FAQ of cell phone jammer
IC mixer circuit mixing circuit applications in the cell phone jammer the most, in the early cell phones, and some mixers use a single integrated component, now cell phones in the mixer are integrated in a complex multi-RF processing or IF processing module. Have to use the phone's receiver IF amplifier. IF amplifier is the most important role is: to obtain high gain: compared with the RF amplifier part, due to a fixed IF frequency and low frequency, can easily get a higher gain, which can be large enough for the next level to provide input . Improve the selectivity: the receiver frequency selectivity is generally close to the IF amplifier passband by the width of the decision. The antenna direction can influence shielding range of cell phone jammer.
For the IF amplifier, not only need high gain, good selectivity, but also have enough good pass-band and frequency response, large dynamic range. The receiver adjacent channel selectivity is generally from the IF amplifier pass band width of the decision, the IF signal into a single fixed frequency, the passband can be done to maximize the small, to improve the adjacent channel selectivity. In practice, the general multi-stage amplifier, and to achieve a certain technical requirements for each level. Whether using one or two frequency receiver technology, IF amplifier frequency is always ranked in the following. In order to avoid mirror-frequency interference, improve the image frequency selective, receiver usually the first local oscillation frequency is reduced to improve the first IF frequency and multiple frequency method, the signal from the radio frequency spectrum and gradually move to a lower frequency. cellular phone jammer designs the shielding signal starting device controlled by the computer for these characteristics.
Phone circuits are mostly used in all on their own dedicated chip. IF amplifier circuit component separation of form and the form of low-noise amplifier circuit is very similar, but also a common emitter circuit, but their work is not the same frequency. Most cell phones in the current circuit, Motorola cell phones are usually used in the IF amplifier IF amplifier discrete components, and other cell phones in the IF amplifier is usually an integrated circuit. As Figure 4-11 Motorola P7689 phone IF amplifier circuit. IF amplifier circuit in the form and the form of low-noise amplifier circuit is almost the same, but they cover different frequency work. Low-noise amplifier is a broadband amplifier, and the IF amplifier is a narrow band amplifier. The first characteristic of cell phone jammer is the good shielding effect.
In the case shown, the signal after the mixer through C460 anyone to FL457, FL457 selected by the 400MHz IF signal, IF signal amplified by Q480 to IF ICU200 demodulation, Q480 bias voltage of C7 by the U200 sent by SW-VCC pin provides. It should be noted: in a conversion superheterodyne receiver circuit, there is an IF amplifier; in the second conversion superheterodyne receiver is usually the first and second intermediate frequency amplifier; in linear direct conversion receiver , there is no IF amplifier. In cell phone communications and cell phone circuit, commonly used demodulation techniques are phase-locked demodulator, quadrature frequency discriminator demodulator. Phase-locked loop (PLL) tracks the input signal can also be used for demodulation. Figure 4-12 is a block diagram of a phase-locked demodulator. Motorola 928 cell phone use is the phase-locked demodulator. Phase-locked demodulator reference signal comes from a 430MHz oscillator. The production task of mobile phone jammer of this month is very tense.
Phase detector input by phase comparison of the two signals, the output signal of a frequency modulated signal tracking, through a low pass filter to filter out high frequency noise obtained after demodulation output. Motorola, Nokia and Samsung cell phones are used in phase-locked demodulation circuit. Figure 4-13 for the orthogonal frequency discriminator block diagram. In orthogonal frequency discriminator, the phase shift network will transform the phase change of frequency changes, phase changes in the multiplier will be transformed into voltage changes. FM signal with the phase shift number multiplied by the multiplier low-pass filter output signal to filter out high frequency components, we obtain the demodulated signal. Typically, the circuit in the modern communications equipment, in addition to quadrature coil, the frequency discriminator of the other circuits are integrated on-chip. The workshop arranges three shifts to manufacturecell phone jammer.
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