Transmitter signal output power. Measuring Parameters in RF Systems How to Measure the Power of a Radio Signal at a Specific Frequency

The main parameter of a radio transmitting device is the power of the signal emitted over the air. It should be noted that the requirements for the signal power in the VHF range are dictated by the characteristics of the propagation of radio waves in this frequency range.

The first feature of the VHF band is the straight-line propagation of radio waves within the line of sight. Figure 1 illustrates this characteristic of radio propagation in this range.

Roughly, taking into account the refraction of radio waves in the VHF range, the line-of-sight range in kilometers L is defined as:

When the height of the base station antenna and the repeater is 70 m, the communication range cannot exceed 70 km:

When the height of the antenna of the base station and the repeater is 70 m, the communication range cannot exceed 70 km. Approximate VHF line-of-sight ranges are shown in Figure 2.

Let us calculate the output power of the transmitter signal required for a given distance. To do this, we use the well-known formula for determining the signal power at the input of the radio receiving device:

It should be noted that in mobile systems, signal strength is measured in dBm. It is the ratio of the absolute value of the signal power, expressed in watts, to the signal power of 1 mW.

For example, a signal power of 2 W corresponds to 33 dBm, and a signal power of 10 W corresponds to 40 dBm. This approach allows replacing the division and multiplication operations with subtraction and addition, respectively. In this case, the formula for determining the signal power at the input of the radio receiving device (2), expressed in decibels, will take the following form:

Let us express from it the power required from the transmitter when operating in free space. For 160 MHz and omnidirectional antennas, this power will be:

With a signal-to-noise ratio at the demodulator input equal to 6 dB, you can limit the transmitter power to 1 mW.

On the other hand, when a radio wave propagates along the earth's surface, it experiences additional absorption. The Huygens-Fresnel principle is used to explain the phenomenon of radio waves bending around various obstacles, their penetration into the shadow and penumbra regions. In accordance with the Fresnel model, the region of propagation of radio waves between the transmitting and receiving devices is limited by an ellipsoid of revolution around the line connecting them. This ellipsoid is multi-layered and can include infinitely many zones.

The zone closest to the line connecting the transmitter to the receiver is called the first Fresnel zone. It is generally accepted that the first Fresnel zone is the most significant in the propagation of radio waves. It contains about half of the transmitted energy. Figure 3 shows a longitudinal section of the first Fresnel zone.

For any point of the radio link, the radius of the first Fresnel zone (R0) can be found by the formula:

Taking into account the influence of the Earth's surface, the largest radius of the first Fresnel zone is important. With the same antenna heights, this radius will be in the middle of the radio link. In this case, formula (6) is transformed to the following form:

With a radio link distance of more than 5 km, it is necessary to additionally take into account the curvature of the Earth as an obstacle. This effect is illustrated in Figure 3. To account for the rise in the ground level in the middle of the radio link due to its curvature, you can use the following formula:

The values ​​of the height of the obstacle created by the curvature of the Earth for the relative distances r tek / L are given in Table 1.

Table 1

Now let's calculate the additional absorption of the signal due to its shadowing by the Earth's surface. To do this, calculate the height h max at the center of the radio path:

In this case, the relative clearance of the radio link will be equal to

Now, according to the graph of the dependence of the signal attenuation relative to the obstacle clearance, shown in Figure 4, we will determine the additional signal attenuation.

For a relative radio link clearance of -0.37, the additional signal attenuation is 50 dB. As a result, the required transmitter power increases from -6 dBm to +44 dBm. This power corresponds to a transmitter power of 20 W.

In this case, we considered a situation where a single radio transmitter is located in one place. However, there are not so many places convenient for placing base station repeaters. Therefore, usually a large number of radio transmitters of radio systems for various purposes are concentrated in one place. In order for them not to interfere with each other, various decoupling devices, such as filters, circulators, combiners, have to be installed at the output of the transmitter. Each of them attenuates the power of the radio signal. In addition, the signal can be attenuated by the antenna-feeder path. The total signal attenuation can be up to 12 dB. This leads to the fact that even if the power at the output of the transmitter is equal to 100 W, then only 6 W will reach the antenna:

To illustrate, let's convert this value to watts:

conclusions

• To work in the VHF range, taking into account the influence of the curvature of the earth's surface and obstacles, a transmitter power of at least 2 W is required
• For stationary radio stations, the required power increases to 50 ... 100 W due to losses in feeders and combiners

Literature:

Other parameters of radio transmitting devices:

A very important characteristic of a radio transmitting device is the radiated frequency range. For the organization of mobile radio communications in the VHF range ...
http: // site / UGFSvSPS / DiapPrdFr /

When forming a radio signal, it is very important that the entire spectrum of the emitted signal is concentrated within the frequency band allocated for a given radio channel ...
http: // site / UGFSvSPS / maska ​​/

Purpose: to study the instrumental arsenal of the laboratories of the department and the main factors that determine the energy of radio lines.

Lines of satellite communication and broadcasting consist of two sections: a transmitting earth station (ES) - a repeater on an artificial earth satellite (AES) and an AES repeater - a receiving ES. The signal power at the input of the ES receiver can be determined from the formula that is used to calculate any line-of-sight radio links:

where P prd- power at the output of the transmitter of the satellite repeater,

γ prd and γ prm- the transmission coefficients of the paths connecting, respectively, the transmitter output with the transmitting antenna on the satellite and the output of the receiving antenna with the ES receiver,

G prd and G prm- the gains of the transmitting and receiving antennas, respectively,

L o and L add- basic and additional losses of signal energy in the space between the satellite and the ES.

Major losses L o caused by energy dissipation in free space at a distance from the radiator

, (2.2)

where λ is the length of the electromagnetic wave

, (2.3)

f- the frequency of the transmitter signal, c ≈ 3 ∙ 10 8 m / s - the speed of propagation of electromagnetic waves,

d- the distance between the satellite and the ES.

Distance d between the satellite and the ES depends on the height H satellite orbit, which determines the size of the satellite's visibility area.

The satellite's visibility zone is the part of the Earth's surface from which the satellite is visible for a given duration of a communication session at an elevation angle of at least some given angle
.

The instantaneous area of ​​sight of an AES is called the area of ​​visibility at a certain point in time, i.e. at zero communication session duration. When the satellite moves, the instantaneous field of view moves, therefore, the field of view during the communication session is always less than the instantaneous one. The size of the instantaneous field of view can be estimated by the arc length
or corners and (Figure 2.1).

Injection is the angular distance of the zone boundary from the subsatellite point (relative to the center of the Earth), and the angle is equal to half the maximum angular size of the visibility zone relative to the satellite located at the point ... Points and are on the border of the visibility zone and are removed from the satellite at a distance
, called the maximum slant communication range.

For a triangle ∆
the following ratios are true:

, (2.4)

, (2.5)

where R Z= 6400 km - the radius of the Earth.

Additional losses L add caused by the atmosphere, precipitation and other reasons.

Antenna gains when using parabolic reflector antennas with a mirror diameter D is determined from the expression:

. (2.6)

Task 2. Using formulas (2.1) - (2.6), determine the signal power at the input of the receiver of the ES located on the border of the visibility zone. The initial data for the calculation are given in Table 2.1. The variant of the assignment is determined by the teacher.

Table 2.1

Using expressions (2.4) - (2.5) determine the distance d between the satellite and the AP.

Substitute the required data into expression (2.1).

Task 3. Determine the signal power at the input of the ES receiver located at the sub-satellite point S (Figure 2.1). The initial data and the calculation procedure are the same as for task 2.

Compare the results obtained in task 2 and task 3.

Report should contain the characteristics and description of the antennas of the department, as well as the results of calculations for tasks 1-3.

WORK IN THE COMPUTER LABORATORY

MODELING

The purpose of the students' work is to acquire programming skills in the MatLab environment.

To enter the MatLab environment, the mouse pointer is brought to the logo of the software system and a double click with the left mouse button (LMB).

Exercise. Building a Simulink-model of the stand.

The transition to the Simulink package can be done in two ways:

after entering the MatLab environment, the simulink command is typed in the command line of the control window opposite the pointer;

using the mouse - one LMB click on the blue-red-black symbol containing the arrow.

After these actions, the library window (Library: Simulink) and the not yet named (untitled) window of the field on which the model will be assembled will open. In the seventh version of MatLab, to create such a field after entering Simulink, click LMB on the blank slate symbol.

Students should first become familiar with the sections of the Simulink library: Sources - sources; Sinks - loads, as well as independently find sections containing blocks Abs, F cn, Relational Operator, Mux, etc.

The blocks required for assembling the structural diagram are dragged with the mouse from the sections of the library with the LMB pressed.

Models of assembled stands are shown in Figure 3.1. Figure 3.1a shows a model containing two harmonic signal conditioners. The argument to the sinusoidal functions forms the Ramp block.

To set the parameters of this and other blocks, the block is first selected by clicking the LMB, and then double-clicking opens a window into which the corresponding parameters are entered. The Slope parameter of the Ramp source is set equal to pi / 50 (in the MatLab language, the constant
written as pi).

With the use of the Mux block, the Scope oscilloscope becomes a dual-beam oscilloscope. Students choose parameters of oscilloscopes models on their own. Set the simulation time (Stop time) equal to 100: Simulation - click LMB, Parameters - click LMB, record the time in the Stop time column.

Launching the program for execution is also carried out using the mouse: Simulation - LMB click, Start - LMB click. You can also run the program by clicking LMB on the icon with the image of a triangle.

It is necessary to sketch (print) the structural diagrams of the models and the observed oscillograms.

Figure 3.1b shows a model of a comparator - a device that generates a single signal when the condition indicated on the block of the comparator - Relational Operator is met.

By selecting the assembled model and using the Create Subsystem command in Edit mode, you can make the comparator model a Subsystem block. Such a block is shown in Fig. 3.1c, which shows a model of a device for comparing the signal levels of the Sine Wave and Constant sources. In this simulation experiment, the amplitude of the harmonic vibration is 1, the angular frequency is 0.1
with the simulation time - 100.

Sketch (print) the diagram of the model and oscillograms.

Individual tasks are shown in Table 3.1. The structural diagram of the models for all variants is the same. It is obtained from the block diagram shown in Figure 3.1a, if the Fcn 2 block and the Mux block are excluded from the latter. Thus, the output of the Ramp block is connected to the input of the Fcn 1 block, and the input

of the Scope oscilloscope is connected to the output of the Fcn 1 block.

The simulation time for all variants is 100.

Report for this section should contain:

structural diagrams of the investigated Simulink-models;

oscillograms;

Table 3.1

Basic parameters of the radio signal. Modulation

§ Signal strength

§ Specific signal energy

§ Signal duration T determines the time interval during which the signal exists (nonzero);

§ Dynamic range is the ratio of the highest instantaneous signal power to the lowest:

§ Signal spectrum width F - frequency band within which the main signal energy is concentrated;

§ The base of the signal is the product of the signal duration and the width of its spectrum. It should be noted that there is an inversely proportional relationship between the spectrum width and the signal duration: the shorter the spectrum, the longer the signal duration. Thus, the size of the base remains practically unchanged;

§ The signal-to-noise ratio is equal to the ratio of the signal power to the noise power (S / N or SNR);

§ The volume of transmitted information characterizes the bandwidth of the communication channel required for signal transmission. It is defined as the product of the signal spectrum width by its duration and dynamic range.

§ Energy efficiency (potential noise immunity) characterizes the reliability of the transmitted data when the signal is exposed to additive white Gaussian noise, provided that the sequence of symbols is restored by an ideal demodulator. It is determined by the minimum signal-to-noise ratio (E b / N 0), which is necessary for data transmission through the channel with the error probability not exceeding the specified one. Energy efficiency determines the minimum transmitter power required for acceptable performance. The characteristic of the modulation method is the energy efficiency curve - the dependence of the error probability of an ideal demodulator on the signal-to-noise ratio (E b / N 0).

§ Spectral efficiency - the ratio of the data transmission rate to the used bandwidth of the radio channel.

• AMPS: 0.83
• NMT: 0.46
• GSM: 1.35

§ Resistance to the effects of the transmission channel characterizes the reliability of the transmitted data when the signal is affected by specific distortions: fading due to multipath propagation, band limitation, frequency or time-centered interference, Doppler effect, etc.

§ Requirements for linearity of amplifiers. To amplify signals with some types of modulation, nonlinear class C amplifiers can be used, which can significantly reduce the power consumption of the transmitter, while the level of out-of-band radiation does not exceed the permissible limits. This factor is especially important for mobile communication systems.

Modulation(lat. modulatio - regularity, rhythm) - the process of changing one or more parameters of a high-frequency carrier oscillation according to the law of a low-frequency information signal (message).

The transmitted information is embedded in the control (modulating) signal, and the role of the information carrier is performed by a high-frequency vibration, called the carrier. Modulation, therefore, is the process of "landing" of the information waveform on a known carrier.

As a result of modulation, the spectrum of the low-frequency control signal is transferred to the high-frequency region. This allows, when organizing broadcasting, to adjust the functioning of all transceiving devices at different frequencies so that they do not "interfere" with each other.

Vibrations of various shapes (rectangular, triangular, etc.) can be used as a carrier, but harmonic vibrations are most often used. Depending on which of the parameters of the carrier oscillation changes, the type of modulation is distinguished (amplitude, frequency, phase, etc.). Modulation with a discrete signal is called digital modulation or keying.

Unfortunately, we have there is no exact information when deliveries of specific goods are expected... It is better not to add missing items to the package, or be prepared to wait for slow-moving items for several months. There have been cases when missing items were excluded from the sale.
It makes sense to separate the packages. One fully equipped, the other missing items.

In order for the missing goods to be automatically reserved for you after arriving at the warehouse, you must issue and pay it in the order.

ImmersionRC RF Power Meter and 30dB Attenuator (35Mhz-5.8Ghz)

The use of receiving and transmitting equipment without preliminary adjustment and testing on the ground threatens with big troubles in the air. RF power meter ImmersionRC allows you to test and tune transceivers, as well as verify antenna specifications. Using this device, you can carry out comparative tests with different types of antennas, plot radiation patterns, and measure the output power of the transmitter using the built-in attenuator (power divider).
The power meter works with both pulsed and unmodulated signal types and has a wide operating frequency range from 35MHz to 5.8GHz, allowing you to test both video and RC systems.
The device will be an indispensable assistant, starting from setting up self-made antennas and ending with testing the video signal transmitter for compliance with the output power after an accident.

Do not hope for chance! Test the equipment!

Peculiarities:
Affordable price of the device, much cheaper than other similar equipment
Measurement of radiated signal levels (e.g. UHF, audio / video transmitter signal)
Calibration on all major channels used in modeling, especially FPV
Dynamic range 50dB (-50dBm -> 0dBm without external attenuator)
Information output in MW or dBm
Includes 30dB attenuator and adapter

Specification:
Frequency range: 1MHz thru 8GHz calibrated on main channels for FPV / UAV
Power level without attenuator: 50dBm thru 0dBm
Adjustment: Programmable attenuator settings, data correction
Power supply: USB or DC power supply 6-16V
Calibrated Hardware Test: > 100 frequency / power ratio
Connector: standard high quality SMA
Attenuation of the standing wave ratio: 8GHz (typical)
Dimensions (LxWxH): L = 90mm x W = 52mm x H = 19mm
The weight: 40g
Supply voltage: 6 - 16V DC
Power consumption: 100mA




Take the guess work out of your setups with proper testing on the ground before risking problems in the air.

The ImmersionRC RF power meter lets you test and tune both your uplink and downlink setups in power and Antenna performance. You can do comparative tests on various antenna designs or plot the radiation pattern, even test the direct output power of your transmitters using the included Attenuator.

The Power meter works with both pulsed and continuous wave signals and a wide range of frequencies from 35Mhz to 5.8GHz, allowing you to test both video and RC systems.

This is an invaluable tool for anything from hand tuning a DIY antenna to testing a video TX after a crash for proper output power. Don’t just guess with your investment… Test it.

Features:
Affordable RF power measurements, a fraction of the cost of similar equipment
Measure pulsed, and continuous RF power levels (e.g. UHF, and A / V Downlinks)
Calibrated on all common bands used for modeling, and especially FPV
50dB of dynamic range (-50dBm -> 0dBm without the external attenuator)
Readout in MW, or dBm
Included 30dB attenuator and adapter

Specs:
Frequency range: 1MHz thru 8GHz, calibrated on common bands used for FPV / UAV
Power level without attenuator: 50dBm thru 0dBm
Adjustments: Programmable attenuator setting, readout corrected
Power: USB, or DC power jack power source, 6V-16V
Calibrated against traceable test equipment at: > 100 frequency / power combinations.
Connector: Standard high-quality SMA
Un-attenuated VSWR: 8GHz.
Attenuated VSWR: 8GHz (typical)
Dimensions (LxWxH): L = 90mm x W = 52mm x H = 19mm
Weight (Grams): 40g
Supply Voltage: 6 - 16V DC
Power Consumption: 100mA

Exercise. 3

Theoretical part. 4

Basic provisions. 4

Units of measurement of radio signal levels. 5

Okamura-Hata model. 7

Model COST231-Hata. eight

Model COST 231-Walvis-Ikegami. eight

Research results. eleven

Exercise

1. Conduct comparative studies of empirical models of radio wave attenuation by Okamura-Khata, COST 231-Khata and COST 231 Walvis-Ikegami with the given characteristics of the communication channel for option 4 of the guidelines;

3. Prepare a report on the work with the following sections: 1) assignment, 2) theoretical part (text attached) and 3) research results - two figures with three graphs each.

Note: Calculation of the COST231 Walvis-Ikegami model is performed only for the case of line of sight.

Theoretical part

Basic Provisions

Studies of the propagation of radio waves in urban conditions are of great importance in the theory and technology of communication. Indeed, the largest number of residents (potential subscribers) live in cities, and the conditions for the propagation of radio waves differ significantly from propagation in free space and semi-free space. In the latter case, propagation over a regular earth's surface is understood when the radiation pattern does not intersect with the earth's surface. In this case, with directional antennas, the attenuation of radio waves is determined by the formula:

L = 32,45 + 20(lgd km + lgf MHz) – 10lgG lane - 10lgG pr, dB =

= L 0 - 10lgG lane - 10lgG pr, dB. (1)

where L 0 - main attenuation of free space, dB;

d km- distance between transmitter and receiver, km;

f MHz- operating frequency, MHz;

G lane and G pr- the gains of the transmitting and receiving antennas, respectively, dBi.

Major weakening L 0 is defined for isotropic antennas that radiate uniformly in all directions and receive as well. Therefore, attenuation occurs due to energy dissipation into space and a small input to the receiving antenna. When using directional antennas oriented with the main beams towards each other, the attenuation is reduced according to equation (1).

The task of the research is to determine the radio channel carrying the message (radio signal), which provides the required quality and reliability of communication. The communication channel in urban conditions is not a deterministic value. In addition to the direct channel between the transmitter and receiver, there is interference caused by numerous reflections from the ground, walls and roofs of structures, as well as the passage of a radio signal through buildings. Depending on the relative position of the transmitter and receiver, there may be cases where there is no direct channel, and the signal with the highest intensity must be considered as the received signal in the receiver. In mobile communications, when the antenna of the subscriber receiver is at a height of 1 - 3 meters from the ground, these cases are dominant.

The statistical nature of the received signals requires assumptions and constraints within which decisions can be made. The main assumption is the stationarity of a random process with the independence of interference from each other, that is, the absence of cross-correlation. The implementation of such requirements led to

separation of urban radio communication channels into three main types: Gauss, Rice and Rayleigh channels.

The Gaussian channel is characterized by a dominant direct beam and low interference. The mathematical expectation of the attenuation of the radio signal is described by the normal law. This channel is inherent in television signals from the TV tower when received on collective antennas in residential buildings. The Rice Channel is characterized by the presence of direct rays, as well as rays reflected and transmitted through buildings, and the presence of diffraction on buildings. The mathematical expectation of the attenuation of a radio signal is described by the Rice distribution. This channel is inherent in networks with a raised antenna over buildings of urban sparse development.

The Rayleigh channel is characterized by the absence of direct beams and the radio signal reaches the mobile station due to multiple reflections. The mathematical expectation of the attenuation of the radio signal is described by the Rayleigh distribution. This canal is inherent in cities with high-rise buildings.

The types of channels and their distribution density functions are taken into account when developing models of signal propagation in urban environments. However, generalized statistics are insufficient for calculating specific propagation conditions under which signal attenuation depends on frequency, antenna height and building characteristics. Therefore, with the introduction of cellular communication and the need for frequency-territorial planning, experimental studies of attenuation in various cities and propagation conditions began to be carried out. The first research results focused on mobile cellular communications appeared in 1989 (W.C.Y. Lee). However, even earlier, in 1968 (Y. Okumura) and in 1980 (M. Hata) published the results of studies of the attenuation of radio waves in the city, focused on mobile trunking communications and television broadcasting.

Further studies were carried out with the support of the International Telecommunication Union (ITU) and were aimed at clarifying the conditions for the applicability of the models.

Below we consider the models that are most widely used in the design of communication networks for urban conditions.

Units of measurement of radio signal levels

In practice, two types of units of measurement are used to assess the level of radio signals: 1) based on power units and 2) based on voltage units. Since the power at the output of the transmitter antenna is many orders of magnitude higher than the power at the input of the receiver antenna, multiple units of power and voltage are used.

Units are expressed in decibels (dB), which are relative units. Power is usually expressed in milliwatts or watts:

P dBm = 10 lg (P / 1 mW),(2)

P dBW = 10 lg (P / 1 W).(3)

For example, a power equal to 100 W, in the given units, will be equal to: 50 dBm or 20 dBW.

In voltage units, 1 μV (microvolt) is taken as the basis:

U dBμV = 20 log (U / 1 μV). (4)

For example, a voltage of 10 mV is 80 dBμV in relative units.

Relative power units are used, as a rule, to express the level of the radio signal of the transmitter, relative voltage units are used to express the level of the receiver signal. The relationship between the sizes of relative units can be obtained based on the equation P = U 2 / R or U 2 = PR, where R is the input impedance of the antenna, matched with the line leading to the antenna. Taking the logarithm of the above equations, and taking into account equations (2) and (4), we obtain:

1 dBm = 1 dBμV - 107 dB at R = 50 Ohm; (5a)

1 dBm = 1 dBμV - 108.7 dB at R = 75ohm. (5 B)

To express the transmitter power, the characteristic is often used - effective radiated power - EIM... This is the transmitter power, taking into account the gain (KU = G) antennas:

EIM (dBW) = P (dBW) + G (dBi). (6)

For example, a 100 W transmitter is driven by a 12 dBi antenna. Then EIM = 32 dBW, or 1.3 kW.

When calculating the coverage areas of a cellular base station or the coverage area of ​​an over-the-air television transmitter, the antenna gain should be taken into account, that is, use the effective radiated power of the transmitter.

Antenna gain has two units of measurement: dBi (dBi) Is the gain relative to an isotropic antenna and dBd (dBd)–The gain relative to the dipole. They are related to each other by the ratio:

G (dBi) = G (dBd) + 2.15 dB. (7)

It will be appreciated that the antenna gain of the subscriber station is usually assumed to be zero.

Okamura-Hata model

The primary version of the model by Okamura and his co-authors is designed for the following conditions of use: frequency range (150 - 1500) MHz, distance between mobile and base stations - from 1 to 100 km, base station antenna height - from 30 to 1000 m.

The model is based on comparing the attenuation in the city with the attenuation in free space, taking into account the correction components depending on the frequency, the height of the antennas of the base and mobile stations. The components are presented in the form of graphs. Longer distances and heights of base stations are more suitable for TV broadcasting than for cellular communications. In addition, the resolution of the graphs is low and less convenient than the analytical description.

Hata approximated the Okamura plots with analytical ratios, reduced the frequency range to 1500 MHz (for Okamura it was overestimated and did not meet the required reliability of the attenuation estimate), reduced the distance range from one to twenty kilometers, and also reduced the base station antenna height to 200 meters and made adjustments into some of the constituents of Okamura's model. As a result of the modernization of Khata, the model was named Okamura-Khata and is popular for assessing the attenuation of TV signals in cellular communications in the range up to 1000 MHz.

For the city power weakening L in decibels (dB) is described by the empirical formula:

L, dB = 69.55 + 26.16 lgf - 13.83 lg +(44.9-6,55 lg d– a ( ), (8)

where f- frequency in MHz,

d- distance between base and subscriber (mobile) station in km,

Suspension height of antennas by base and subscriber stations.

In formula (8), the component a () determines the effect of the antenna height of the subscriber station on the attenuation of the signal power.

For an average city and average building height, this component is determined by the formula:

a ( ) = (1.1 lgf - 0.7)- 0.8, dB. (nine)

For a city with high buildings a () is determined by the formula:

a ( ) = 8,3 (lg 1.54) 2 - 1.1 for f< 400 МГц; (10)

a ( ) = 3,2 (lg 11.75) 2 - 5 for f> 400 MHz. (eleven)

In suburban areas, propagation losses are more dependent on frequency than on the antenna height of the subscriber station, and therefore the component Δ L, dB defined by the equation:

Δ L, dB = - 5,4 – (lg (0.036 f)) 2. (12)

In open area conditions Δ L, dB with isotropic antennas is described by the equation:

Δ L, dB = - 41 – 4,8 (lgf) 2 + 18,33lgf. (13)

The disadvantage of the Okamura-Khata model is the limitation of the frequency range to 1500 MHz and the inability to use it for distances less than one kilometer.

Within the framework of the COST 231 project of the European Union (Cooperation for Scientific and Technical Research), two models were developed that eliminated the noted disadvantages of the Okamura-Khata model. These models are discussed below.

Model COST231-Hata

1 , < 200m, 1 < < 10m.