Headend Equipment
The Headend includes the equipment necessary to operate the overall Leaky Feeder distribution system. The Headend provides for the following roles:
- Connection to the Leaky Feeder cable network.
- Connection to the surface antenna network.
- Modulation and Demodulation of the VHF signals.
- Splitting and combining of multiple channels.
- Powering the overall Leaky Feeder network.
- Diagnostics via an Amp/Voltmeter.
- Correct impedance matching.
The Headend equipment can also include additional items such as telephone interconnect units for interfacing to the mine PABX system. The Headend is usually contained within a suitable 19" rack enclosure, this allows for easy maintenance and servicing of the system. Typically for an average VDV system of 4 channels the Headend can be installed in one enclosure. For larger systems, that is when up to 16 channels are utilised, the Headend will usually be installed in two (2) enclosures.
The Headend comprises several components or modules, these include the following:
- Transmitter/Receiver Splitter Combiner
- 16 Channel Line Splitter Combiner
- Radio Repeaters
- Power Supply
- 19" Rack Enclosure
| INSERTION LOSS | Insertion Loss -Tx input to Leaky feeder | 38dB max. |
|---|---|---|
| Insertion Loss - Leaky Feeder to Rx input | 23dB max. | |
| RX / TX | RF Drive Level (Tx input) | +40dBm |
| RF Drive Level (Leaky Feeder) | +2dBm | |
| Isolation | 20dB min | |
| Transmit Frequency Band | 146 to 158.5 MHz | |
| Receive Frequency Band | 168 to 220 MHz | |
| POWER SUPPLY | Leaky Feeder Line Voltage (mains) | 30 VDC |
| Leaky Feeder Line Voltage (battery) | 5 VDC to 32 VDC | |
| Leaky Feeder Line Current (Max) | 5 Amps | |
| IMPEDANCE | Impedance of Tx, Rx and Antenna | 50 Ohms |
| Impedance of Leaky Feeder Ports | 50/75 Ohms (Optional) | |
| Impedance of Leaky Feeder Cable | 75 Ohms | |
| CONNECTIONS | Leaky Feeder Connection | N Female |
| Antenna Connection | N Female | |
| Tx & Rx connections | TNC Female |
Surface Communications
Direct relay of the VHF signal to surface areas, or interface to a separate surface communication system (such as UHF), can be provided when required.