Closed network is a radio network which is closed in the sense that only radios programmed to the frequency (channel) network operating on that can be used in the system. That's telecommunications authorities providing licensing and allocates frequency to new systems. Advantages of closed networks is that only by one keystroke you reach several people at once, without delay. This is the great strength of two-way communication, while not getting incurred call costs.
To get the approval to have a own closed network, a license is required. This is assigned by the Post and Telecommunications Authority. It has no intention to purchase radio equipment before a license is awarded. Please refer to the page about rules and general info regarding PMR.
VHF ribbons for commercial radio starts at about 136 MHz and runs up to 174 MHz. Benefits of VHF radios is that they have a longer range off-road, but stopped in turn facilitated by structures such as buildings, oil installations, etc. UHF band is currently divided into two, high band and low band. Low band go from 403 to 430 MHz. High band goes from 440 to 470 MHz. Advantages of UHF radios is that they have better "penetration" and is thus better to use in buildings such as hotels, industry or oil platforms. Radios in the UHF band is often also divided into high / low band model, but more and more radio types cover the entire band.
PL-tone, or Private Line which letters stand for, is a low frequency tone between 67 and 250 Hz which is superimposed on the carrier-wave. This tone is constant as long as the radio transmits. If all the radios within a system programmed not to open the speaker before the proper PL tone is received, one can to a certain extent "shut out" disruptive radios from other system. However, please note that this does not restrict the radios in the other system to listen to what is said in a system with PL admitted. This signaling is also called CTCSS (Tone Coded Squelch Continuos System).
5 tones may have additional features. Often it works almost like a telephone number to call up a particular radio, but can equally well be used to boot repeaters or remote other features. Also used as identification when calling, so it is called up to see who calls. Actually, the only real limit the use of this type of signaling. The most used tone system today called CCIR, but there are also other systems ZVEI use
If the radio is to be used in hazardous areas, ie areas where such hydrocarbons may occur in the air, required Ex-approved radios. That is, the radio of undergoing a test CE. Modified to ensure that the surface temperature does not exceed certain values on some of the surfaces in the radio. This also applies to the internal components. Ex batteries are also protected against excessive power outlet to prevent overheating and sparking.
A repeater is as its name indicates, one that repeats, and is usually a standalone radio receiver / transmitter. The receiver part of the repeater receives the transmitter signal from radio devices in a system. Signal "converted" to another frequency and amplified and then sent out on repeat the antenna. This is received as the radio system devices. A repeater is usually placed on a detached and high geographic point, and will thus make that coverage for a radio system improves dramatically. Since the radio unit in such a system transmits and receives on different frequencies, they can not be used against each other if one goes out of range of the repeater.
MOTOTRBO and TETRA is an example of this. The former is intended for smaller systems up to 30-100 terminals and the latter for larger systems, such as an oil terminal or a nationwide network that the new emergency network. Common to both systems is that rekvensressursene utilized in a more efficient manner, have better voice quality and the possibility for data traffic (eg. GPS and SDS (SMS)). Man goes into discussion groups instead of radio channels that are common in analog networks. Discussion groups and one-on-one conversation implemented without others hear this. Encryption can also be introduced into the systems. MOTOTRBO is a standalone system corresponding to an analog radio. By using repeater gets 2 slot / channels for the price of one. It comes radios with and without built-in GPS for fleet management. TETRA is a system that is controlled from the panel. One defines who has permission from what admin console. The system is similar to GSM as you have on your mobile phone: The radios will connect to the base as you are within. The system can handle SDS (SMS) internally (replace alarms / pagers), like a telephone to telephone or trunk lines, fleet management, data traffic, database, image transmission to mention a few. It is also ATEX terminals available for the offshore industry.