Editors note – If you might have ever used a walkie talkie you will appreciate the technology, you push a button and talk into the radio, you depress the push button and you recieve a communication back, more likely you’ve worked with a conventional system, but to extend the area of the communications or to tap into a mobile phone style structure you will need a trunked system.
Put simply, where a conventional system is limited by the number of users calling on its capacity at the same time, a trunked system allows you to create virtually unlimited users groups and provides the most efficient use of the radio frequencies and channels allocated to a system.
When you place a call on a trunked system, a channel is allocated to all participants, once the call is completed, the channel is returned to the pool for other users. This sharing of the channel capacity increases the availability of the system to all radio users, maximising availability, especially important at times of peak utilisation.
A trunked radio system is configured on the basis that with any given number of users, not all of them will require channel access at the same time, so fewer individual radio channels are required, providing a number of benefits including savings in the cost of channel licences, the ability to accommodate more users and user groups, the flexibility to configure access between user groups, increased security against eavesdropping and not least, increased availability of the system at all times.
How does a trunked two-way radio system work?
Where conventional two-way radio communications take place on one frequency a trunked system employs multiple frequencies and is able to scan all the frequencies used in the network to prioritise and allocate availability.
A database lies at the heart of a trunked radio system where it controls access to talk groups and the rules applied to individual users and groups at all times. Typically, at least one frequency will be assigned as a control channel to manage the hand-portable or mobile in-vehicle radios telling them which frequency to monitor for incoming and outgoing transmissions.
When a user makes a call by depressing the Push-To-Talk (PTT) button on their handset, the control channel will automatically find and allocate a free channel and send a message to the radio units involved in the talk group instructing them to change to the free channel. This means a conversation can take place via any available channel rather having to wait for a particular channel to be available.
The control channel is a vital instrument in the seamless management of a trunked radio system, ensuring seamless operation in all situations. It can be used to transmit small data messages between radios even if all other channels are occupied and it provides pre-emptive call handling to ensure radio access in case of emergencies.
When renewing your analogue trunked radio system or upgrading to a digital trunked system, you should specify it to include a dedicated control channel which offers better resilience and the ability to send messages even in the event of equipment failure.
What equipment is required for a trunked digital two-way radio system?
In its most basic form, a digital trunked radio system will comprise of:
– A PC (system manager) to manage and configure the systems’ software and network operation (this is only required for configuration).
– An Ethernet Switch link to a base station repeater.
– Base Units (Up to 30 in per site).
– An antenna system to provide radio coverage.
– Hand portable walkie-talkie and/or in-vehicle mobile units deployed in the field.
Systems requiring more channels (more user groups) will feature additional base units/repeaters or where increased range is required, for example in a regional, national or international network, the system manager could be fixed to an IP connection to link up to 48 digital trunked sites together for wide area roaming and calling capabilities. There are many companies specialising in the design and installation of bespoke private digital two-way radio networks,
Original Source PDF