The Transmission System
The Transmission System (refer to Figure 1 following), in its simplest form, consists of the following:
- An IBM compatible PC running Windows
- A proprietary Modulator Unit
- PEDCALL Software package
- A PED ULF Transmitter
- A Loop Antenna
PEDCALL PC & Software - The Operator Interface
The Windows (95, 98, or NT) computer which is running PEDCALL controls the Transmission System. The PEDCALL software provides the interface from the operator to the system in a simple and efficient manner.
The operator inputs information, such as the destination and the message content, then the PEDCALL software will encode this information. Encoding of the destination and message utilises advanced encryption methods to eliminate any chance of invalid information being transmitted. These encryption methods also ensure the receivers can decode the information precisely in adverse signal conditions.
Modulator Unit
The Modulator Unit, as its name suggests, modulates the encoded information and produces a frequency shifted output signal. The Modulator provides the interface between the PC and the transmission system.
The Transmitter
The Transmitter is connected to the incoming 0-20 mA Current Loop. The main role of the Transmitter is to boost the signal into the transmitting antenna.
Antenna
The PED system uses a Loop Antenna. The layout will determine the range of signal transmission. Generally, the larger the loop the better the coverage will be. Typically loops are 0.5 km to 10 km (1/3 to 6 miles) in length.
The Loop Antenna carries 5 amps of current (nominally) and, due to this current flow, an electromagnetic field is created around the Loop Antenna. This field, appears as concentric bands radiating off the cable. The concentric pattern ensures signal is present inside, above, below and off the edge of the loop.
Due to the signal radiation pattern, one centrally located loop can cover an average size mine.
Surface loops are most desirable, due to the infrastructure being on the surface rather than underground. Underground loops are used where surface access is difficult. Underground loops work as effectively as a surface loop and are usually smaller, as the signal does not have to travel as far.
Antenna Safety Unit
The ASU offers selectable Earth Leakage protection and also Impedance Monitoring. In this way, any unsafe condition that may occur will result in the shut-down of the system. Any voltages will be removed from the Loop Antenna.