Fixed-site and portable repeaters
It may not always be possible to use radios in ‘simplex’ mode (direct radio-to-radio) to cover an entire incident ground; the signal coverage may weaken because of the distance and the number of obstruction between radios. Repeaters, also called ‘talk-through base stations’, can be used to extend the range of handsets; they act as a ‘middle agent’ to rebroadcast radio messages.
Repeaters may be permanently installed in fixed locations, such as shopping centres, tall buildings, tunnels and hospitals. Fixed repeaters give fire and rescue services the benefit of knowing the coverage they provide before they need to be used.
Some manufacturers have designed portable repeaters that are battery powered and easy to deploy. These portable repeaters can be deployed quickly and easily in areas that have no power sources. Fixed repeaters may give better coverage because of better planning and installation.
In simplex mode, radios transmit and receive on the same frequency. When radios use a repeater to communicate, they operate in half-duplex mode. In half-duplex mode, the radios transmit and receive using different frequencies, although this is invisible to the user.
For optimum coverage, repeaters are usually positioned in a central position between the radio users. Radios must be within the coverage range to access a repeater. If two radios have selected a half-duplex channel and no repeater is available, they will not be able to communicate, no matter how close they are.
Depending on the model, repeaters may be operated in analogue or digital mode; the radios accessing the repeater must be using the same mode.
Some radio manufacturers produce repeaters that can be connected over an IT network to allow wide-area radio coverage. In this configuration, the radios will choose the closest or best repeaters to communicate, and the messages are relayed across the IT networks to be rebroadcast via the other connected repeaters. Not all radios have this capability, and careful planning is required.
In the UK, repeater base stations should transmit on the lower of the frequencies and receive on the higher frequency; radios to be used with repeaters should therefore be programmed in the opposite configuration. (See also Fireground radio frequencies)
Fire and rescue services should consider the resilience of the repeater equipment they may rely on for effective communications. Incident commanders should consider a fallback procedure that can be implemented in the event of a communications breakdown (e.g. repeater power failure).