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RF jammer

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pimster987

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Hello this is my first time using this board and from looking around a little bit most people seem knowledgeable about electronics. Well I'm studying to be an electrical engineer and for a course project my group has decided to build an RF jammer. I know it is illegal to use but we are only building it for educational use. My partner is analyzing the tank circuit, while I'm left with the rest. The first part I am analyzing is the transistor and three biasing resistors. I did a DC analysis by hand than ran it through PSpice and got the same values. My question is is the transistor being used as an amplifier and what are the functions of the two capacitors on the left. I'm guessing its for filtering. I know the jammer is the related to an RF transmitter but I cant seem to find alot of information about the circuit. Most of the information is just about building the circuit but I need to analyze it. I would appreciate it if anyone can point me in the right direction of resources.
 

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There's no such thing as "educational use", it's illegal and that's it?.

Or perhaps you "educationally" rob banks?.

It's just a crude oscillator, with the feedback from collector to emitter, operating in common base mode.
 
Well you don't have to believe what I say and I have no need to lie. We already have it built and working but now I need to analyze the circuit. Perhaps you never heard of the term "for educational use only". Also , in my lab course we have another group building an EMP. It's good for engineering students to understand how different circuits work. Even though we could read all the research about how something works, I think its better that we actually get to see a working circuit. Well thanks for what information you provided
 
My question is is the transistor being used as an amplifier and what are the functions of the two capacitors on the left. I'm guessing its for filtering.

To actually answer your questions:

Yes, the capacitor across the battery is a filter, to isolate the circuit from power fluctuations. Probably totally unnecessary, by the way, since the power source is a battery wired right close.

The other capacitor is, I'm guessing, an AC bypass for the base resistor.
 
I know what your doing I did the same stuff in my electronic class. You build an oscillator that operates at the same frequency of a transmitter like a radio station signal your receiving from 60 miles away. Your oscillator only transmits 15 ft but it sets next to your radio and jams the radio station signal. For educational purpose it proves that it works. Last thing I heard 30 years ago any transmitter less than 100 mw is legal no matter what the transmitter is designed to do.

If you want a real jammer check this out. It jams everything within 10 city blocks of my house. Home security system go on and sirens blast, motion detector lights flash on/off, it totally destroys TV you can not watch it at all, radio in the car will not work either, it screws up CB radio and lots of other things. Even the old hard wire telephones will not work the phone is nothing but static. It freaks out computers and the internet service too.

Check out my 10KW tesla coil it makes 12 ft sparks. I did not build this to jam anything but it does. **broken link removed**
 
[FONT=&quot]The 10n capacitor is designed to hold the base steady. The transistor is connected in a configuration called COMMON BASE.
In this configuration, the base is designed to remain fixed.
So how does the transistor work?
The circuit start-ups due to the fact that the transistor is turned on via the base resistor and also due to the noise produced by current flowing through the junctions of the transistor.
We will start the discussion after a number of messy cycles and where the transistor is only partly turned on.
The base is fixed and rigid via the 10n and current flows in the collector circuit and charges the 35p capacitor. This allows a voltage to appear across the coil and thus current flows in the coil.
This current cuts the turns of the coil and produces a “back-voltage” that reduces the current though the coil. The capacitor is charging during this time and allows a higher voltage to appear across the coil. This higher voltage produces more flux and this continues.
This is as far as the cycle would go if it were not for the 6p feedback capacitor.
At the beginning of this cycle, the transistor was turned on a small amount by the base resistor and this creates a voltage across the emitter resistor.
It is important to understand how a transistor in COMMON BASE configuration can be turned ON and OFF, once it is biased as in the circuit under discussion.
Normally, a transistor in COMMON EMITTER configuration is turned on more by increasing the voltage on the base. This increases the current into the base and the transistor turns on more.
In a COMMON BASE configuration, The base cannot move, so DECREASING the voltage on the emitter will increase the current in the collector circuit.
And that’s what the 6p does.
As the 36p capacitor charges, it passes the decreasing voltage on the collector to the emitter and this turns the transistor ON MORE.
This action continues until the transistor cannot be turned on any more.
Up to this point in time the current through the coil has been increasing and this has produced EXPANDING FLUX.
But the transistor can no longer produce additional current and the flux in the coil begins to COLLAPSE.
This collapsing magnetic flux produces a voltage in the opposite direction. The voltage discharges the 36p capacitor and starts to charge it in the opposite direction.
This voltage is also passed via the 6p to the emitter, where it increases the voltage on the emitter.
This action begins to turn OFF the transistor and we can consider the transistor to be OUT OF THE CIRCUIT.
The coil produces a voltage that is actually higher than rail voltage and the 36p capacitor is charged with this voltage.
Very soon the magnetic flux that was present in the air around the turns of the coil starts to decrease and the reverse voltage produced by the coil reduces. This voltage is passed to the emitter and the voltage on the emitter drops. This starts to turn ON the transistor and the next cycle begins.
Because this action is happening at very high repetition, the 6p capacitor is passing the CHANGE IN VOLTAGE on the collector and passing it to the emitter. It will not be passing the full change but it only requires a very small change in emitter voltage to produce a much larger change in the collector activity.
Secondly, you will note that no current is entering the base during the cycle. It is being held rigid by the 10n.
This is only a tiny discussion of how the circuit works. There is a need for the analysis of the value of the base resistor, the base capacitor, the emitter resistance, the value of the feedback capacitor and the inductance of the coil as well as the capacitor across it.
The capacitor and coil in the collector circuit form a TANK CIRCUIT and this can be a further discussion.

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This is a very old circuit, we built it in the late 70s, high school electronics, but it was called TV Jammer. Works, but lucky to get 30 feet. Our biggest challenge was to make the smallest working version, and of course many failed attempts to boost the range. Doubt of much use any more, too many alternatives to broadcast entertainment.

Have to agree though, deliberately interfering with any signal, is illegal, regardless of power or range. Just unlikely the FCC is going to hunt you down over such a low power toy.
 
This is a very old circuit, we built it in the late 70s, high school electronics, but it was called TV Jammer. Works, but lucky to get 30 feet. Our biggest challenge was to make the smallest working version, and of course many failed attempts to boost the range. Doubt of much use any more, too many alternatives to broadcast entertainment.

Have to agree though, deliberately interfering with any signal, is illegal, regardless of power or range. Just unlikely the FCC is going to hunt you down over such a low power toy.

The FCC will not hunt you down. There use to be a guy that lived 2 blocks away every day after work from about 3:45 pm to 10:30 pm he was on his short wave radio. The whole neighbor hood was mad as hell it came in on the TV even if the TV was connected to cable. It came in on all channels. The guys radio was legal so he refused to stop transmitting. I contected the FCC they sent me papers to fill out with questions I could not possible know the answer too. What is the Make, Model and Serial Number of the transmitter in question? Can you see me knocking on the guys door and asking What is the Make, Model and serial number of your transmitter. LOL!!! One day I left for work about 6:40 am as usually I had to drive around the bent twisted wreckage of the guys antenna in the middle of the street. Someone pulled it down in the middle of the night and just left it laying in the street. The guy was back on the air 2 weeks later and 2 days later the bent twisted wreckage of his antenna was in the middle of the street again. A month later the guy moved to a house with 5 acres of land about 5 miles east of town. I drive by his house sometimes on my way camping the guy has the whole 5 acres covered in antennas. "WOW", the guy is really into talking to people on his radio.
 
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gary350- That thing looks like a beast. After my finals next week I was thinking of building something similar but in a smaller scale. I have been looking into flyback transformers and driver circuits. We used a 7555 chip in lab and other students have used them in their projects so I interested and the many uses of this IC. I picked up a free old computer monitor and plan on taking it apart soon.

colin55- This information will help me alot and this is exactly what I was looking for. I been looking all over the internet and found some useful information, but its mostly information for a technician. I understand the basics on how BJT and MOSFET's work but the information you provided helps me understand it more clearly. My partner is analyzing the tank circuit and my part is the transistor, biasing resistors, and the 10nF and 10uF capacitor.

Nigel Goodwin- I understand that this project is illegal, but we are only using the transmitter in our lab at the university. I doubt the FCC will come to my university and shut down the engineering department. I see your point but if I was making an excuse to do something illegal, I would at least pick something that would benefit me financially.

Thanks for all the replies. I will now add this message board to my favorites. There is alot of information to be learned here.
 
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It is exactly the same circuit as a simple (also illegal) FM transmitter toy.
 
The FCC will not hunt you down. There use to be a guy that lived 2 blocks away every day after work from about 3:45 pm to 10:30 pm he was on his short wave radio. The whole neighbor hood was mad as hell it came in on the TV even if the TV was connected to cable. It came in on all channels. The guys radio was legal so he refused to stop transmitting. I contected the FCC they sent me papers to fill out with questions I could not possible know the answer too. What is the Make, Model and Serial Number of the transmitter in question? Can you see me knocking on the guys door and asking What is the Make, Model and serial number of your transmitter. LOL!!! One day I left for work about 6:40 am as usually I had to drive around the bent twisted wreckage of the guys antenna in the middle of the street. Someone pulled it down in the middle of the night and just left it laying in the street. The guy was back on the air 2 weeks later and 2 days later the bent twisted wreckage of his antenna was in the middle of the street again. A month later the guy moved to a house with 5 acres of land about 5 miles east of town. I drive by his house sometimes on my way camping the guy has the whole 5 acres covered in antennas. "WOW", the guy is really into talking to people on his radio.

Radio amateurs have a legal obligation NOT to cause interference, and if they don't act responsibly they can lose their licence and have all their equipment confiscated, plus potential fines as well.

Owning a 'legal' radio doesn't mean you can operate it illegally, it's fairly obvious he was doing something completely wrong, and operating it outside it's correct parameters - and as a licenced radio amateur he should now that, and how to correct it.
 
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