The basic principle behind this circuit is the idea of using a Schottky diode to detect the cell phone signal.
The detector circuit consists of an inductor, diode, a capacitor and a resistor.A  Here an inductor value of 10uH is chosen. In normal condition, when there is no RF signal, the voltage across the diode will be negligible.
Now when a mobile phone is present near the signal, a voltage is induced in the choke and the signal is demodulated by the diode. BJT or bipolar junction transistor in its common emitter form is the most common amplifier used.
This circuit can be used at examination halls, meetings to detect presence of mobile phones and prevent the use of cell phones. It can be used for detecting mobile phones used for spying and unauthorized transmission of audio and video. Can you suggest other type of schottky diode aside from Bat54 that can be used to replace it in the circuit. I want a circuit diagram for binary to decimal converter for 4 bit inputs which is low in cost and easy.please sir help. If i want to check this circuit on proteus or any other stimulation software, what should i do to give it input of 0.9 to 3 GHZ RF ? I have build the whole circuit.But when i movea cell phone over it nothing happens.Why it does not have an antenna to sence signal? Is it possible to place something inside the circuit in order to give an indication of signal strength. The project illustrates the construction and design of a wave bubble that contains a wide bandwidth and self-tuning portable RF jammer. The circuit was built to read and decode the RFID tags with 125 KHz frequency using a single low cost ATtiny2313 ATMEL microcontroller. This is a mobile phone sniffer circuit that can detect the signals being used in the GSM (Global System for Mobile Communication) band at about 900 MHz. This Mobile Phone Detector can detect regular or concealed GSM mobile devices, making it perfect for counter surveillance!
Today, more than ever, mobile phones are being used to illegally record and send both audio and video to third party locations. 2,Bank Transfer is only available for order's value above US $1000, such as wholesale order.

We are specialized in the development, manufacture and marketing of jamming devices for GPS, cellular and wireless RF communications. With its 5 specific cellphone frequency band antennas and multiple notifications of cellphone usage including a flashing sign as well as a customizable audible alarm message, this device is perfect for detecting everything and letting you know about it. With advancement in communication technology, the requirement of cell phones has increased manifold.
A Schottky diode BAT54 is chosen as the detector diode, which can rectify low frequency AC signal. Since the output signal is of low value, the emitter resistor is not required in this case.
The reference voltage is set at the inverting terminal using a potential divider arrangement.
Even though this voltage is amplified by the transistor amplifier, yet the output voltage is less than the reference voltage, which is applied to the inverting terminal of the comparator.
When a mobile phone is present near the circuit, the RF signal from the mobile induces a voltage in the inductor via mutual induction.
A transistor amplifier works on the fact that the input base current is amplified to the output collector current by a factor of I?.
I am a novice with electronics, at best and I am trying to build this circuit for a school project. Of course there are many other facts that are not listed below but for the beginners these may be enough for now. Since the signals are digitally encoded, it can detect only the signal activity, not the speech or the message contents. Whether you need a way to control an office with sensitive materials, secure facilities, or even control specific environments such as standardized testing rooms, this device is perfect.
A cell phone typically transmits and receives signals in the frequency range of 0.9 to 3GHz.
A Schottky diodes have a unique property of being able to rectify low frequency signals, with low noise rate. The collector resistor value is determined by the value of battery voltage, collector emitter voltage and collector current. Since output voltage from the amplifier is quite low, the reference voltage is set low of the order of 4V. Since the voltage at non inverting terminal of the OPAMP is less than the voltage at the inverting terminal, the output of the OPAMP is low logic signal.

When the voltage at non inverting (+) terminal is higher than the voltage at inverting terminal, the output voltage goes high. This article provides a simple circuit to detect the presence of an activated cell phone by detecting these signals.
When an inductor is placed near the RF signal source, it receives the signal through mutual induction. Now the battery voltage is chosen to be 12 V (since maximum open source collector emitter voltage for BC 547 is 45V), operating point collector emitter voltage is 5 V and collector current is 2 mA. This is achieved by selecting a resistor of 200 Ohms and a potentiometer of 330 Ohms.A  An output resistor of value 10 Ohms is used as a current limiting resistor. The output of the OPAMP is thus a logic high signal and the LED starts glowing, to indicate the presence of a mobile phone. The circuit is biased using a voltage divider circuit formed by combination of two resistors. Schottky diodes are special diodes formed by combining N type semiconductor material with a metal and are typically low noise diodes, operating at a high frequency. This low power signal can be amplified and used to power any indicator like an LED in this case. There are two separate detector units.  Every detector unit consists of a dipole antenna, a choke and a diode.
The input resistor is used to provide bias to the transistor and should be of larger value, so as to prevent the flow of maximum current. This enables the diode to provide high switching speed and better system efficiency.A  The low noise is due to the very low reverse recovery time of about 100 per sec. If your PCB design includes only two layer, the top layer should include the power stage, RF signal lines and RF components.
Since the forward voltage of a silisium diode is high, it won't give a sufficient result in this circuit.

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Comments to Cell phone detector frequency division


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