Overview of Jammer Circuit for 850 - 2100 MHz Engineering Project

A jammer is an RF emitter, usually emitting wide band noise at an high power level, that serves to overpower other RF signals with lower power level in that band, and thus the jammer prevents the receivers in its vicinity to receive those low power radio emissions. With very high power levels, it eventually can overpower the RF emmitters nearby and so in this case it "smashes" the radio emissions at its bare source.

Jamming devices overpower the cell phone by transmitting a signal on the same frequency and at a high enough power that the two signals collide and cancel each other out also known as phenomenon of destructive interference.

A jammer is also defined as a device that is used to block signals by jamming Bluetooth or wireless signals for cell phones, GPS signals, and Wi-Fi systems. Jammers flood a specific area with noise that covers the radio bands to be jammed. Jammers can be used for many reasons, such as preventing unwanted calls from telemarketers; as well as keeping people in certain venues, such as restaurants, from using their cell phones in that specific vicinity.

Working of Cell Phone Jammer Circuit

The jamming device broadcasts an RF signal in the frequency range reserved for cell phones that interferes with the cell phone signal, which results in a “no network available” display on the cell phone screen. Because of which, all phones within the effective radius of the jammer are silenced. Keeping aside the convenience of this device, it has been declared illegal in most countries. According to the Federal Communications Commission (FCC) in the USA;


“The manufacture, importation, sale, or offer for sale, of devices designed to block or jam wireless transmissions is prohibited”. However recently, there has been an increasing demand for portable cell phone jammers. We should mention that this project, presented in this report, is solely done for educational purposes. There is no intention to manufacture or sell such devices in Nepal, or elsewhere. In this project, a device that will jam both GSM 900 and GSM 1800 services will be designed, built, and tested.

Circuit diagram :

( Source : website )

PARTS LIST OF MOBILE CELLPHONE JAMMER CIRCUIT

Resistors (all ¼-watt, ± 5% Carbon)

R1 = 250 Ω
R2 = 750 Ω
R3, R4, R6= 2 KΩ
R5 = 100 KΩ
R7 = 10 Ω
R8, R9 = 1 KΩ
R10 = 2 KΩ

Capacitors

C1, C3 – C7, C9 = 0.1 µF (Ceramic Disc)
C2, C15, C16 = 1nF (Ceramic Disc)
C8, C10 = 10 µF, 16V (Electrolytic Capacitor)
C11, C13 = 4.7 µF, 16V (Electrolytic Capacitor)
C12, C14 = 0.01 µ (Ceramic Disc)

Semiconductors

IC1 = NE555 (Timer IC)
IC2 = LM741 (Operational Amplifier)
IC3 = LM386 (Low power audio power amplifier )
IC4, IC5 = PF08109B (Power Amplifier Module for E-GSM and DCS1800)
IC6 = CVCO55CL (Voltage Controlled Oscillator, 925-970MHZ)
IC7 = CVCO55BE (Voltage Controlled Oscillator, 1785-1900MHZ)
T1 = 2N3904 (Smaller Signal Bipolar Junction Transistor)
ZD1 = 6.8V Zener Diode
D1, D2 = 1N4148 (silicon switching signal diode)

Miscellaneous Components:

Antenna 1 = GSM antenna (Frequency = 850MHz-1GHz, 

Input Impedance = 50Ω, VSWR<2)
Antenna 2 = DCS antenna (Frequency = 1700MHz-1900MHz, Input Impedance = 50Ω, VSWR<2)

Some Questions which should be clear about this Device.

Q: How Do you know or detect a jammer circuit has been placed near to you.

A: It depends on the level of sophistication of the jammer. Using jammers that deliberately transmit in cellular frequencies is normally illegal, although there may be some accidental transmissions, in the same way that a spark from a faulty central heating thermostat can interrupt your analogue radio.

So, what are the symptoms that suggest jamming is taking place? Indoor coverage can be less reliable because signals can be blocked/interfered with by stone walls, wire mesh forming a Faraday cage (including ‘fake’ leaded windows) and insulation involving metal such as tin foil. I would also check with a friend who has a cellphone on a different operator (and so frequencies) to see if they get the same effect, as well as trying to force the phone to use only 2G say, or 3G, to try and localise the problem.

If you have other symptoms that lead you to suspect then I would suggest a suitable frequency scanner with direction finding to check that there are transmissions in the cellular frequency bands, when and where they are coming from, and if this is a different direction from your local cell tower. ( Source: Quora)

Q: Using of a cellular phone Jammer is Lligal or Illigal ? Is there any anti Jammer device available?

A: Cell phone jammers are illegal, in any form.

Frequencies for cell phones are licensed to the carrier by the **Federal** Communications Commission, and jamming those signals is a violation of **federal **law, the 1934 Communications Act, which deals with laws around all types of communications. So violations are investigated by the FBI, not the local police. Additionally, since cell phones have become vital for first responders in emergencies and disasters, man made or natural, FEMA, the Federal Emergency Management Agency takes an interest, and they are part of the Department of Homeland Security.

If you're caught, it's not like getting a parking ticket. It is **big** deal.

Obviously, the cellular carriers don't like jammers much, and they've become very good at finding them. I worked for a carrier for 30 years, and in my early days as a technician, I helped track one down. It is remarkably easy if you know how, and have the right specialized equipment. The carriers do.

One more thing to think about. If you're running your jammer, and someone tries to diall 911, and then someone dies because of their inability to get through to vital emergency services, you are morally and legally liable. Your legal liability will be criminal, because jamming the signal is in itself illegal,and by causing the death you could be charged, at the very least with manslaughter, possibly murder. You will also have civil liability, as those that were harmed by the inability to get emergency services will likely sue you, and win.

Denying service to all but one phone, still has all the problems I mentioned above. And nothing you could build would be selective enough to allow one phone and block all others. ( Source : Quora )

Q: Do jammers just block the 4G internet from accessing or they also reduce my phone signal?

A: If the jammer is working in GSM technology then it will jam both the phone signals and 4G connectivity. As the 4G connection use the same SIM card used for phone calls. It is been observed that when there is a network blockage by security agencies of the state, the phone signals as well as the 4G connectivity is blocked. (Source : Quora)

More Questions are requested to post in comment.