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This cell phone jammer operates at GSM800 frequency since most mobile phones use it to operate. So the selected VCO is a sweeping oscillator, which is very effective but may be hard to construct for the beginners without nice RF-testing equipment.

As a noise source you can use 45MHz clock oscillator which is driving Local Oscillator port located on a mini-circuit mixer. There is also an impedance matching network for Local Oscillator signal to pass through it. It is used to equate impedances of the clock oscillator and the port of the mixer.

RF input (which is this port of the mixer) connected to the first 800MHz cell phone antenna, and the RF output is sent to the mini-circuit amplifier. This amplifier increases the output power for 15-16dbm. The amplified signal then sent to the second cell phone antenna.

All cell phones which use GSM800 have their transmitted and received frequencies always separated by 45MHz. So when the mobile phone tries to call it is blocked by its own signal returning to it! Isn’t that cool? When the phone blabber annoys you – turn your jammer on and that wrongdoer will hear own voice in his or her cell phone.

Oh, by the way, you can also use this mobile signal jammer to block any cell-based tracking systems which use your GPS to track and record your car’s moves. And it is quite possible (though I didn’t actually tested it) to jam IEDs which detonated using cell phones.

The mixer used is designed to work up to 600MHz but in this case it works pretty well.

 

RF amplifier is doing its job perfectly yet (as it was mentioned in the Jammer Store blog post) draws additional power.Old aluminium box was used as a frame for the jammer and old UHF connectors from Motorola cell phone as input/output.You need to attach RF connectors to the circuit. Nine volt battery and voltage regulator were used to supply all components. The battery was placed inside and separated by the foamed plastic from the other components.The power on/off switch is placed on the top. The input and output antennas (also from old Motorola mobile phone) are screwed onto UHF connectors.Your cell phone jammer is ready. Enjoy!

 

This simple Telephone Record Control Circuit Diagram will allow you to connect any tape recorder that has a mic and remote input to a phone line and automatically record both sides of a conversation when ever the phone is in use. You will need to take a couple of voltage readings before connecting the circuit. First determine the polarity of your phone line and connect it to the circuit as shown and then determine the polarity of the remote input and connect it to the circuit.

Circuit operation is as follows. When the phone is on hook the voltage across the phone line is about 48volts dc. When the phone is off hook the voltage will drop to below 10volts dc. When the line voltage is at 48volts the FET is off which causes Q2 and Q3 to be off. When the phone is picked up the FET turns on along with Q2 and Q3 which turns your recorder on. The tape recorder must be in the record mode at all times. As you can see the power source for the circuit is the phone line. 

 

This is a Simple Telephone In Use Indicator Circuit Diagram. With this circuit mounted in or near every phone in the house, it will allow users to know if the phone is being used and not to pick up the phone. When a phone is taken off hook, the voltage across the tip and ring terminals drops to 10 volts or less. This will cause the FET (2N4360) to turn on and also turn on the transistor (2N2222). When the transistor turns on it will allow current to flow through the LED and make it light. A blinking LED could be used to make the effect better.