The small-power cell phone jammer should replace the directional antenna

 In this paper, the actual development, presents a new TPMS solutions such as choice of chips and systems programming strategy, and discuss system development in the three key issues - the antenna design, low power and wireless signal transmission, and finally on system performance were measured and analyzed. The results show that the system is fully able to meet the requirements of practical application. If external factors cause the VCO frequency decreases, the control loop perform the opposite process. The above is a description of how to make the VCO output frequency stability. But how to make the VCO frequency change it? In explaining this question, first to explain why the frequency of the VCO to change this problem. Because mobile phones are mobile, moving to another place, for the cell phone service cell (CELL) becomes another of the frequency, so they must change their mobile phones to receive and transmit frequency. cell phone jammer uses the backflow welder machining. In the mobile phone circuit, usually contains several frequency synthesis loop: a local oscillator VCO frequency synthesizer loop (UHFVCO, RFVCO, RXVCO), two oscillator VCO frequency synthesizer loop (1FVCO, VHFVCO, etc.), transmit IF VCO frequency synthesizer loops and so on. No matter which one frequency synthesis loop, the circuit structure are basically the same, and their frequency reference signal from the reference clock circuit. Voltage-controlled oscillator referred to as VCO (VoltageControlOscillator). VCO is a "voltage - frequency" converter. It will phase detector PD output voltage difference between signal changes into frequency changes. The small-power cell phone jammer should replace the directional antenna in some locations.Transmit IF VCO frequency synthesizer mainly produce emission frequency carrier signal. Phone in the design, in order to simplify the circuit, often firing IF frequency synthesizer and two local oscillator VCO frequency synthesizer together, so that the second local oscillator VCO frequency synthesizer and transmitter IF VCO frequency synthesizer on the synthesis of a circuit. In addition, a description is: launch VCO (TXVCO) circuit from the principle of analysis is a frequency synthesizer, the front has been analyzed here not to repeat. Mobile communications equipment is often used conversion superheterodyne receiver. This is because the antenna sensing the received signal is very weak, while the frequency discriminator requires a high input signal level and stable. The total gain of the amplifier normally takes in more than 120dB. Put such a large lot, use the multi-stage tuned amplifier and should be stable, it is difficult to do actually get. Another high-frequency selective frequency amplifier passband width is too wide, when the frequency is changed, all the multi-stage amplifier must be followed to change the tuning circuit, and tuning to achieve unity, which is difficult to achieve.