The network layout is a geographical presentation of the network. It can be build-up, either

• manually by the operator, or
• semi-automatically via the site co-ordinates

In the first case, the operator places the sites on the network layout chart with the help of the mouse. This procedure is mainly intended for the first stage of planning a network, eg during the offering process, when the co-ordinates are not known yet, or if there is no time to obtain the co-ordinates. The network layout will not be due to scale.

In the second case, RLTool determines the position of the sites on the network layout chart by utilising global spherical co-ordinates (International Spheroid). The co-ordinates can be inserted individually for each site or a block via a site list. The sites have to be interconnected with help of the mouse. The scale for the chart can be either be determined by the operator, eg to 1:250 000, 1:100 000, etc, or RLTool selects the scale which gives the best utilization of the chart.

A manually designed network layout can, at any time, be transferred to the co-ordinate controlled layout by applying either individual or a block co-ordinate insertion.

The network chart generated by RLTool will be printed on any paper size.


Co-ordinates, distance and bearing.
For a network layout due to scale, and for the interference calculation it is necessary to know the exact position of the RL sites. The positions are to be defined by their co-ordinates. The co-ordinate system used is the global spherical co-ordinate system (International Spheroid).

Based on the co-ordinates, RLTool calculates the length of the radio hop, the beam path length  and the bearing.

RLTool presents the path profile as a chart. It shows

• the contour of the terrain crossed by the radio beam,
• superimposed objects, such as single trees, forests, buildings etc.,
• the 1st Fresnel zone for the selected antenna heights,
• the surface type as a colour bar below the distance-axis, and
• if relevant, ground reflections.

As default, the profile chart is presented for a k factor = 1.33. It can, however, be shown for any other k factor.

 The input data, given as samples as distances referred to site A and associated alti-tudes can be given by the operator via an input data dialog window, a data file, or be loaded from a map database. At the same time the surface type can be defined. If no surface type is specified, RLTool sets it to Other reflective area.

Additionally to the map data, objects not shown on a map – buildings, trees, etc., can be inserted and overlaid on the profile.

To utilize the chart space for the profile by the best way, the program selects the scale for the x and the y-axis accordingly. In case the path includes a passive repeater, two profile charts will be shown, one for each partial hop (or leg). Likewise, the calculations will be performed for each leg.


Calculation of antenna heights
If only one site's antenna height is known (or assumed), RLTool calculates the opposite site's antenna height. To perform this calculation, the program

• investigates the profile for the most critical point over a k factor range between 0.5 and ¥,
• considers 2 clearance criteria, normally 100% for k = 1.33, and 30% for kmin

Other figures for clearance percentage and k factor can be selected. For kmin, the value according to ITU-R Rec.P.530 can be obtained from an internal data bank.

If both antenna heights are unknown, the program can be directed to propose the two antenna heights: both heights will be of the same height, within a difference of 5 m. The clearance criteria will be the same as above. All antenna heights, either given as input data or calculated ones, can be edited at any time.


Calculation of path clearance
If both antennas heights are given as input data, and also when the heights have been calculated according to above, RLTool performs a clearance analysis, where the clearance of the 1st Fresnel is calculated versus a k factor range between 0.5 and infinite.


Ground reflection and its calculation
In order to investigate the profile with respect to ground reflections, RLTool splits the terrain up into a number of sections, each section identical with the interval between two profile samples. The program investigates section for section.

Ground reflections are only investigated for those sections of the hop, which surface is classified as reflective. The following reflective surfaces can be selected:

• water (sea, lakes rivers etc.)
• glacier, snow-covered area
• mash, bog or swamp
• meadows, acres or savannas
• sand gravel
• other reflective areas

No reflections are calculated for the below surface types, which are considered to be non-reflective:

• rocks
• forest
• bush or tree-covered ground
• build-up areas

Identified ground reflection areas are indicated on the profile chart as grey areas between the antennas and the reflection point is shown as a black line.


Transformation of antenna heights
When calculating the position of a potential reflection point, the antenna heights are referred to the altitude of the reflection area. If the reflection area is a slope, eg a sloping meadow, RLTool transfers the antenna heights above sea level (asl) into antenna heights above the terrain section subject to investigation.


Location of a reflection point
If the reflective area is a horizontal one, eg an over-water path, only one reflection point is possible. If, however, the terrain consists of reflective surface lying on different altitudes or having different inclinations, more than one reflection point is possible.

RLTool feature:

• RLTool calculates all possible reflection points on a profile.

The calculation is performed for a k factor range between 0.5 and infinite.

• If the location of the reflection point lies outside the investigated terrain interval, no reflection is possible.
• The clearance is tested for the reflected ray. If any obstacle, man-made or natural, interrupts the path for the reflected ray, this will be indicated in the printout.

Difference in path length between direct and reflected ray
This calculation shows the severity of the reflection by calculating the phase difference between direct and reflected ray, again for the above range of k values. The difference is shown in terms of  wavelength. Each time, the difference is an integer, the influence of the reflected ray on the wanted signal is a maximum, ie the receiver input level passes through a minimum.
This calculation is only carried out in case a reflected ray affects the receiver antenna.


Antenna discrimination
RLTool calculates the angle between the direct and the reflected ray at both the transmitting and receiving antenna. Knowing this angle, the antenna discrimination can be read from the antenna’s radiation pattern.
Note:
The angle between the direct and the reflected ray shown on the profile chart is not correct due to the large-scale distortion (km for the distance and m for the height).


Optimum antenna spacing with space diversity protection
Space diversity can be applied to protect the hop against ground reflections. Optimum antenna spacing is achieved when the difference between direct and reflected ray corresponds to n + 0.5 wavelengths (n = 0, 1, 2…). However, the optimum spacing is a function of the k factor. As we cannot change the spacing with varying k factor, we have to decide for a particular spacing. Thus, the effectiveness changes with the k factor. This will also be shown in the printout.


Consideration of sloping terrain
Normally, topographical maps or database don't offer information about the correct course of the slope between two contour lines. The PRO element of RLTool assumes a linearly increase or decrease of the terrain's altitude between these contour lines. Thus, the location of a reflection point is only correct, if the terrain at that location has the calculated slope. This will hardly coincide with the real terrain. Consequently, there is a risk that this section of the terrain may cause harmful reflections, also if the reflection analysis - which is based on a continuously varying slope - says: No reflection point.

RLTool feature:

• To consider the above problem, the slope of the section is tilted ±10 m  , and new calculations are carried out. If the result is still: No reflection point, one can be quite sure, that no reflections will be present. If the result is the opposite, the result is a reflection area, in which a reflection point may be located. It is not possible to calculate the exact location of a reflection point on sloping terrain, unless we know the sloping at that point, but we get an indication in which area we have to expect the risk for ground reflected waves.