Radiofication is a system of sound broadcasting, in which the sound (speech, music) is transmitted to a large number of listeners (subscribers) via electrical oscillations propagating over wired networks (autonomous or telephone networks).
The main advantages of wired radio are - its high efficiency and reliability, high transmission quality, ease of subscriber speaker use. The prospect of the development of this system is mainly related to the need for public notification in accordance with the requirements of civil defense.
Radio feeder installation is undeniably an important and complex process, and therefore it requires a skilled approach and execution of works in accordance with approved standards. Improper installation of radio feeder usually leads to a deterioration of the signal and the appearance of interference on the telephone, intercom and other cables, which in turn affects the quality of communication. Feeder of radio is laid by overhead lines. While mounting the cable feeder on the outer or internal walls or the floor decks a separate cable channel must be used.
Normal operating feeder is balanced and therefore is not the source of any kind of interference. Incorrect installation and insulation of radio feeder causes asymmetry - all feeder network becomes an antenna of low frequency band and has the effect of "radio on the phone". Asymmetry is radio feeder state while a wire emits signal by its surrounding electromagnetic field. A pair second wire, assuming that the electrical current flows in it in the opposite direction, completely balances this field, which creates interference. If one of the wiresof the pair of disconnected or grounded, balancing doesn&t occur. The signal on this line creates crosstalk in the surrounding cables, and on the contrary, any external interference acts onto this line. So the asymmetry affects the protection of the radio network from interferences, as well as its influence on other networks.
Implementation of a network of radio objects is made by two core copper cable in grounded metal hose. Without hose installation is made no more than 100 cm from the junction box or outlet. Connecting the stationary loudspeakers to the line is made with consistent connection of limiting resistor 80±20 Ohms, which is located in the subscriber outlet. Mounting the resistor can also be performed in the junction box under the ceiling or mounted on the wall. In some cases, the limiter is in junction cabinet, that prevents access to it non-technical personnel.
Limiting resistor prevents a short circuit across the radio link in case of failure of subscriber&s receiver, as well as in situation of its unauthorized revision (for example, the removal of the distribution transformer).