Do you have any idea how many existing laws you'd break by shooting down one of these over a populated area? Last I checked the unsafe discharge of a firearm, destruction of government property, and public endangerment are all illegal in most cities/states.
Just do it the Soviet way: the best defense against a tank is a better tank.
How much monofilament would it take to disable a drone in flight? I have always wanted a reason to apply my embedded design and programming skills to flight and fighting a lost cause.
I took "Higher frequencies allow for MIMO communications . . . You can't pull off MIMO in the 700 MHz spectrum . .." in your original post to mean that there was some technical reason MIMO would not work in the 700 MHz band. I was thinking that something changes enough in the multipath characteristics to preclude MIMO.
My own experiences with multipath and fading (I used to do a lot of VHF and UHF transmitter hunting with my own equipment) lead me to believe operation down to almost 6 meters would be possible with a lower limit of 2 meters for anything except rather large and unwieldy antenna arrays. My estimate is that 700 MHz is about the lowest frequency where a portable but fixed or mobile antenna would be acceptable.
The UHF channels used on your television (most households in the USA have some cable or Satellite feed so don't use broadcast television really) have a small amount of bandwidth between each. If you combined that bandwidth with multiple radio links or some transmission technique, you could use it for WiFi like services locally in the home. The strength of signal could be such that it wouldn't interfere with neighbors reception ( as most aren't using broadcast television anyway) and it gives out more spectrum for home use.
Even well designed and built RF receivers can suffer problems from limited selectivity and consumer equipment is far from that. The guard bands between channels serve a real purpose.
I am not particularly fond of MIMO but what precludes its use at 700 MHz? The 1/4 wave distance is about 4.2 inches so it would be inconvenient for most mobile devices but not for fixed installations.
My response would be based on an apocryphal story about a homemaker who wrote a similar letter of outrage to Quaker Oats expressing her displeasure after finding weevils in her newly opened cylinder of oats. She received a copy of her original letter stamped:
eSATA combined with port multiplication looks promising for external hard drive cabinets but what would preclude using link aggregation to combine multiple gigabit ethernet ports?
If the cheapo companies leave it out, the inductive ballast will have a power factor of 0.5, and the power company will have to generate twice as much power as the lamp uses.
It is not quite that bad. A low power factor increase the generation and transmission losses in the same way that a poor SWR in an RF transmission line does. Losses are proportional to the square of the line current.
RF antenna impedance matching can be done from the generator side by using low loss transmission line although the high SWR (low power factor) can cause insulation breakdown or arcing if the standing wave voltage get high enough. The same technique is sometimes used in AC power distribution by adding capacitive or inductive reactance at discrete locations in the distribution system. Free running synchronous motors are often used in place of inductors or capacitors.
I often wondered what is stopping a mesh network from spreading. It would be basically the type which the OLPC has, except essentially a router with an antenna could be put on top of your house and connect with others of its type, from spreading.
I have done a little work on this problem over the years and I suspect there is just a lack of all the necessary pieces for a good high performance mesh network solution. Here are some ideas off the top of my head while ignoring economic and political reasons:
1. Current radio hardware and band allocations only support half-duplex communications. WiMax uses transmit and receive synchronization to lower the dead time and prevent collisions which helps but how do you synchronize an arbitrary number of half-duplex stations in a variable geometry environment without a significant loss of throughput?
2. How well does IP handle a constantly changing network topology with hidden nodes? I suspect overlaying IP onto a protocol specifically designed to handle routing in an adverse wireless environment would help. Every node should maintain an extensive situational awareness of its local routing environment to provide for instant failover and redundant routing.
3. QoS would require some type of sharing scheme that does not rely on the good intentions of every node. BitTorrent accomplishes this using Tit-for-Tat. IP accomplishes this by using flow control and assuming a largely benign network. While computationally expensive, I suspect some type of cryptography based token scheme would allow both trust metrics and something like a packet routing barter system. Notice that this automatically allows the client to assign priorities to different types of traffic while intermediate nodes can accept the client's word given enough trust.
Like I said, I would not worry too much about the cost of materials unless I was going into mass production or building something really big. I have used copper plated steel welding rod for prototypes which works well and is easy to solder but the eventual rusting always bothered me. Dilute HCl makes an excellent cleaner and flux for low temperature soldering on steel.:)
Be careful bending brass rods that are large in diameter. In some materials and in at least some brasses, it is very easy to cause so much work hardening and displacement in one bend that it will become fragile. For a 90 degree bend in thick material I would be tempted to cut at a 45 degree angle and silver solder it. I guess I lucked out in that all of my own designs used either circular or straight elements except for the impedance matching sections.
If that seems like nit-picking, well, it is. A couple of times I have gotten caught in the field with antenna failure do to unreliability when faced with real world conditions. For that reason, I tend to do things like use non-contaminating feed lines with teflon dielectrics (at least for the exposed part) and lower Q antenna designs which do not require as much dimensional (or electrical if it gets wet) stability for good performance.
I have seen longer lengths but normal is 36 inches which is good enough for 1/2 wave 2 meter elements supported in the center if the rod is 1/8 inch. Beyond that, elements would need auxiliary support anyway or a larger cross section. Copper may be expensive but the cost for the element material is pretty small compared to the rest of the structure and the time to build it unless you are doing something really simple. Pure copper or brass tend to be a little soft compared to bronze, steel, or stainless steel which are all relatively springy. Working with bronze rod is a lot like working with stainless steel except it is just soft enough to not put divots in your diagonal cutters.
Without specialized equipment, aluminum is very difficult to solder or weld. I only worked with it as a last resort when fixing existing antennas.
If you want to do without soldering it would be worth studying how good crimp connections are made. Wire wrap prototyping uses square posts and soft copper wire. When you wind the wire under tension around the post, the square edges of the post bite into the soft wire and the materials actually merge under deformation. When unwrapping the wire, you can feel each corner as it separates from the wire. Round posts will not work. That gives a good idea of the pressures and process involved in making a good crimp connection which can withstand real world mechanical stress and chemical attack.
The models are obviously made with wire. You have some leeway on cross-section. Clothes-hangar wire might work:-) Solid copper somewhere between 12 and 18 gauge is easier to work and has the mechanical stiffness you will need.
I have designed and built many different types of directional antennas (yagis, quads, circular element beams, colinear) that had to stand up to rough handling and the weather and my favorite material is still bronze rod made for brazing. Low temperature solder is actually notoriously poor for all but the weakest joints because of mechanical considerations but jeweler's silver solder, with about 50% silver, works fine even for butt joints.
you're not going to use an ID card with a picture that doesn't at least resemble you vaguely.
I remember stories about a man who did security testing at various government installations who had ID cards made with various pictures like Hitler, an orangutan, etc. To be fair however, some guards do take security seriously: a distracted scientist leaving LRL got shot in the leg while leaving when he inadvertently ignored the guard's request to show his badge as he walked out of the fenced area.
If our government was trustworthy and competent then I might believe national IDs would do more good then evil, and perhaps not even then.
Oddly enough, that will not work well for direct impacts although it might be worthwhile at sea level. If you add shielding around the chip and it is directly exposed to a cosmic ray event, the shielding just serves to create a shower of particles which then affect a much larger area and transfer much more energy.
Cosmic ray impacts can inject carriers into the substrate which is a detectable condition. In older processes and especially in CMOS processes that do not use well isolation based on an insulator, carrier injection into the substrate can cause problems from random bias changes to destructive SCR latchup. You can see this in some analog processes where multiple circuits share the same substrate when you overdrive an input or output pin forward biasing the protection diode injecting carriers into the substrate and causing very odd problems in seemingly unrelated areas of the chip.
Early radiation hardened processes avoided using junction isolation for this very reason. By avoiding it, they became much more resistant to single event upset.
I will lose my membership for not knowing this, but aren't there 11 channels (not sure how many non-overlapping channels though). How can 4 machines DoS every wifi channel when they aren't even doing anything!
In the US, the 2.4 GHz ISM band has 11 channels spaced 5 MHz apart. 802.11b and 802.11g require 25 MHz of separation to prevent interferance which limits the non overlapping channels to 1, 6, and 11. 802.11n and many 802.11g systems support double channel widths of 40 MHz which limits the 2.4 GHz ISM band to just one non overlapping channel.
The 5.0 GHz band used for 802.11a and for some 802.11n radios has 19 20 MHz channels alleviating much of the congestion problem at the expense of cost and using a higher frequency.
Switching power supply design becomes much more difficult when variable voltage ranges beyond 2:1 are involved. Wide range converters typically handle 4:1. Compromises have to be made if the power switching elements have to be rated for both high voltage and high current during different parts of the charge and discharge cycle.
Sealed electrolytic capacitors fail through bursting when the pressure inside becomes too great which is usually caused by too high a voltage. That does not have the characteristics of a dialectic failure in a high energy capacitor which happens much more quickly and is limited only by inductance. I have seen 1 x 1/2 inch aluminum bus bars used for connecting capacitor banks in high energy physics experiments with holes punched through them from when the capacitor bank shorted out. I have had my own glass plate capacitors short out and 0.1 microfarads at 15000 volts makes quite a bang.
Ultimately for car applications what is going to matter is discharge rate and recovery. If the capacitor bank completely discharges in an event then figure anything in current path is now molten. Any electrolyte will become a vapor. Don't the double layer carbon capacitors use sulphuric acid as an electrolyte?
AMD does however own the cache coherency protocol that they use over HyperTransport for processor to processor communication so Intel would either have to design their own or license AMD's implementation.
A lot of state gun control laws were passed to disarm various minorities and African descendant Americans with the thought that they would never apply to good upstanding white people. The specific ones that come to mind include limiting purchases to specific and expensive manufacturers and requiring letters from prominent citizens (bankers, store owners, etc.) attesting to the character of the purchaser which Missouri had until relatively recently. Later these laws were applied much more indiscriminately.
He makes a lot of sense in what he says. But he needs to learn that running a snowballs chance in hell campaign every 4 years where he only siphons away votes from the lesser of two evils doesn't help the country.
It is a good thing the Democrats have been advocating election method reform then to prevent the spoiler effect.
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Just do it the Soviet way: the best defense against a tank is a better tank.
How much monofilament would it take to disable a drone in flight? I have always wanted a reason to apply my embedded design and programming skills to flight and fighting a lost cause.
I took "Higher frequencies allow for MIMO communications . . . You can't pull off MIMO in the 700 MHz spectrum . . ." in your original post to mean that there was some technical reason MIMO would not work in the 700 MHz band. I was thinking that something changes enough in the multipath characteristics to preclude MIMO.
My own experiences with multipath and fading (I used to do a lot of VHF and UHF transmitter hunting with my own equipment) lead me to believe operation down to almost 6 meters would be possible with a lower limit of 2 meters for anything except rather large and unwieldy antenna arrays. My estimate is that 700 MHz is about the lowest frequency where a portable but fixed or mobile antenna would be acceptable.
Even well designed and built RF receivers can suffer problems from limited selectivity and consumer equipment is far from that. The guard bands between channels serve a real purpose.
I am not particularly fond of MIMO but what precludes its use at 700 MHz? The 1/4 wave distance is about 4.2 inches so it would be inconvenient for most mobile devices but not for fixed installations.
As obscure as this is likely to be, I have to use it:
."
"You can't eat flowers, . .
My response would be based on an apocryphal story about a homemaker who wrote a similar letter of outrage to Quaker Oats expressing her displeasure after finding weevils in her newly opened cylinder of oats. She received a copy of her original letter stamped:
Send this chick the bug letter.
eSATA combined with port multiplication looks promising for external hard drive cabinets but what would preclude using link aggregation to combine multiple gigabit ethernet ports?
It is not quite that bad. A low power factor increase the generation and transmission losses in the same way that a poor SWR in an RF transmission line does. Losses are proportional to the square of the line current.
RF antenna impedance matching can be done from the generator side by using low loss transmission line although the high SWR (low power factor) can cause insulation breakdown or arcing if the standing wave voltage get high enough. The same technique is sometimes used in AC power distribution by adding capacitive or inductive reactance at discrete locations in the distribution system. Free running synchronous motors are often used in place of inductors or capacitors.
People do not want to ruin a good thing. You can have sword fights with the tubes.
My amplifiers are connected to my speakers using Kelvin connections you insensitive clod!
I have done a little work on this problem over the years and I suspect there is just a lack of all the necessary pieces for a good high performance mesh network solution. Here are some ideas off the top of my head while ignoring economic and political reasons:
1. Current radio hardware and band allocations only support half-duplex communications. WiMax uses transmit and receive synchronization to lower the dead time and prevent collisions which helps but how do you synchronize an arbitrary number of half-duplex stations in a variable geometry environment without a significant loss of throughput?
2. How well does IP handle a constantly changing network topology with hidden nodes? I suspect overlaying IP onto a protocol specifically designed to handle routing in an adverse wireless environment would help. Every node should maintain an extensive situational awareness of its local routing environment to provide for instant failover and redundant routing.
3. QoS would require some type of sharing scheme that does not rely on the good intentions of every node. BitTorrent accomplishes this using Tit-for-Tat. IP accomplishes this by using flow control and assuming a largely benign network. While computationally expensive, I suspect some type of cryptography based token scheme would allow both trust metrics and something like a packet routing barter system. Notice that this automatically allows the client to assign priorities to different types of traffic while intermediate nodes can accept the client's word given enough trust.
Like I said, I would not worry too much about the cost of materials unless I was going into mass production or building something really big. I have used copper plated steel welding rod for prototypes which works well and is easy to solder but the eventual rusting always bothered me. Dilute HCl makes an excellent cleaner and flux for low temperature soldering on steel. :)
Be careful bending brass rods that are large in diameter. In some materials and in at least some brasses, it is very easy to cause so much work hardening and displacement in one bend that it will become fragile. For a 90 degree bend in thick material I would be tempted to cut at a 45 degree angle and silver solder it. I guess I lucked out in that all of my own designs used either circular or straight elements except for the impedance matching sections.
If that seems like nit-picking, well, it is. A couple of times I have gotten caught in the field with antenna failure do to unreliability when faced with real world conditions. For that reason, I tend to do things like use non-contaminating feed lines with teflon dielectrics (at least for the exposed part) and lower Q antenna designs which do not require as much dimensional (or electrical if it gets wet) stability for good performance.
How to jump to nuclear fusion based power from the stone age would be a good one.
I have seen longer lengths but normal is 36 inches which is good enough for 1/2 wave 2 meter elements supported in the center if the rod is 1/8 inch. Beyond that, elements would need auxiliary support anyway or a larger cross section. Copper may be expensive but the cost for the element material is pretty small compared to the rest of the structure and the time to build it unless you are doing something really simple. Pure copper or brass tend to be a little soft compared to bronze, steel, or stainless steel which are all relatively springy. Working with bronze rod is a lot like working with stainless steel except it is just soft enough to not put divots in your diagonal cutters.
Without specialized equipment, aluminum is very difficult to solder or weld. I only worked with it as a last resort when fixing existing antennas.
If you want to do without soldering it would be worth studying how good crimp connections are made. Wire wrap prototyping uses square posts and soft copper wire. When you wind the wire under tension around the post, the square edges of the post bite into the soft wire and the materials actually merge under deformation. When unwrapping the wire, you can feel each corner as it separates from the wire. Round posts will not work. That gives a good idea of the pressures and process involved in making a good crimp connection which can withstand real world mechanical stress and chemical attack.
I have designed and built many different types of directional antennas (yagis, quads, circular element beams, colinear) that had to stand up to rough handling and the weather and my favorite material is still bronze rod made for brazing. Low temperature solder is actually notoriously poor for all but the weakest joints because of mechanical considerations but jeweler's silver solder, with about 50% silver, works fine even for butt joints.
I remember stories about a man who did security testing at various government installations who had ID cards made with various pictures like Hitler, an orangutan, etc. To be fair however, some guards do take security seriously: a distracted scientist leaving LRL got shot in the leg while leaving when he inadvertently ignored the guard's request to show his badge as he walked out of the fenced area.
If our government was trustworthy and competent then I might believe national IDs would do more good then evil, and perhaps not even then.
Oddly enough, that will not work well for direct impacts although it might be worthwhile at sea level. If you add shielding around the chip and it is directly exposed to a cosmic ray event, the shielding just serves to create a shower of particles which then affect a much larger area and transfer much more energy.
Cosmic ray impacts can inject carriers into the substrate which is a detectable condition. In older processes and especially in CMOS processes that do not use well isolation based on an insulator, carrier injection into the substrate can cause problems from random bias changes to destructive SCR latchup. You can see this in some analog processes where multiple circuits share the same substrate when you overdrive an input or output pin forward biasing the protection diode injecting carriers into the substrate and causing very odd problems in seemingly unrelated areas of the chip.
Early radiation hardened processes avoided using junction isolation for this very reason. By avoiding it, they became much more resistant to single event upset.
In the US, the 2.4 GHz ISM band has 11 channels spaced 5 MHz apart. 802.11b and 802.11g require 25 MHz of separation to prevent interferance which limits the non overlapping channels to 1, 6, and 11. 802.11n and many 802.11g systems support double channel widths of 40 MHz which limits the 2.4 GHz ISM band to just one non overlapping channel.
The 5.0 GHz band used for 802.11a and for some 802.11n radios has 19 20 MHz channels alleviating much of the congestion problem at the expense of cost and using a higher frequency.
http://en.wikipedia.org/wiki/List_of_WLAN_channels
Switching power supply design becomes much more difficult when variable voltage ranges beyond 2:1 are involved. Wide range converters typically handle 4:1. Compromises have to be made if the power switching elements have to be rated for both high voltage and high current during different parts of the charge and discharge cycle.
Sealed electrolytic capacitors fail through bursting when the pressure inside becomes too great which is usually caused by too high a voltage. That does not have the characteristics of a dialectic failure in a high energy capacitor which happens much more quickly and is limited only by inductance. I have seen 1 x 1/2 inch aluminum bus bars used for connecting capacitor banks in high energy physics experiments with holes punched through them from when the capacitor bank shorted out. I have had my own glass plate capacitors short out and 0.1 microfarads at 15000 volts makes quite a bang.
Ultimately for car applications what is going to matter is discharge rate and recovery. If the capacitor bank completely discharges in an event then figure anything in current path is now molten. Any electrolyte will become a vapor. Don't the double layer carbon capacitors use sulphuric acid as an electrolyte?
Since CBC mode is sequential, why not use CTR mode to allow both random access and resistance to replay or even better, use ESSIV?
AMD does however own the cache coherency protocol that they use over HyperTransport for processor to processor communication so Intel would either have to design their own or license AMD's implementation.
A lot of state gun control laws were passed to disarm various minorities and African descendant Americans with the thought that they would never apply to good upstanding white people. The specific ones that come to mind include limiting purchases to specific and expensive manufacturers and requiring letters from prominent citizens (bankers, store owners, etc.) attesting to the character of the purchaser which Missouri had until relatively recently. Later these laws were applied much more indiscriminately.
It is a good thing the Democrats have been advocating election method reform then to prevent the spoiler effect.