Leaky Feeder Cable

A leaky feeder cable consists of a coaxial cable running along drivages which emits and receives radio waves.

The cable is leaky in that it has gaps or slots in its outer sheath to allow the signal to leak into or out of the cable along its entire length. Because of this leakage of the signal, line amplifiers are required to be inserted at regular intervals, typically every 350 to 500 meters, to boost the signal back up to acceptable levels.

The system has a limited range, and because of the high frequency it uses, transmissions cannot pass through solid rock, which limits the system to a line-of-sight application. It does, however, allow two-way mobile communication.

Creation

Leaky feeder cables can be created using the mouse tool or by importing the coordinates of the cable from an ASCII file. New cables can be inserted by choosing Project > Site > Site: New or by selecting the icon. Afterward, a dialog opens, where the type of the new transmitter can be selected.

Figure 1. The Transmitter Type dialog.


Note: The mouse tool can only be used if the Edit Project Parameter dialog is not displayed. If the Edit Project Parameter dialog is displayed, new transmitters can only be entered via the Transmitter tab.

In case the cable is drawn with the mouse, the z-coordinates can be defined right after the mouse tool is closed with the right mouse button. The z-coordinates of all definition points are initialized with the same height, which can be specified in the following dialog. However, all points can also be edited later.

Figure 2. The Height dialog.


The selected height can be chosen to be an absolute value or to be relative to the contained floor levels or the topography, respectively.

Tip: The definition of the height relative to floor levels or topography is only possible if the database contains floor levels or topography, respectively. If neither floor levels nor topography is contained, the specified height is absolute.

Modification of Parameters

Parameters of leaky feeder cables can be modified by selecting the site to be edited on the Sites tab of the Project dialog or by using the corresponding toolbar icon.

Figure 3. The Site dialog.


Note: Each site can contain only a single leaky feeder cable. There is no possibility to define multiple cables within one site.

After selecting the cable, the following dialog is displayed:

Figure 4. The Cell dialog.


The left part of the dialog shows settings and parameters, which are common for all types of transmitters. Additional leaky feeder cable specific properties on the right are as follows:
Location of Cable
The coordinates of the cable definition points can be edited, imported or exported from or to an ASCII file using the following dialog.
Figure 5. The Coordinates dialog.


Note: The z-coordinates displayed in this dialog are always absolute coordinates.
Cable Loss [dB/100m]
The cable loss is based on resistance (Ohm) and frequency dependent losses of a cable. The value must be specified in dB per 100 meters. Reasonable values are between 1 and 30 dB per 100 meters. This parameter is used to determine the loss along the whole cable. Depending on the length of the cable an additional loss will be determined
Coupling loss (Begin of cable) [dB]
The coupling loss is the attenuation applied at a specific distance (distance coupling loss) perpendicular to the radiating cable. A coupling loss of 20 dB combined with a distance of 2 meters leads to a path loss value of 20 dB at a distance of 2 meters from the feeding point (source) of the cable. 
Coupling loss (Gradient) [dB/100m]
The coupling loss can be reduced by defining a (positive) coupling loss gradient. If the coupling loss at the begin of the cable is 10 dB for example and the coupling loss gradient is 2 dB/100m, then the coupling loss at the end of a 100-meter long cable is 8 dB. Along the cable, there is a linear decrease in the coupling loss.
Distance coupling loss [m]
This parameter is the distance used to determine the path loss based on the coupling loss. It must always be seen in relation to the coupling loss
Note: For the wave propagation prediction of leaky feeder cables, special leaky feeder cable models are used, which can be specified and parameterized on the Computation tab.