Portable two way radios are a convenient and relatively low priced means of communication. Two way radios are transceivers - that means they can both receive and transmit messages simultaneously. They are unlike broadcast receivers (such as the ordinary radio) which only receive messages or signals. A good example of the two way radio concept is the mobile phone and the hand held radio referred to as the walkie talkie. There are different categories of portable two way radios and each has its benefits and the circumstances for which it is most suitable.
The conventional portable two way radios operate on a fixed RF (radio frequency) channel. Even where a two way radio has the ability to tune into more than one channel, the user is required to select only one since the radio can only operate on a single channel at a time. Radios with multiple channel capability have a button or a channel selector as part of their control panel. Often, the frequency regulator responsible for a certain area will allocate different channels to different organizations. For instance, one channel can be assigned to a cab company in order to facilitate communication between the dispatcher and the taxi drivers.
A trunked radio is another type of portable two way radio - it uses a set of pre defined rules to automatically pick the radio frequency channel on its own. Digital versions of the trunked radio have the ability to multiplex - in other words, they can handle multiple conversations using the same frequency channel.
The other type of portable two way radio is the duplex radio. It can transmit and receive messages on different frequency channels. Equipment used for communication in a duplex system can only function where there is certain core infrastructure such as a repeater and a base station. The base station is used to re-transmit the signals received from one portable radio to the others as long as both radios are within the range of the base station's signal reach.
There are three types of duplex system radios - the half duplex that requires the user to press a push button before relaying a message, the full duplex which can simultaneously receive and transmit signals and the hybrid duplex which applies both the half and full duplex systems. The advantage of this type of radio is its ability to extend the geographical area within which communication takes place between the end users.
Another classification of portable two way radios is the analogue radio and the digital radio. The analogue includes the AM radios used in aircraft and the walkie talkie. Its advantage is that, in areas with weak signals it has a better ability to communicate (but only as long as good quality equipment is used). The digital radios include the standard safety radio. This portable two way radio allows simultaneous communication between multiple users and can also send non voice data such as a text message.