Reliable communication is vital in all types of transportation and in particular communication systems need to work effectively in marine vessels. Typically, a ship will use a number of transmitter-receivers or 'transceivers', for example a marine VHF radio, an automatic identification system Class B signal and an FM radio signal, with each transceiver normally requiring its own antenna.
SRT Marine Technology Ltd of Bristol recently obtained a patent for a radio transceiver which allows multiple transceivers to share a single antenna.
Since the above transceiver devices operate in similar frequency bands, they are able to use identical antennas. Therefore, in order to reduce costs and the required installation effort, GB patent no. 2460012, granted on 27 June 2012, allows these transceivers to share a single antenna by utilising a customised detection and switching scheme. However, in order for such an arrangement to operate successfully, it is necessary to ensure that the intended signals are correctly passed to and from the antenna.
To solve this problem, SRT has devised splitter circuitry for an antenna which has a first terminal for connection to first radio transceiver circuitry, and a second terminal for connection to second radio transceiver circuitry. There is also a connector to be attached to the antenna itself.
The system taps off a small fraction of each signal to be transmitted via a coupler and provides the tapped off signal to a detector. This determines if a signal is present at the first and second terminals. Switching circuitry within the transceiver allows the first terminal to be connected to the antenna terminal when a first input signal is detected on the first terminal and the second terminal to be connected to the antenna terminal when a second input signal is detected on the second terminal. In this way, both the first and second input signals can be transmitted in turn via a single antenna.
It is possible that both transceivers will attempt to transmit on the antenna simultaneously. This issue can be avoided by detecting when each signal is to be transmitted and determining which signal should have a higher priority and transmitting that signal first.
In a further enhancement of the invention, the circuitry includes an additional terminal to be connected to a third transceiver in order to enable three transceivers, such as the three types of radio listed above, to use the same antenna.
