Introduction: Radio Frequency Jamming Circuit 555 Timer
A radio frequency (RF) jammer circuit is self-explanatory in what it does. It is a device that interferes with the reception of RF signals of certain electronics that use similar frequencies and are near the jammer's vicinity. This jammer circuit works similar to an RF transmitter. In this circuit, you can adjust the frequency of waves sent out, which can interfere with the signals of many electronics, such as mobile phones, TVs, radios, and wireless devices. This particular circuit can interfere with frequencies of about 2.4 GHz. If the RF jammer works successfully, your phone will not know which signals it should be receiving, and you will have effectively blocked the signal. You will lose signal to contact people and cannot use particular apps, and buttons on your remote will not function to operate your TV, and nor will your wireless keyboard. In addition, your radio will also experience static and become unusable.
9V battery clip
24 AWG wire- (15 turn antenna, 3 turn, and 4 turn coils)
30pF trimmer capacitor
Resistors: 72k, 6.8k, 5.1k, 10k
Capacitors: 4.7u, 5p, 56p, 2p, 2p
Step 1: Schematic
The schematic above shows my layout when creating the jamming circuit, using all the components mentioned above.
This circuit works in theory, after some testing, I can confirm it has blocked signals from my remote control to my TV, in the range of about 2.4 GHz. The jamming device has a short radius of about 5 feet. I am still experimenting with the effectiveness of this circuit and trying to adjust for different frequencies.
The use of different frequencies by wireless devices makes it challenging to have a single jammer that works for all frequencies. The formula below can be used to calculate the required values.
F= 1/ (2*pi*sqrt ((L1*L2)*Ctrim))
Depending on the frequencies you need to block, the values of the inductor L1 and L2 and trim capacitor can be altered (components from the schematic above).
Step 2: Understanding the Circuit
Any jammer circuit has three main subcircuits. All three work together to create a device that jams wireless signals.
The three subcircuits are:
1. RF amplifier
2. Tuning circuit
3. Voltage controlled oscillator
When looking at the RF amplifier subcircuit, it is composed of the Q1 transistor, C4, and C5 capacitors. This is used to amplify the signal that is coming from the tuning circuit.
The tuning circuit which is a subcircuit is composed of the trimmer capacitor and the inductors L1 and L2. Thus creates an LC circuit, which acts as a bandpass filter. So this tuning circuit passes frequencies at a narrow range, and it will reject lower and higher frequencies that are outside of the narrow range.
The 555 timer in this circuit is the voltage controlled oscillator. The ne555 timer is operating in astable mode. So this acts as an oscillator, and it generates square waves. The voltage output from the timer is connected to the base of the transistor, which is part of the RF amplifier subcircuit. This jamming circuit sends square waves at a particular frequency (which you can adjust) to interfere with any outside frequency within the same specific range.
Step 3: Setting Up the Ne555 Timer
Voltage controlled oscillator subcircuit
When starting to build this circuit, I began by focusing on the ne555 timer, and to operate it in astable mode. From the schematic, at the top, you can see where to place each component. The transistor Q1 is plugged into the output, which means that there is a periodic pulse of voltage between 0V and 9V. The purpose of this subcircuit is to send the square waves to the transistor. By adjusting the resistance (R1 & R2) and capacitance (C2) values, you can change the frequency at which the output voltage is sent to the transistor Q1.
Step 4: Setting Up the Transistor Q1
RF amplifier subcircuit
Moving from the ne555 timer, we see the output voltage leads us to the transistor. The square waves sent from the output voltage are combined with the frequency generated by the tuning circuit and sent through the capacitor C5 and then the antenna. The purpose is to boost the power of the RF frequency enough so it can jam other frequencies. If this subcircuit were not present, this would be a very weak jammer, and the range would be extremely limited.
Step 5: Setting Up the Inductors and Trimmer Capacitor
The RF amplifier will amplify the signal sent from the tuning circuit. This subcircuit creates the high frequency which the jammer circuits use. The trimmer capacitor or variable capacitor is frequently used for tuning purposes, like in this particular case. This variable capacitor allows you to determine the frequency that is generated through this tuning subcircuit or LC circuit. You can adjust the frequency that this jammer circuit sends out by adjusting the variable capacitor as well as the two inductors.
Step 6: Conclusion
After testing, I can confirm that this circuit works and blocks signals from the remote control to my TV. I am continuing to experiment on other wireless devices and remote control toys to see how effective this circuit jammer is in practice.