How to build a TV Jammer Written by: The BOY! & The Infidel 06/05/88 17:00:00 * Be Sure To DL The Graphics Page Which Accompanies This File Description: This is a simple circuit that can be used to take instant revenge on someone you hate. With the flick of a switch, you can black out any television set, FM Radio, or Cordless Phone communication within 50 Feet. For best results, put this device on top of the victim's roof, or Satellite Dish . Though this is an "Interesting" project, be advised that you are breaking 3/4 of the FCC Regulations on signal Jamming. Parts List Q1 - 2N3904 Transistor R1 - 10k ohm Resistor R2 - 4.7k ohm Resistor R3 - 1k ohm Resistor C1 - .001 uF Capacitor C2 - 30 to 80 pF Variable Capacitor C3 - 10 pF Capacitor L1,L2 - .05 uH Coils S1 - SPST Slide Switch B1 - 9v Battery Snap Step By Step in Mounting the Components Refer to graphics page for pictorial representation of schematic. Step 1 - First a short (4-6 inch) piece of wire for the antenna and solder it to the board. Step 2 - Identify the two coils. With a razor blade or file, carefully strip their ends. They are covered with an insulating varnish that must be removed before soldering. Avoid deforming the coils. Be Sure to leave coils 3/4" to 1" above board. Step 3 - Identify the C2 3-80 Variable capacitor. Insert its odd sized leads into two predrilled holes. Bend the leads outward and solder. Step 4 - Identify the following resistors: R1 10k ohm (Brown, Black, Orange) R2 4.7k ohm (Yellow, Violet, Red); R3 1k ohm (Brown, Black, Red). Bend the leads at right angles and mount them to the board. Bend leads slightly to hold the resistors in place, then solder, and cut of excess. Step 5 - Identify Q1, the 2N3904 transistor. Mount it to the board with the flat side in the correct direction. Leave about 1/8 - 1/4 inch between the body of the transistor and the surface of the board. Solder and cut off excess leads. Step 6 - Identify the following capacitors: C1 .001 uF (This capacitor may be marked: .001, 102 or 102z) and C3, 10 pF (This capacitor may be marked: 10j, 10k, 10 or 100m). Mount them to the board as shown in the schematic. Bend leads slightly, solder and then cut off excess. Step 7 - Identify S1, the switch. Solder two wires to its leads and then solder the other end of these wires to the board. Step 8 - Identify and install the 9v Battery snap B1, paying close attention to the red and black wires. Solder it in place. Operating Procedures Attach a 9 volt battery to the battery clip. Turn on a FM radio, and start adjusting the screw on the 3-80 pF variable capacitor. Use something that does not conduct electricity, such as a stiff piece of paper, or a piece of plastic. If you must use a screwdriver, get one that has an insulated handle. The idea is it should have as little conductive material touching the capacitor as possible, including your body. The tuning circuit is directly dependent on how much capacitance the variable capacitor is adjusted for and any conductor will add to the capacitance enough to change the tuning. Slowly turn the adjusting screw until there is heavy disturbance in the radio. If you do not find a station anywhere within the range of the capacitor's adjustment, slightly separate the turns of the wire in the two coils. They also play a very important role in the tuning of the circuit. Now try adjusting the capacitor again. If you still have trouble, change the spacing of the coils again, and slowly tune the variable capacitor. Once tuned, the jammer is ready for full use. Theory of Operation A Signal Jammer You have built nothing less than a miniature radio transmitter. The Oscillator transmits an unmodulated carrier frequency of from 54 MHz to 210 MHz a distance of approximately 10 to 50 feet. While your Oscillator puts out a weak signal in comparison with a FM Broadcast station, at close range it's signal is strong enough to override the standard broadcast message. The Basic Transmitter An oscillator is a circuit that produces an alternating current in the audio or radio frequency range. That current is then run up and down an antenna wire and converted into electromagnetic radiation or radio waves. An oscillator consists of three basic parts. 1> A tuned circuit consisting of C2, L1 and L2. The tuned circuit determines the frequency of transmission. That frequency can easily be varied as we will see in a moment. 2> A transistor amplifier circuit that will take the LC circuit voltage and boost it. It consists of transistor Q1 along with biasing resistors R1, R2 and R3. 3> A method of feeding the tuned signal back to the amplifier in order to maintain oscillations. Capacitor C1 preforms this feedback function. Let's take a look at each of these circuits in turn. The Tuned LC Circuit An LC tuned circuit consists of a coil and a capacitor in parallel across a voltage source. Our circuit uses two coils with an antenna wire brought out from the junction. However we can think of L1 and L2 as one coil. If, for an instant, a voltage is placed across the LC circuit, C2 will charge in the direction indicated. The capacitor then discharges through L1 and L2 with electrons flowing from Plate A to Plate B. The capacitor then discharges back again with Plate A becoming the negative and Plate B positive. The process will repeat itself until all the electrical energy is dampened out. The waveform for such as signal is shown in the graphics page. A way must now be found to reinforce these "Oscillations" so that the signal will not dampen out and be lost. - As we stated earlier, the function of the LC circuit is to determine the frequency of oscillation, of the amount of time it takes current to travel back and forth between C2 and L1-L2. It is the size of the capacitor and coil(s) that determines this frequency. - If either C2 or L1-L2 is increased the frequency of oscillation will decrease. - If either C2 or L1-L2 is decreased the frequency of oscillation will increase. In our circuit C2 is made to vary from 5 to 80pf. When it is placed in the 5pf position it is electrically quite small and the frequency of oscillation of the LC circuit is high or at its maximum. That would be around 200 Mhz. With C2 adjusted to 80pf the frequency of oscillation in the LC circuit is at its lowest point, approximately 54 Mhz. Adjusting C2 across its variable range will cause the LC circuit to approximately 200 Mhz. The Amplifying and Feedback Circuit Transistor Q1 provides amplification for the otherwise extremely weak signals that would be oscillating in the tuned circuit. For Q1 to conduct and thus amplify the oscillating signal, the following conditions must be met: - The emitter of Q1 must receive a negative voltage. - The collector of Q1 must receive a positive voltage. - The base of Q1 must receive a positive voltage somewhat less than that applied to the collector. Q1's emitter receives a negative voltage through R3 from battery, B1. R3 also acts to provide "Thermal Stability" to Q1. Q1's collector receives a positive voltage from battery B1 through the LC tuning circuit. Base voltage to Q1 is provided via a voltage divider network consisting of R1 and R2. With the values chosen a 3v base or "Bias" voltage is obtained. Q1 now conducts. To maintain oscillations in the tuned circuit, energy must be fed back from it to the transistor where it is again amplified. Capacitor C1 provides for such a feedback by placing the weakened LC signal onto the base of Q1. _____________________________________________________________________________ Star League Wants YOU! Call Rylos 3rd Planet - (516) 361-6744 - 20 Megs - 9600 Baud _____________________________________________________________________________