1. Introduction
With rapid development of communication technology, functions of interchangers increasingly grow and functions and flexibility of communication terminal equipment are also improved constantly. However, environmental noise is large at some occasions like wharfs, coal yard and power station system. In addition, broadcast instructions only need be issued in one direction. Nevertheless, common automatic telephones cannot satisfy this kind of requirements. For the foregoing reasons, via surveys on existing communication terminal equipment and based on technical experience that it has accumulated in work related to production dispatching and command communication system and researches on various communication terminal devices for many years, the company studies and develops a general digital anti-noise telephone loudspeaking terminal, which is appropriate for all kinds of environment conditions as well as has high performance and reliability.
II Features of anti-noise telephone loudspeaking terminal
2.3 The general anti-noise telephone loudspeaking terminal is a loudspeaking device which is used and matched with interchangers or dispatching machines. It makes up the disadvantage that automatic telephones have no loudspeaking function. The teminal has good anti-noise performance, so it is especially appropriate for sites with strong noises, such as coal yards, wharfs and power plants. Usually, it can be used as loudspeaking communication for dispatching and communication terminal for alarming.
2.2 The general anti-noise telephone loudspeaking terminal device has power amplifier output terminal, so it can be connected with a loudspeaker externally. Thus, it is quite appropriate for large squares.
2.3 The general anti-noise telephone loudspeaking terminal device has power supply indicator and loudspeaking indicator.
2.4 The general anti-noise telephone loudspeaking terminal device has two specifications, i.e., 15W and 20W.
2.5 Service conditions of the general anti-noise telephone loudspeaking terminal device
Temperature: -15—+40℃
Relative humidity: not more than 95% (+25℃)
Atmospheric pressure: 86—106kPa
Environmental noise: not more than 120dB
III Main technical parameters and performance
3.1 Adaptability that it can be connected and matched with dispatching machines or interchangers
a. Subscriber line DC open-circuit voltage: 40—64V
b. Subscriber line DC feed current: 25—60mA
c. Ringing current voltage: 75±15V 25Hz±3Hz
d. Busy signal
Frequency: 450Hz±20Hz
Break-make ratio: (0.3—0.4)s:(0.3—0.4)s
Level: -8 — -12dB
3.2 Power supply mode
AC: 220V±10%