HERALD Lab #2

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Link Budget & Fade Margin

HERALD Functions

Exercise 2.1 : Compute Link Budget

Exercise 2.2 : Adjust Fade Margin

Exercise 2.3 : Print Hop Report

Exercise 2.4 : Include a Passive Repeater (Herald Professional only)

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HERALD Functions

Each time the Hop Report is displayed, an updated Link Budget is computed. The Link Budget is displayed and can be printed. It leads to the evaluation of the Hop Fade Margin.

Exercise 2.1 : Compute Link Budget

Run Herald and open the "LBudget1_Sample.hpf" project.

· In the Radio Hops dialog, select the ALPHA-BETA hop and click the "Config / Modify" button to display the Hop Configuration dialog; check how the sites and hop are presently configured; click the "OK" button to display the Hop Report; check the Configuration section of the Hop Report; check the Link Budget (in the Performance section of the Hop Report).

· Return to the Hop Configuration dialog and complete the Hop Configuration, using the "Propagation Losses Define" button (Radio Hop frame); the Various Losses dialog is displayed, where you can set several loss and degradation parameters, related to the radio transmitter and receiver structure and to propagation conditions.

· Compute again the Link Budget and examine the Propagation losses section; practice with the iterative process of revising configuration / checking link budget.

· Complete the Configuration and compute the Link Budget of other hops in the "LBudget1_Sample.hpf" project.

Exercise 2.2 : Adjust Fade Margin

Run Herald as in the previous exercise.

· Select the ALPHA-BETA hop and revise the site configuration (Antenna and Equipment selection) to obtain a Fade Margin approximately equal to 40 dB, with a 140 Mb/s or STM1 capacity; find at least two alternative solutions.

Tip : Set a tentative configuration, check the link budget and take note how much the fade margin target is missed. Go back to Hop Configuration, modify the Antenna and/or Equipment selection in order to adjust appropriately gain / Tx power / Rx threshold (browse the Antenna and Equipment libraries); use Tx or Rx attenuators ("Losses/Degrad. Define" button) if necessary.

· Comment on the alternative solutions you've found to the above problem.

Tip : Main factors in comparing the antenna / equipment configurations are :

· Antenna installation problems;

· Emitted power, antenna directivity (interference produced / received)

· Overall cost (antenna, equipment).

· Repeat the above for the other hops :

BETA-CHARLIE, 34 Mb/s capacity, fade margin objective 48 dB;

BETA-DELTA, 2 Mb/s capacity, fade margin objective 48 dB.

Find the maximum fade margin achievable using the existing antenna / equipment libraries.

· Sample projects close to the above objectives are given in "LBudget2_Sample.hpf" (note that propagation losses to be considered in the Hop Configuration dialog will be discussed in later sessions)

Exercise 2.3 : Print Hop Report

Run Herald as in the previous exercises, select one hop and display the Hop Report.

Tip : Alternative ways to display the Hop Report are :

· Execute the "Define / Hops " command, select the desired hop, then click the Report button (the selected hop is set as the Active Hop);

· Execute the "Display / Hop Report" command: you get the Hop Report referring to the presently set Active Hop (shortcut: CTRL + H);

· Execute the "Define / Active Hop Configuration" command, in the Hop Configuration dialog revise the Site / Hop configuration (if necessary), then click the "OK" button.

· Arrange settings related to output documents: Language (Display / Language & View options command) and Project information (File / Project Info command).

· Execute the File / Print command (if this command is not supported in your HERALD release, you can anyway check the print result using the File / Print Preview command);

Exercise 2.4 : Include a Passive Repeater

(Herald Professional only)

Run Herald and open the "LBudget3_Sample.hpf" project (this is the project produced in the Hop Configuration Exercise 1.6).

· Select the ALPHA-BETA hop and click the "Config / Modify" button to display the Hop Configuration dialog. Click the "Passive Repeater / Define" button and check the passive repeater configuration parameters (single reflector). Do not modify parameters at this stage.

· Close the Hop Configuration dialog with the "OK" button so the Hop Report is displayed. Check the Topology and Reflector parameters in the "Configuration / Repeater Site" section of the Report and the link budget results in the "Performance / Repeater Loss" section.

· Return to the Hop Configuration / Passive Repeater dialogs and modify the reflector size; check the Repeater Loss in the Hop Report. Note the dependence of repeater loss on reflector size (6dB reduction if size is doubled). Set again the reflector size to 25 m².

· Move the ZEBRA (repeater) site position closer to the ALPHA site (Define / Sites command). Set the same longitude of the ALPHA site (E 7°39'52"), do not modify latitude. Note that the ALPHA-ZEBRA distance is 1.19 km only. In the Hop Report, note that a "Near field correction" in the Repeater Loss is included (1.0 dB).

· With the new ZEBRA position, reduce the reflector size to 16 m². In the Hop Report, note that the "Repeater Basic Loss" increases (reduced effective area), while the "Near-field Correction" decreases (see parameters a, b used to estimate Near-field correction) . Similarly, select a smaller (2 m) antenna at the ALPHA site; the near-field correction is reduced (larger antenna mainlobe, smaller b parameter).

End of HERALD Lab#2

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