Catch up on stories from the past week (and beyond) at the Slashdot story archive

 


Forgot your password?
Close
typodupeerror
×
Technology

Engineers Build Satellite Jammer 212

Posted by Hemos from the now-no-one-will-know-where-i-am dept.
cencini writes: "According to this article, U.S. engineers developed a device for $7,500 which generated UHF signals strong enough to jam mobile GPS systems. My question is, couldn't you build something like that for less?!" Update: 04/20 02:42 by H : The folks at New Scientist wrote with the original article - the device actually blocks UHF signals, but can be modified for other bands.
This discussion has been archived. No new comments can be posted.

Engineers Build Satellite Jammer More

Engineers Build Satellite Jammer

Comments Filter:

  • Re:WHY?!?!?!?! (Score:1)

    by Anonymous Coward
    The method for defeating the error is very difficult to implement on a missile in flight. :)

    Nobody uses GPS to target their nukes. US missiles use inertial/celestial navigation. As the warhead is in its ballistic arc, it takes images of the stars to determine if it's on target (stars are difficult to jam).

    Cruise missiles carry a fairly small warhead. To really damage the building/bunker you need to be dead on target. Hitting the parking lot may scare the crap out of the occupants, but won't hurt them. US missiles also have backup navigation systems (the Tomahawk takes pictures of the ground and compares them to images downloaded prior to launch).

  • Re:WHY?!?!?!?! (Score:1)

    by Anonymous Coward
    As I recall, the military has the ability to put deliberate errors into the civilian GPS signal.

    Even if they removed the error, it would seem unlikely that civilian units in the US would become more accurate since you could simply remove the error in the satellites over the Gulf.

  • Re:WHY?!?!?!?! (Score:1)

    by Anonymous Coward

    It's been a long time since I worked on GPS (at Rockwell and some University contracts with NASA and a couple of DoD orgs.), but if my fading memory the P-code PN sequence was one week in length, not one month. There was also something in the stream of GPS data blocks that was encrypted using DES (Crap! Now I'll be down in the basement tonight looking through boxes for old copies of ION transactions). Receivers in those days were pretty much limited to positioning accuracies that you could get from tracking the C/A or P code itself. Newer designs were getting down to millimeter accuracies by tracking the L1 and L2 carrier frequencies and using that information to hone the position solution. AFAIK, anyone getting those kind of accuracies in a civilian receiver is probably using Differential GPS (as well as carrier tracking).

    Also, I cannot see how this $7500 piece of equipment can be useful in supposedly jamming GPS signals. I suspect that what they're really doing is swamping the front ends of some of the cheaper civilian receivers that are in the vicinity of this low-cost transmitter. Even then, I would guess that the receiver might not lose lock unless it was engaged is some drastic manuevering and was close enough to the jammer. We looked at this back in the early '80s; it was damned difficult to jam a GPS receiver (well, the military ones anyway).

  • Earth to fruitcake (Score:1)

    by Anonymous Coward
    Err.. you don't need to responde to every single post, especially when you don't have anything to say.

  • Re:WHY?!?!?!?! (Score:1)

    by Anonymous Coward
    Narf! GPS isn't a geosynch system, it is a high LEO system. Turning off the "error" would involve switching the system as it transitioned past the horizon of the gulf.


  • You said:

    "Because in the case of the Chinese Embassy
    we hit exactly what we were aiming for
    (+/-1cm). Unfortunatly what we were aiming
    for was the wrong target."

    Seems like you have bought the entire "intel screwed up" theory stock, hook and barrel. Everybody knew that we WANTED to hit the Chinese embassy. It's the RIGHT target.

    Those intel guys who were sacked or gotten "warnings" are fallguys. Their only fault is that they have become the scapegoats for a political decision that went sour.

  • Sigh

    I really miss the days when moderators had a sense of humor. :-(

  • The article was a little vague as to whether we're talking about screwing up GPS receivers here on earth or screwing up the actual orbiting transmitters themselves.
    I assume that interfering with reception of the GPS signal within a limited area would be considerably less of a technological and financial challenge, but if you can stick this thing in a truck or jeep and take it where it's needed, wouldn't it be just as easy to carry weapons instead and inflict enough damage to disable whatever you wanted to jam?
    That way, you're in and out quickly instead of hanging around waiting to get shot or captured, because anything this would be used against wouldn't be sitting around unguarded and unprotected.

  • This post is as daft as whoever moderated it 'insightful'. Two really serious flaws in your argument:

    • 'Was bringing about' implies that some change had already occured. These changes were far from 'imagined'.
    • Which part of the difference between 'technology' and 'social change' do you not understand? Yes, they were scared of losing their jobs. No, they were not scared of wheels with cogs on them.

    I take it that English is not your first language. Failing which, I take it that rationality is not your favoured reaction.

    Hamish

  • Because in the case of the Chinese Embassy we hit exactly what we were aiming for (+/-1cm). Unfortunatly what we were aiming for was the wrong target. GPS guided missiles are only as accurate as the intel they are fired with. If you don't know where the enemy is you can't hit them.

    If troops had been sent in to take out the embassy they would have been able to
    1. See it was the wrong target before it was attacked (Provided they were informed what the target was).
    2. Radio back to command and confirm that this is what they wanted to do.

  • You can get the parts to build somthing like this at the Dayton Hamfest [hamvention.com].
  • There are some pretty astounding military repercussions of this device (which explains the price - it's not a product aimed at pranksters). Since Most modern military weapons (guided missiles, SAMs, SSMs, fighter jets, etc) are GPS guided, land bases and ships can easily defend themselves by switching on a GPS jammer. A $7500 device to defeat million-dollar technology is a very good investment. The American military is particularly dependent on GPS tech (having invented it, they jumped on the bandwagon with more vigour) so this bad news for their fleet of GPS navigators.
  • Ok, so you don't tailgate when you switch on so you can swerve around the guy when he eats the guardrail. Besides, the guy is already weaving due to USING the phone.
  • see above on the crash part. I just wish there was something I could do about the people I see reading the paper with two hands and driving with their knees. I commute an hour each way and the stuff that goes on is insane. I can almost believe the joke about the guy that puts it on cruise control and then climbs in the back seat to go through his briefcase. When I read the article on the japanese jammers I contacted the company about them but the frequencies we use are different than theirs. I even thought about the EMP gun in Cryptonomicon 8^)
  • Very similar to the japanese version I read about. They were marketing theirs towards movie theaters. Were you able to get a price? The email info request form never completed/submitted.
  • Cant wait to see this one in my next meeting... Ill take mine to the movies too http://www.cguard.com/English/latests/index.html
  • You are correct. Hands-free units were no more safe than normal hands-on units. The danger arises from the distraction of the call. Phone conversation is worse than person to person conversations in the car because the lack of visual context (gesture, expressions, etc.) requires greater attention to the aural cues. On the phone you actually have to concentrate more attention on hearing at the expense of seeing. Within the car listening is supplemented by seeing, even if its limited to peripheral vision. And I imagine you'd find that drivers have to talk more on the phone than they do in a driver to passenger converstion. (Actually the study avoided making any conclusions about the nature of the increased risk, but I'm less restrained in my opinions!)
  • An altitude offset wouldn't be a big problem. The warhead would use a contact or radar fuze to control the timing of the detonation.
  • From what I understand, the error inserted is about 100 metres. Would that make a lot of difference if you were using a nuclear device?

    Yes, if you were attacking a hardened missile silo.

  • It is not clear to me why anyone in the goverment thinks that a terrorist wouldn't just run a binary editor on the firmware and change the limits to some number 100 times larger. It isn't that simple. Algorithms that work at slow speeds may not work reliably or accurately at high speeds. Getting accurate results might require new firmware and a faster CPU.
  • This wouldn't be surprising; some military units in the field during Desert Storm were using commercial (handheld) GPS units, not military ones. SAS were using small Magellan units, I'd put money on them being commercial ones. OTOH, ground pounders don't necessarily need the pinpoint accuracy that the fine folks moving at 500 mph over the desert do.
  • (Yeah I know I misspelled it.)

    We are expected to believe that these things cost a lot because they are very "technical" and therefore costly. The government is just as dumb so the companies get to rape us blind with huge markups. Oh well. By now we should be used to it.


    <SIG>
    I think I lost my work ethic while surfing the web. If you find it, please email it to crispy@crotch.caltech.edu.
    </SIG>
  • hehe... It's not quite midnight here on the Pacific Coast but I got started early. I am going to wake and bake tomorrow morning in celebration. Too bad we can't just make this a national holliday.

    <SIG>
    I think I lost my work ethic while surfing the web. If you find it, please email it to crispy@crotch.caltech.edu.
    </SIG>
  • True, mid-air nuclear blasts are more destructive (I guess it gives a pressure wave enough space to form), but I was thinking more along the lines of "conventional" weapons, rather than nukes.

    With a non-nuclear missile, you really do need to be pretty accurate if you want to be sure of destroying the target, unless you throw lots of explosives at it, and I was kind of assuming that it was this type of missile that the GPS offset was designed to hinder. After all, with the exception of hardened targets, detonating a nuke 200 feet or 500 feet above the target isn't going to make a great deal of difference; either way, there isn't going to be much of it left :-)

    Cheers,

    Tim
  • Hehe - the only trouble with your idea is that it'll probably cause more crashes than it prevents, as your victims flap about wondering what's happened to their 'phones :-)

    It certainly has merit, though - a few times I've been on a bus only to find the driver is using his mobile - taking your own life (and that of anyone you hit) into your own hands is one thing, but the lives of a couple of dozen passengers? Talk about irresponsible...

    Cheers,

    Tim
  • Okay, if the offset is in altitude, not the position on the ground, then couldn't you just target your missile for a spot above the target, then guide it down at it?

    (Don't think "along, then down", think "up, arcing over, and down", kinda like a mortar with last minute targetting correction)

    Cheers,

    Tim

  • Hmmm. (Score:1)

    by X-Type ( 15655 )
    Yes, I think so.
    I will have to get to work on this right away.
    Driving through downtown could be much fun with one of these. Hmmm.. maybe follow an out of state Jaguar or Seville around for a while. Heck, no need for it to be out of state, everyone gets lost anyway.
    Yes, oh, and if someone builds one before I, they should submit it to /.

  • Well, pete-classic, there goes your TS.

    Better luck next time.

    Don't sweat too much, though. You haven't let anything slip that wasn't obvious already. Just remember to preview in the future.
  • Ok i have a two way radio modified to transmit whereever it can hear (VHF, UHF, SHF) which covers the UHF band. I only spent 250 on this radio. It does 5W out and is portable. Now, couldnt they make a GPS jammer for less?

  • "Nobody uses GPS to target their nukes. US missiles use inertial/celestial navigation. As the warhead is in its ballistic arc, it takes images of the stars to determine if it's on target (stars are difficult to jam). "

    However, AFAIK, missle subs use it to determine where THEY are in order to give launching coordinates to the missles. This number is important for hard target kills.

    "All those tubes and wires and careful notes!"

  • KITT (Score:1)

    by toofast ( 20646 )
    Do you remember KARR? What did KARR stand for, if KITT was Knight Industries Two Thousand?

  • The Russians also have their own version of GPS - called Glonass. If I remember correctly, Trimble sells a dual-mode system.

    Also, one of the previous posters referred to using differential GPS. This is publicly available only in coastal areas and is supplied by the Coast Guard in addition to Loran. It's not available in the central US unless you set up your own DGPS station. It's typically provided by an add-on module to you CA code GPS receiver and operates by time-correcting the incoming satellite signals.

  • Re:WHY?!?!?!?! (Score:2)

    by Anonymous Coward
    30 feet in CEP is the difference between getting a hard kill against a hardened target, and merely damaging it, especially with non nuclear weapons. With nuclear weapons against hardened silos, even a CEP of 100 feet can be iffy to make sure the missile's been taken out before launch.
  • Yes, but that's including the postprocessing.


    ...phil
  • I'm quite surprised it took this long. I heard a rumor about 2 years ago that a GPS jamming device was available in Russia with a 30 mile radius.
    The news isn't that it's possible, just that it's so easy. People aren't used to the fact that any reasonably bright person with access to a library could build a GPS jammer (or a nuke. or poison gas. or conventional explosives. or cryptography software).

    I'd expect the usual blithering lusers to talk about banning this (probably "for The Children!") for awhile until reality intrudes.

    It's also worth noting that the easiest way to feel more comfortable about this sort of thing would be to realize that a) GPS counts as a vital military service, b) jamming it could be seen as a threat to the country and that civilian usages also cause threats to a variety of important services, c) to jam, it must transmit and finally d) if it transmits, you can drop something nasty on it from a squad of pissed-off Marines on up.
    __

  • I.N.S. (Score:2)

    by hawk ( 1151 )

    In some of these parks, the rescue attempts are known as "I.N.S."--Interference with Natural Selection . . .
  • It's really off-topic here, but OK. Software that I had written was in question. I write it as a contribution to the free software community exclusively. I do not want to be somebody else's unpaid employee, which is what I effectively am when somebody takes my software and does not return anything to the community or to me - does not distribute their modifications, does not distribute source code at all. That is the quid-pro-quo implicit in free software. If people want to use it in a way that is outside of the GPL, they are welcome to get a commercial license from me, so that there is some return to the community for the software - I'll take the money and use it for some free software cause. So, the point here is that I do not consider free software to be a gift. It's part of an exchange. Generally, that exchange means that I get more, and better, free software in return for my efforts. OK, your question didn't get moderated off-topic, so maybe my reply won't be. Thanks Bruce
  • Heh you can say that again. CA grade GPS (what civilians get) is accurate to about 100m, and gets even better if differential GPS is used. In terms of positioning a nuclear bomb, that's like arguing over a few microns.. utterly pointless. Let's not forget that nukes could be accurately aimed long before the advent of GPS, BTW.

    --
  • Differential GPS relies on being able to yank the signal over the selected area in an emergency. It should be noted, though, that the Russian GLONASS system doesn't have Selective Availability, and that a combined GPS-GLONASS receiver can be build to achieve very good accuracy. The European Galileo system is supposed to be launched this decade, too.
  • Jamming radio signals isn't high tech exactly -- dicatorships have been doing it for many decades to keep real news out. The only question is: how big an area do you want to jam? The bigger the area, the fancier the jamming.

    You need wideband jamming to block GPS, since it uses spread spectrum, so the cost goes up (you need wideband amplifiers etc; you may be able to boost the efficiency by mimicing the real spreading sequence, which would add complexity.) However, the biggest cost is still going to be your wideband power amplifier stage. The bigger area you want to jam, the higher the cost.

    Oh, the military has played with GPS jamming for years. There has been several Notices To Airmen (NOTAMs) from the FAA warning of GPS outages around <military base> at <time> over the past few years.
  • Oh, it's spread spectrum/CDMA alright, specifically the kind referred to as Direct Sequence Spread Spectrum (DSSS). That's what the pseudo-noise (PN) sequence, also known as a spreading sequence, is all about. Look up the definition if you don't believe me.

    The Russian GLONASS system doesn't use spread spectrum; there *each satellite* has its own operating frequency.
  • GPS uses 12-hour inclined orbits. Not exactly Low Earth Orbit (LEO), but definitely not geostationary. Apparently the 12-hour orbits wasn't such a great choice... it makes them cross one of the Van Allen radiation belts which wears on the satellites.
  • You don't need a lot of transmission power if you can get the jammer really close to your target. Jammer artillery shells bury themselves in the ground and their protroding antennas are made to look like the vegetation making them hard to find and disable. They are cheap and very effective.

    ----
  • What does Heroically Resistant mean? Well, IANA ECCM expert, but there are a number of tricks used by modern satellite comm systems to overcome jamming and inteference. Most of them have been around a while, too:
    • Frequency Modulation
    • Spread spectrum and frequency hopping
    • Encoding and Compression
    • Error correction
    • Contingency Link Margin
    • Active Channel Seeking
    And those are just the ones that come spontaneously to mind...

    Also, I would say that, if we're gonna pick on colorful adjectives, we should at least give credit to the engineers who designed the comm equiment on "the latest generation of global communications satellites" for their "heroic" efforts to create a robust system, before we start calling people "naive."

  • Reminds me of an anecdote related to my by a venerable old EE I worked with long ago...

    While performing field tests out of Nellis AFB for an onboard ECCM system for fighter jets, the engineers noticed that intermittently, there was another jamming source, in addition to the one they were using to test their countermeasure. In fact, this source was so much better than the jammer they were using for the test that the countermeasure under test was completely ineffective.

    So they got the USAF to send out planes to locate this mystery source, and it turned out to be in a small town outside Nellis. When investigators went to the town, they discovered the jamming signal eminated from an old auto garage. Inside was a weathered old man using a pre-WWI DC arc welder. It turned out to be the arc welder that was radiating like a banshee from DC to light.

    When the Air Force and engineers learned this, they offered to buy the welder from the mechanic, but he refused every offer, citing his preference of the old DC welders, and his dislike of anything he would be able to find to replace it.

    So. Moral is, if you want a cheap, low-tech jammer, pump a few dozen amps DC across an air gap.

  • Inertial systems drift and have to be recalibrated on a regular basis. This has always been a problem for nuclear missile submarines and one of the reasons that the Navy has spent so much money on satellite navigation systems such as Transit and GPS.
  • Bruce,

    I asked you a question at:
    http://slashdot.org/comments.pl?sid=00/04/18/133 4211&cid=293
    You responded to my original comment, but completely misinterpreted what I said, and did not address my question in any way, shape, or form. I would appreciate a meaningfull response.

    Thanks,

    Fall
  • I really wasn't expecting you to reply here. You could have replied in the comment. However, this thread is labeleled offtopic (OT), and I think most people can just step around it. Since you replied here, I might as well do the same....

    My problem with this your reply is that a great many of these Open Source advocates claim (including you, I believe, but i'll give you the benefit of the doubt) that Open Source is superior in every way. Their excuse for the lack of Open Source domination in most areas, goes something like: "Open source hasn't been around long enough", "Not enough eyes here", "this is too new", etc. However, with your example (and others, where software derives from GPL software) these arguments do not hold water. The companies are merely adding to something that already exists--they do not have any sort of headstart or propietary advantage. If the propietary/commercial process is inferior as claimed, the companies have nothing to add (atleast nothing that would withstand matching efforts by an involved Open Source community). What rational person would buy a commercial product, when they can get Open Source software that services (according to numerous advocates) their needs better? Virtually no one. Thus, why the need for "publicity against Be"? Why the need for implicit or explicit legal threats? Why make GPL viral--as opposed to BSD style license (other than allowing for certain eventualities)?

    If you merely feel that GPL is less than a perfect replacement for commercial/propietary software, but morally superior (or superior from a long term utilitarian perspective), and thus needs protection, that makes sense (in the context of the assertions). But this is not what I've heard from the vast majority of advocates. If I am reading you wrong, or if you disagree with these "advocates", then I wish you'd step out of only-positive-open-source-words-allowed mode, and speak candidly. I don't believe you're doing Open Source any good in the long run by allowing these clearly contradictory messages to go unchallenged; it will ultimately serve to discredit the movement.
  • Ooooo, big coverup...

    Everyone I know who knows about GPS has known about Selective Availability (SA for short) for years.

    Funny thing is, they had to turn it off during Desert Storm (probably the only time it might have served a purpose) because they didn't have enough military receivers :-)

    That would be your government at work.

    --
    grappler
  • AFAIK, your GPS receiver shouldn't get more accurate at speed. However, you may get a better fix for your present position if there is some way of telling your GPS receiver that you are stationary, since you are fixing some of the variables (velocity & acceleration) that your unit is trying to determine.

    Your basic accuracy depends on where the satellites you are getting a fix off are located, with the ideal being 3 satellites at 5 degrees above the horizon, and a 4th directly overhead.
    Vertical accuracy is less accurate than horizontal accuracy, due to the fact the entire constellation is normally 'above' you.
  • I would say that the resolution that consumer grade GPS provides is more than enough to allow an ICBM with a nuclear bomb to be more than effective. The GPS drift that the consumer devices are subject to is much more likely there to help prevent accurate conventional weapon attacks.

  • For a great introduction to the GPS system (and technologies such as differential GPS) check out the Trimble web site:

  • What do you mean - "what they don't tell you about GPS?" If you mean that owners - the US Air Force, they tell lots., including all that.

    This is widely known and common information - obviously. I mean, if you know about it, its not that unknown now, is it?

    Space Times, Jane's, and other Federal geek rags have told you all about this many times over. And I'm sure that you can find the info at either www.laafb.af.mil (they guys that bought and built it) and/or www.schriever.af.mil (the guys who fly it).

    Not only everything you said - but Clinton wrongly told everyone that the AF was going to give everyone 1m resolution with consumer gear. Unfortunately, he didn't give them an executive order - so they ignored him, as usual. Consumer gear without using multisampling (sitting in one spot for a while to get a more accurate position by taking more samples) give you around 30 m accuracy (that is, its off by about errrr at least 30 m in all directions (like you were in a 30 m hampster ball)

    Surveyors use multisampling GPS do this all the time.

    Many people use it just for timing anyway - not caring about the location, but use it to keep lots of clocks across a wide area in sync.

    i'm rambling - but i was concerned that "they" have told us a LOT about GPS... none of this info should be shocking and none of it is secret or unknown in any fashion.
  • That would only be true if it weren't for the fact that the four satellites must be above the horizon in order to be seen. Because they are all "above" you to one degree or another, the ideal configuration for altitude solution (a tetrahedron with you at the center) can never be achieved. The upshot is that the altitude fix has an error of about 1.5 times that of the latitude and longitude. It's not deliberate, it's an artifact of the fact that you're standing on a big ground plane. Also, it's possible to get a really horrible configuration of satellites (for example, due to being in an "urban canyon" or a real canyon) that makes it impossible to get the same precision in all directions horizontally, regardless of the fact that you're tracking four or more birds. Good GPS receivers (and not-so-good ones) report the quality of the horizontal solution and the quality of the vertical solution as separate numbers. Civilian GPS receivers are designed to stop reporting fixes above certain altitudes or faster than certain velocities. It's this fact, not the quality of the altitude solution, that prevents their use in long-range weapons delivery systems.
  • Oh shit! My nuke missed by 100 meters. Damn!
  • There are already UHF sources like TV stations that disrupt the civil GPS signals.
    There are also a few spots where the interference from different sources just keep GPS from working. There's one somewhere on the east coast (PA/NY?) and a spot near St Louis (on the Ill side of the river) where GPS just doesn't work.

    GPS does some interesting frequency hopping. If you can mess with that, 1W would be all it takes.

    For what its worth the GPS signals are something like 20 dba below the background radiation noise level at the frequencies used so you could consider it always jammed anyway.
  • From what I understand, the error inserted is about 100 metres. Would that make a lot of difference if you were using a nuclear device?

    Dana
  • The signal is encrypted at the satellite. Military receivers can decode this encryption to get better accuracy , but not 1 cm accuracy. My ship was issued a cheap civilian GPS receiver during the gulf war, as were many others. They revolutionized navigation but I can confirm that they did _not_ have 1 cm accuracy even with the encryption turned off at the satellite.

    Another way to defeat the encryption that was not mentioned here is to use a ground-based GPS transmitter of your own construction to calibrate the satellite signals. There was talk a while back of using them to assist in automatic aircraft landing systems at airports since they would be a lot cheaper than the alternatives that were supposed to be under design.

    Need I mention that such a system would be a prime target for jamming?
  • The NavSat network is a series of satellites w/ atomic clocks located in Geosynchronous orbit (so they hold steady above the equator) at over 20,000 miles distance. The timing pulses they send are low power, necessarilly so for them to last as long on their available power output.

    Wrong. The GPS constellation is in low earth orbit, and they are on inclined orbits, so that they cover the whole earth's surface.


    Furthermore, the GPS system uses spread spectrum modulation to make it much harder to jam: you would have to create a very wide bandwidth signal at 1.2GHz to block the signal.


    Probably, what the military did was come up with a system that not only blocks the signal, but spoofs it, so that rather than just getting no answer you get a wrong answer (since most military gear has both GPS and intertial nav, if your GPS stops giving you any data you fall back, but if it gives you bogus data you screw up your INS).


    The reason they are doing this is probably the same reason a good sysadmin tries to break into his own system: once you know what can be done and how, you can begin to act to prevent it.

  • In reading the thread, I've noticed another misunderstanding about GPS, and the difference between civilian and military GPS units.


    The GPS system that civilian units use operates on about 1.2GHz (which is way above the UHF TV band and cellular band). The problem with a single frequency system is that you have no idea how much the atmosphere is bending the signal, so you have a systemic error right there. Add to this selective availability, and you get the 30-100 meter error most people quote.


    Military units use 2 freqs: the civilian accessable 1.2GHz frequency, and 1.5GHz. Since atmospheric bending is frequency dependant, you get two different readings, and can then derive the real data from that. So, even when they turn off SA, civilian units will not be as accurate as military units.

  • I don't know exactly how it works, but the signal does not change. The GPS unit itself determines if you get "high" or "low" accuracy. For this reason they are stored in arms rooms. I used to be an armorer. We had a bunch of them. -AC (For obvious reasons)
  • What purpose does building one of these devices have apart from annoying the military or doing illegal activites ? seems rather pointless to me
  • Like this is going to bother the military - "Hey, some loser is jamming our GPS! They've got to be putting out a pretty powerful signal to do that - where's that RF-seeking missile?"

  • Slightly used VHF/UHF signal jammer for sale (built 1975). Also cleans carpet and comes with handy stair attachment. Only $25

    Dual purpose "just like new" VHF/UHF signal jammer for sale (built 1978). Comes with 1 cookbook and 4 components for mixing cake frosting, whipped cream, etc... Only $10.00

    My mom ruined so many good Saturday morning "Looney Tunes" with those damn things.

    --Clay

  • Why not simlply let Darwin do his stuff?

    Perhaps soak the GPS in some grizzly pheromone for added effect :-)

  • untrue. you can buy a $30,000 Leica GPS reciever and get 1cm accuracy. it's civilian in the sense that anyone can buy the damn thing but it's not civilian in the sense that it'll take a 30,000 dollar chunk out of your preffered nostril...
  • The reason for this is that the American military use something called spoofing. There are two type of GPS transmission as far as I can remember from University : S-CODE and P-CODE. When the US or Nato is involved in a conflict, the spoofing is turned off, allowing accuracies down to about 30cms (I think 1cm is a fallacy). You can always get around the spoofing using something called fast-static GPS. The reason the military code cannot be easily cracked or jammed is because it is only repeated approx once a month, whereas the civilian frequencies are repeated frequently. This is all from memory of my studies over 3 years ago, so don't flame me if im wrong!
    B
  • The "offset" cuts accuracy to something less than a quarter mile, I think. Civilian GPS receivers counteract that to get us back within plus or minus 100 feet. That's plenty close for a handgrenade, let alone a nuke. I would also suggest that if you have the ability to build or steal a nuke, and a missile, you can make or steal a military GPS.

    When the military first announced their "selective availability", I thought that it was a remarkably stupid idea. The Russians would simply steal the plans for the military receivers, and the plans for the factory that made them, and then the US would give them a loan and technical assistance to build it, and so on. Over the years since, I think that the idea has proven itself to be at least as stupid as I thought. The only reason Congress hasn't been beseiged by a campaign to end selective availability is that it just doesn't matter; to us or to the terrorists. If the military moved to end it on their own, they'd have to admit they were wrong.

    Back to the topic at hand: I agree with you, barrage jamming would be tough to beat. But have you seen some of the recent adaptive filtering work? Pretty impressive stuff, and might make this a lot harder.

  • It's not spread spectrum.

    The L1 frequency (1575.42 MHz) carries the navigation message and the SPS code signals. The L2 frequency (1227.60 MHz) is used to measure the ionospheric delay by PPS equipped receivers.

    Three binary codes shift the L1 and/or L2 carrier phase.

    The C/A Code (Coarse Acquisition) modulates the L1 carrier phase. The C/A code is a repeating 1 MHz Pseudo Random Noise (PRN) Code. This noise-like code modulates the L1 carrier signal, "spreading" the spectrum over a 1 MHz bandwidth. The C/A code repeats every 1023 bits (one millisecond). There is a different C/A code PRN for each SV. GPS satellites are often identified by their PRN number, the unique identifier for each pseudo-random-noise code. The C/A code that modulates the L1 carrier is the basis for the civil SPS.

    The P-Code (Precise) modulates both the L1 and L2 carrier phases. The P-Code is a very long (seven days) 10 MHz PRN code. In the Anti-Spoofing (AS) mode of operation, the P-Code is encrypted into the Y-Code. The encrypted Y-Code requires a classified AS Module for each receiver channel and is for use only by authorized users with cryptographic keys. The P (Y)-Code is the basis for the PPS.

    The Navigation Message also modulates the L1-C/A code signal. The Navigation Message is a 50 Hz signal consisting of data bits that describe the GPS satellite orbits, clock corrections, and other system parameters.

  • It's not a secret--it's just not advertised alot.

    If I remember right, without the p-code, the accuracy is only about 100-200 meters, but with it, you can get to down around 1-2 meters. That's almost too accurate. I remember that there are even some satellites that are only available with the p-code, which is part of selective avbailability, even in peacetime.

    The military GPS also has averaging techniques, which takes the average of as many fixes you can take without moving the receiver.

    One problem with barrage jamming is that it is very rough on the transmitter. You need some way to cool off the transmitter, or it will overheat. It depends on the distance between the transmitter and the receiver and the jammer, but usually you have to jam with more power than the transmitter.

  • Process gain is basically the improvement in signal-to-noise ratio that can be had in exchange for letting your signal take up more space than Mr. Shannon says it needs.

    For example, Dixon's Spread Spectrum Systems [amazon.com] says that for FM/FSK signals with over-unity deviation ratios, the process gain is 3 * (maximum deviation^2). The S/N ratio for the narrowband information being transmitted is effectively improved by allowing it to occupy more spectrum space than necessary. This is why I have my microwave link [qsl.net] tweaked to chew up several dozen more MHz of prime 10-GHz real estate [qsl.net] that it probably really needs. :-)

    As I understand it, another way to think of process gain in the general case is in terms of jamming immunity; i.e., how much power is it going to require in order to use an uncorrelated transmitter to jam the channel.

    I'm sure there are different process-gain equations for various modulation mechanisms, but they are all going to boil down to the same basic idea: trading occupied BW for S/N.
  • IIRC, there were reports that during the Gulf war, all the GPS systems (including civilian units) suddenly became accurate to the 1cm resolution you speak of.
    This suggests the deliberate error is in the actual timing signals sent out and is controlled from the satellites, although this seems a little silly from the military's perspective.

    Can anyone verify this?
  • The site's in South Africa. Is it that, or the /. effect, causing it to load so slowly?

    Drop the commentary, and give us just the news! That way I wouldn't have to write the following piece of flamebait:

    It apparently cost these people $7,500 to build one of these devices. In mass production, the cost would be much less, perhaps down to $99 or so. Just think, anybody could walk into Fry's and pick up a box which could screw up aircraft navigation!
    ---

  • Actually, since the GPS is operated by the U.S. military, they're not the ones that would be so interested in the technology. I wonder if other countries such as China might want this technology in case they go to war with the U.S. The U.S. is the country that's going to lose out if this tech becomes available to certain nations.
  • By using different modulation/transmission techniques, one may be able to reduce the effect of stochiastic noise on the demodulation side. Take a look at the new cell/portable phones. There is a lot less static on those than there was 5 years ago. Transmissions are always battling the signal to noise ratio. Satelites have to worry about radiation, solar winds, coronal discharges and whatnot screwing up the transmissions. It may not be heroic to you, but to us ham radio freaks it sure is! I remember being in 3rd grade and writing "when I grow up I want to be a jam-proof satelite defending my carrier frequency from the evil-doers! :)

    Give them a break. Radios are only 50 years old. We've come a long way. Where would this world be if all these transmission that we rely upon went down 10 times a day?
  • Luddites were not scared of technology, although the word is often misused in this way. They were simply opposed to the humanistic changes that technology was bringing about.

    So they were opposed to the changes that were coming right? Since they hadn't come yet, these were imagined changes yeah? So when they imagined these changes, they were moved to disruptive and sometimes violent actions - not really a calm reaction.

    It does sound a lot like they were scared, really.

    To whit, if mobile phones had been available at the time, they would doubtless have used them as a tool for mobilising against the factory bosses.

    I guess they would have to leave the mobile phone factory for last then ;-)

  • Re:WHY?!?!?!?! (Score:3)

    by Anonymous Coward on Wednesday April 19, 2000 @06:39PM (#1122495)
    You're right about that 30 feet. With a nuclear device, I wouldn't be thinking 'oh, great, it's going to miss me by 50 feet'. At least, I probably wouldn't complete that thought. The military/government/TPTB put several limits on commercially available GPS units that render them useless on missiles. The first is an altitude limit of 60,000 feet. The other limit is a velocity limit (I don't know what it is.) Both of these limits are required on all GPS units sold, so that people can't use them for guidance systems. It is possible (I have access to one without the altitude limits) to get ONE of those limits waived, but it requred some governmental paperwork, and a very good reason. I would think it impossible to get one with both limits disabled, but I've never tried :).

  • Re:first post? (Score:3)

    by Anonymous Coward on Wednesday April 19, 2000 @06:08PM (#1122496)
    The first post in the United States was established by Benjamin Franklin in 1775 [usps.gov].

  • Correction (Score:3)

    by phil reed ( 626 ) on Thursday April 20, 2000 @12:39AM (#1122497) Homepage
    It's only 1 centimeter with post processing (the errors are made available the next day for correcting readings). The best that can be achieved immediately is 1-3 meter error, due to atmospheric affects.


    ...phil

  • slowly changing the offset (Score:3)

    by hawk ( 1151 ) <hawk@eyry.org> on Thursday April 20, 2000 @05:07AM (#1122498) Journal

    ahh, the possibilities.

    Bad guy launches missle relying on GPS.

    Change just a little to steer it. "Here, missle missle"

    A bit more. "C'mon, you're still drifting away."

    Finaly change: "THere you go. You're on target now. GO say 'Hi' to
    mommy . . ."

    And little Mikey the Missle, thinking that he has cleverly found D.C.,
    returns to his launcher in Bahgdad.

    :)

    hawk
  • Selective Availability was turned off during Desert Storm because the military didn't have enough of the special cryptographic GPS units and had to use consumer GPS units instead. Imagine some poor military officer hitting all of the boat stores and snapping up those things.

    Selective availability can be defeated using differential GPS. I got a Trimble dual differential receiver for a good price at a West Marine clearance sale, and my GPS reads out to a few meters uncertainty rather than 100 meters. Broadband jamming requires a whole lot of power and is thus less effective. Signal strength at any one frequency = power / bandwidth. GPS jamming is easier because there are a number of discrete frequencies. Military GPS uses spread spectrum with an undisclosed spreading sequence, so you must cover all frequencies in a wide band. It also uses tricks like processing gain to recover a usable signal in the presence of a lot of noise.

    Hm. Anyone have a simple explanation of processing gain? I'm not enough of an RF person.

    Thanks

    Bruce

  • Re:An obvious contradiction (Score:3)

    by hobbit ( 5915 ) on Wednesday April 19, 2000 @11:17PM (#1122500)

    Allow me to set the record straight.

    Luddites were not scared of technology, although the word is often misused in this way. They were simply opposed to the humanistic changes that technology was bringing about.

    To whit, if mobile phones had been available at the time, they would doubtless have used them as a tool for mobilising against the factory bosses.

    Without contradiction.

    Hamish

  • Re:Build a cellphone jammer and they will come (Score:3)

    by locust ( 6639 ) on Thursday April 20, 2000 @02:32AM (#1122501)
    I want something I can use in my car on the highway, possibly even directional so I can take out specific callers. It be great, but consider the driver weaving and cursing as he or she tries to figure out why the signal has gone dead. The problem with cell phones in cars isn't the fact that they exist, its that most people don't have hands free sets for them. As it is if you have people in the car you can and do talk to them, and for the most part when you need to concentrate on driving you fall silent. --locust

  • Build a cellphone jammer and they will come (Score:3)

    by coreman ( 8656 ) on Thursday April 20, 2000 @12:11AM (#1122502) Homepage
    I'd like a cellphone jammer so I could get the clueless drivers to pay more attention to the road than the phone and notepad. I know the Japanese have a device that has about a 150 meter range that they use in theaters but I want something I can use in my car on the highway, possibly even directional so I can take out specific callers. There's got to be a couple of hardware hackers out there that could throw a design out open source for some field trials 8^)

  • Re:Why (Score:3)

    by Robotech_Master ( 14247 ) on Wednesday April 19, 2000 @06:14PM (#1122503) Homepage Journal
    Why, so you can start a war between Britain and China and get the exclusive media rights [imdb.com], of course! I mean, why else?

  • About the offset... (Score:3)

    by brad.hill ( 21936 ) on Wednesday April 19, 2000 @06:44PM (#1122504)
    The offset is pretty much a dead issue.

    1: You can get differential GPS broadcasts now almost everywhere on the globe. You get a GPS receiver that picks up two signals: one from the satellites, and one from a ground base that knows its own location and broadcasts the difference between that and where the satellites tell it it is.

    2: Not only did they not increase the offset during Desert Storm- they turned it off completely! The military GPS units are expensive and were in short supply, so many soldiers were using civilian units from home to find their way in the desert.

    It's only a matter of time now before the offset is removed for good so the signals can be used for more accurate civilian tasks like surveying without all the expense to of the differential units or the expense to the military of their offset decoders.

    The really scary thing about this jamming is that commercial airliners are starting to use GPS signals for navigation and bad weather landing.

  • It's a secret plot by women! (Score:3)

    by sporty ( 27564 ) on Wednesday April 19, 2000 @07:25PM (#1122505) Homepage
    It's a secret plot by women to get men to put down these things and actually get men to get out of the car and ask directions... or at least look at the road signs.. </joke>

    ---

  • Re:What they don't tell you about GPS... (Score:3)

    by sbeitzel ( 33479 ) on Wednesday April 19, 2000 @10:20PM (#1122506) Homepage Journal
    (rockets can't be steered, missiles can)

    Excuse me? A rocket is simply a motor that generates thrust by hurling mass out the back. You can, too, steer a rocket: just point the exhaust nozzle in a different direction. A missile, on the other hand, is an object that is flying (has been hurled) through space (air, usually, but not necessarily) -- for instance, a spitwad is a missile (ballistic), as is a dart (ballistic), as is a Sidewinder (rocket powered). Some of these things are steerable and some of them aren't, but the words "rocket" and "missile" are not the appropriate ones to use to identify that distinction.

  • Why? Here's a coupla reasons... (Score:3)

    by costas ( 38724 ) on Wednesday April 19, 2000 @06:26PM (#1122507) Homepage
    GPS is so prevalent in the 'new', 'modern' battlefield that a device like this makes a lot of sense and I am sure that a lot of militaries have already built their own --or if not, they are starting up similar projects as we type...

    Just some potential uses of a GPS jammer: Handheld and dashboard-mounted GPS is used all the time in tanks/helicopters/ships and by troops in the field. In most cases (i.e. outside of the US) these are *commercial* grade GPS, not US Military-grade GPS --i.e. they will be much less resistant to jamming.

    The US Military, OTOH, has put so much faith into GPS, it's now using it to guide smart bombs and cruise missiles... so, you can see, the fact that the US Air Force itself has proven that it is feasible to jam GPS with COTS (commercial off-the-shelf) technology will be a HUGE deal to the defense planners of the world...

    Now, I am not a EE, much less a DSP/GPS specialist, but from my knowledge of the system I am guessing that: a) the system described above won't be much use against fast-moving airborne GPS (fighters), and b) US Military-grade GPS can be affected just as effectively --as I believe that the US Navy is using an encoded higher time-resolution signal to achieve more accurate measurements. But if the signal is jammed, encryption won't be much use, right?


    engineers never lie; we just approximate the truth.
  • as far as I understand, the error is mainly introduced into the altitude precision. this way civilians can get around, everyone knows where everything is, but no one can be certain they are going to be able to hit it if they launch a missile at it.

    Daniel

  • Surprised it hasn't happened earlier (Score:3)

    by CharBoy ( 100343 ) on Wednesday April 19, 2000 @06:07PM (#1122509) Homepage
    I'm quite surprised it took this long. I heard a rumor about 2 years ago that a GPS jamming device was available in Russia with a 30 mile radius.

    The NavSat network is a series of satellites w/ atomic clocks located in Geosynchronous orbit (so they hold steady above the equator) at over 20,000 miles distance. The timing pulses they send are low power, necessarilly so for them to last as long on their available power output.

    Anyone with knowledge of which frequencies are used and the abillity to transmit their own quasi timing pulses in a manner which would interfere with at least 12 possible sats over the horizon at once could make their own jammer for much less.

    It's easy to see that not many people are doing this, or GPS would be effectively knocked out in metro areas.

  • Re:WHY?!?!?!?! (Score:3)

    by CharBoy ( 100343 ) on Wednesday April 19, 2000 @06:13PM (#1122510) Homepage
    The Military can already jam or disable GPS at will. Part of the spec for GPS allows for them to disable or limit the civilian aspect of GPS during wartime and specific sorties.

    Remember, the NavSat spec allows for a loss of accuracy for civilian GPS units (eg, you can't get better then 30 foot reliable position) but allows for 1 centimeter resolution for military units which know how to defeat the deliberate error. It's probably a timing sequence that milspec units can alter for.

    What I've never understood about this is why. If it's to foil enemy cruise missles with civilian GPS units, 30 feet doesn't seem like that much of a difference for a nuke or large conventional explosive.

    You can defeat this deliberate error, btw, by using three GPS units arranged equidistant with special software which knows the exact relative positions of the three GPS receivers and compensates accordingly.

  • old news (Score:3)

    by Racer X ( 140445 ) on Wednesday April 19, 2000 @06:10PM (#1122511)
    Wow, this must be a record for old news on /. Anyone watching tv in the 80's knows that frequency jamming was perfected with the advent of knight rider's car, KITT. And it didn't take a team of U.S. engineers, either; it was single-handedly perfected by Bonnie in that roving semi.

  • That's why we are developing adaptive arrays (Score:3)

    by HuskyDog ( 143220 ) on Thursday April 20, 2000 @01:55AM (#1122512) Homepage
    Here in DERA [dera.gov.uk] we have known for many years that GPS is VERY easy to jam. This is not very surprising realy. Any jammer is likely to be much closer to the receiver than the satellites are, plus, since the satellites run off solar power there is a serious limit to their own transmit power. It is no secret at all that an aircraft transmitting only a few watts can disable all GPS receivers (including the military ones) for many miles. There was an article about this in Aviation Week & Space Technology several years ago. The problem is not how to make a jammer, but how to get it close to the enemy and keep it there. This leads to numerous wacky schemes involving unmanned aircraft, parachutes, balloons etc.

    The only anti-jam feature on most current GPS systems is the spread spectrum modulation. This is a complex topic in communications engineering and I realy don't have room to explain it in detail. However, the nub is that the signal is mixed with a high speed pseudo-random bit stream. This greatly increases its bandwidth (which BTW in this case does not provide any inherent signal to noise advantage) and causes the energy/Hz to drop below the thermal noise level. The receiver generates an identicle bit stream synchronised with the one on the satellite, but offset by the delay between satellite and receiver (this synchronisations is what's going on whilst your receiver is acquiring). When the second bit stream is combined with the signal from the satellite the energy is "de-spread" and basically gets piled back up into a narrow spike again. The inportant point is that any other signal will not correlate with the bit stream in the receiver. A wide band jammer stays wide-band and a narrow band jammer gets spread. In either case the recovered spike now sticks up above the jammer power. Generating a signal spread in the same way as that from the satellite doesn't help unless you can arrange for it to arrive at the receiver in exact synchronism, and to do this you need to know the exact distance between your jammer and the receiver. BTW, this pallaver is not just done for jam resistance, the synchronised bit stream is a critical part of the navigation solution. If anyone knows of an explanation of the above with diagrams, I suspect that many readers who are not RF engineers would find it useful.

    Unfortunately, the above scheme only gives you a spreading gain of about 100. I.E. if your jammer is 100 times louder than the satellite then you still win. Since the satellites are a long was away, this is very easy to achieve.

    One solution being actively persued by me and my colleagues in DERA's airborne antennas group and presumably the military research labs of other nations is the use of adaptive antennas. I won't even begin to try and explain how these work, but the bottom line is that by using several antennas combined via some clever electronics one can form nulls in the combined antenna pattern which point at the jammers. This makes the job of the jammer significantly more difficult, but not impossible.

    BTW, there is nothing secret in the above. One of our industrial partners exhibited a prototype adaptive GPS antenna at the Farnborough Air Show at least 4 and possibly 6 years ago. Also, as might be expected, most current work in adaptive antennas is aimed at using them to defeat multi-path problems in mobile communications.

  • Set them up in national parks. PLEASE! (Score:4)

    by Anonymous Coward on Wednesday April 19, 2000 @06:20PM (#1122513)

    Everytime I take off a few days from my demanding job in the Valley, I like to head off to places like Yosimite and Yellowstone. But each month it seems that there are more and more untrained yuppies, grinding up the roads with their SUVs, displaying their designer hiking outfits (Tommy Hilfiger backpacks, anyone), and *always* carrying a GPS.

    Granted, most of them have no idea how to actually *use* a GPS, or how to coordinate it with a map, but a few manage to figure it out if they haven't succumbed to heat stroke after the first mile or so (apparently they believe that there are Starbucks's scattered every 100 feet, just like in Manhattan). Having conquered the navigation system, they feel supremely condfident, and stride forward in their fashionable Donna Karan outdoorwear. But just sit back, and in a few hours, after wandering a few yards off the path, those newbies will be crying for help, and they expect the rangers to spend their time to go off and rescue them! How absurd! It is the *user's* job to be prepared, not the staff. Why won't they learn? The last thing we need is to devote our time, as a community, to digging these helpless newbies out of a trench they've buried themselves in. If you want to enter *our* territory, you better do it on *our* rules, pal.

  • For Luddite Guerrillas Only (Score:4)

    by greenplato ( 23083 ) on Wednesday April 19, 2000 @06:12PM (#1122514)

    I have this friend that has a navagation system in his truck. It's a nice system, between the GPS and a CD map of the east coast he is able to get just about anywhere.

    But he uses it to get everywhere. He punches in the address for the grocery store (a mile away) and then punches in the address for back home. Maybe the novelty of a $3000 toy wears off slowly, maybe he is really that bad with directions.

    For some reason the thought of wacked-out luddite guerrillas jamming his satellite signal on his way home from the corner market really cracks me up. I can just see him driving aimlessly for hours waiting for the navigation system to tell him when to turn.

    Man-oh-man, a GPS jammer is a toy that may not lose it's novelty for a while....

  • Re:Why? Here's a coupla reasons... (Score:5)

    by drix ( 4602 ) on Wednesday April 19, 2000 @08:56PM (#1122515) Homepage
    RF jamming is hardly a new technology, and the people who came up with GPS aren't stupid. This possibility has without a doubt already been considered and dealt with - give them a little credit here. Jamming a spread-spectrum carrier means using a broadband jammer, which is expensive, sucks a lot of power, generates tons of heat, and has a paltry range. Even a theater-based GPS jammer would be inconcievable; barring a massive technological investment, at most only a small portion of the theater could be jammed (realistically). Also, neither smart bombs nor cruise missiles are solely reliant on GPS.

    --

  • Heroically Resistant to Jamming? (Score:5)

    by Zarf ( 5735 ) on Wednesday April 19, 2000 @06:07PM (#1122516) Journal

    [it is] believed that the latest generation of global communications satellites would be immune to similar home-built equipment, as they are "heroically resistant to jamming"

    What does Heroically Resistant mean? I can see this satellite in orbit straining: must resist jamming! grr! ... must get signal through!

    It must be wonderful to be so naive that you trust technology to be heroic.

    - // Zarf //

  • Re:What they don't tell you about GPS... (Score:5)

    by hpa ( 7948 ) on Wednesday April 19, 2000 @06:26PM (#1122517) Homepage
    Actually, this isn't any kind of secret at all.

    GPS contains the following capabilities:

    Selective Availability adds some noise to the signal received by civilian receivers; military receivers can tune this one out using a specific cryptographic key. Selective Availability was actually turned off during Desert Storm, because the U.S. military didn't have enough "military" receivers for their troops!

    Anti-Spoofing makes it cryptographically impossible to give a bogus signal to a military receiver.

    The P code (P for Precision) gives very high precision to certain military receivers which have been equipped with receivers for the P code signal, in addition to the regular (CA, for Coarse Aquisition) code. The P code is not receivable by civilian receivers.

    The GPS signal is jam resistant by being spread spectrum, but as the poster points out, there isn't any defense against wideband ("barrage") jamming.

  • What they don't tell you about GPS... (Score:5)

    by razvedchik ( 107358 ) on Wednesday April 19, 2000 @06:13PM (#1122518)
    The GPS signal coming from the sattelite has a deliberate offset so that they are never 100% accurate. This is because any moron with a steerable missile (rockets can't be steered, missiles can) that can carry a nuclear bomb can wire up a GPS as a precision-guidance system to deliver this missile very accurately.

    In time of war, the offset increases dramatically, though supposedly that didn't happen during Desert Storm. I think it has something to do with the GPS capabilities of the enemy.

    The military GPS was designed with anti-spoofing (just like IP spoofing) and anti-jamming (I think it dynamically changes frequencies, but not sure) capabilities, but these are not built into the civilian models.

    The military GPS can be given a cryptological key that significantly increases the accuracy and enables all the other Electronics Counter-Countermeasures (ECCM--Electonic Countermeasures, or ECM, is what normal people call jamming, ECCM is what you do to combat ECM).

    Of course, once you start barrage jamming (blocking out the entire radio spectrum), all bets are off. Nothing can make it through barrage jamming.

Slashdot Top Deals

Brain off-line, please wait.

Close