Help for RFProp Radio Propagation Calculator

Introduction

RFProp is a utility for calculating signal characteristics of radio propagation paths. It includes algorithms for line-of-sight, free space, through-building and obstructed (diffracting) paths.

Range and path budget margin can be rapidly calculated and viewed while modifying the model parameters conveniently using the graphic mode main window.

Version 1.3 now supports 32 and 64 bit architectures, and has been built and tested on Windows 10.

RFProp is free software for general use. No registration or licensing is required.

Contents

• Installation and Uninstallation
• Main App Window
• Main Menu
• Menu for file text window
• Model Parameters
• Results
• General References
• Revision History
• Licence Conditions
• Central Research Laboratories Limited (CRL)
• Contact Information
• Limitations
• Year 2000 Compliance

Installation and Uninstallation Instructions

The RFProp installation files will normally be supplied as a Zip file which needs to be unzipped using a suitable program.

For version 1.3 the Zip file name is InstallRFProp130.zip. Unpack the zip file to a temporary location.

The 32 bit installer is in the folder 32Bit and the 64 bit installer is in the folder 64Bit.

The 64 bit installer has 2 files: setup.exe and RFPropSetup64.msi. Normally either of these can be used (setup.exe will load the msi file). Then follow the straightforward instructions from the installer. If you select "install for all users" you will be asked for permission to continue with elevated privileges during the installation - click Yes to continue.

The 64 bit installer installs to C:\Program Files\CJS\RFProp64 unless you have changed the Program Files location.

The 32 bit installer has 2 files: setup.exe and RFPropSetup32.msi, otherwise you use it the same way as the 64 bit installer.

The 32 bit installer installs to C:\Program Files (x86)\CJS\RFProp32 unless you have changed the Program Files location.

The executable file is RFProp.exe for 64 bit and 32 bit installs.

Uninstalling RFProp

Automatic:

Use the uninstall option given on the Start menu (click the start icon, start typing RFProp until the link appears, right click on it, and choose Uninstall, then find RFProp on the list of programs, right click and select Uninstall) or use the Add or Remove Programs on the Control Panel (On the Apps and Features Add/Remove list, you click left on the app name).

Manual:

Delete all the files in the directory where the software was installed.

If you wish you may delete the user settings in the registry, which are stored under the key:

Computer\HKEY_CURRENT_USER\Software\CJS\RFProp

and subkey:

Computer\HKEY_CURRENT_USER\Software\CJS\RFProp\Options

Main App Window

Main App Window Screenshot

This is the main window of RFProp.

The main window contains a graphic display which illustrates the scenario of a radio transmitter and a receiver, separated by some distance, and with (optionally) an obstruction (or hill) in between. The parameters used in the model to calculate the range are arranged on this graphic display in relation to the transmitter, receiver and environment.

The intention is to make it convenient to navigate around the various parameters when experimenting with the options that can be changed to arrive at a viable radio link, while viewing key range and signal margin on the same window. More detailed results are given in a text window that can be opened when needed and used to list results to a file.

Tip Window

Parameters can be changed directly in the floating edit boxes on the main screen. When you start entering data, a tip window is shown to remind you to use the return key to finish editing and get the results updated.

Main Menu

File

There are two options here; Text Output, which opens a text output window showing a list of the parameters and results of the calculation and allows an Ascii text file to be saved, and Exit, which shuts down the program.

Text Output Window

Text Output opens a text output window showing a list of the parameters and results of the calculation and allows an Ascii text file to be saved.

Exit

Shuts down the program.

Recalculate!

This causes the results to be recalculated using the current values of the parameters. If there are any parameters that were in the process of being changed in their edit boxes but haven't been entered by using the return key, they will be restored to the previous values.

Params

LOS

LOS Parameters Dialog

Selecting Params/LOS allows you to change the Line of Sight parameters. This is simply an alternative method for entering the data instead of using the edit boxes on the main window.

Diffraction

Single Diffraction Parameters Dialog

Selecting Params/Diffraction selects the single diffraction model and allows you to change the single diffraction model parameters.

There is no support in this program for multiple diffraction models.

Default Parameters

Selecting "Params/Default Parameters" allows you to set the LOS and diffraction parameters to their install defaults. A message box will ask you to confirm this with a Yes/No choice.

Options

Font

Font has three sub-menu items which set up the font for different parts of the app.

• Graphics area font - image area and parameter entry box annotations
• Control/Status area font - range and margin results, hill type and diffraction buttons
• Edit Boxes font - parameter entry edit boxes

You may want to change the font selection for personal preference, or if you find that the control boxes and text appear to be truncated (possible on certain system and font setups).

To change the fonts for the graphics area (the image area and parameter entry box annotations), the control/status area (range and margin results, hill type and diffraction buttons), or the parameter entry edit boxes, select Options/Font and pick one of the three font setups. A standard Windows font selection box will appear, and if you select OK the specified font will be selected, and saved in the system registry for the next session.

Default Font

Default Font has three sub-menu items which set the fonts that you edit on the Options/Font dialogs to the installation defaults for the application. The three sub-menu items match the same ones on Options/Font.

• Graphics area font
• Control/Status area font
• Edit Boxes font

For each default font item, a message box will ask you to confirm this with a Yes/No choice.

Normal window size

If you select Options/Normal window size, the RFProp window will be set to the normal size; this may be useful if you have changed the size of the window. Changing the size of the window is done using the usual Windows frame controls.

Help

Contents

"Help/Contents" opens this HTML Help File with a Contents index near the top of the page.

About

"Help/About" brings up an information box including version, architecture (32 or 64 bit), build date and author's website.

Menu for file text window

File

The menu options here are Save As Ascii Text and Close.

Save As Ascii Text

This option prompts you for the name of a file, in which you can save the contents of the text output window.

Close

"Close" will close the text window, but the main RFProp window will remain open and the program will continue to run. You can open up the text window again at any time.

Options

The Options submenu allows you to change tabulated column spacings in the text output, and to change the display font.

Selecting "Options/General" will bring up a Windows dialog box which allows you to change the column width for tabulated output. In addition to Cancel and OK buttons, there is a Recalculate button to allow you to view the effect of changing column widths on the text window without closing the dialog box.

Text Window Options/General Dialog

This dialog shows the minimum, maximum and default settings for the column spacings, and allows you to change the current setting for the column spacing. Click Cancel to ignore any changes and return to the original setting. Click OK to use the current setting in the Column Spacing (chars) edit box. While changing the value, you can click Recalculate to preview the effect on the text window.

Selecting "Options/Font" allows you to change the font for the text window. A standard Windows font selection box will appear, and if you select OK the specified font will be selected, and saved in the registry for the next session.

Selecting "Options/Set default font" allows you to set the font to the install default for the text window. A message box will ask you to confirm this with a Yes/No choice.

Model Parameters

All variable parameters are displayed on the main graphic screen and can be changed using floating edit boxes. Scientific notation can be used, i.e. 2.45E9

The calculation of results is not performed while parameters are being edited, since a partly completed number can be invalid or produce erroneous results. When you have completed editing a changed parameter, press the Enter key to update the results.

A control button selects whether diffraction parameters are included in the graphic window's results, and another button selects which type of rounded hill excess loss is allowed for (rough or smooth) in the diffraction calculation.

The values entered will be saved (in the system registry) and re-loaded when you next run the program.

• Nominal Range
• Fading margin, Building Loss and other losses
• Carrier frequency
• Temperature
• Propagation Range law
• Tx antenna gain
• Tx Power
• Rx antenna gain
• Rx noise figure
• Rx required detector Signal to Noise (S/N)
• Receiver Sensitivity
• Signal bandwidth
• Diffraction parameters
• Input Intercept
• Example 1
• Example 2
• Example 3

Nominal Range

This is the range that is required between the transmitter and receiver. It also plays a part in defining the effects of diffraction when there is an obstacle between the transmitter and receiver. This doesn't mean that the radio link will actually work reliably at this range- to determine the viability of the link, you need to look at the path budget margin (abbreviated to just "margin"). This is displayed at the bottom of the main window together with the maximum feasible range. If the margin is, say, 10dB, that means at the specified nominal range, you have 10dB signal strength over the minimum needed for a feasible link taking into account all the model parameters. The amount of margin needed depends on statistical factors, and subjective factors such as how much confidence you have that all potential loss contributions have been accounted for and how well the propagation path has been characterised.

The nominal range is measured between the transmitter location and receiver location points as projected on to the baseline, for the purpose of diffraction calculations. It is assumed that the slant range is the same as the projection on the baseline. If your receive-transmit antenna height difference becomes a significant part of the range, you need to redefine the baseline. For example, for a vertical path (such as up to a satellite, or between floors in a building), the baseline should be taken between suitable points on or near each antenna.

Fading margin, Building Loss and other losses

Fading occurs when wave interference occurs at the receiver as a result of transmitted waves having travelled via different paths (e.g. by reflection from walls), or when a variable loss is involved (e.g. rainfall, atmospheric refraction, ionospheric attenuation, vehicles or persons blocking the line of sight). A great deal of literature exists to describe the effects of fading in various circumstances.

A simple method for accounting for fading is to set a marginal loss figure which represents a maximum bound for the fading losses, which will guarantee a radio link except for a small fraction of down time representing the low-probability statistical tail of the fading distribution. The fading margin is typically selected on a statistical basis, with various types of distribution function applicable dependent on the environment in question. The statistics depend strongly on whether there is a strong direct, unobstructed signal from the transmitter, or whether the received signal tends to arrive more by scattering of multiple reflections of the transmitted signal. These two cases illustrate extremes of the different types of signal statistics. There are also statistical models treating the in-between cases, where a variable mixture of direct and reflected signals are received. There are also empirical studies that give signal statistics in measured environments.

In cellular radio systems, fading loss can vary rapidly over up to 20 or 30 dB due to Rayleigh-statistics fading, caused by multipath propagation, where multiple received signals arrive via different routes from the transmitter, with different phases and amplitudes.

Building Loss

This is a loss factor included in the attenuation factors taken into account in the signal path. In some models, the propagation of signals through buildings are assessed by estimating the loss caused by each obstruction (wall) and adding them up to form the building loss figure. Another model estimates the signal inside a building from, for example, radio paging transmissions, by specifying a building penetration loss to account for the absorption and reflection of radio waves as they pass through the walls of a building. Naturally, these losses depend on the construction of the building and the radio frequency. For line of sight unobstructed operation, the building loss factor can be set to zero.

Building penetration losses are measured across the interior to exterior wall, and Skomal & Smith (1) have presented detailed charts for steel multistory, concrete masonry low-rise and residential structures. The table below represents a brief summary of that data:

The sample standard deviations in these surveys vary, but are generally less than or equal to 10.3dB.

A worst-case loss can be estimated, not to exceed Ls = L + phi*sd, where phi*sd is the location variability, sd is the sample standard deviation in dB, based on the probability P that building loss L exceeds the value Ls given by equation 4-8 in Skomal & Smith:

P(L>Ls) = 0.5 (1-erf(phi/Sqrt(2)))

Davies, Simpson & McGeehan (2) measured internal wall & floor losses at 1.7GHz inside the Queens Building at Bristol University, a prestressed concrete and brick 1950's building, finding a vertical floor loss of 27dB between corridors, and of 13dB between rooms.

Cox et. al. (3) measured RF signals in and around suburban houses, finding range laws between 3 and 6.2, typically 4.5 (attributed to ground effects). Building penetration losses were between 0.7 and 12.1 dB to first and second floors, and 0 to 21.3 dB into basements.

In the VHF frequency range, ground reflection is often at a high level and not diminished sufficiently by narrow antenna beamwidth obtainable at higher frequencies, and this modifies the free space range equation such that the power decreases with an inverse fourth power law.

Walker (4) at 850MHz found urban building penetration losses in Chicago to average 18 dB, while suburban buildings averaged 13.1dB. Windows reduced average penetration loss by 6 dB. However, the copper-sputtered windows of the Chrysler building blocked all measurable signals. Open areas had 3dB lower penetration loss than hallways or enclosed areas.

At 60GHz, P. W. Huish et. al. (5) quote 3 to 7dB loss for a double glazed window, 4dB for 1cm plasterboard, 13 dB for 1.9 cm chipboard, and more than 40dB for 10cm autoclaved aerated concrete blocks.

Chia et. al (6) quote 12dB for 2cm of wood, 2dB for 1cm plasterboard, and 6dB for 3mm glass.

Building loss references

(1) E. N. Skomal, A. A. Smith, Jr., Measuring the Radio Frequency Environment, Van Nostrand Reinhold 1985.

(2) R. Davies, A. Simpson, J. P. McGeehan, Preliminary Wireless Propagation results at 1.7 GHz using a half wave dipole and a leaky feeder as the transmitting antenna. Radio Receivers and Associated Systems, 1989., Fifth International Conference on, Issue Date: 23-27 Jul 1990, Location: Cambridge , UK, Print ISBN: 0-86341-705-1

(3) D. C. Cox, R. R. Murray, and A. W. Norris, 800-MHz Attenuation measured in and around suburban houses, AT&T Bell Labs Tech. J., V. 63, No. 6, July-Aug 1984.

(4) E. H. Walker, Penetration of Radio Signals into Buildings in the Cellular Radio Environment, Bell System Tech. J., V. 62, No. 9, Nov. 1983.

(5) P. W. Huish & G. Pugliese, A 60 GHz Radio System for Propagation Studies in Buildings, 3rd int. conf., on antennas & propagation.

(6) S.T.S. Chia, D.R.Greenwood, D. C. Rickard, C. R. Shepherd, R. Steele, Propagation studies for a point-to-point 60GHz microcellular system for urban environments.

Other Losses

As a matter of convenience, any other fixed losses (e.g. antenna pointing errors, atmospheric attenuation over a fixed path, ageing, circuit losses, feeder losses) can be added in to either the fading margin or the building loss parameter.

Carrier frequency

The frequency of the radio wave being transmitted = 2.99792458E8/wavelength.

Temperature

The temperature used for calculating the thermal noise generated at the receiver. Expressed in degrees Kelvin, which is approximately 273 degrees higher than the equivalent in Celsius/Centigrade. A figure of 290 or 300 degrees K is often used.

Propagation Range law

Radio waves travel in free space according to an inverse square law, i.e. the power per unit area in the direction of travel is inversely proportional to the distance from the transmitter (since the energy is being distributed on part of an expanding sphere, and the area of a sphere is proportional to the square of the radius).

All other types of radio wave propagation can be considered modifications of free space propagation. The basic propagation law is derived as follows:

A transmitter radiates a certain amount of RF power, call it Pt. It radiates power from an antenna, which has a gain Gt compared with an isotropic antenna. This antenna gain definition is convenient for our calculation, since in the case of zero gain- a true isotropic antenna, but one that is not achievable in practice, we can assume that the power Pt spreads out equally in all directions, allowing us to use geometry to find the power flux density at distance d, which is simply Pt spread over a surface area of 4 pi d^2, i.e.:

Pd = Pt/(4 pi d^2)

The range law here is the natural one of R=2.

The receiving antenna has an effective aperture Ar which relates the power available at the antenna termination for the receiver, Pr, to the power flux density Pd:

Pr = Ar Pd

We need to know Ar. The derivation is beyond the scope of this text, so assume that Ar = lambda^2/(4 pi), where lambda is the wavelength. The resulting equation for Pr is:

Pr = Pt * lambda^2/(4 pi d)^2

or

Pr = Pt / (4 pi d / lambda)^2

If we have transmitting and receiving antennas with gains of Gt and Gr respectively, the receiver power is increased by those gains, so that:

Pr = Pt * Gt * Gr / (4 pi d / lambda)^2

This is known as the Friis free-space equation. If miscellaneous losses (such as fading margin Mf, diffraction loss Md, building loss Bl) are included, the equation becomes:

Pr =              Pt * Gt * Gr
        ---------------------------------------------------------------------------
        (Mf * Md * Bl) * (4 pi d / lambda)^2

An approximation to the extra distributed losses in certain urban/indoor environments can be made by changing the propagation range law- on a largely empirical basis. This modified law may be described by convention as "R-4", denoting that the power per unit area is taken as being inversely proportional to the fourth power of the distance. An R-4 law is sometimes used to describe the propagation in urban cellular radio environments.

The range law modification is calculated in RFProp as follows:

Pr =              Pt * Gt * Gr
        ---------------------------------------------------------------------------
        (Mf * Md * Bl) * (4 pi / lambda)^2 * d^R

where:
Pr is the received power
Pt is the transmitted power
Gr is the receiver antenna gain
Gt is the transmitter antenna gain
Mf is the fading margin
Md is the knife-edge diffraction loss margin
Bl is the building loss factor
Pi is 3.14159265358979323846...
lambda is the wavelength
d is the Tx - Rx distance (range)
R is the range law (=2 for normal free space calculations)

Rearranging:

Pr * (Mf * Md * Bl) * (4 pi / lambda)^2 * d^R = Pt * Gt * Gr

(4 pi / lambda)^2 * d^R = (Pt * Gt * Gr) / (Pr * Mf * Md * Bl)

d = [ (Pt * Gt * Gr) / ( (Pr * Mf * Md * Bl) * (4 pi / lambda)^2 ) ] ^ (1/R)

This gives the range at which the received power is Pr.

Note that only the power to which d is raised is modified. This means that according to the above equation, the signal strength is the same at 1m range and falls off more rapidly if the range law R is increased from 2 at distances greater than 1m. In environments in which the fall-off in signal strengths varies according to a modified range law, there may also be a constant attenuation factor arising from scattering, absorption, or multipath ray interference, which may be accounted for by modifying the "building loss factor".

In the VHF frequency range, ground reflection is often at a high level and not diminished sufficiently by narrow antenna beamwidth obtainable at higher frequencies, and this modifies the free space range equation such that the power decreases with an apparent inverse fourth power law.

Tx antenna gain

The gain of the transmitter's antenna in dBi (relative to an isotropic antenna).

Typical antenna gains:

Isotropic (theoretical concept, radiates equally in all directions): 0 dBi
Small lossless dipole: 1.76 dBi
Half wave dipole: 2.1 dBi
Microwave horn, 3 by 1.5 wavelengths across aperture: 16.5 dBi
Parabolic dish, 1 metre diameter, efficiency 55%, at 12 GHz: 34 dBi

Tx Power

The RF power transmitted by the antenna (after transmitter to antenna cable losses have been allowed for).

Rx antenna gain

The gain of the receiver's antenna in dBi (relative to an isotropic antenna).

Rx noise figure

The amount by which the receiver noise (equivalent noise referred to the antenna input) exceeds the noise that would be generated by thermal noise in an otherwise noise-free receiver. This can range from fractions of a dB for microwave low noise downconverters through typically 2 to 10 dB for most receivers, and up to 30 or 40dB for test instruments such as a spectrum analyser.

Thermal noise in a matched load is given by Pthermal = kTB where:

k is Boltzmann's constant = 1.38 x 10^-23 J/K
T is the temperature in degrees Kelvin
B is the bandwidth in Hz

Rx required detector Signal to Noise (S/N)

This is the signal to noise ratio required for a specified performance level (e.g. bit error rate), which depends on many factors such as the type of modulation, whether the detector is coherent or not, fading and multipath, etc.

Receiver Sensitivity

Receiver sensitivity (receiver power) is a calculated result rather than an input term. Sometimes it is desirable to use receiver sensitivity as an input parameter for a calculation.

In RFProp, receiver power (Min.) is the minimum power required at the receiver input.

This is the signal level that must be available from the transmitted signal to achieve the signal to noise ratio required by the signal demodulator. It is defined by the receiver temperature, noise figure, bandwidth, and signal/noise ratio required for whatever modulation scheme is in use.

The minimum required receiver power is kTBSN where:

k is Boltzmann's constant = 1.38 x 10^-23 J/K
T is the temperature in degrees Kelvin
B is the bandwidth in Hz
S is the signal power / noise power ratio
N is the noise figure (as a linear multiple in this equation, not dB as entered in the software)

These parameters are specified as they are more fundamental than receiver sensitivity.

If you wish to use a receiver sensitivity figure, start off with the default values, look at the calculated receiver sensitivity, and modify one of the fundamental parameters T, B, S or N as described above so that the calculated receiver power is the same value as your specified receiver power. If you know three of the parameters you should alter the remaining one to arrive at the receiver sensitivity. If you don't know the fundamental parameters, it doesn't really matter which one you alter as long at the resulting receiver power is the value you need to specify.

For example, assume initially you have Rx Noise Figure 6dB, Signal Bandwidth 10000 Hz, Rx Detector S/N 16dB, and Temperature 290K, then the receiver power (Min.) will be calculated as -111.977 dBm.

If you have a receiver sensitivity specification of -118 dBm, you can change the Rx Detector S/N to 9.977 dB (i.e. 16 - (-111.977 - -118) ) then the receiver power (Min.) will be calculated as -118 dBm.

Once you have set the minimum receiver power figure for the setup you are using, it should remain the same regardless of the path loss being calculated. The difference between the minimum required receiver signal power, and the actually received signal power, gives you your signal margin.

Signal bandwidth

The effective bandwidth for the overall baseband signal transmission path, normally dominated by the receiver filter bandwidth. In spread spectrum systems, this is the baseband bandwidth after despreading, not the spread signal bandwidth, as the despreading process allows most of the noise in the spread bandwidth to be filtered out before detection.

Diffraction parameters

These heights, relative to a baseline, determine the relative position of the obstruction with respect to the line of sight between the transmitter and receiver antennas, and hence allow diffraction losses to be calculated.

This distance is measured between the transmitter location and obstruction location points as projected on to the baseline.

This distance is measured between the obstruction location and receiver location points as projected on to the baseline.

When you enter a nominal range, the Tx and Rx to obstruction distances are automatically scaled to add up to the nominal range. If you change one of the distances to the obstruction, the range will be modified assuming that the other distance to the obstruction is unchanged, and the nominal range must add up to the two distances to the obstruction.

The knife-edge diffraction loss is calculated from the distances entered as described above. The physics of this model assumes that the obstruction is an infinitely wide and deep sharp wedge, perpendicular to the propagation path. An additional "excess loss" is calculated to allow for rounded obstructions; this excess loss also depends on whether the rounded obstruction is "smooth" or "rough" (an example of a rough versus a smooth case is a forested hill as opposed to a grassy hill).

Caution: If the obstruction height is set very low (negative) or high compared to the line of sight, the algorithm used to calculate diffraction will run slowly (the hourglass cursor may appear for some time). To assess paths without diffraction, simply read the results listed for no diffraction rather than setting a negative obstruction height.

A parameter sometimes quoted in connection with diffraction is the diffraction angle, which is calculated and listed on the text output window:

Input Intercept

Intercept point is an extrapolated fictitious level of signals producing intermodulation and the intermodulation to the level where all are equal. This parameter is used to calculate intermodulation, blocking and spurious-free dynamic range results. For further information see: Results

Example 1

From "Radio wave propagation and antennas", J. Griffiths, Prentice-Hall, 1987, p. 129:

A UHF television transmitter has 500kW erpd and operates with wavelength 0.4m (749.5 MHz).

Tx to obstruction distance: 22 km
Rx to obstruction distance: 2 km
Diffraction angle: 0.033 radians (1.891 degrees)
Rough rounded hill radius: 3km

Adjusting the hill height results in the angle 1.9 degrees when the height is 63m (antenna heights each being 2m). RFProp calculates the knife-edge diffraction loss to be 23.0 dB and the rough hill excess diffraction loss to be 38.3 dB, which agrees closely with the figures L(ke)=23 dB and L(ex)=38 dB stated in the book.

Diffraction loss will be 6dB when the obstruction is directly in-line. The excess loss for rounded obstructions is zero when the obstruction is below the line of sight.

Example 2

From "Radio wave propagation and antennas", J. Griffiths, Prentice-Hall, 1987, p. 289:

Find the minimum signal power from a direct broadcast TV satellite with minimum CNR(R) 12dB, receiver noise figure 5dB, bandwidth 27MHz, and temperature 290K.

Entering the CNR(R) value as the Rx required detector S/N, plus the noise figure, bandwidth and temperature figures, the receiver power level (min.) is listed on the text output window as -82.66 dBm, i.e. -112.66 dBW, which agrees with the book. The rest of the parameters do not affect the required receiver power level, but determine the actual received power, which after subtracting the required receiver power gives the margin.

Example 3

From "Antennas", F. R. Connor, Edward Arnold Ltd., 1972, pp. 15-16:

An earth station is receiving transmissions from a space research satellite on a frequency of 136 MHz. The satellite is at a range of 500km and its transmitter supplies 0.5W into an aerial having a gain of 3dB with reference to an isotropic aerial. Assuming free space propagation, and taking the impedance of free space as 120 pi ohms, calculate

(a) the power flux density in watts/m^2
(b) the field strength in uV/m at the earth station.

If the aerial at the earth station has a gain of 20dB with reference to an isotropic aerial, what is the signal power received? (C & G Comm. Radio C, June 1968)

Entering the values specified above, the following results are obtained in the text output window under "Actual received signal; no diffraction":

Rx power density = 3.1831e-013 W/m^2 = 0.31831e-12 W/m^2 (book value: 0.318E-12 W/m^2)

Rx field strength = 1.09545e-005 microVolts/m = 10.9545 microVolts/m (book value: 11 microVolts/m)

Receiver power = 1.23091e-011 W = 12.3091e-12 W (book value: 12.3E-12 W)

Results

The maximum range, and path budget margin available at the specified nominal range, are displayed on the main graphical window.

The margin is displayed at the bottom of the main window together with the maximum feasible range. If the margin is, say, 10dB, that means at the specified nominal range, you have 10dB signal strength over the minimum needed for a feasible link taking into account all the model parameters. The amount of margin needed depends on unknown factors, and subjective factors such as how much confidence you have that all potential loss contributions have been accounted for and how well the propagation path has been characterised.

A margin is normally required to account for potential variations in estimated loss factors outside known limits, unknowns that might not be accounted for, ageing of equipment, increasing cable losses due to wear and ageing, antenna losses etc., or changes in the environment (e.g. in an urban radio environment, there could be new building construction in the radio path).

More detailed results are available in the text output window, which can be saved to a file if required. First, the parameters entered for the calculation are listed, from design centre frequency to obstacle/hill height. This provides a complete reference for archival and documentation.

Next, the diffraction parameters are listed. The auxiliary parameter v is used in the evaluation of Fresnel integrals to calculate the knife-edge diffraction. The calculations will be accurate to around 0.015% (in terms of power loss) for values of v up to +/-80. The knife-edge diffraction loss is always 6.0dB at v=0. The loss increases rapidly as v increases negatively. The loss decreases as v increases positively, and actually shows an interference phenomenon due to the reflected wave, with the signal peaking by 1dB at v=1, then oscillating asymptotically above and below the ideal free space loss (i.e. zero) as v increases.

The knife edge parameters d1 and d2 are not simply the distances from the antennas to the obstruction. The diffraction theory is based on the shape of the triangle joining the two antennas and the obstruction. The distances d1 and d2 are the distances between the antennas and the perpendicular from the obstruction to the line joining the two antennas (line of sight) measured on the line of sight. The knife edge parameter h is the height of the perpendicular distance from the obstruction to the line of sight.

The Fresnel zone clearance is a distance between the obstruction and the line of sight joining the two antennas. The first Fresnel zone is the minimum distance at which the reflected signal path is a half wavelength longer than the direct path. Further Fresnel zones occur at integral multiples of a half wavelength path difference. The first Fresnel zone is the one listed here. Minimum clearance specifications to guarantee an "unobstructed" path can be set typically at around 0.7 times the first Fresnel zone clearance. Note that this distance is relative to the line of sight, not the baseline.

A list in tabular form shows the knife edge diffraction loss calculation, and the angle between the transmitted ray to the obstruction and the diffracted ray from the obstruction to the receiver (positive angle means the path is obstructed, negative angle means the obstruction is not blocking the line of sight between the transmitter and receiver). It also shows the correction factors, or excess losses, that allow the knife-edge theory to be adjusted for a more realistic rounded hill or obstruction. Correction factors are given for "rough" and "smooth" hills or obstructions.

A "rough hill" bends more signal through a given diffraction angle than a "smooth hill". The correction factors are attributed to K. Hacking, in "Propagation over rounded hills", BBC Research Report RA-21, 1968. According to J. D. Parsons, in "Land Mobile Radio Systems", Peter Peregrinus (Chapter 2), although strictly valid for horizontal polarization only, measurements have shown that at VHF and UHF Hacking's corrections can be applied to vertical polarisation with reasonable accuracy.

General propagation results are listed next. The wavelength is given, which is calculated from the radio frequency as: wavelength (m) = 2.99792458E8/frequency (Hz).

The thermal noise at the Rx i/p is the noise caused by thermal motion of electrons and is calculated from kTB, where k is Boltzmann's constant, T is the temperature in degrees Kelvin and B is the bandwidth.

The thermal noise & Rx noise result includes the effect of receiver noise figure on the effective receiver input noise, which is to increase the real noise above that expected from thermal considerations alone.

The Rx G/T figure of merit is often used in satellite and microwave link work, indicating the performance of the receiver antenna and low noise front end combination. The T in this case is the noise temperature of the receiver:

T = 290 * (Noise figure - 1)

The noise figure in this formula is expressed as a ratio rather than in dB.

The path loss is the component of signal attenuation between the transmitter and receiver that is attributed to the distance between the antennas. It is calculated as:

Path loss = (4.0 pi d/lambda)^2

Path loss in dB = 20.0 * log10(4.0 pi d/lambda)

where d is the range, and lambda is the wavelength. Note that this is independent of range law, i.e. it is the conventional free-space path loss (or spatial attenuation) formulation.

The propagation results for the limiting case of the minimum required receivable signal that will give the required S/N ratio are listed next. These results depend only on the receiver characteristics, namely required signal/noise, temperature, noise figure, and antenna gain.

Receiver power (Min.) is the minimum power required at the receiver input. This is the signal level that must be available from the transmitted signal when fading corresponds to the set margin, and all other transmitter and propagation path characteristics are accounted for.

Rx power density (Min.) is the radio wave power density per unit area at minimum signal condition.

Rx field strength (Min.) is the radio wave electric field strength in Volts/m at minimum signal condition. This parameter is often used in a broadcasting context.

Rx pwr / noise density (Min) in dB-Hz is the ratio of minimum carrier power (W) to noise density (W/Hz), expressed in dB form. This parameter is used in satellite and space telemetry and other digital radio applications.

Next, the receiver power, power density, field strength and margin are listed for the actual received signal (excluding diffraction loss). The margin is the difference in dB between the actual received power and the minimum required receiver power.

Next, the receiver power, power density, field strength and margin are listed for the actual received signal (including diffraction losses for a smooth hill).

Next, the receiver power, power density, field strength and margin are listed for the actual received signal (including diffraction losses for a rough hill).

A table of propagation results is listed next for the signal strength and margin calculated at the specified nominal range, and also listing the maximum range obtained using the minimum receivable signal strength. The table lists cases for:

(1) no diffraction loss being included,
(2) diffraction loss being included for a smooth hill,
(3) diffraction loss being included for a rough hill.

The table includes a column for the height of the obstruction, which is the single value entered as a parameter, and columns for power density, field strength and margin at the specified (nominal) range. These results are repeats of earlier values, but presented in a table as an alternative format.

Next, maximum range obtainable at minimum receivable power is tabulated for no diffraction, smooth-hill diffraction, and rough-hill diffraction.

For diffracted paths, the maximum range will be an under-estimate if the nominal range is less than the maximum range, because the diffraction angle will be reduced at the maximum range. Similarly if the nominal range is set higher than the maximum range, the maximum range will be an over-estimate. The diffraction loss is calculated only for the specified nominal range. Consequently, if you vary the nominal range or the transmitter/receiver to obstruction spacing, the maximum range will be seen to change. For a better estimate of maximum range you can adjust the nominal range and spacings until the nominal range is close to the maximum range.

In normal radio systems however, it is not recommended to rely on operation at maximum range because, due to normal variations in environment and parameters, the signal may easily drop below that required for reliable communication. The preferred approach is to decide on a comfortable signal margin and ensure that it is obtained at the selected nominal range.

Finally, intermodulation, blocking and spurious-free dynamic range results are listed. Intermodulation and blocking calculations are based on methods described in Radio Receivers, William Gosling, Peter Peregrinus, 1986, ISBN 0-86341-056-1. These may include approximations suited to narrow-band radio systems. Further study is advised if you apply these calculations to wide band systems, and please note that the non-linearities in later stages of a receiver may have an effect over that of a front end considered alone in terms of its input intercept.

Let Vip be the level of two signals in dB above 1 microvolt (1uV) to produce 1uV intermodulation. Thus:

Intercept point = (n/(n-1)) VnIP dBuV for nth order, = 1.5 V3IP dBuV for 3rd order.

1 microvolt in 50 ohms is equivalent to -106.99 dBm.

The blocking performance of a receiver is usually specified by the level of an unwanted signal 20 kHz off-tune, which will change the output level of the wanted signal by 3dB (in the absence of AGC). Although the level of the wanted signal is irrelevant it must be well above the noise level for convenient measurement. A good receiver, without the aid of front-end selectivity, should be able to withstand signals of at least 300mV without noticeable blocking, according to Gosling.

Let Vip be the level of the signals in dBuV to produce 1 uV intermodulation. Thus the level of the blocking signal is approximately:

3/2 V3ip - 3 dBuV as produced by the 3rd order

5/4 V5ip - 4.5 dBuV as produced by the 5th order

7/6 V7ip - 6 dBuV as produced by the 7th order

e.g. if V3ip = 82dBuV, blocking signal will be 120 dBuV or 1V.

Spurious free dynamic range (SFDR) is defined in conjunction with the Minimum Detectable Signal (MDS) as:

2 tone SFDR = 2/3 (IP3 I/P in dBm - MDS in dBm)

where MDS in dBm is commonly defined as either one of the following:

MDS = -113.8 + 10 log10(BW in MHz) + NF + SNR (as used for example by Miteq)
MDS = -113.8 + 10 log10(BW in MHz) + NF + 3dB (as used for example by HP)

General References

These references may be of general interest:

(1) Antennas, F. R. Connor, 1972, Edward Arnold ISBN 0 7131 3279 5

(2) Radio Wave Propagation and Antennas, An Introduction, John Griffiths, 1987, Prentice-Hall ISBN 0-13-752304-1

(3) Mobile Communications Engineering, William C. Y. Lee, 1982, McGraw-Hill, Inc., ISBN 0-07-037039-7

(4) Concepts and Results for 3D Digital Terrain-Based Wave Propagation Models: An Overview, Thomas Kurner, Dieter J. Cichon, Werner Wiesbeck, IEEE Journal on Selected Areas in Communications, Vol. 11, No. 7, September 1993

(5) Terrain-Based Propagation Model for Rural Area- An Integral Equation Approach, Jan T. Hviid, Jorgen Bach Anderson, Jorn Toftgard, Jorgen Bojer, IEEE Transactions on Antennas and Propagation, Vol 43, No. 1, January 1995

(6) A Power-Spectral Theory of Propagation in the Mobile-Radio Environment, Michael J. Gans, IEEE Transactions on Vehicular Technology, Vol. VT-21, No. 1, February 1972

(7) Modelling and Simulation of Mobile Satellite Propagation, R. Michael Barts and Warren L. Stutzman, IEEE Transactions on Antennas and Propagation, Vol. 40, No. 4, April 1992

(8) Radio Receivers, William Gosling, Peter Peregrinus, 1986, ISBN 0-86341-056-1

Revision History

RFProp version 1.00, 11/10/96, was never publicly released.

RFProp version 1.01, 18/10/96, was initially distributed free of charge at the 1996 Radio Solutions Conference at the National Exhibition Centre, Birmingham, England, at which the author delivered a paper on spread spectrum radio.

It was part of a free promotional disk handed out at the industry exhibition associated with the Conference.

RFProp version 1.02, 12/6/98, has been revised to fix bugs, and make improvements that were mostly suggested by interested users.

RFProp version 1.03, 19/6/98, has units of dBm (missing in v. 1.02) added to the Input Intercept annotation.

RFProp version 1.1, 2/1/04, is mainly an upgrade to 32 bit code.

Principal Changes in version 1.1:

Ported to 32 bit version, non-standard .ASC file extensions have been replaced by .TXT, a default file extension is now added if it is not specified in the save file dialog, and the units quoted for "Margin at spec. range" have been corrected from m to dB.

RFProp version 1.2, 18/3/11, is an update for improved Windows 7 compatibility.

Principal Changes in version 1.2:

Settings are now stored in the registry, instead of saving .ini files. File saving has been modified for better Windows 7 compatibility. The help file has been translated to HTML format as the previous format is no longer supported in Windows.

System Requirements

The target platforms are Windows XP or higher. Older versions may be used for older versions of Windows. There are no special requirements as normal PC resources should be sufficient.

RFProp version 1.3, January 2021, is an update to provide a 64 bit build with code safety improvements and other changes to suit running on Windows 10.

Principal Changes in version 1.3:

• Migrate code for 64 bit build compatibility
• Port source code to a more recent build environment
• Make recommended changes to Win32 functions to use updated "string safe" versions
• Fix various issues with window data, window function parameters and 64 bit pointers
• Update the About box for Windows 10 compatibility
• Add help accelerator keys
• Updated the help file and ported it to responsive HTML5 using better CSS from recent HTML projects
• Fixed some bugs in the text window options dialog and added boxes for min, max and default values
• Added menu options to allow setting parameters and fonts to installation defaults

System Requirements

The target platforms are Windows 7 or higher. Windows XP is not supported in this version. Older versions may be used for older versions of Windows. There are no special requirements as normal PC resources should be sufficient.

Licence Conditions

LICENCE CONDITIONS AND AGREEMENT

RFProp program

For version information, see Revision History.

This program was originally developed by Colin Seymour for Central Research Laboratories Limited (CRL), "out of hours". As such it has not received special funding, does not form part of any contractual obligation, quality control system, or project control, although "good practice" has been applied as far as possible.

RFProp version 1.01, 18/10/96, was initially distributed free of charge at the 1996 Radio Solutions Conference at the National Exhibition Centre, Birmingham, England, at which the author delivered a paper on spread spectrum radio.

It was part of a free promotional disk handed out at the industry exhibition associated with the Conference.

RFProp is provided purely on a NO WARRANTY AS-IS basis. No guarantee is given regarding the performance or results obtained by using the software. This applies to all versions including updated maintenance releases that may be made from time to time.

Bug reports and comments are welcomed, but replies and support services will not generally be provided.

This software is licensed for use by:

1. Any person

(hereafter referred to as the LICENSEE) who is prepared to accept the terms and conditions of this licence as a licence agreement to use the software.

The LICENSEE may use the software at any location or on any computer.

The LICENSEE may freely distribute the software, providing that all the files forming part of the original distribution package are included, unaltered, including this licence agreement.

No charge may be made for the software (excepting reasonable charges made for media supplied which contains the software).

Any installation of the software must include this licence agreement.

Neither the Author of this software, the Author's employers, or any of the Author's previous employers accept any liability should any person incur expense or damage by using the software including consequential, incidental or special damages, lost profits, or lost savings, even if said parties have been advised of the possibility of such damages or any claim by any third party, and no warranty is made either expressed or implied as to non-infringement of third party rights, merchantability, or fitness for purpose, in so far as such limitations are permitted by local law.

You may not modify, adapt, translate, reverse engineer, decompile, disassemble or otherwise attempt to obtain the source code of the software. This license agreement does not grant LICENSEES any intellectual property rights in the Software.

This software is Copyright (c) 1996, 1997, 1998, 2004, 2011, 2021. All Rights Reserved.

Central Research Laboratories Limited (CRL)

Central Research Laboratories Limited (CRL) was part of Scipher PLC, and formerly the corporate research laboratories of Thorn EMI, and was based at Dawley Road, Hayes, Middlesex in the United Kingdom.

Before October 1979, when Thorn Electrical Industries merged with EMI, it was known as EMI Central Research Laboratories. It was formed from a merger of the research and development departments of The Gramophone Company and The Columbia Graphophone Company in 1931, which formed EMI.

CRL moved from its old building, Schoenberg House on Trevor Road, Hayes, Middlesex, to a new, purpose-built building a short distance away in Dawley Road, Hayes, in 1984.

It is perhaps most famous for the late Sir Godfrey Hounsfield's invention of the X-ray CT scanner in 1967-1968. He won the Nobel prize for his work in 1979.

Other achievements at CRL include the world's first public high definition television service, stereo records, radar systems in WW2, and more recently digital Ferroelectric Liquid Crystal Displays, Sensaura 3D Sound, and digital audio watermarking.

Scipher PLC raised £30m when it was sold in 2000, but never made a profit. Its directors called in the receivers in September 2004. The CRL buildings were demolished in 2008.

Contact Information

Additional information, and information about any bugs, should they be discovered, is posted at:

https://colinjs.com/contact.htm

Limitations

The propagation calculation algorithms are mainly limited to line-of-sight and diffracted paths. Other types of propagation that occur over long distances or at low radio frequencies may not be accounted for, such as: Ionospheric reflection and atmospheric refraction, troposcatter, ducting, E-layer superionisation, meteor trail scatter, ground wave, and surface waves. Under some conditions, a loss or gain factor can be estimated by other means for other propagation factors and incorporated by adding to the fading margin, building loss or antenna gain, or a modified range law may be used.

The program is aimed mainly at short range radio applications, such as in-building LAN and point-to-point links up to a few km where there is a direct line-of-sight or a simple diffraction profile, or a modified range law model, but it can also support calculations for satellite, aeronautical and space communications where the line-of-sight model can be applied.

Year 2000 Compliance

There are no date or time related functions used in this program, so as long as the underlying operating systems on your computer are Year 2000 compliant, this application should run with Year 2000 compliance.