Mobile Phone Sensor -900MHz RF Indicator ---- Cell Phone Signal Sensors-900MHz RF Indicator

Mobile Phone Sensor -900MHz RF Indicator, Cell Phone SIGNAL SENSORS-900MHz RF INDICATOR Keywords: mobile phone sensor production, mobile sensor circuit After the mobile phone in standby, after receiving the call signal sent by the base station, a response signal will be issued, and the antenna of the phone will also have a short RF signal. At this point, if there is a mini sensor next to the phone, it will make a sparkling red, and some kinds of sensors will also make music sound. The anatomical sensor circuit found that it is actually a 900MHz RF indicator, and the working principle is analyzed below. According to the figure, the radio frequency signal is received as the spring wire L1 of the antenna (W) (L2 is only one 扼 扼 圈), the signal is sent to VT1, VT1 Under the role of the bias resistors R1 and R2, the collector of VT1 is extremely high when there is no signal, so that the PNP tube VT2 is turned off, and the multi-resonator consisting of VT3 and VT4 does not work. At this time, the collector of the VT4 is also at a high level, the VT5 is cut off, and the LED does not illuminance; once the signal enters the base of the VT1, the VT1 in the critical state is turned on, the VT1 collector is at a low level, VT2 is turned on, By R7, R8 gives the base of the multi-resonator VT3 and VT4, the multi-resonator is low-frequency oscillation, and the collector voltage of VT4 is also in the oscillation, resulting in a vT5 intermittent conduction, and the LED is shining. However, there is no radio frequency signal near the antenna, everything is calm. The sensitivity adjustment of the circuit has two sites: one is to change R1, but R1 cannot be too small, otherwise VT1 will turn on when there is no signal, and cannot function. The size of the R1 is also related to the magnification of VT1. The second is L2, the number of turns to increase can increase the sensitivity. If the L2 is removed, the circuit sensitivity will increase the maximum amplitude, although it is susceptible to the interference signal to be triggered, but the sensitive indicates the existence of the surrounding electromagnetic field, if used Check if the wireless phone has 48MHz RF emission, when the antenna of the open cordless phone is adjacent the antenna of the RF indicator, if the LED sparkles, the cordless telephone is indicated by the cordless telephone. In this sense, such a radio frequency indicator is a broad-spectrometer strength, which has no significant selectivity to the indicated electromagnetic field frequency.

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