Medical pager The working principle of is the called user receiver in the wireless paging system. It consists of superheterodyne receiver, decoder, control and display. It selects the useful signal to be received from the paging signal and interference transmitted by the base station, restores it to the baseband signal of the original paging machine, and generates audio (or vibration) and digital (or letter, Chinese character) messages. The BP machine has two modes of manual tandem and automatic tandem, and the corresponding paging stations are called manual paging stations and automatic paging stations. The manual paging station needs manual operation to encode these information and send signals through the transmitter. According to the line number of the incoming phone, the automatic paging station automatically finds out the caller's phone number and sends it out at the same time, so that the callee can know which phone is calling. Pagers often used are divided into two categories: digital pagers and Chinese pagers. Digital pager is small, cheap and practical. The Chinese pager displays Chinese characters directly, and the information is easy to recognize.
Try to achieve small size, light weight, low price and low power consumption. Pagers can receive a wide range of services from numbers and simple phrase messages to Chinese characters, documents, notifications, stock markets, and even serve as terminals for telegrams and data networks. The sensitivity of Chinese character display or digital display pager is better than 10 μ V/m or 5 μ V/m； Adjacent channel selectivity is better than 60dB (VHF band); Digital display bit length shall not be less than 12 bits; Mean time between failures shall not be less than 30000 hours.
In 1983, Shanghai opened a paging station, and the BP machine entered China. In the late 1980s, pagers began to appear in China. With the maturity of science and technology and the increase of social demand, since 1990, paging stations have sprung up everywhere. The prosperity of the paging market has made the competition between paging stations increasingly fierce. In 1993 and 1994, mobile phones began to appear slowly. Since the second half of 1995, the paging service has gradually failed under the strong attack of mobile phones, and the number of paging users has stopped increasing. Since 1996, there has been a decline, with fewer users and a sharp decline in the number of paging stations. After 2005, pagers gradually faded out of the Chinese stage.
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