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Old 09-10-2017, 10:00 AM   #1
Dannyx
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Question FM Jammer project

Good day folks. This may be totally stupid and off-topic, but I wanna build an FM jammer Ok, let me explain: aside from obviously learning about how such a device functions and what makes it tick, it would have a practical application as well: shutting off annoying neighbours who insist on playing their radio through the night, driving me absolutely bananas and nobody seems to do anything about. Sure, it would instantly become useless if they switch over to a CD or something, but at least I can block off some of the nuisance and keep them on their toes long enough to allow me to get some shuteye without ear plugs. Mind you, we'll leave the legality of such a device out of the discussion for now, since I know it's technically illegal

Of course the internet is full of circuits, so my main point here is to ask for some basic guidelines and tips, like if anyone ever built anything like this I'd like to hear their thoughts, or perhaps there some audio and broadcasting pros out there who may step in and say "nope, this won't do, you need this" and so on...you get the gist. The circuits seem to be fairly similar and look like this...I suppose the variable cap can be extracted from an old radio, which luckily I have lying around (several of them in fact). My main problem is trying to get my jammer to penetrate several layers of concrete walls and floors, since I'm not entirely sure where the offending radio is located, though I believe it's diagonally on the floor above me and I don't think such a small circuit will reach that far.....need something with a bit more grunt, perhaps still based on the same idea but with up-sized components....EMP I'm telling you, that's what we need - Photonicinduction could probably help me Ok, joking aside, what would be the useful range of such a device ? Would it even function at all ? Cheers.
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Old 09-10-2017, 10:12 AM   #2
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Default Re: FM Jammer project

Rather than make a big powerful one in your flat, make is small and easy to hide and just place near the offending flat. Make more for each offending flat.
Or sound proof your bedroom. I sound proofed one whole side of my house internally. Not 100% sound proof but much better. I still hear my neighbours lady torch from time to time perhaps more work in the bedroom required.
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Old 09-10-2017, 10:37 AM   #3
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Default Re: FM Jammer project

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Originally Posted by diif View Post
Rather than make a big powerful one in your flat, make is small and easy to hide and just place near the offending flat. Make more for each offending flat.
Or sound proof your bedroom. I sound proofed one whole side of my house internally. Not 100% sound proof but much better. I still hear my neighbours lady torch from time to time perhaps more work in the bedroom required.
The noise is rather faint, but it IS there and definitely annoying...sadly I had already renovated the room, so I can't stick any insulation over the wallpaper now. Not really easy to sneak near said apartment...if I could, trust me I would've definitely made them stop by now using less friendly means
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Old 09-10-2017, 10:57 AM   #4
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Default Re: FM Jammer project

Encapsulate in rubber, coat in thick sticky glue, sneak in the dark, launch with catapult to outside their window so it sticks to the wall, sneak away chucking ?
Anything with the range to reach rather faint is surely likely to piss a fair few people off ?
And there it is, sat in your place. You might as well run your own pirate station, at least you'd get to hear the music you enjoyed
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Old 09-10-2017, 11:23 AM   #5
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Default Re: FM Jammer project

they could be streaming it.
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Old 09-10-2017, 12:21 PM   #6
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Default Re: FM Jammer project

Just get one of the more powerful FM transmitters meant for CD players, etc. and tune to the same station they're playing, don't even need to connect it to anything. If you don't know what station they're playing, well, it could be streaming or CD so this wouldn't have worked anyway.

All a jammer is - is a transmitter than transmits unusable data across the whole band that it was meant for...
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Old 09-10-2017, 12:38 PM   #7
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Default Re: FM Jammer project

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they could be streaming it.
It's definitely a radio station yapping away, but yes, of course, I mentioned that in my post, if they switch over to anything other than FM, it's game over....would need a bloody EMP pulse to fry everything in the building, including my own stuff
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Old 09-10-2017, 12:40 PM   #8
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Default Re: FM Jammer project

a friend had this problem in his workplace.i loaned him the solution.
his office is full of electronics and computer stuff so a wavetek rf generator blended right into things.obnoxious c rap replaced by 1 khz tone.
so the target moved the radio across the room to get better reception and turned it up louder.knock a few more steps off the attenuator and back to tone.
then silence.after a week the idiot with the radio gave up and started using a walkman.
others in the office kinda knew what was up and had a hard time keeping a straight face.
very effective.
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Old 09-10-2017, 01:04 PM   #9
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Default Re: FM Jammer project

Hi Dannyx,

Believe it or not, several years ago when I was in university and living in some students-only apartments, I wanted to build the same thing, as the window to my room was overlooking the pool and it seems that people often liked to play crappy country music at the pool, from dawn till dusk (I don't mind country that much, but after 12 hours of non-stop country, I think anyone can get sick of it).

Thus I ended up experimenting with / building many of those jammer circuits above. One thing you should know right-of-the-bat is that the above "jammer" is not a wide-frequency device. As such, simply building it according to the above schematic will not automatically block all radio stations. Rather, it may block only one station at a time, so you have to know what station your neighbors are listening to. If you can't clearly hear what they are listening to and you can't find their station, then all the work in this project will not achieve what you are looking to do at all.

So for starters, get a good radio tuner / receiver with digital tunning (and preferably one that can move at increments of 0.1 MHz). By "good" receiver, I mean something that has an input for an FM antenna and is a know brand (i.e. Sony, Panasonic, Yamaha, etc.). Then, get a good FM antenna or make your own (this will also come handy when building the above jammer, as a good antenna will greatly increase the broadcasting/jamming range).

Next, some technicalities regarding the above circuits: even with a good antenna, none of these small 9V battery-operated jammer circuits will be powerful enough to block anything beyond about 20 meters of range (if even that much). And if you are trying to block a commercial radio station with powerful broadcasting, the range will be even smaller. So indeed the components in the circuit above need to be upscaled so that you can use a higher operating voltage (higher operating voltages usually directly translates to higher broadcasting range). This can be a challenge when looking for BJTs for the above circuit, as they will need to be rated for HF/VHF/UHF operation.

And lastly, some of these sample circuits may not mention it, but to avoid frequency drifting while broadcasting/jamming, the circuit will need to be built on a PCB and everything soldered. Experimenting on a breadboard will give you experimental results at best - I know because I tried it already many times. I was able to build a working circuit, but it was very temperamental. The hardest part is figuring out what your circuit is doing once you've built it - i.e. what frequency it is broadcasting at, as it may be outside of the radio's FM range (and many times it is). This is where having a good radio receiver / tuner will come to be helpful again. I was using my Yamaha RX-830 RS receiver with a 1 meter long wire as the antenna - the antenna wasn't great, but I could catch almost every station there was around. This helped me find empty-unused frequencies that I could broadcast on to test my transmitter/jammer cirucit (so instead of a jammer, I ended up building a transmitter circuit, which is actually the same thing, but with "jammer" connected to a signal.)

On a finishing note, I would like to add that you don't need to extract a variable capacitor from a radio for this project. In fact, building your own vari-cap may be better and allow you greater control. With FM broadcasting, your vari-cap will probably only need to be in the 10s of pF. So for a cap like that, you can easily build your own with two plates of thin sheet metal. Then build a mechanism so that the plates can slide past each other. As they are fully against each other (but not touch, of course), the capacitance will be at its maximum. And when they are fully past each other, that's when the capacitance will be minimum. So depending on how you build your vari-cap, you may actually end up with a lot of control over the broadcasting frequency of your circuit. I made the mistake of using a small 5-35 pF vari-cap with a very sensitive variable range. As such, tuning my circuit was not easy at all.

So to sumarise what I just wrote:

1st, find the offending station you want to jam or play your music over. I ended up finding that I couldn't do that with the pool music at my apartment, because the radio they used at the pool also turned out to have XM radio.

2nd, build your transmitter/jammer and make sure it actually works as it should. It's best to do this by broadcasting a signal or music that you know and finding it with your radio receiver / tuner.

Only after the two steps above are done, then you can "upscale" your transmitter/jammer to increase the range.

I also have found a few useful videos on the matter from YouTube, but they are bookmarked on my other computer. I will post them here when I get a chance.

Last edited by momaka; 09-10-2017 at 01:43 PM..
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Old 09-10-2017, 01:39 PM   #10
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Default Re: FM Jammer project

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Originally Posted by eccerr0r View Post
Just get one of the more powerful FM transmitters meant for CD players, etc. and tune to the same station they're playing, don't even need to connect it to anything.
Ugh, I hope you don't mean those cheap car FM transmitters found on eBay and Amazon. I have one, and it's pretty crappy to say the least. Even next to my radio, that thing will get overpowered by just about every commercial radio station I want to broadcast over. To make it work, I actually have to find a frequency that is not used and then tune the transmitter to broadcast on that. And even then, the signal is often weak.

Thus, what I ended up doing with mine is I opened it up and soldered a long wire to the internal "antenna" (it was a 1 cm -long trace on the PCB, lol) sticking out of the case. With the wire stretched across my dash, the broadcasting power is just strong enough to overpower most commercial radio stations. But the sound quality is ugly, to say the least. So I still try to look for an unused frequency to broadcast on, as that gives "the best" signal quality.

Moreover, these FM "trasmitters" tend to have terrible frequency spill-over into all kinds of frequencies. I suppose that may be a good thing if trying to build a frequency jammer, but not so much for a pirate station. I'm sure I pissed of more than a few truckers on their CBs when driving late at night with mine, because with the long antenna, I could catch my audio stream onto several more stations besides the station I was broadcasting on, lol.

Last edited by momaka; 09-10-2017 at 01:47 PM..
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Old 09-10-2017, 01:57 PM   #11
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Default Re: FM Jammer project

Thanks for the tips. GREAT advice. I do have a Sony home theater thingy with digital tuning and yes, I know I'd have to know what they're listening to as the device can't block everything - it has to be tuned to a specific station and then pray to god the bastards don't change it or switch to something digital, thus rendering the jammer useless. See, here in our country we have sh!tty laws: you'd call the cops, they'd knock on their door (if they're lucky to make it past the intercom to enter the building) and if lucky, they'd take it seriously and stop. If not, they'd slam the door in their face and the police would calmly give up and leave because they don't have enough authority to smash the damn thing....you're the bloody POLICE, just cuff the bastards for disturbing the peace, are you kidding me ?! :|

Making a varicap: sounds very challenging, especially since my plain ol' meter doesn't have a cap setting to know what I'm doing.
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Old 09-10-2017, 03:15 PM   #12
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Default Re: FM Jammer project

here is some advice,
tune into the same radio station.
if it's synchronised then your in luck,
if there is a slight delay then they are streaming or using a sat feed.
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Old 09-10-2017, 03:57 PM   #13
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Default Re: FM Jammer project

Yeah, really the trick is power, building the final stage RF amplifier. Indeed the problem with those RF modulators, they were meant to be low power so that they can't overtake nearby commercial stations specifically for FCC rules. Thus, finding a powerful one is the trick.

If I had an RF amplifier, couple that with an RF signal generator with a continually variable range, you could sweep it across the range searching for the spot that it kills their radio... I do wonder what the peak to peak voltage is on a tube oscillator, perhaps that by itself could generate significant noise on the frequency if radiated... again due to FCC rules it is very low power specifically to not interfere with those who licensed each frequency channel.
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Old 09-10-2017, 04:18 PM   #14
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Default Re: FM Jammer project

^ As if the FCC has the funds to waist on hunting down noise like such...
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Old 09-10-2017, 08:17 PM   #15
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Default Re: FM Jammer project

a spot-beam antenna will help to focus the energy while not pissing the wrong people off.
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Old 09-10-2017, 11:11 PM   #16
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Default Re: FM Jammer project

Well , you should do like one psycopath friend used to do , lol . His father was a TV repairman , and he grew a hobby of remote controllers collector . He had different brands and was able to shut down most of the neighboring TVs .

Further , his hobby grew more easy , with the Universal remote controllers invention , leaving a whole neighborhood dazzled , but quiet ..

If you're lucky , their radio could be a remote controlled one .

As for me , back in early University , i made a small Radio station FM , covering a range of 1km approximately . We used it to broadcast songs mainly . Of course it was illegal , but back then , my country was in war and no one cares .

You can use the same frame to jam their frequency .
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Old 09-11-2017, 02:14 AM   #17
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Default Re: FM Jammer project

Please remember that operating an unlicensed transmitter is illegal. I do have a few amplifier circuits that i built for souping up FM modulators, but i strongly suggest against using them for anything else than testing into a dummy load.

Also, you will need at least some RF measurement gear to figure out what your amplifier is doing. The absolute minimum i would recommend would be building a power meter with germanium or special RF schottky diodes (the latter you can find on ebay, the former you might be able to scavenge from an old, communist-era radio) and a RTL-SDR type receiver to see the harmonics your transmitter is putting out. A poorly tuned RF amplifier will easily interfere with a lot more comms than your neighbor's radio, even at a relatively low power. And then you'll be the one getting complaints...
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Old 09-11-2017, 02:29 AM   #18
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Default Re: FM Jammer project

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Originally Posted by Th3_uN1Qu3 View Post
Please remember that operating an unlicensed transmitter is illegal. I do have a few amplifier circuits that i built for souping up FM modulators, but i strongly suggest against using them for anything else than testing into a dummy load.

Also, you will need at least some RF measurement gear to figure out what your amplifier is doing. The absolute minimum i would recommend would be building a power meter with germanium or special RF schottky diodes (the latter you can find on ebay, the former you might be able to scavenge from an old, communist-era radio) and a RTL-SDR type receiver to see the harmonics your transmitter is putting out. A poorly tuned RF amplifier will easily interfere with a lot more comms than your neighbor's radio, even at a relatively low power. And then you'll be the one getting complaints...
I'm aware of that, but being realistic, there's no real way for someone to find out why their radio suddenly only plays static...nobody would bother and would just blame it on poor reception, the weather or just switch to something digital way before that IMO.
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Old 09-11-2017, 07:25 AM   #19
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Default Re: FM Jammer project

just wire a 12v relay up as a "buzzer" that disconnects it's own coil at power-up
those put out soo much shit they wont have anything!
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Old 09-11-2017, 10:26 AM   #20
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Default Re: FM Jammer project

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just wire a 12v relay up as a "buzzer" that disconnects it's own coil at power-up
those put out soo much shit they wont have anything!
Yeah, I thought about suggesting something like that too.

My original idea was get a butt-load of the cheapest Deer/L&C power supplies you can find, remove them from their case, and run a bunch of computers like that.... but that's probably too dangerous (though I will give you bonus points if you connect the BJTs on the primary heatsink through long wires wrapped around the AC input. )

But yes, relay coils from appliances produce a crap-ton of noise - even more than a cheap Deer PSU without any filtering. Just make 20 of those devices and put them everywhere in the building. Then no one would be watching TV or listening to music, because even if that doesn't screw up the reception, the speaker popping noises one would hear on their TV or radio will drive them insane.

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Making a varicap: sounds very challenging, especially since my plain ol' meter doesn't have a cap setting to know what I'm doing.
It's not hard at all, but you do need some equipment.

If you are serious about learning and building electronics, you should invest in a good multimeter with more functions, like capacitance, frequency, PWM, AC current, as well as Mix/Max and Rel. functions. The cheap transistors testers on eBay and elsewhere online are also quite useful - they will provide you with capacitance, inductance, and cap ESR measurement, which can come in very handy when re-using components.

Last edited by momaka; 09-11-2017 at 10:34 AM..
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