VK3UM Electro Magnetic Radiation Calculator. Table of Contents

Transcription

1 Table of Contents VK3UM EMR Calculator 2 Disclaimer 2 Background 3 Program Objectives 4 Calculations Provided 5 Screen Options 7 Circular Apertures 14 Calculation Methods 16 Examples 17 Author 19 References and Acknowledgements 20 Page 1

2 VK3UM EMR Calculator Disclaimer Disclaimer The accuracy of this software is in accordance with the calculation methods prescribed in the Standard chosen in the software. The On Axis Exclusion Zone value calculated in this Software is the exposure limit that applies to the General Public for the Standard selected. (Uncontrolled environment) The calculated Safety Exclusion Zones should only be taken as a guide and must not be relied upon as safe for human exposure. External influences can cause significant variations to predicted values. The Exclusion Zone should be accurately measured in the prescribed manner and the readings thus obtained treated as absolute with respect to safety matters and not those predicted by this software. Footnote In the process of obtaining High Power permits for both 23 and 70cms, the Author (VK3UM) was subjected to rigorous testing, inspection and RF radiation measurements. The EMR values were measured with precision equipment and the levels were found to be extremely close to the theoretical calculations as predicted in this software. Page 2

3 Background Background Throughout the World, most Government Authorities have implemented mandatory standards of radiation limits pertaining to Electro Magnetic Radiation. These requirements include the Amateur Radio Service. Note.Electro Magnetic Radiation (EMR) is now generally known as Electro Magnetic Emission (EME) which is a more 'public friendly term'. Because of the nature of EME (Earth-Moon-Earth) and many other Amateur communications, radiated power levels can be quite high and may, under certain situations, pose a radiation hazard. This software calculates the level of Far Field bore site RF Radiation levels and indicates if the safety limit will be exceeded with respect to the parameters entered into the program. The default calculations are for Public or un-controlled environments, however controlled environment calculations are provided where situations permit such limits. Warnings are provided on entering this option. The software also addresses the near field radiation characteristics of a circular aperture radiating antennae. This characteristic could be of significance to provide substantiating evidence that the installation is able to meet the Governing Authority's radiation limits. The most widely accepted Safe level of RF Radiation is that which has been recommended by the International Commission on Non-Ionizing Radiation Protection. (ICNIRP) It is a body of independent scientific experts consisting of a main Commission of 14 members, 4 Scientific Standing Committees covering Epidemiology, Biology, Dosimetry and Optical Radiation and a number of consulting experts. This expertise is brought to bear on addressing the important issues of possible adverse effects on human health of exposure to non-ionising radiation. Its recommendations have been accepted by most countries as well as the Council of European Union (CEU). The ICNIRP works in close collaboration with the many health protection related agencies both national and international, including, for example, WHO, ILO, ICOH, IRPA and EUROSKIN. [Reference 6] Page 3

4 Program Objectives Program Objectives The prime purpose of the software is to define the Electro Magnetic Radiation (EMR) (Electro Magnetic Emission (EME)], level of the On Axis Exclusion Zone, commensurate with the stations effective radiated power and mode of operation. The default calculation is for Public or the un-controlled environment. The operator of an Amateur Radio Station may then be confident of complying with the Safe Operating Standards applicable to their specified licensing conditions. The Electro Magnetic Radiation (EMR) level from the Station can be determined to a high degree of accuracy (refer also Disclaimer statement) so that it will not cause harmful health effects to the Public, family and Station operator in accordance with levels recommended by the International Commission on Non-Ionizing Radiation Protection. (ICNIRP) and also those of the Federal Communication Commission (FCC). The calculations are presented in numerical as well as graphical format to allow simple visual indication of the relationship of tower to safety distances. The ability to vary the Tower height (and other parameters) in the software and instantly observe the changes in the safe operating distance from the radiator is a feature of the software. Circular Aperture Near Field calculations are also presented in a graphical format. Page 4

5 Calculations Provided Calculations Provided The EMR Radiation Calculator provides the On Axis Exclusion Zone (General Public), for both near and far field radiation levels, and is displayed in both text and graphical formats. The Tower Height Calculator provides a graphical representation of the safe distance from the tower to comply with Safety requirements. Using the mouse or mouse roller you can change the tower height (white rectangle) and display the safe tower height and safe distance from the tower. It should be noted that at the 3dB antennae beam width and the on-axis distance calculations are combined to provide this display. The safe head height is given as 1.8 metres (chosen as an arbitrary average human height), and can be removed for bore site on axis calculations. The Circular Aperture Calculator provides a graphical representation of Near and Far field Exclusion Zone boundaries. (for Parabolic Reflectors only) Page 5

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7 Screen Options Screen Options The Main Screen The three large buttons in the center of the screen enable you to:- VHF-SHF Screen Page 7

8 It covers the frequency range from 50MHz to 48GHz and provides access to the Parabolic Reflector and the yagi Array options. To select the yagi array click on the button to the left of the display. Similarly to reselect the Parabolic Reflector display, click on its associated button. HF Screen The options available within this screen may be selected by clicking one of the available options (Low Gain Antennae, Yagi Array or Parabolic Reflector). Access to all the Low Gain Antennae options may be gained by clicking on the associated panel (it will high light in white) and further choose other options by use of the up/down arrows. Frequency. Select the frequency of operation as required. This will define the default quiet sky temperature (T K Sky). The default values have been chosen as the minimum quiet sky achievable for the frequency selected. It will most likely have to be varied to equate to the actual sky temperature behind the selected source at the time of measurement. (refer System Performance Calculator T Sky) Circular Aperture Page 8

9 This option screen provides selection of a graphical representation of Near Field of the RF Exclusion Zone calculations in a graphical format. Note.. it is only applicable for Parabolic Reflectors Transmission Mode Form Factor These options should be selected in accordance with the Standard chosen. In the case of the FCC OET Bulletin 65 select Carrier or 100%. [reference 1 & 4] Six Minute Period Average These options should also be selected in accordance with the Standard chosen. In the case of the FCC OET Bulletin 65 they select Conversational or 100%. You will note that in the case of the FCC Standard the period average is 30 minutes. You may select Controlled Exposure by clicking on the green button. (a warning is given on entering the Controlled Exposure option). The Controlled Exposure option is provided for specific situations that can use such levels but normally this is not appropriate for the Amateur Service. RF Radiation Standards. Three standards are provided as indicated plus a variable option to allow for any other Radiation Limit. Many Countries have as yet to define their Standard and the variable option is provided for any such eventualities. Note that the ARPNSA and CEU Standards are identical except that the former requires Level 2 compliance documentation with EIRP power levels exceeding 3200 watts. CEU Council of European Union Page 9

10 FCC ARPNSA Federation of Communication Commission (USA) Australian Radiation Protection and Nuclear Safety Association (almost identical to CEU) Difference between Standards The FCC OET Bulletin 65 Supplement B (Amateur Stations) calculations are based on 100% Form Factor and 100% 30 minute period average. (Public environment). Selecting the FCC defaults to Carrier, Conversational includes Ground reflection and the transmission loss should be adjusted zero. The figures will correspond to those on pages 23 and 24 of the document. Controlled environment calculations are also provided as an option. Variable Radiation Level Option You may select this option to adjust to any other Radiation Standard. By double clicking on the radiation limit panel enables adjustment in steps. Double clicking again second time reverts to 0.01 increments. Ground Reflection. Select his option where required. This will depend upon the situation under question and should be applied as appropriate. In the case of the FCC OET Bulletin 65 they stipulate this option (in most instances) as a worse case scenario and are selected as default. Transmitter Power. Power levels from watts are provided to cover most Amateur situations. Note that the current data file (*.dug) is also displayed in this panel. Parabolic Reflector. Adjust for the size you are using and adjust the efficiency to reflect the characteristic of the reflector. Note this is reflector efficiency and not f/d. Page 10

11 Yagi Array. If you are using a single yagi or yagi array, first select the button adjacent to the Yagi array. This will highlight the Yagi Array box and darken the Parabolic reflector area. Adjust the Single Yagi dbi gain and the number of yagi to match your installation. You may wish to vary the single yagi figure to reflect your realised array gain. This can vary depending upon the stacking distances chosen and the cumulative losses of your system. Additional Yagi Options. There are three buttons contained within the Yagi Array box that allow you to choose many of the currently available, commercially manufactured, or design optimised antennae. (blue top button ) The lower green button provides the ability to choose between dbi (default) or dbd reference gains In addition you may also select in (the VHF-UHF option) a dipole or a vertical antennae. In selecting a vertical you also have the option to select the length of that vertical. Low Gain Antennae. (HF selected option) Page 11

12 This panel provides selection of ½ Dipole, ¼ to 1 wavelength vertical antennae, selection of 3 element beams for MHz as well as a variable option to adjust gain to any value desires. Transmission Loss. Actual power measured at the radiator. Adjust to suit your particular situation. Remember to include all feed, relay, balun, and divider losses as appropriate. You will note that in this box a notation is provided for users of the ARPNSA Standard (as used in Australia) where the Authorities (ACMA), require a documented record of compliance when Average EIRP levels exceed 3200 watts. In the case of the FCC standard the "power threshold for routine evaluation" is provided. Additional Screen Options Disclaimer Button. Provides the disclaimer message commensurate with the software. Metric/Imperial Button. Selecting either will reflect on all displayed calculations. Note that this function is also a 'stored parameter'. X 10 Multiplier. This provides a ten times increment on program input data. The relevant options are highlighted in yellow when selected. Default Option. This allows for the retrieval of user defined set up parameters. When the program is first initiated the parameters displayed should be changed to suit the users preferred options. They should be stored as 'default.dug'. This file will be recalled automatically when clicking on the default button. If the file has not been created then the user will receive an error message warning of the requirement. On screen help allows you turn this function off Reset Screen size allows you to return the screen size to its default size should you desire. Note. the program saves your screen position and size when exiting and restores to Page 12

13 these values on the next time you run the program. Help provides the Help file you are viewing here. About provides the Build Date and other program information parameters. Exit will close the program. File Handling Options The first time the program is run, it is advisable to set your default parameters as you wish and save them under the default file name. You may subsequently save as many other configurations as you require and recall them at will with the file option. (vk3um432.dug vk3um1296.dug etc.) Note. all the screen variables available to the user are stored. Page 13

14 Circular Apertures Circular Apertures This software provides all the RF Exclusion Zone calculations as described earlier but it is now displayed in a graphical format. The level of radiated power with in the Near field region is displayed. This characteristic and the predicted Exclusion Zone could, in some circumstances, permit operation where space or elevation separation can take advantage of the safe area within the Near Field. Explanation. The X axis of the graph is the normalized on-axis distance where 1.0 equates to the Far field distance. The X base line is logarithmic. The Y axis is the normalized on-axis power density gain correction. The curve depicted in red is the on-axis power flux density curve for a circular aperture (1-q²) taper. The near-field power density is determined by calculating the far-field distance (r = 2D²/λ) and the power flux density at this point [S = GP/(4r²)] and multiplying this power flux by the gain correction factor. [Reference 3 page 28]. Example. Given a 2.16 W/square metre radiation limit, a frequency of 1296 MHz, 28.1 foot dish, efficiency 55%, 0.5 db transmission loss, 700 watts Tx O/P, a CW Transmission Mode Form Factor with a 2½ minute EME 6 minute Period Average then the display will show := Page 14

15 An Exclusion Zone as indicted by the 'red humps'; and a Far Field Distance of feet This can be interpreted as the distance from the radiator up to a distance of 21.6 feet is below the radiation limit as are the other 'holes' between the humps. As the power is increased, additional danger areas (above the set radiation level) are then revealed. The green horizontal line is the graphical representation of the radiation level in Watts/square metre as set by the user. Below this green line is below the radiation limit.. Page 15

16 Calculation Methods Calculation Methods The On Axis Exclusion Zone is the direct line (bore sight) distance from the radiator. The distance is that where the radiation level exceeds the Radiation Limit as specified by the Standard chosen. In most Standards this will vary with frequency in accordance with the requirement. The actual level will be displayed in both Watts/metre² and mw/cm². The calculation method used by this software is that as detailed in the Australian Standard AS Radiofrequency radiation - Principles and methods of measurement khz to 100 GHz and those similarly described in FCC OET Bulletin 65. [reference 3 & 4] The program calculates the near field values for both circular and rectangular apertures depending upon the user selecting either a Parabolic reflector (circular aperture) or a Yagi, dipole or vertical radiator. (Rectangular aperture) In the case of a Parabolic reflector the near field correction follows the (1-q ²) taper curve where q is the radial distance from the center of the circular aperture, normalized to the aperture radius. The program utilises the power density (PD) in the Near Field Normalized to unity at CD ²/ where PD = 26.1 [1-16x/ sin /8x + 128x ²/²(1 - cos /8x)] [reference 5] The curve is displayed in the Circular Aperture option and highlights the near field radiation characteristic. This characteristic, where the radiation level falls below the Exclusion Zone within the near field, may of significance when establishing safe distances from antennae installations. The near field safe distance characteristic may permit operation as result of the height separation of the antennae or the elevation of the antennae. This may not be the case if the Exclusion Zone alone were the sole determining factor. It should be noted that in the On Axis Exclusion Zone calculation, only the 'first near field' curve is calculated and displayed whilst the Circular Aperture displays all near field curves and their distances. Rectangular aperture calculations (yagi) are based upon the uniform line source power density in the near field. [reference 3 & 5] Ground Reflection is as detailed in the FCC Standard. This is derived by multiplying the power density by a factor of 2.56 to equate to the predicted ground reflection as stipulated in the Standard. This option may be turned on or off as required. Check with your Licensing Authority if this is a required option for compliance. Page 16

17 Examples Examples Example 1. My tower height is 3 metres, what is the closest distance I can approach the tower? Frequency 432 MHz Power 400 watts PEP SSB (processed) Conversational 1dB Transmission Loss Antennae DJ9BV (Opt) 6 Lambda ARPANSA.. - Set the program to the above parameters (or recall Example 1) - Select the specific antenna by first clicking on top blue button on Yagi Panel and then click on DJ9BV (Opt) 6 Lambda. - Close Antennae selection by clicking elsewhere on screen. - Adjust the tower height with the mouse roller or drag the height pointer to 3.0 metres. The safe distance is given as 4.09 metres. Example 2. What is the closest distance I can approach the dish given:- Frequency 1296 MHz Power 750 watts.. CW.. 2½ minute sequence 1dB transmission loss 28ft dish (0.55% efficiency) at ground level CEU.. No ground reflection. - Set the program to the above parameters. (change to Imperial from Metric) - Select un-safe head height - Reduce tower height to zero (or recall Example 2) - The safe distance is given as feet. Example 3. What is the minimum tower height for safe operation given:- Frequency 10GHz Power 30 watts CW.. 1 minute sequence 1dB Transmission loss ARPANSA.. No ground reflection. - Set the program to the above parameters.. (or recall Example 3) The minimum safe tower height is 2.24 metres. Should you wish to increase the power to the dish (e.g. 37 watts) the near field exclusion boundaries will be indicated as and metres. This can also be seen graphically by selection of the Circular Aperture option (blue label). Page 17

18 Example 4. What is the closest distance I can approach my HF Antenna given:- Frequency 3.5 MHz Power 1500 watts Carrier.. Conversational.. 0 db transmission loss.. dipole antennae FCC.. Ground Reflection - Set the program to the above parameters. (or recall Example 4) The safe distance is given as 1.81 metres. Refer to Page 26 Tables 6 and 7 of FCC OET Bulletin 65 [ Ref 4] Example 5. What is the Exclusion Zone of my Parabolic Reflector Antenna given:- Frequency 432 MHz Power 300 watts CW.. 2½ minute sequence 2.0 db Transmission loss Mounted at ground level ARPANSA.. No ground reflection. - Set the program to the above parameters. (or recall Example 5) Using the Circular Aperture option it can be seen that it is safe from the reflector out to a distance of 14.7 meters, and above the safe radiation limit from that point out to 29.2 metres. Viz it is above safe limits from metres but less than 14.7 metres it is safe and greater than 29.2 meters it is safe as well. (safe being below the EMR limits) Example 6 What is the minimum tower height for safe operation given:- Frequency 144 MHz 4 x 2MXP32 yagi... Power 1500 watts JT db Transmission loss FCC (ground reflection).. - Set the program to the above parameters. (or recall Example 6) - Note the 2MXP32 yagi may be selected from the yagi data base (blue button) and incrementing the number of yagi to 4. Page 18

19 Author This program is written by Doug Mc Arthur (VK3UM) 'Tikaluna' 26 Old Murrindindi Rd, Glenburn. Victoria AUSTRALIA. (QF22ro) Page 19

20 References and Acknowledgements References and Acknowledgements [1] Australian Communication and Media Authority Human Exposure to Radiofrequency Electromagnetic Radiation [2] Australian Standard AS Radiofrequency radiation- Principles and methods of measurement khz to 100 GHz. [3] Australian Government (Common Law) Radiocommunications (Electromagnetic Radiation - Human Exposure) Standard F2011C [4] FCC OET Bulletin 65 [5] Microwave Engineers Handbook - Volume 2 [6] International Commission on Non-Ionizing Radiation Protection. (ICNIRP) I wish to make specific acknowledgement and thanks to the following persons that provided most valuable suggestions/help and beta tested versions of the software. Mr Graham Daubney (F5VHX) Mr Lyle Patison (VK2ALU) Mr Peter Blair (G3LTF) Mr Peter Sundberg (SM2CEW) Mr John Drew (VK5DJ) Mr Peter Freeman (VK3PF) Mr Trevor Pitman VK3VG and to all the other Amateurs that have provided suggestions and comment from around the World. Updated 18th May 2012 Page 20

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