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#61
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"Thomas Schoene" wrote in message k.net...
"Kevin Brooks" wrote in message om Think of it as another system using the same concept as current spaced armor and ceramic composites, which also hinge upon diffusing the jet over a larger area, a;beit one with extremely fine tolerances for successful initiation. As I understand it, the system actually self-initiates -- the plasma jet actually bridged the gap and shorts out the capacitor on impact. No timing mechanism required. OK, I can see where that would complete the circuit, though now you are left with a plate capacitor with a hole in one plate, if I am understanding this properly--how well is it going to work a second time? How much power is required? How are other systems to be protected from your own protective capacitance discharge? Sorry, but this does not sound like the most promising of developments against the HEAT round, and I can't see how it would be that effective against a kinetic round, so is this another wonderful research project that sees little opportunity of realistic fielding? Again, you seem to have the defeat mechanism wrong, from the way I read it. And pray tell what this wonderful system does to a shaped charge using a non-conducting liner (glass (which is a liquid in its customary "solid" state, as we know it...) is a not uncommon alternate liner in place of the usual copper)? In the very heated, very compressed sonditions of a shaped charge plasma jet, I suspect you'll find that even glass is conductive. Mea culpa. You are right, Tom; I was a bit surprised to find that this is true for glass, which apparently has some level of sodium in its structure. Brooks |
#62
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On 22 Sep 2003 18:23:29 -0700, Kevin Brooks wrote:
And just as usual, the accuracy of computer simulations of tactical ground fights is strongly suspect. Garbage in, garbage out. No, not so much GIGO as it is a matter of the goals of the simulation, which is usually to stress the side being exercised. That retired USMC GO who ran the JFC exercise last year was whining about how he could not conduct true "free play", and that certain actions of his were rescinded by the exercise controllers, but that ignored the fact that the game had for one of its primary goals, for example, the validation of the IBCT/SBCT as a tool for the JTF commander--sliming the APOD that was to serve that unit might be a "real world" thing to consider, Care to "de-jargonize" that? I get the general gist, just not the details. -- "It's easier to find people online who openly support the KKK than people who openly support the RIAA" -- comment on Wikipedia |
#63
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(I'm not an electronic engineer, so I've cross-posted this to some
newsgroups which might be able to give informed comment on a number of points.) On 23 Sep 2003 05:51:41 -0700, Kevin Brooks wrote: (phil hunt) wrote in message ... [regarding battlefield internet] The signal must be such that the extended receiver can hear it. So others can too, in principle. (Though detecting the signal and knowing where it's from aren't the same thing). I'm not a radio engineer but I can imagine a few ways how direction-finding might work; for example place two (or 3) detectors a few meters apart and calculate the time delay between each one receiving the signal. No. Paul is correct, DF'ing a "frequency agile" (or "hopping") transmitter is no easy task. For example, the standard US SINCGARS radio changes frequencies about one hundred times per *second*, Bear in mind that I'm talking about automated electronic gear here, not manual intervention. Electronics works in time spans a lot quicker than 10 ms. over a pretty wide band of freq's (this is why synchronization of the radios on a time basis is critical to succesful operation of the net). So the frequency changes are pre-determined on a time basis? If there is a radio receiver, is it better able to detect/deceive a signal whgen it knows the frequency in advance? Or can it "sniff" for lots of frequencies at a time and pick out what looks interesting? If two receivers, placed say 10 m aparet, both pick up a signal, how accurately can the time difference between the repetion of both signals be calculated? Light moves 30 cm in 1 ns, so if time differences can be calculated to an accuracy of 0.1 ns, then direction could be resolved to an accuracy of 3 cm/10 m ~= 3 mrad. Alternately, would something like a pinhole camera work? What I mean here is: imagine a cubic metal box, 1 m on its side, with a vertical slit, about 1 cm wide down one of its vertical faces. On the opposite face, there are detectors for detecting radio waves. If the elevctromatnetic ratiation coming into the box can only go in through the slit, and goes in a straight line, then knowing which detectors are lit up would allow someone to tell where the radiation was coming from. It may be that, depending on the wavelength, the incoming radiation would be diffracted by the slit and would get spread all over the detectors. If this is the case, perehaps multiple slits could be used, and the diffraction pattern would differ dependent on the angle with which the radiation strikes the slitted face? (because the radation at each slit would be out-of-phase with the radiation at other slits). Has anything like this been tried? It is hard enough for the average "rest of the world" intel unit to DF an old fashioned non-hopping transmitter if the radio operator uses good RTO procedures--trying to pluck enough of these random fractional-second bursts out of the ether to determine a direction is more difficult by a few orders of magnitude. What methods are used to do DF? -- "It's easier to find people online who openly support the KKK than people who openly support the RIAA" -- comment on Wikipedia |
#64
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"Kevin Brooks" wrote in message om... "Thomas Schoene" wrote in message k.net... "Kevin Brooks" wrote in message om Think of it as another system using the same concept as current spaced armor and ceramic composites, which also hinge upon diffusing the jet over a larger area, a;beit one with extremely fine tolerances for successful initiation. As I understand it, the system actually self-initiates -- the plasma jet actually bridged the gap and shorts out the capacitor on impact. No timing mechanism required. OK, I can see where that would complete the circuit, though now you are left with a plate capacitor with a hole in one plate, if I am understanding this properly--how well is it going to work a second time? How much power is required? How are other systems to be protected from your own protective capacitance discharge? Sorry, but this does not sound like the most promising of developments against the HEAT round, and I can't see how it would be that effective against a kinetic round, so is this another wonderful research project that sees little opportunity of realistic fielding? It seems far-fetched to me as well although for long rod rounds. I went back and re-read the article and the jet "is virtually instantaneously dispersed by the high temperatures and powerful fields generated by a pulsed power system carried by the vehicle". A Warrior was used as the testbed and it was subjected to multiple attacks with no major damage. As far as holes in the capacitor are concerned, an enemy may have difficulty hitting the same spot twice. I would have said "unlikely" except last week's AwWeek mentioned that two JASSMs hit the same spot in rapid succession without benefit of a LASER spot. If the optical tracker used for precision targeting for JASSM can do that, a similar seeker can do that for ATGMs. Which also means "let reactive armor designers beware". Power apparently isn't a problem. The IDR article says that the electrical load is "no more arduous than starting the engine on a cold morning" If you're interested, the (brief) description is found in the current IDR (September) on page 55. |
#65
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#66
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#67
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"phil hunt" wrote in message . .. So the frequency changes are pre-determined on a time basis? Oh yea. If there is a radio receiver, is it better able to detect/deceive a signal whgen it knows the frequency in advance? Or can it "sniff" for lots of frequencies at a time and pick out what looks interesting? Both. To "sniff" takes the time needed for a bunch of transmitted cycles to come through so the receiver can determine it's not random noise. The receiver for a hopper *assumes* there is a signal in the expected slot and integrates it into a bigger signal for the rest of the system. If two receivers, placed say 10 m aparet, both pick up a signal, how accurately can the time difference between the repetion of both signals be calculated? Light moves 30 cm in 1 ns, so if time differences can be calculated to an accuracy of 0.1 ns, then direction could be resolved to an accuracy of 3 cm/10 m ~= 3 mrad. Measuring the time difference between reception by two antennas yields a curve (all points such that the distance between the two antennas and the point is a constant). Add another antenna and the possible transmitter locations are the points where the curves cross; by doing the A-B, B-C and A-C comparison you should have a single point left. If your antennas are too close together the curves stay in proximity to each other so long you don't have the angular resolution to get a good fix. You can measure the angles quite accurately by using multiple directional antennas and measuring the phase & amplitude differences. Alternately, would something like a pinhole camera work? What I mean here is: imagine a cubic metal box, 1 m on its side, with a vertical slit, about 1 cm wide down one of its vertical faces. On the opposite face, there are detectors for detecting radio waves. If the elevctromatnetic ratiation coming into the box can only go in through the slit, and goes in a straight line, then knowing which detectors are lit up would allow someone to tell where the radiation was coming from. It may be that, depending on the wavelength, the incoming radiation would be diffracted by the slit and would get spread all over the detectors. If this is the case, It all most certainly will defract. perehaps multiple slits could be used, and the diffraction pattern would differ dependent on the angle with which the radiation strikes the slitted face? (because the radation at each slit would be out-of-phase with the radiation at other slits). Has anything like this been tried? Sounds good, unfortunately your detectors hung on the wall still have that problem with determining a short burst signal is really there and not random noise. There's also the problem with which slice of the spectrum they are listing too at any one time. There are ways to do the listing with a really wide band but they require boat loads of processing that's not done real time and none I'm aware of preserve the phase information for DFing. |
#68
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In message , phil hunt
writes On 23 Sep 2003 11:22:50 -0700, Kevin Brooks wrote: this does not sound like the most promising of developments against the HEAT round, and I can't see how it would be that effective against a kinetic round, so is this another wonderful research project that sees little opportunity of realistic fielding? Sounds a bit like a waste of money to me. Perhaps the MoD should be more concerned with making sure British soldiers have rifles and radios that work. *Still* waiting on Bowman, but PRR works really well at unit level. As for L85/L86, after such a shrill whine the silence is suddenly deafening. Where _are_ all those stories about British soldiers doomed to death by their flawed faulty useless rifles? Did the rifles actually *work*? How embarrassing! What will people complain about now? -- When you have to kill a man, it costs nothing to be polite. W S Churchill Paul J. Adam MainBoxatjrwlynch[dot]demon{dot}co(.)uk |
#69
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On 23 Sep 2003 20:00:32 -0700, Kevin Brooks wrote:
No. Paul is correct, DF'ing a "frequency agile" (or "hopping") transmitter is no easy task. For example, the standard US SINCGARS radio changes frequencies about one hundred times per *second*, Bear in mind that I'm talking about automated electronic gear here, not manual intervention. Electronics works in time spans a lot quicker than 10 ms. So what? Unless you know the frequency hopping plan ahead of time (something that is rather closely guarded), you can't capture enough of the transmission to do you any good--they use a rather broad spectrum. OK, I now understand that DF generally relies on knowing the frequency in advance. BTW, when you say a rather broad spectrum, how broad? And divided into how many bands, roughly? Both radios have to be loaded with the same frequency hopping (FH) plan, and then they have to be synchronized by time. When SINGCARS first came out the time synch had to be done by having the net control station (NCS) perform periodic radio checks (each time your radio "talked" to the NCS, it resynchronized to the NCS time hack); failure to do this could result in the net "splitting", with some of your radios on one hack, and the rest on another, meaning the two could not talk to each other. I believe that the newer versions (known as SINCGARS EPLRS, for enhanced precision location system) may use GPS time data, ensuring that everyone is always on the same time scale. That would make sense. If two receivers, placed say 10 m aparet, both pick up a signal, how accurately can the time difference between the repetion of both signals be calculated? Light moves 30 cm in 1 ns, so if time differences can be calculated to an accuracy of 0.1 ns, then direction could be resolved to an accuracy of 3 cm/10 m ~= 3 mrad. The fact is that the direction finding (DF'ing) of frequency agile commo equipment is extremely difficult for the best of the world's intel folks, and darned near impossible for the rest (which is most of the rest of the world); that is why US radio procedures are a bit more relaxed than they used to be before the advent of FH, back when we tried to keep our transmissions to no more than five seconds at a time with lots of "breaks" in long messages to make DF'ing more difficult. So transmissions of 5 seconds tend to be hard to DF? Of course, with the battlefield internet, a text transmission will typically be a lot less than 5 s (assuming the same bandwidth as for a voice transmission, i.e. somewhere in the region of 20-60 kbit/s). transmissions still very clear), and the use of FH combined with crypto key makes it darned near impossible for the bad guy to decypher it in any realistic timely manner. Modern crypto is good enough to withstand all cryptanalytic attacks. -- "It's easier to find people online who openly support the KKK than people who openly support the RIAA" -- comment on Wikipedia |
#70
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On Wed, 24 Sep 2003 21:32:39 +0100, Paul J. Adam wrote:
In message , phil hunt writes On 23 Sep 2003 11:22:50 -0700, Kevin Brooks wrote: this does not sound like the most promising of developments against the HEAT round, and I can't see how it would be that effective against a kinetic round, so is this another wonderful research project that sees little opportunity of realistic fielding? Sounds a bit like a waste of money to me. Perhaps the MoD should be more concerned with making sure British soldiers have rifles and radios that work. *Still* waiting on Bowman, but PRR works really well at unit level. I heared the army had radio problems in Kosovo -- don't know which model of radio. As for L85/L86, after such a shrill whine the silence is suddenly deafening. Where _are_ all those stories about British soldiers doomed to death by their flawed faulty useless rifles? Did the rifles actually *work*? Oh, the rifles, have always worked... it's just they were prone to not working if they got dirty. If I'd been the MoD, I'd have specified burying them in sand overnight then firing them as part of the acceptance tests. -- "It's easier to find people online who openly support the KKK than people who openly support the RIAA" -- comment on Wikipedia |
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