The wireless pager evolved from the wired pager, reducing the line connecting the pager host and the pager button from the appearance, and adopting the wireless technology, the device generally consists of the transmitter button and the receiver host, and the button transmits the command through the radio wave. For the pager system, the transmitter extension(pager button) is mainly divided into four types, frequency hopping, frequency modulation, amplitude modulation, and phase modulation. The wireless pager mainly uses amplitude modulation and frequency modulation. What are the main differences between them?
1. The characteristics of the pager frequency modulation are narrow bandwidth and long distance. A narrow bandwidth means that the penetration of the obstruction is weak, but the transmission distance is long. This technology is generally used in products such as mobile phones and pagers that require long distance (5 km or more) transmission.
2. The pager amplitude modulation is characterized by wide bandwidth and short distance. The wide bandwidth means strong penetration of obstacles, but the transmission distance is short. This technology is generally applied to wireless pager alarms in buildings, wireless emergency callers in nursing homes, and so on. Because the most important thing in a building is not the distance, but the ability to penetrate.
3. The wireless pager comparison
1) Frequency modulation has better anti-interference ability than amplitude modulation
The influence of external interference, processing industry, and sky-light interference, etc., on the modulated wave of the wireless pager, is mainly caused by parasitic amplitude modulation and noise formation. The frequency modulation system can use the limiting method to eliminate the parasitic amplitude modulation caused by the interference. In the amplitude modulation system, the amplitude of the amplitude modulated signal is changed, so that the clipping cannot be used, and it is difficult to eliminate the external interference.
In addition, the greater the signal-to-noise ratio of the wireless pager signal, the stronger the anti-interference ability. The signal-to-noise ratio of the signal obtained after demodulation is related to the modulation factor. The larger the modulation coefficient, the larger the signal-to-noise ratio. Since the frequency modulation coefficient is much larger than the amplitude modulation coefficient, the signal-to-noise ratio of the caller's FM wave is high, and the interference noise in the FM broadcast is small.
2) FM wave has a larger bandwidth than amplitude modulation
The width of the pager is related to the modulation factor, that is, the modulation factor is large and the frequency bandwidth is. In the frequency modulation, the frequency modulation coefficient is often greater than 1, and the wireless pager amplitude modulation coefficient is less than 1, so the frequency bandwidth of the frequency modulation wave is much larger than the frequency bandwidth of the amplitude modulation wave.
3) Wireless pager frequency modulation system power utilization is greater than the amplitude modulation system
Among the total transmit power, the sideband power is the effective power of the transmitted modulated signal, and the sideband power is related to the modulation factor, the modulation factor is large, and the sideband power is large. Since the frequency modulation coefficient mf is larger than the amplitude modulation coefficient ma, the power utilization rate of the frequency modulation system is higher than that of the amplitude modulation system.
Frequency modulation: frequency modulation. Translate information into a corresponding frequency change. For example, the audio signal is modulated on a carrier of a certain frequency, which includes frequency modulation of the analog signal and frequency modulation of the digital signal. Pager amplitude modulation: amplitude modulation. It modulates the information in the form of amplitude on the Ten Commandments. Its amplitude represents the variation of the audio signal.
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