I have done all the field modeling for phased arrays, dipole, crossed dipole, circle, etc. The intensity drops off by 1/r^2 but regardless of direction the phase of the pattern should be the same so when they intersect it should not really matter what incident it is (just thinking about the patterns). So my transmitter will be generating a pattern (depending on the antenna I choose) and as long as that field encompases the “victem” it should jam it. I dont need to jam the cell tower or the drone driver just the cell phone itself or the drone. Their reciever antennas will be trying to recieve canceled (or greatly reduced) signal.
I am looking at this as an aviation safety device since the FAA is slow as molasses in nailing these drone “pilots” to the cross and there have been close calls with manned aircraft, its just a matter of time before someone gets killed from some one wrecklessly flying a drone without calling positions and getting proper permits to fly above tree tops or near air ports. However I have been doing more research on the drones themselves and they have fail safe modes so even if they are jammed they will just hover rather than fall out of the sky and smash to pieces like I was hoping.
I am still intellectually interested in building an advanced jammer though, at the very least it would be nice to have in a theater.
Maybe I misread the links, but I think you are overthinking the interpretation. You guys are thinking about cancelling loops, Cartesian feedback, and all sorts of cool things we enjoy in the comfort of very expensive equipment. The way I read the links rppearso posted are simple brute-force SNR (signal-to-noise) jammers. They take a power detector tuned to a specific frequency band, if a signal is present and triggers the detector, then a “desired” signal is deemed present (i.e. a signal wanted to be “jammed”). At this point a VCO is triggered to do a frequency sweep (i.e. sawtooth control signal at its tuning input), and its output is amplified. That output is broadcasted in as omnidirectional a pattern as possible, effectively broadcasting wideband noise, so the SNR in that vicinity is degraded. The faster the speed of the frequency sweep, the more this interfering signal looks like white noise. Any signal within that bandwidth is affected by it, whether is the intended signal or not.
rppearso, I am sure somebody already mentioned this is highly frowned upon (and illegal in some places).
rppearso:
I am looking at this as an aviation safety device since the FAA is slow as molasses in nailing these drone “pilots” to the cross and there have been close calls with manned aircraft, its just a matter of time before someone gets killed from some one wrecklessly flying a drone without calling positions and getting proper permits to fly above tree tops or near air ports. However I have been doing more research on the drones themselves and they have fail safe modes so even if they are jammed they will just hover rather than fall out of the sky and smash to pieces like I was hoping.
Yeah, that is way out there on the "lookout for the Feds if they catch you doing this". If you managed to jam a UAV, and the UAV fell and, God forbid, killed someone; you would be in a heap of trouble. More so than the person flying the UAV. You have better luck (legally) shooting it down (especially if it's in your property).
rppearso:
So my transmitter will be generating a pattern (depending on the antenna I choose) and as long as that field encompases the “victem” it should jam it. I dont need to jam the cell tower or the drone driver just the cell phone itself or the drone.
I understand all that. I think you're missing part of the problem. And now you've moved the goalposts, at least wrt to the original problem. That formulation had the jamming transmitter at location B (going back to my post above) and jammed a radius around B. The measurement of the signal to be jammed was also made at B. You now want to measure at C and jam at B. I'm curious as to how you'll know the amplitude and phase of the signal at B ? To know those quantities at location C doesn't tell you anything about them at location B. At least not w/o other knowledge, at a minimum the geometry of A, B and C.
Let me use a simple example to illustrate the above. Imagine that the transmitter (A), the jammer (C) and the victim (B) are all collinear and far away from everything else. Further more B is about 1/2 way between A and C. You measure the signal at C and transmit another signal which matches it’s frequency exactly. Let’s also say you can adjust the relative phase of your signal to whatever you want. So what’s your formula for adjusting that phase difference ?
If the jammer at C and victim at B were both exactly an integer number of wavelengths away (from A), it would simple. The relative phase at B is the same as at C (where you are and can measure it). Cancellation at C will cancel at B (assuming you match the amplitude at B, etc, etc). What if C isn’t “N” wavelengths away ?
What happens when they aren’t collinear ? What’s the phase at B when it’s “above” being collinear by some cm ? Or by many meters ? Or not close to 1/2 way in-between (so matching power becomes hard) ? When you don’t know the radiation pattern of the transmitting antenna, gain and phase ? Or where the victim is, relative to boresight, in that pattern ? When there are real life effects such as multipath, etc ?
ETA : Added the pic below for clarity. Note the direct LOS path lengths aren’t equal. Also note that the angles (off boresight) for each path are different and so each antenna will have a different gain and phase for each path.
rppearso:
it looks like the AD8302 might do the trick. I could design the cirucit so that the tranmitting antenna does not turn on unitl the recieving antenna gets a signal from the band pass filter the AD 8302 could then measure the signal between the bandpass filter and the ossilator. It would not be active phase shifting but I could get decent signal cancelation from the first incoming signal. Once I started transmitting then the reciever antenna would be getting 2 signals unless I was able to design the antennas so that they did not interfere but that would be tough and likely impractical.
That’s true, my receiving antenna would have to pick up the transmitting signal from A. If I was out of range of A but in range of B then I would not be able to phase shift but I could still produce 2.4 ghz noise. I would guess most transmitting antenna are either dipole, crossed dipole or some variation to give a less directed pattern (doughnut, blob, etc). Once I pick up the signal from A that is what I will need a phase measuring circuit for, to measure the difference in phase between A and my noise broadcast at C then change my signal to be 180 degrees out of phase. Depending on where B is it may not be perfect cancellation but it will be better than just broadcasting noise.
If I had onboard radar I could determine the locations and phase shift accordingly but I dont have the energy to get that fancy. I just want to get a little more fancy than JUST broadcasting noise.
I have read up that the FCC has only had one bust and it was on a company that was selling mass quantities of jammers. From what I read the law on this sort of thing is sort of gray, its illegal to sell these sorts of things but the law is really gray on making your own and using it. If a drone pilot could not keep control of his own drone (jamming or now jamming) then that is another legal grey area especially if he was flying above the legal limit of 400 feet or near an airport. I have thought about shooting them down but if you accidentally shoot someone then it is for sure your fault. If a drone pilot looses control he has to prove it was jammed AND that he was in legal air space.
Mee_n_Mac:
rppearso:
So my transmitter will be generating a pattern (depending on the antenna I choose) and as long as that field encompases the “victem” it should jam it. I dont need to jam the cell tower or the drone driver just the cell phone itself or the drone.
I understand all that. I think you're missing part of the problem. And now you've moved the goalposts, at least wrt to the original problem. That formulation had the jamming transmitter at location B (going back to my post above) and jammed a radius around B. The measurement of the signal to be jammed was also made at B. You now want to measure at C and jam at B. I'm curious as to how you'll know the amplitude and phase of the signal at B ? To know those quantities at location C doesn't tell you anything about them at location B. At least not w/o other knowledge, at a minimum the geometry of A, B and C.
Let me use a simple example to illustrate the above. Imagine that the transmitter (A), the jammer (C) and the victim (B) are all collinear and far away from everything else. Further more B is about 1/2 way between A and C. You measure the signal at C and transmit another signal which matches it’s frequency exactly. Let’s also say you can adjust the relative phase of your signal to whatever you want. So what’s your formula for adjusting that phase difference ?
If the jammer at C and victim at B were both exactly an integer number of wavelengths away (from A), it would simple. The relative phase at B is the same as at C (where you are and can measure it). Cancellation at C will cancel at B (assuming you match the amplitude at B, etc, etc). What if C isn’t “N” wavelengths away ?
What happens when they aren’t collinear ? What’s the phase at B when it’s “above” being collinear by some cm ? Or by many meters ? Or not close to 1/2 way in-between (so matching power becomes hard) ? When you don’t know the radiation pattern of the transmitting antenna, gain and phase ? Or where the victim is, relative to boresight, in that pattern ? When there are real life effects such as multipath, etc ?
ETA : Added the pic below for clarity. Note the direct LOS path lengths aren’t equal. Also note that the angles (off boresight) for each path are different and so each antenna will have a different gain and phase for each path.
(click to enlarge)
[attachment=0]RFpaths.jpg[/attachment]
I’d tend to think most “drones” to worry about are going to be UAVs, following a pre-programmed course. If I wanted to jam (or better yet spoof) one, I’d start by putting my drone above it and broadcasting false GPS signals. It I really wanted to I’d just drop lot’s of strings from above and let the blades try to chew on them.
Then again given my prior employment experience, I might find it more fun to use a DIY ground to air missile to down the miscreant ! An optical or IR guided Estes rocket kit would probably work.
The other option to being liable for stray .308 rounds is to build a CO2 laser or Exemer laser and set up shop where people like to play with drones. That way its line of sight and im not responsible for stray lead hitting someone.
That being said I still think it would be fun to build a jammer just to see if I can do it as long as I can do it for a few hundred bucks which I think I can get 90% of the parts from mini-circuits.com
A laser would likely be 1-2k to buy all the parts and possibly more for tools but totally worth it. I just want to see if I can actually build something useful with all of this schooling I have done.
I would want a diamond laser eye and other high temp parts to reduce complexity with cooling (circulate cooling water rather than having to circulate the gas itself).