscilloscope are supplied with voltage from a generator that acts as a frequency modulator of the microwave generator. As a result, a curve of the square of the reflection coefficient versus frequency is observed on the tube screen (curve 1 in Fig. 13 ).
To calibrate the SWR at some frequencies, an electronic commutator is used, which alternately supplies either the amplified output voltage of the ratio meter or a reference voltage to the vertical deflection channel. As a result, on the screen against the background of the curve 1 the luminous hairline is visible 2. By changing the reference voltage, we achieve alignment of the sighting line with the point of interest on the curve 1. The SWR value at this point is counted on the scale of the device, calibrated in SWR values, and the frequency is determined using a built-in frequency meter.
Difficulties in the practical implementation of the circuit are associated with the need to use a sweep generator with a linear frequency change in the sweep range, as well as the same or similar transient characteristics of both directional couplers and the same or similar characteristics of the diode chambers over the entire operating frequency range. Typically, a VOC is used as a sweep generator. A linear change in frequency in the sweep range is achieved by applying periodic exponential pulses to the slow-wave system of the lamp.
In another version of the panoramic SWR meter, the signal from the coupler's diode chamber, proportional to the amplitude of the reflected wave in the path, is fed directly to the vertical plates of the oscilloscope. The measurement accuracy now depends on the constancy of the power of the sweep generator throughout the entire sweep range. To stabilize changes in signal power that inevitably occur during frequency modulation, the generator is equipped with an automatic power regulator. Part of the branched incident power is supplied to the input of the automatic control circuit, where it is compared with the reference voltage. The error signal generated by the circuit is applied to the first anode of the BWO (internally controlled stabilization) or to an electrically controlled attenuator (external stabilization), thereby ensuring a constant power level across the frequency band.
Table 3.
Parameters of automatic panoramic SWR and attenuation meters.
Panoramic meters can operate in amplitude modulation mode with a rectangular pulse voltage with a frequency of 100 KHz. Along with periodic frequency tuning with different periods and sweep stopping at the selected frequency with automatic counting, manual frequency tuning is also possible using a frequency meter with tracking setting of the measured value.
Panoramic SWR meters allow you to measure the attenuation introduced by quadripoles. Measuring attenuation comes down to determining the ratio of the powers of the output and input signals of a quadripole network.
Automatic panoramic SWR and attenuation meters produced by industry cover the frequency range from 0.02 to 16.66 GHz. The main parameters of some of them are given in table. 3. In the table, A is the attenuation set on the attenuator scale. The RF power input of the first three devices is coaxial, while the rest are waveguide.
Another type of automatic meters are panoramic impedance meters and complex gain meters. The measurement results are presented in polar or rectangular coordinates on the screen of an oscilloscope 1B in the form of the dependence of the total resistance of the object under study as a function of frequency.
The device consists of three blocks: a sweep generator, an impedance sensor and an indicator (Fig. 14 ). The impedance sensor is an HF unit with four measuring heads, from the output of which LF voltages are removed. The heads are located at a distance of λ in /8 from each other.
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Rice. 14 . |
Let us establish a connection between the signal at the output of the quadratic detector of the measuring head and the reflection coefficient in the line. Let us write the voltage on the first probe in the form
(13)
where ψ=2k z z-ψ n; z - distance between probes and load; ψ n and |G| -phase and modulus of reflection coefficient from the load. Let's imagine the voltage on the first probe like this:
Then the current passing through the detector with a quadratic characteristic:
(15)
Where b - constant. The current through the detector connected to the third probe and separated from the first by a distance λ in /2 is equal to
(16)
Accordingly, the currents through the second and fourth detectors
(17)
(18)
Measuring heads must be adjusted so that 
.
Then at the output of the subtractor associated with the first and third measuring heads, there will be a signal defined by the expression
(19)
and at the output of another subtractor connected to the second and fourth; measuring heads, the signal will be presented in the form
(20)
Where k And k ’- permanent.
After amplification in appropriate DC amplifiers, these signals, phase-shifted by 90°, are fed to the horizontal and vertical plates of the oscilloscope. Their amplitudes are adjusted to ensure equal beam deflection in both directions. This means that when the phase of the reflection coefficient changes by 360°, the beam will draw a circle of radius on the screen. corresponding to the module of the reflection coefficient.
If the generator frequency changes linearly in time, then the complex reflection coefficient from the measured object also changes, i.e. change |G|=F(f) and ψ n =F(f) . The beam draws a curve, the radial deviation of which is proportional to |Г|, and the azimuthal position corresponds to ψ n.
The accuracy of impedance measurement over a frequency range depends on the identity of the four indicator devices and the stability of the output power of the frequency modulated generator as the frequency changes.
The automatic impedance meter RK.4-10 is designed for the frequency range 0.11-7 GHz with measurement limits for phase shift 0-360°, gain modulus 60 dB and SWR 1.02-2. Measurement error: phase shift 3°, phase reflection coefficient 10°, SWR 10% (at SWR ≤2)
LITERATURE:
1. Lebedev I.V. Microwave equipment and devices. M., Higher School, vol. I, 1970, vol. II, 1972.
2. Sovetov N.M. Ultrahigh frequency technology. M., Higher School, 1976.
3. Kovalenko V.F. Introduction to microwave technology. M., Sov. radio, 1955.
4. Feldshtein A.L., Yavich L.R. Handbook on elements of waveguide technology. M.–L., Gosenergoizdat, 1963.
5. Krasyuk N.P., Dymovich N.D. electrodynamics and radio wave propagation. M., Higher School, 1947.
6. Weinstein L.A. Electromagnetic waves. M., Sov. radio, 19557
7. Mattei D.L., Young L.E., Jones M.T. Microwave filters, matching circuits and communication circuits: Per. from English M., Communication, 1971.