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Old 07-28-2011, 09:55 AM
ImranSabir ImranSabir is offline
Join Date: Feb 2008
Location: Pakistan
Posts: 48
Exclamation Differnce in Simulation between Fixed Height and Terrain Obstruction.. adding

Hi In PL4,
Recently i observed a strange things.
Keeping all the parameters same, the Path Profile shows LOS Blockage when i put 20m of Tree in Terrain data but when i remove 20m tree from Terrain data and put a fixed height of 20m in Antenae Clearance Criteria i am not getting any Blockage?
What is the reason and rational to use these two parameters?

On a parital obstructed path, when i draw the Fresnel Zone in Diffraction Module i am getting 80-90% clearance but the same profile when checked in Antenna View is showing the blockage on the main LOS and in the Path Profile View the result is also different.

Can anybody help on it...

Imran Sabir
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Old 07-29-2011, 03:36 PM
Carlos Torrenegra's Avatar
Carlos Torrenegra Carlos Torrenegra is offline
Pathloss Aficionado
Join Date: Jan 2010
Location: Bogota, Colombia
Posts: 29

Hi Imran,

For the first issue:

Those are 2 totally different things... One thing is to add obstructions of 20m in height(trees, buildings, etc), and another thing is to consider a certain height above ground with a known k in the clearance criteria. These are not related.

For the second one:

Make sure you go through the modules in order, and specially that you set well the antenna heights in that particular module. The difraction and worksheet modules are after that module, so check that the antennas have the heights you set before, they have to match.

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Old 08-02-2011, 04:20 PM
ImranSabir ImranSabir is offline
Join Date: Feb 2008
Location: Pakistan
Posts: 48

Hi Cate,

thanks for your response.
Regarding your first response:
If i put a vegetation of 20m in Terrain data and if i put a 20m fixed height the Path Clearance should be same (irrespective of whether i use 20m in Fixed Height or 20m in Terrain Data). The Antenna CL clearance is always calculated based on K-factor so the affect of the two additional clutters should be same not different. Can you please clarify why they are not related to each other?

Regarding the response to 2nd point:
The antennae heights are fixed but when Fresnel zones are drawn in different modules, result is different. Any reason for that??
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Old 09-23-2011, 11:24 AM
syed.hassanr syed.hassanr is offline
Join Date: Feb 2009
Location: Pakistan
Posts: 45

I don't know whether you have figured out the problem, but I tried your query in my system but i am getting same results. Actually adding X meter fixed clearance means that you suspect any object to block the LOS, so to keep your LOS clear a fixed clearance is added. Antenna heights are calculated using that fixed height. But when you view Path Profile, you will not see any object or an elevated terrain. But when u add 20 m vegetation, this vegetation is shown in Path Profile.
That is why both results are different and should be different.
You can try this other way, add 20m vegetation and calculate antenna heights, then note down these heights. Now add 10m fixed clearance, also keep vegetation. now re-calculate antenna heights. you will see that new antenna heights have been increased 10m. now view profile, your clearance will be 10m more than that of vegetation.

2nd Query Response:
The results of fresnal zones view should be same in diffraction & Path profile view. But as you mentioned that ur LOS is partially blocked and u see RED line cutting the terrain. If your fixed antenna heights are at 100% fresnal clearance which u say is blocked partially, then u will see line crossing the terrain "u said block". The reason is that, main line is not basically showing main beam line but the position of %F1 of fresnal zone, it can be 60% or 100% depending on what u have set for clearance criteria.

you can check this in following way.
calculate antanna heights in antenna module keeping %F1 clearance to 60% for main. line will be touching the heighest clearing point. now change %F1 to 100% (do not re calculate antenna heights), you will see los is blocked (line crossing through terrain) while if u draw profile u will see 60% clearance.

Hope this answer ur query.

Last edited by syed.hassanr; 09-23-2011 at 12:04 PM.
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