HERALD Lab #3

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Path Clearance

HERALD Functions

Exercise 3.1 : Define path profile

Exercise 3.2 : Check clearance

Exercise 3.3 : Modify antenna height

Exercise 3.4 : Estimate obstruction loss

Exercise 3.5 : Display Profile Report (Herald Professional only)

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HERALD Functions

The following Herald functions are related to Profile analysis, clearance criteria, and obstruction loss estimation :

· The path profile is specified as a set of points (distance from first site, ground elevation above sea level, and obstruction above ground level, if any). It can be defined (or modified) using the Define / Path Profile command; also in the "Hop Configuration" dialog, the Hop Length / Profile button gives access to the profile definition dialog.

· Clearance criteria are set using the Evaluate / Clearance / Criteria command. Two (median and minimum) k-factor values are set; for each k-factor value, the percentage of the Fresnel ellipsoid, that is required to be free from any obstruction, is specified; data derived from ITU-R Rec. P-530 are set as a default (including the minimum k-factor value, computed as a function of path length).

· The path profile is displayed using the Display / Path Profile command; if clearance criteria are not yet set, only the terrain profile is shown, with radio site data; otherwise, two Fresnel ellipsoids, for given radius percentages, are plotted (see the blue and green lines in the example given in the Course Notes).

· The path profile view is completed with a table, where results on normalized clearance and margins are displayed; indication about compliance with clearance criteria and estimate of obstruction loss are reported below the table.

· The antenna height definition is part of the "Hop Configuration" dialog; the antenna height can be modified also by means of the Evaluate / Clearance / Antenna Height command.

· The Evaluate / Clearance / Obstruction Loss command displays a dialog where the estimates of the obstruction loss are given for the three obstacle models indicated by ITU-R Rec. P-530 (knife-edge, smooth spherical earth, intermediate terrain), as well as for a “rounded obstacle” (ITU-R Rec. P-526); it is assumed that the operator enters the final estimate of the Obstruction Loss.

Exercise 3.1 : Define path profile

Run Herald and open the "LBudget2_Sample.hpf" project (this is the result of exercises in Herald Lab #1 and Herald Lab #2).

· Select the ALPHA-BETA hop and check the Hop Configuration; if the antenna height was not selected previously, set 25 m at the ALPHA site and 20 m at the BETA site.

· Execute the Define / Profile command; in the "Path Profile" dialog. Click the “Read Points from ASCII file" button and load the "Profile.txt" file. Check the profile table, where the profile points should be :

Distance from first site [km]	Terrain elevation [m]	Obstacle above terrain [m]
1	375	0
5	366	0
11.5	280	0
20	245	0

· Test the alternative import function: in the "Path Profile" dialog click the "Read Profile from Digital Elevation Maps". Check the profile table with more detailed data.

· Close the "Path Profile" dialog and check the profile displayed; practice with the profile definition process, by adding and deleting points; at the end, take care to set the profile according. to the table above.

Tip : Use the Herald icon:

Define / Hop Configuration command

Define / Path Profile command

Display / Path Profile command

Exercise 3.2 : Check clearance

Run Herald and open the "Clearance1_Sample.hpf" project; select the ALPHA-BETA hop and display the path profile.

· Execute the Evaluate / Clearance / Criteria command to display the "Planning Criteria for Path Clearance" dialog. In the upper frame, check that the Relevant factors are correctly set: frequency above 2 GHz, Temperate climate (as indicated by radio site coordinates), single obstruction; then, in the lower frame, the ITU-R criteria are set as a default; check the standard and minimum values of the k-factor and the corresponding Fresnel radius percentages (compare with minimum k-factor diagram and the chart of ITU-R clearance criteria); note how the criteria modify if you change the settings in the upper frame.

· Click the OK button to display the path profile with Fresnel ellipsoid margins for given percentages (blue and green lines); examine the table above the diagram, with indication of the assumptions relevant to the blue and green curves and the results on normalized clearance and margin.

· Return to the "Planning Criteria for Path Clearance" dialog; Tip : Use the Herald icon . Set clearance criteria different from the ITU-R default. Take note of the result in the path profile diagram.

Tip : You can set the k-factor and the F1 percentage in order to display ray trajectories or Fresnel ellipsoids of your interest. For example, with a given k-factor, if you set the Fresnel Radius % to zero, then the line in the diagram is the ray trajectory for that k-factor value; if you set 100%, then the line displayed is the lower margin of the full Fresnel ellipsoid..

· When the profile and Fresnel ellipsoid diagram is displayed, move your mouse along the path profile and click the left button: a path position is selected, where clearance parameters are computed. The "Profile Check Point" dialog is displayed, where you have options to save that point and/or display results in the profile diagram table.

Exercise 3.3 : Modify antenna height

Run Herald and open the "Clearance1_Sample.hpf" project, select the ALPHA-BETA hop.

· Display the path profile and set the k-factor and Fresnel radius percentages to the correct values, as discussed in the previous exercise; then execute the Evaluate / Clearance / Antenna Height command Tip : Use the Herald icon .

· In the "Antenna Height Definition" dialog, modify the antenna height values and check the new results.

· When you modify the antenna height, the indications below the table in the profile diagram are updated.

Note that :

a) the "Clearance criteria (NOT) satisfied" label depends on the Margin values: only if both margins (referring to standard and minimum k-factor) are positive, then criteria ARE satisfied;

b) the Obstruction Loss estimate is set to "0 dB" as long as the Normalized Clearance for standard k-factor is > 0.5 (see diagram). So, it may happen that clearance criteria are not satisfied even if the estimated obstruction loss is zero. To explain this, consider that : (i) clearance criteria require some margin; (ii) clearance criteria apply both to standard and minimum k-factor.

Exercise 3.4 : Estimate obstruction loss

Go on with the same project as in the previous exercise. Select the ALPHA-BETA hop and display the profile and Fresnel ellipsoid diagram.

· Modify the antenna height so that the "Obstruction Loss NOT estimated" label appears below the table.

· Execute the Evaluate / Clearance / Obstruction Loss command; the "Obstruction Loss Estimate" dialog is displayed, with the results referred to the three obstacle models (knife-edge, smooth spherical earth, and intermediate terrain), and to the “rounded obstacle” model. Note that the operator selects the preferred model or is enabled to enter an intermadiate estimate of the Obstruction Loss. In most cases, the "Rounded obstacle" value can be a reasonable (somewhat conservative) choice.

· Execute the Display / Hop Report command ( Tip : Use the shortcut: CTRL + H). Check the Link Budget, where the previously set Obstruction Loss must be included.

Exercise 3.5 : Display Profile Report (Herald Professional only).

Continue with the "Clearance1_Sample.hpf" project, as revised in previous exercises :

· Select the ALPHA-BETA hop, then execute the Display / Profile Report command; check the Profile point list and results of clearance analysis (do not consider warnings about reflection analysis).

· Display the Path Profile ( Tip : click the icon). Then, click the mouse along the path profile, to add points to the "Check Point" list (in the "Profile Check Point" dialog, set to ON the checkbox "Add to check point list").

· Execute the Define / Path Profile command ( Tip : click the icon) to display the "Path profile" dialog, where you can find the selected check points added to the profile points. Delete undesired points (if any).

· Again, display the Profile Report and verify that the Profile Check Points are listed (for those points, the elevation is the result of linear interpolation and is written in brackets).

End of HERALD Lab #3

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