Atmosphere Attenuation

Transcription

VK3UM Atmosphere Attenuation Calculator
Table of Contents
Over View
Menu Options
Input Variables
Input application data.
Screen Display Calculations
Reference ITU Graphs
Terrestrial Dry Air [O²] and W V [H²O] Attenuation
Zenith Dry Air [O²] and W V [H²O] Attenuation
Rain Attenuation
Slant Paths
Acknowledgement
References
Author
Page 1
2
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5
7
11
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Atmosphere Absorption Attenuation [Attenuation by
atmospheric Gasses]
Electromagnetic waves are absorbed in the atmosphere according to wavelength. Two
c ompounds are responsible for the majority of signal absorption, Oxygen (O ) and water
²
vapor (H O).
²
The first peak occurs at 22 GHz due to water vapor, and the second at 63 GHz due to oxygen.
The actual amount of water vapour and Oxygen in the atm osphere normally declines with an
increase in altitude because of the decrease in pressure.
Total attenuation through the atmosphere at any frequency, through unobstructed
atmosphere, is the sum of free space path loss, attenuation caused by oxygen absorption, and
attenuation caused by water vapour absorption. Rain attenuation, when present adds an
additional element.
Total path attenuation = Attenuation Free Space Path Loss + Attenuation caused by Oxygen
+ Attenuation due to Water vapour + Attenuation due to Rain.
This program [Atmosphere] calculates the absorption attenuation at Microwave frequencies
for both terrestrial and slant paths for Am ateur frequencies from 10-241 GHz.
The calculations applied in this program are based upon the International
Telecommunication Union (ITU) recommended methods as listed in the Referenc e section
of this Document.
The program has been written primly as a supplement to my EME Calculator Program
to refine overall loss calculations for frequencies above 10 GHz where these factors
become a significant.
refer .. The EMECalc program available for download from http://www.vk3um.com
This program has been designed to be best viewed under Windows XP Style.
This can be set from the Desk Top by Properties/Display Properties/ Appearanc e and
then choose Windows XP Style.
Menu Options
Save default Data
All the parameters that appear on the sc reen will be saved and will be used when the program
is run again.
The following message will be displayed on its com pletion.
Page 2
Change Display Accuracy
The calculation displayed accuracy may be changed as desired by c licking on the required
decimal points.
The display below indicates 3 dec imal digits will be displayed.
On Screen Help Display
This allows for the time the on screen help messages (yellow) are displayed.
Reset Screen Size
Resets the Screen size to the default dimensions.
Cloud yearly % location maps
Select the Cloud Columnar content map that is appropriate to your loc ation.
Then adjust the slider commensurate with you loc ation.
Page 3
Help
Displays this Help File
About
Provides the Build version and date of the software.
Exit
Soft Exit from this program
Version
The software version of this software.
Page 4
Input Variables
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Temperature in °c.
Pressure in hPa.
Frequency in GHz.
Humidity in %.
Distance in kMs [for Terrestrial calculations].
Elevation in degrees [for Slant Attenuation].
Rain precipitation rates in mm/h [for both terrestrial and Slant attenuation c alculations].
Selectable Polarisation [horizontal, vertical, circular].
Calculations provided.
Terrestrial
 Dry Air Attenuation in dB per kilometres at Sea Level.
 Water Vapour attenuation in dB per kilometres at Sea Level.
 Total attenuation of Dry Air and Water Vapour in dB per kilometres at Sea Level.
 Total combined attenuation over a path length per kilometres as input by the user
 Rain Attenuation for horizontal, vertical or circular polarisations at various rain
precipitation rates.
 Path Aperture Loss.
Page 5
Slant Attenuation for both (independent) Home and Dx Stations
 Dry Air Attenuation in dB per kilometres at Sea Level.
 Water Vapour attenuation in dB per kilometres at Sea Level.
 Dry Air height in kilometres. [refer Rec . ITU-R P.676-7]
 Wet Vapour height in kilometres. [refer Rec . ITU-R P.676-7]
 Dry Air attenuation at height in dB at zenith.
 Water Vapour attenuation at height in dB at zenith.
 Total Attenuation (Dry Air + Water Vapour) at zenith.
 Total Attenuation (Dry Air + Water Vapour) at user selected Elevation angle. (5-90°)
 Rain Attenuation for horizontal, vertical or circular polarisations at various rain
precipitation rates.
 Fog Attenuation at various fog distance visibility distanc es.
 Cloud Attenuation at a specific Cloud Columnar content.
 Added attenuation to Earth Moon Earth (EME) path.
Page 6
Input application data.
The following input variables may be changed to suit your application.
Use the Up/Down arrows to change the parameter as required.
Temperature : Humidity : Pressure
The combination of the humidity and the temperature will give the
water vapour density in grams per cubic centimeter.
By clicking on the Water vapour Density label you can change to Ice Vapour Density.
Frequency
Selectable for all Amateur Bands from 10 GHz to 241 GHz.
The 100 GHz option is provided to check measurements against known values.
Note. Although the frequencies of 10, 24 and 47 GHz are shown in the display the ac tual
frequencies used in the program are 10.368, 24.048 and 47.088 GHz.
Rain and Polarisation (Relevant to Rain attenuation.)
Cloud Columnar Content.
Click on this button to select the Average Year % Liquid Water m aps.
which will reveal this panel
Page 7
Choose the Cloud yearly % map applicable to your location and time of year.
Note the value and adjust the Cloud Columnar Slider to this value.
The value of Cloud attenuation will be provides as well as the specific H²O attenuation
coefficient.
Height above Sea Level.
This option is currently not incorporated in the program overall end calculations.
It provides the temperature (in centigrade and Kelvin) , pressure (in hPa) and water vapour
content (in g/cm³) commensurate with the reference standard atmosphere at selectable
heights above sea level (HASL) adjustable by the arrow keys.
First click on the Ref Latitude and season button to reveal the Reference Latitude Panel.
Choose the Latitude applicable to your location and the season applicable to your time of
year.
Note that the Season selection only applies to latitudes greater than ± 22° from the equator.
The data will be computed as shown in the following panel.
Reference ITU Recommendation P.835-4
Standard Temperature 288.15 k Standard pressure 1013.25 hPa
Calculations as per pages 4-6 (inc)
Distance
Page 8
Adjust for Terrestrial applications.
The 3 adjustment arrows provide for x100, x10 and x1 variations.
The Free Space Path Loss is calculated from the Distance and frequency selected.
Elevation
Adjust for the angle of the slope path for Space applications [eg EME] through the
atmosphere.
Default is Zenith [90°] and variable down to 5° degrees.
Additional Features.
Save Default Data.
Click on this to save your set up that will load at start of the program .
On Screen Display Accuracy
It should be noted however that the maximum accuracy of the calculated values is
approximately 10% and to utilise the higher resolution provided is not an indic ation of
increased accuracy.
This value may be saved as part of you default start up values.
On Screen Help Delay
This option provides the selection of the time that the on screen help display shows the
message under the cursor (where provided). It may be varied from off (no message displayed
to a maximum of 8 sec onds).
This value may be saved as part of you default start up values.
Help .. About .. Exit .. Version
Help provides this help information.
Page 9
About
Provides the Author details, Build number and Date.
Exit
Provides a safe Exit from the program.
Version
The on screen version number of the Program release.
Page 10
Screen Display Calculations
Calculations
Terrestrial Attenuation
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Free Space Path Loss (aperture Loss) for the path distance selected
Dry Air Attenuation (O ) in dB per kilometres at Sea Level.
²
Water Vapour attenuation (H O) in dB per kilometres at Sea Level.
²
Total attenuation of Dry Air and Water Vapour in dB per kilometres (as selec ted by
the user) at Sea Level.
Total combined attenuation [O + H O] over the path length as chosen by the user.
²
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Rain Attenuation for either horizontal, vertical or circular polarisations as selec ted.
.
Slant Attenuation (for both Home and Dx Stations)
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Dry Air Attenuation (O ) in dB per kilometres at Sea Level.
²
Water Vapour attenuation (H O) in dB per kilometres at Sea Level.
²
Dry Air (O ) equivalent height in kilometres.
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Wet Vapour (H O) equivalent height in kilometres.
²
Dry Air attenuation (O ) at equivalent height in dB at zenith.
²
Water Vapour attenuation (H O) at equivalent height in dB at zenith.
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Total Attenuation (Dry Air + Water Vapour) at zenith.
Total Attenuation (Dry Air + Water Vapour) at user selec ted Elevation angle. (5-90°)
Rain Attenuation for either horizontal, vertical or circular polarisations as selec ted.
Fog Attenuation.
Cloud Attenuation.
Additional attenuation added to Earth Moon Earth (EME) path, and the
Home and Dx Station added combined losses.
The Home and Dx Station Total additional Loss values are those to be inserted into the
VK3UM EMECalc program which will then provide the additional accuracy of c alculations for
frequencies above (inc luding) 10
GHz
Current Moon Distance
When the program is started the current Moon distance, path loss and phase values are
calculated.
The current Moon distance will be shown as above and the slider will show its position.
The slider may be varied as required (from Perigee to Apogee) and may also can be reset to
the current (local computer time) Moon Distance.
Page 12
Reference ITU Graphs
The included graphs provide a means of checking the programs calculated values to those of
the ITU recommended calculation procedure.
It should be noted that the computed figures may [in some cases], be within 10% of the
theoretical values due to the nature of the applicable form ulae commensurate with the c urve
form fit procedures used.
Page 13
Terrestrial Dry Air [O ] and Water Vapour [H O]
²
²
Attenuation
This graph is from ITU RECOMMENDATION ITU-R P.676-7,
"Attenuation by atmospheric gases." [ Page 16]
The graph provides the attenuation values at terrestrial paths for both Dry Air, Water
Vapour and the combined total
for an Atmospheric pressure of 1013 hPa, a temperature of 15°c and a water vapour c ontent
of 7.5 g/cm³.
Page 14
Page 15
Zenith Dry Air [O ] and Water Vapour [H O]
²
²
Attenuation
This graph is from ITU RECOMMENDATION ITU-R P.676-7,
"Attenuation by atmospheric gases." [ Page 19]
The graph provides the attenuation values at zenith for both Dry Air, Water Vapour and
the combined total
for an Atmospheric pressure of 1013 hPa, a temperature of 15°c and a water vapour c ontent
of 7.5 g/cm³.
Page 16
Page 17
Rain Attenuation
This graph is an extract from the "PROPOSED REVISION TO
RECOMMENDATION ITU-R P.838". [page 13]
The proposed changes have been applied in this program.
-o-
Page 18
Slant Paths
Page 19
Page 20
Acknowledgement
I wish to acknowledge the c onsiderable help from John Drew VK5DJ http://www.vk5dj.com
, in converting many of the c omplex mathematical expressions into the Pasc al language,
and also
Dr Mike Willis G0MJW for his assistance in obtaining the latest ITU Recom mendations (as a
member of the Study Group directly involved) as well as his valued suggestions and help with
some of the complex calculation scripts.
Page 21
References
International Telecommunication Union Publications
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ITU-R P.676-8 Attenuation by Atmospheric Gases.
ITU-R P.840-4 Attenuation Due to Clouds and Fog.
ITU-R P.618-10 Propagation data and prediction methods required for the design of
Earth-space telecommunication systems
ITU-R P.838-3 Specific attenuation model for rain for use in prediction methods.
ITU-R P.836-4 Water vapour: surface density and total columnar content.
ITU-R P.453-9 The Radio Reflective Index : its formula and reflectivity data.
Page 22
Author
This program has been written by Doug McArthur [VK3UM].
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Web Site
http://www.vk3um.com
Contact ... tikaluna at bigpond.com
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Program written with the Delphi 2007 platform in the Pasc al language.
First draft concept release July 2011.
First Beta restricted release Septem ber 2011
Page 23

Index
-1100 GHz option 7
-AAbout 13
Additional attenuation 11
Additional Features 7
Amateur Bands 7
Apature Loss 11
Atmosphere Absorption Attenuation 2
Attenuation by Atmospheric Gases. 22
Attenuation Due to Clouds and Fog. 22
-CChange Display Accuracy 13
Cloud Attenuation 11
Cloud Columnar Content 7
Cloud Columnar Slider 7
Cloud yearly % location maps 13
Current Moon Distance 11
-Ddesign of Earth-space telecommunication systems 22
Distance 7
Doug McArthur 23
Dry Air Attenuation 11
-EElectromagnetic waves 2
Elevation 7
EME Calculator Program 2
EMECalc www.vk3um.com 2
Exit 13
-FFog Attenuation 11
Free Space Path Loss 7, 11
Frequency 7
-HPage 24
Height above Sea Level. 7
Help 13
Help .. About .. Exit .. Version 7
Home and Dx Station added combined losses 11
Home and Dx Station Total additional Loss 11
Humidity 7
-IIce Vapour Density 7
input variables 7, 5
International Telecommunication Union (ITU) 2
ITU-R P.618-10 22
ITU-R P.676-8 22
ITU-R P.836-4 22
ITU-R P.838-3 22
ITU-R P.840-4 22
-LLattitude 7
-Mmaximum accuracy 7
Menu Options 2
-OOn Screen Display Accuracy 7
On Screen Help Delay 7
onscreen help display 7
Oxygen (O²) 2
-PPolarisation 7
Pressure 7
-RRain 7
Rain Attenuation 11
Ref Lat and season 7
Reference Latitude Panel 7
Reset Screen Size 13
-SSave default Data 13
Save Default Data. 7
season 7
Slant Attenuation 11
Slant Paths 19
Page 25
slope path 7
Space applications 7
Specific attenuation model for rain 22
specific H²O attenuation coefficient 7
-TTemperature 7
Terrestrial Attenuation 11
The Radio Reflective Index 22
Total attenuation of Dry Air and Water Vapour 11
Total combined attenuation 11
-Wwater vapor (H²O) 2
Water vapour 22
Water Vapour attenuation 11
water vapour density 7
-ZZenith [90°] 7
-[[Attenuation by atmospheric Gasses
Page 26

Atmosphere Attenuation

Transcription

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