Link Examples

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Link Design Examples

The following examples are intended to be used with the stand alone PL50L application. The files are located in the

examples directory in the Pathloss program directory. The default installation directory is C:\Program files\Pathlss 5.

PROBLEM PATHThis example uses the file examples/problem/problem.pl5

The design frequency is 6175 MHz and the pertinent performance data is given in the table below

Table 1: Multipath performance calculations

TX power (dBm) 32.00 32.00

RX threshold level (dBm) -76.50 -76.50

Main receive signal (dBm) -36.90 -36.90

Diversity receive signal (dBm) -38.80 -38.80

Thermal fade margin (dB) 39.60 39.60

Climatic factor 2.00

Terrain roughness (m) 6.10

C factor 6.58

Average annual temperature (°C) 14.28

Cheriton

Latitude 37 17 55 .00 NLongitude 075 55 52.00 WAzimuth 25.79°Eleva tion 7 m ASLAntenna CL 60.0, 52.0 m AGL

Accomac

Latitude 37 43 05.00 NLongitude 075 40 33.00 WAzimuth 205.94°Elevation 12 m ASLAntenna CL 98.0, 88.0 m AGL

Frequency (MHz) = 6175.0K = 1.33, 1.33

%F1 = 100.00, 60.00

Path length (51.74 km)

0 5 10 15 20 25 30 35 40 45 50

E l e v a t i o n ( m )

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The overall performance objective for this path is 99.999% annual availability which has been met based on theabove calculations; however in practice the actual path performs poorly.

Given that rain attenuation is not significant at 6 GHz, and that multipath fading mainly occurs under super refractive

conditions, this leaves sub-refraction as the most likely cause of the problem. This situation will be analysed as asurface duct and as obstruction of K fading.

Surface duct

In the Multipath - reflections design section, select the Method - Variable gradient ray trace menu item. Then click

the Set M profile button. Select the Surface duct ITU 453-8 M profile. The data for this M profile is taken from the ITU

453-8 data base based on the path center coordinates of this problem path. The “P = 9.9%” term means that theprobability of occurrence is 9.9% of the time.

Annual multipath availability (%) 99.99976 99.99984

Annual multipath unavailability (sec) 76.79 51.71

Annual 2 way multipath availability (%) 99.99959

Annual 2 way multipath availability (sec) 128.50

Table 1: Multipath performance calculations



Set the Number of rays and the Total display

angle as shown on the right. Set the Ground reflections to None to simplify the overall ray

trace display.

The resulting display shows that the rays arebent above and below the receive site. In this

condition there would be a signal null.

If the profile is reversed using the Operations - Reverse profile menu item , it is apparent

that the same signal null occurs in both direc-tions

51.70 5 10 15 20 25 30 35 40 450

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Obstruction (K) fading

Select the Transmission analysis design section and then select the Operations - Obstruction fading menu item.

Set the Obstruction fading method t o Iterative diffraction loss calculations and the Diffraction algorithm to Pathloss.

The thermal fade margin on this path is 39.6 dB. The program determines the value of K which results in a diffractionloss of 39.6 dB (i.e. the thermal fade margin). The example show uses the Public obstruction fading data. This data

consists of a median value of dN/dh (K) and its standard deviation for four different time periods. This is used in anormal distribution to determine the probability or the value of K actually occurring. At this location, the months of

August and November have high standard deviation values. The overall result is that the total outage time due to

obstruction fading is 9572.29 seconds which reduces the annual availability to 99.969%

Corrective Action

In the case of obstruction fading, increasing the antenna heights will reduce the outage; however this will not haveany appreciable effect on ducting.



CLEARANCE CRITERIAThis example uses the file examples\clearance_criteria\clearance_criteria.pl5 to illustrate the adverse effects of us-ing the classic heavy route clearance criteria on long paths.

The antenna heights were calculated using the clearance

criteria shown. The second criteria (30%F1 at K = 2/3) isthe controlling clearance criteria. The original intent of a

second clearance criteria was to provide some clearanceat a low value of K and therefore prevent signal loss due to

diffraction or obstruction fading. The effect of this secondclearance criteria will result in excess clearance a the me-

dian value of K

Site 1

La ti tude 53 59 28.29 NLongitude 103 08 01.82 WAzimuth 94.25°Elevation 320 m ASLAntenna CL 77.7 m AGL

Site 2

Latitude 53 56 47.58 NLongitude 102 11 55.19 WAzimuth 275.01°Elevat ion 301 m ASLAntenna CL 86.0 m AGL

Frequency (MHz) = 1925.0K = 1.33, 0.67, 1.33%F1 = 100.00, 30.00


0 5 10 15 20 25 30 35 40 45 50 55 60


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The first and second clearance criteria are shown in the Antenna heights design section display below. The red Fres-

nel zone and effective earth radius profile represent the first clearance criteria (100% F1 at K = 1.33). The corre-

sponding green curves represent the second clearance criteria.

An estimate of the outage due to obstruction fading is available in the transmission analysis design section. Selectthe Operations - Obstruction fading menu item. The annual outage is shown to be 0.26 seconds based on a fade

margin of 40.8 dB and can be safely neglected.

The effects of the excess clearance will be analysedin the Multipath - reflections design section. Select

the Operations - Fresnel zones menu item. Selectthe Fresnel number 2 reference and click the Apply

button. Reflected signal along the F2 Fresnel radius

will arrive out of phase with the main signal and re-sult in signal cancellation. It is important to note that

F2 does not equal 200% F1.

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The display shows that the path has second Fresnel

zone clearance at the median value of K.

Two methods are available to analyze the effects of a

reflected signal on a path. The first method uses a re-flective plane definition. This is a highly idealized

method when the actual path profile is replaced by the

plane. In this case, the analysis is based on a single re-flected signal

The second method uses ray tracing on the actualpath profile All reflected signals on the path are consid-

ered in the analysis and provides a more realistic rep-resentation or the actual situation.

Select the Variable - Analyze using ray tracing menuitem. This method uses the actual path profile and

does not require a reflective plane. The results belowshow a the effects of the main reflected signal with

smaller reflected signals superimposed on the trace.

At the median K or 1.33, the operation would be problematic.

2

R e l a t i v e r e c e i v e s i g n a l ( d B )

Earth radius factor K arctan(K) (°)

89.435.0 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81 83 85-15-14

-12

-10

-8

-6-5

-3

-1

12

4

6

89

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13

1.00 1.33 2.00 5.00 10.00

1 H1=77.7 m, H2=86.0 m, F=1925.0 MHz, H234



Corrective action

The antenna heights were recalculated using a single clearance criteria of 100% F1 at K = 4/3. The ray trace resultsare shown below. Signal enhancement now occurs at the median K of 1.33.

With the same fade margin, the obstruction outage increases from 0.26 seconds to 18 seconds.If the transmissionline lengths are reduced for the new antenna heights, the performance using the different clearance criteria is sum-

marized in the table below.

In this example, the overall performance improved using the lower antenna heights; however, this is not always the

case. This path is in a northern climate. Results in a temperate climate will be different. The purpose of this exampleis to provide a method of analysing excess clearance on a path.

Table 2:

Clearance criteria Antenna heights Fade margin Obstruction outage Multipath outage

100% F1 at K = 4/330% F1 at K = 2/3

78 and 86 meters 40.8 dB 0.26 seconds 854 seconds

100% F1 at K = 4/3 50 and 71 meters 43.6 dB 2 seconds 454 seconds

R e l a t i v e r e c e i v e s i g

n a l ( d B )

Earth radius factor K arctan(K) (°)

89.435.4 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81 83 85-38-36

-34-32

-30-28

-26-24

-22-20

-18-16

-14-12

-10-8

-6-4

-20

24

68

1012

14

1.00 1.33 2.00 5.00 10.00

1 H1=49.4 m, H2=71.2 m, F=1925.0 MHz, H

234



A clearance criteria must specify both a value of K and a percent of the first Fresnel zone. If the Fresnel zone is left

out the path will be grazing at the specified value of K and will result in loss in the order of 6 dB.

SPACE DIVERSITY - SPECULAR REFLECTIONSThis example uses the file examples\refelect\refelect.pl5. The path will be analysed for a specular reflection. Space

diversity will be implemented and the antenna spacings will be determined to minimize the effects of the specularreflection. The analysis will be carried out in the Multipath - reflections design section

TAU Nevis

Latitude 52 23 04.00 NLongitude 113 01 35.00 WAzi muth 112.68°Elevation 808 m ASLAntenna CL 50.0, 44.0 m AGL

Lonepine

La titude 52 14 34.00 NLongitude 112 28 45.00 WAzimuth 293.12°Elevation 853 m ASLAntenna CL 65.0, 55.0 m AGL

Frequency (MHz) = 7590.0K = 1.33

%F1 = 100.00


0 5 10 15 20 25 30 35 40


800

810820830840850860870880890900910920930940



Constant gradient ray trace

A constant gradient ray trace is used to determine if the path profile ge-ometry can support a specular reflection. From an inspection of the

path, it is not evident whether this is the case Select the Method - Con-stant gradient ray trace menu item. Set all parameters as shown in the

dialog on the right and click the green check button to generate the ray

trace.

In the description below, the rays are transmitted fro site 1 on the leftside of the display. The rays are receive at site 2 on the left site of the

display

The ray trace shows that there is a section along the

path profile where the reflected rays arrive at site 2above and below the elevation of the site 2 antenna.

There is a the possibility of a specular reflection on thispath. The actual ground cover along the reflective sec-

tion will determine the severity of the problem.

Another simple test for a reflection points on the path

profile is available under the Method - Mark reflection points menu item The profile is scanned from site 1 to site 2.At each point, the angle of incidence and the angle of reflection is calculated. The angle of incidence / reflection is

the angle formed by the line to the site 1 / site 2 antenna and the actual terrain. If the difference between these twoangles is less than the Reflection angle tolerance then a green mark is drawn on the profile with an amplitude pro-

portional to the magnitude of the difference. This line drawing process continues and if the difference between angleschanges sign, then this indicates that a geometric reflection point has been passed over. The location of the reflection

point is interpolated and marked on the profile.



The ray trace can be used to calculate the receive sig-

nal variation at site 2 a as a function of height. Selectthe Method - Site 2 height - gain menu item.The results

show that there is no signal variation below 45 metersas there are no reflected rays below this elevation. The

remainder of the display shows the addition of main

and reflected rays in the classic peak and null pattern.The vertical blue line marks the site 2 antenna height.

This is properly located near the peak of the curve.

Space diversity implementationSpace diversity will be used on this path and the diversity antenna spacing will

be set based on a reflective plane definition.

To clear the display, select the Method - Constant gradient ray trace menu itemand then click the red X to cancel the operation.

Select the Operations - Define plane menu item. Click the Calculate button sev-

eral times and note the calculation method used at the bottom of the display.The first calculation using the standard deviation of the points which are visible

to each antenna does not result in a valid plane. The second calculation usesthe first range in the ray tracing display and produces the correct plane defini-

tion. Note that there may several ranges in the ray trace and each successive

click of the calculation button produces a different result.

The Space diversity planning feature is only enabled for a space diversity an-tenna configuration. Select the Configure - Set antenna configuration and then

check the TRDR - TRDR configuration

R e l a t i v e r e c e i v e s i g

n a l ( d B )

Lonepine Antenna height (m)

85.011.6 20 30 40 50 60 70-6

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Select the Variable - Analyse using reflective plane menu item. The default variable parameter is the earth radius

factor K. The start and end values are 0,70 and 100. The values for the site 1 and site 2 main antenna heights areset. Note the up-down controls on these values. The space diversity antenna heights will be set using the three step

procedure in the Space diversity planning group box using the criteria:

• Simultaneous nulls on the main and diversity antennas do not occur at any value of K.

• At the median value of K (4/3), a signal null does not occur on either the main or diversity antenna.

Click the 1 - Set site 1-2 main antenna heights button. The receive signal versus K is calculated and displayed. Note

the effect of moving the up/down controls on either the Site 1 or 2 antenna heights . The distance is incremented andthe graph is recalculated. The effect is to slide the curve along the horizontal axis. If necessary, set the main antenna

heights for a receive signal peak at K = 1.33

Click the 2 - Set site 1 diversity antenna height. The Site 1 antenna height edit - up/down box is set to the site 1 di-

versity antenna height and the Site 2 antenna height up/down - edit box is set to the site 2 main antenna height andinhibited. The receive signal versus K is calculated for the site 1 diversity to site 2 main antenna combination and

displayed. Set the site 1 diversity antenna height so that the signal nulls are not coincident with the main to main nullsand the relative signal level at K = 1.33 is greater than 0.

Click the 3 - Set site 2 diversity antenna height. The configuration is the reverse of that in step 2. Set the site 2 diver-sity antenna height so that the signal nulls are not coincident with the main to main nulls and the relative signal levelat K = 1.33 is greater than 0.

If the radio configuration does not allow diversity to diversity transmission, it does not matter if simultaneous nulls

occur on the diversity antenna combinations; otherwise, the final antenna heights should take this requirement into

consideration.



Note the dotted lines on the curves at the high end of the K values. This means that the reflection point has movedoutside the reflective plane definition range. Depending on the path geometry this could mean that the curve is not

valid in this area and can be ignored.

R e l a t i v e

r e c e i v e s i g n a l ( d B )

Earth radius factor K arctan(K) (°)89.435.0 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86

-17

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1.00 1.33 2.00 5.00 10.00

1 H1=50.0 m, H2=65.0 m, F=7590.0 MHz, V2 H1=46.2 m, H2=65.0 m, F=7590.0 MHz, V3 H1=50.0 m, H2=55.0 m, F=7590.0 MHz, V4



Dispersion

The final check on any reflection analy-sis is made on the relative time delay

and amplitude of the reflected signal.Click the Dispersion button to access

the Dispersion analysis data entry form.

Any of the parameters in black print can

be varied without affecting the file data.The reflection loss and delay are critical

performance parameters.

If the reflection delay approaches thedata symbol rate, the path will not be

workable

The dispersive fade margin measure-ment is made with a time delay of 6.3

nanoseconds. If the reflection delay is

significantly greater than this, then seri-

ous performance impairments will occurunless the reflection loss is correspond-ingly high.

The reflection delay is completely deter-

mined from the path geometry. The re-flection loss is affected by the antenna

discrimination, terrain roughness andground cover - clearance loss.

ANTENNA ORIENTATIONThis example illustrates the differences in the vertical plane antenna orientation in land mobile and microwave /adap-

tive modulation applications. The file orient.pl5 is located in the examples/orient directory.



This is a short path with an extreme elevation change.In the Transmission analysis design section, note that the sta-tus bar shows that this is a microwave application.

6.100 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5-200

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Click on an antenna icon to bring up the antenna data entry form

The vertical angles are 21 degrees; however there is no orientation loss shown. In microwave and adaptive modu-

lations, it is assumed that the antennas are perfectly orientated in the horizontal and elevation planes.



Click the View antenna data button. The click the elevation option and note that the orientation loss at an

elevation angle of 21.5 degrees is 16.2 dB

Close the antenna pattern view and then close the Antenna data entry form.

Click on the Microwave box on the status bar. This is a short cut to the calculation options



Now set the Application to Land mobile. Click the green check to close the calculation options. Note that the status

bar now shows a Land mobile application. Click on the antenna icon and not that the orientation loss is now 13 dBat S1 and 16 dB at S2.

In land mobile applications, it is assumed that the antenna boresight is in a horizontal plane. To correct this situation

it would be necessary to downtilt the antenna at S1 by 21.49 degrees and uptilt the antenna at S2 by 21.46 degreesas shown below.

Date post:	14-Apr-2018
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