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Amateur Radio activity at FR5DN

 

EME on 70cms - Using the moon as a passive wave reflector

VHF Tropospheric ducting and other propagation modes tests on South Indian Ocean

Some Radio-astronomy tests 



---LINK TO TROPO PAGE QSO IS HERE---


NEW : my tropospheric forecasts in test
 - valid for sea path.



One of the challenge of tropoducting qso is to get good forecasts data to display a map of what can be the situation in an area or on a particular path, at a given time.
With all qso's made and maps around, we see that on ZS-FR path the real world doesn't match exactly the forecast  maps all time... Hummm, why? Just to mention some reasons :

-First, we use meteorological models of what should be the troposphere at a given future time, in a given area. Models are models, with their part of uncertainty, with a level of confidence, and there are different models.
-Second, on the path, at a given time, the troposphere is a 3D medium, longitude, latitude and ....height!
-Third, the color scale to display the maps are not  the same with the different sources.
-Fourth, the altitudes taken in account for drawing a map play a big  role in the way they show forecasts
-Fith, the location of the stations, altitude, inland path, make difference.
-.....

To make things very short, best tropo occurs when there is increase of T in altitude and decrease of  humidity, more than the standard way they should (which would give normal tropo conditions). These anomalies make the N refractive index to change more than standard at some altitudes. We can have several layers of good tropo.
As these anomalies can happen at different altitudes, giving what i call High Tropo, or Low tropo, that we experienced on ZS-FR paths...we  sometimes see, very nice forecast maps but no qso, and also the opposite!

So i try to show more about the situation.  Not perfect, but just an approach.
I made  maps of troposphere from ZS2 and ZS5 to FR, showing the Relative Humidity and the T fonction of the altitude, in hPa.
1000 hPa is sea level, 950 hPa is 500m altitude, 900 hPa is 1000m and 850 hPa is 1500m. Not perfectly true, but quite closed.

My main maps so far show only difference of N between 1000m and sea level, coded in color, could be acceptable for inland < 250m altitude.
If for the same time, you look at the vertical troposphere map for a path, you can see the predicted zones and altitudes with T increase and decrease in Humidity. X is approximative longitude on the path, Y is altitude.
The color code (humididy) is not perfect but i tried to match  the  main map colors.
Curves are T. So you can see that some areas are low, some others high tropo... So that is probably why sometimes, we don't have qso, even if main area maps show potential... Again, this is experimental, but can be extra indicator...

Grid Analysis and Display System (GrADS) is used to build images.

Vertical maps here : will open in new window so you can compare, between 2 windows of your browser, between standard area maps and vertical troposphere view, for the ZS-FR paths.



Scale used in images for tropo conditions - Again, valid for 1000m asl. See vertical test maps at same hours.

Nil Very low Low Normal- Normal Normal+ Good Good + Strong Strong++ Excellent whaou!




 


Nil Very low Low Normal- Normal Normal+ Good Good + Strong Strong++ Excellent whaou!

 


Nil Very low Low Normal- Normal Normal+ Good Good + Strong Strong++ Excellent whaou!

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