Radio jargon explanation

1. Walkie-talkies

DevicesWalkie-talkies are mostly being used as portable radiotelephones in a radiotelephone system, but apart from that, they are also used in short range radio systems. In these systems, hand-held portables can be used to communicate without the need for a base station. In built-on areas, the maximal range is about thousand metres, while the range can reach up to 4000 metres in vacant sites. Walkie-talkies usually have to be switched from receiving to sending (Push To Talk). It is not possible to send and receive at the same time. This is called a half-duplex system.

These systems are best used in security, on construction sites or during big events.

2. Radio telephony

Although cellular phones are being used on a very largse scale nowadays, radio telephones are still needed. They have a couple of unique properties which, in some cases, make it impossible or undesireable to be replaced by cellular phones. For example, unlike cellular phones, radio telephones are not being charged for each call or fixed time interval.

In the most simple form, radio telephony can offer a way to communicate between a number of base station, on a fixed position, and a number of walkie-talkies. Usually, this system works with half-duplex connections. This means it is impossible to send and receive at the same time. By default, the walkie-talkie will be receiving (listening). To be able to send (talk), a button on the microphone has to be pressed. This mechanism is better known as "push to talk".

All communication will go between a group of people who already know each other, in most applications. Mobile users will use their walkie-talkies to make contact with the base station. Most networks will have a limited connection range. However, there are several networks with a range spanning a complete country. In The Netherlands, a good example of such a network if the one for public transport buses. Other than that, radio telephony is being used by emergency services like the police, fire brigade and ambulance.

Although most conversations will be held between a mobile user and the base station, it is possible for mobile users to communicate with each other, but this cannot be done directly. The base station has to be put in relais mode: this means it will retransmit everything it receives, but it transmits it using another frequency.

3. Conventional radio telephony

Devices for conventional radio telephonyConventional systems for radio telephony also go by the name of Private Mobile Radio (PMR). They consist of a base post and a number of mobile units. The base post is being used to contact the people carrying a mobile unit. Although these systems have been designed to keep in touch with people from the base post, it is also possible to make a connection to the regular telephone network (via the base post) using a radiotelephone. PMR systems can cover an area of several ten kilometres around the central antenna. With conventional (first-generation) radio telephony, each group of users has been assigned their own frequency band.

4. Temporarily Closed Nets

For the temporary use of walkie-talkies with events etc., it is possible to use the TCN-regulation. This regulation is used in The Netherlands. Five frequencies are available: 169,930; 169,950; 169,990; 170,050 and 170,090 Mhz. The latter two frequencies are also used for common walkie-walkie communication.

5. Trunking

Conventional PMR systems are perfect for local professional use. However, these systems become more inefficient when deployed on a large scale, as they take up a lot of frequencies, only some of which are continuously needed. The solution for PMR systems with many users or in a geographically large area is to use trunking.

Trunking means only a limited number of frequencies is being used at the same time. Users can get a specific frequency assigned, but only when they really have to use it and only as long as they need a connection. An individual user will never need a frequency continuously. So if a pool of frequencies is being used by a large number of users, the total number of frequencies (the bandwidth) can be much lower than in a system that does not utilize trunking.

During the connection setup phase, the user makes a connection request over a predefined or randomly chosen free channel. The system will return a traffic channel which should be used to perform all communication from that moment on.

In analog trunking systems, the MPT1327 standard is widely being used. This system allows for large networks with multiple base station, because the 'connection request' channel is also being used to announce a user when he turns his terminal on or if the user walks out of the station's range and enters another area with a different base station. Because of this, the system is able to know where its users are located.

6. Traxys - Public mobile trunking

Mobilofonie-apparatuurIn The Netherlands, KPN Telecom made a countrywide public trunking network named Traxys. This network can be used for radio telephony and walkie-talkie traffic. Companies who do not want to build their own (trunking) network can choose to subscribe to Traxys. A choise has to be made between investing time and money in building their own network, or paying a monthly fee and an amount of money per call.

Networks like Traxys are also known as Public Access Mobile Radio (PAMR) network. A company using Traxys gets its own base station which is connected by wire (for large companies) or by radio (smaller companies) with the regional Traxys station. Because all regional stations are linked to the countrywide network, users can have a regional or countrywide network of their own.

Just as with PMR trunking, Traxys uses MPT1327. Radio connections use FM in 12,5 kHz-wide channels. Used frequencies are in the range from 410 to 430 MHz.

7. PMR446

DeviceSince a while, there is a European standard for Short Range Radio applications that goes by the name of PMR446. This system works in the frequency band from 446.0 - 446.1 Mhz. Eight 12,5 kHz-channels are defined in this band. The maxmimal broadcast power is 500 mW. PMR466-systems can be used without the need for an individual license. To address a single walkie-talkie, a tone slot is being used. This makes it possible to address a single walkie-talkie using a five-digit code, but also to address groups of people with special codes. Most walkie-talkies have a setting switch the tone slot on or off. When you switch it off, all tone slots and conversations can be heard.

8. Low Power Devices

Low Power Devices (LPDs) are small walkie-talkies that can be used without the need for a license, because they work within the global regulation for Short Range Devices. The walkie-talkies have an output capacity of 10 mW at most. There are 69 channels available in the frequency band from 433,0500 to 434,7900 MHz. A tone slot is commonly used to prevent other users from bothering you. These devices are very popular with children and walkers.