|
Reception of radiosignals inside a Faradaycage is limited to frequencies
that are smaller then the holes in the cage. "Geoff Glave" schreef in bericht news:HxHud.9448$eb3.8331@clgrps13... Any explanation for this? FM radio generally operates at longer range than AM radio, however it's limited to line-of-sight. However, when you're 40,000 feet up you can "see" a lot of transmitters hence the FM signals. Cheers, Geoff Glave Vancouver, Canada |
"Some Guy" wrote in message ... You guys are acting as if the engines and flight control surfaces of an aircraft are intimately tied to the plane's radio receiver, and the slightest odd or out-of-place signal that it receives is enough to send any plane into a tail spin. Not at all; however, there IS obviously a connection between various flight control functions (such as, say, the autopilot) and the information given by the avionics (esp. "nav" radios using ground-based sources such as VORs, etc.). It's not going to "send any plane into a tail spin", but it can certainly cause some problems. All this while the air travel industry is considering allowing passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT by adding cell-phone relay stations to the planes and allowing any such calls to be completed via satellite. So I guess the feeble radiation by my FM radio (powered by 2 AAA batteries) is enough to cause a plane to dive into the ocean, but the guy next to me putting out 3 watts of near-microwave energy is totally safe. You DO realize that these are on very different frequencies, and that the emissions of an FM superheterodyne radio are very likely to fall right in the aviation band, don't you? Hint: if you have to go look up "superheterodyne" to understand this question, I have serious doubts regarding your qualifications to comment on it. Getting back to the original question (poor to non-existant AM reception), I understand the idea of aperature and long wavelenths of AM radio and the size of airplane windows - but what about the effect of ALL the windows on a plane? Don't they create a much larger effective apperature when you consider all of them? No. It's not the TOTAL area of the "apperatures" [sic] that is important, it's the size of the individual openings. If this were not so, then a conductive mesh could never be effective as a shield. And since the plane isin't grounded, isin't the exterior shell of a plane essentially transparent to all RF (ie it's just a re-radiator) because it's not at ground potential? No. "Ground potential" has absolutely nothing to do with it. Hint: what do you think is the RF environment within a perfectly conducting sealed enclosure, with respect to outside sources, even if that enclosure is completely isolated from any other surface or conductor? Bob M. (KC0EW) |
"Charles Newman" . on.sight wrote in message ... What is a Pitot tube anyway? I have seen a switch for most aircraft in Flight Simulator marked "Pitot Heat", what is that? A pitot tube is a tube which protrudes from the aircraft body into the path of the air through which the aircraft is flying. They are used for such things as determining airspeed (which is the speed of the aircraft through the air, not over the ground), and in some meteorological conditions are prone to becoming clogged with ice. Hence, "pitot heat" is just that - the switch in question controls a heater (most often, electric) built into the pitot tube, which keeps in clear of ice. Losing pitot pressure due to having the damn thing plugged up is generally considered a Bad Thing, and unfortunate events have been known to follow such an occurence. Bob M. |
cabin. But has anybody ever heard a cabin announcement during flight
to turn off any devices? Fred F. There have been numerous postings in various scanner, shortwave and ham groups by people who have been ordered to turn off their radio and other PEDs. More than one person has been ordered off, or met by the authorities on landing and at least one passenger who refused to turn off a cellphone ended up with some jail time after landing in the U.K. - it was pretty widely reported a year or so ago. Dave |
My world is as an instrument rated pilot and one who services aircraft avionics. And you must have missed my other post where I said PEDs should be off at all times. Fred F. The I presume you specified AM because the LO operates outside aviation frequencies (now that LORAN A is gone), unlike the LO in an FM broadcast receiver which covers the VHF localizer and VOR frequencies very nicely. Dave |
All this while the air travel industry is considering allowing passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT by adding cell-phone relay stations to the planes and allowing any such calls to be completed via satellite. So I guess the feeble radiation by my FM radio (powered by 2 AAA batteries) is enough to cause a plane to dive into the ocean, but the guy next to me putting out 3 watts of near-microwave energy is totally safe. I can't provide technical details of the operation because I don't know them; but I am familiar with a number of totally RF screened environments where use of electronic devices are tightly controlled. However, internal relays are used to permit operation of cell phones - which I always understood were specific models which had been certified for such use. Dave |
Dave Holford wrote:
All this while the air travel industry is considering allowing passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT by adding cell-phone relay stations to the planes I am familiar with a number of totally RF screened environments where use of electronic devices are tightly controlled. However, internal relays are used to permit operation of cell phones The point was not how the planes are being equipped to handle in-flight cell-phone use. The point was that consideration is being made to allow cell phones to be used while the planes are in flight. That intentional radiating PED's are even being considered for in-flight use when so much hype and concern is being given to the weak radiation potential of some non-intentional radiators like am/fm radios. BTW, what is the potential of the local oscillators of small hand-held LCD-screen TV's to overlap with aviation frequencies? |
On the way back, I spoke with a commercial pilot who was deadheading, on this issue. He said that it's not all that unusual to hear radio interference once they have allowed the devices on, but when they are in cruise, they aren't normally doing any urgent communications, so it isn't much of an issue. If something comes up, then they will pass the word to shut down the PEDs. On takeoff and landing though, the comms are much more rapid, and the consequences of missing one transmission are much higher. They need to hear all the comms, not just between themselves and the tower, but what the other pilots are saying as well. Add to this, the fact that aircraft comms are AM, which is inherently muddy, and it's easy to see why they take the extra precautions. |
"Some Guy" wrote in message ... The point was that consideration is being made to allow cell phones to be used while the planes are in flight. That intentional radiating PED's are even being considered for in-flight use when so much hype and concern is being given to the weak radiation potential of some non-intentional radiators like am/fm radios. Because, as has already been pointed out, of the differences in emission characteristics (and specifically the frequency ranges likely to be affected) of the two classes of devices. BTW, what is the potential of the local oscillators of small hand-held LCD-screen TV's to overlap with aviation frequencies? I believe they should be somewhat less than is the case with an FM receiver, but they're still a bad idea for the same reason. Note that the analysis of the likely frequencies provided so far has dealt solely with the first-order effects of the receiver's local oscillator; we have NOT discussed harmonics or other unwanted emissions. The problem is most obvious with FM receivers because the standard 1st LO frequency is 10.7 MHz, and the top of the FM broadcast band is adjacent to the bottom of the aviation band (108 MHz) - which means that simply adding the LO frequency to standard FM broadcast frequencies can take you instantly into overlap with the bottom 10.7 MHz of the aviation band (and unfortunately, that's where a lot of the radionavigation systems within that band tend to be). But this does not mean that receivers for other services would not cause similar problems. VHF television covers frequencies below and above both FM and aviation (two bands, 54-88 MHz for channels 2 through 6, and 174 to 216 MHz for channels 7 through 13). It is certainly very possible that receivers intended for these bands would emit in the aviation band. Other adjacent services that may be of concern include public-service and commerical communication bands (i.e., police scanners) and the 2-meter amateur band. Bob M. |
"Dave VanHorn" wrote:
They need to hear all the comms, not just between themselves and the tower, but what the other pilots are saying as well. Add to this, the fact that aircraft comms are AM, which is inherently muddy, and it's easy to see why they take the extra precautions. The design of newer comms doesn't help either. If they have automatic squelch, set to break at say 1uV RF in, then obviously it doesn't take much interference to break squelch. Then, they also may have "audio leveling" -- a great feature when commonly using headphones -- but the effect there will be to take a few uV of noise and amplify the audio component to the level you hear when ATC hits you with as much as 50W, and it's heard constantly between transmissions, to be hopefully silenced when ATC talks. But not necessarily the case in monitoring comms of other aircraft, where especially general aviation, less-than-properly-functional 7W units can be relatively weak. Fred F. |
"Geoff Glave" wrote in message news:HxHud.9448$eb3.8331@clgrps13... Any explanation for this? FM radio generally operates at longer range than AM radio, Nonsense! AM radio stations can be heard for thousands of miles, FM for 'line of sight', which is usually less than a hundred miles. however it's limited to line-of-sight. However, when you're 40,000 feet up you can "see" a lot of transmitters hence the FM signals. Nonsense! The passenger is sitting in a Faraday Cage, a fuslage made of alumninum. The FM wavelength is short enough to go thru the windows, but mot the AM signals. Cheers, Geoff Glave Vancouver, Canada |
"Ian Jackson" wrote in message ... In message HxHud.9448$eb3.8331@clgrps13, Geoff Glave writes Any explanation for this? FM radio generally operates at longer range than AM radio, however it's limited to line-of-sight. However, when you're 40,000 feet up you can "see" a lot of transmitters hence the FM signals. Cheers, Geoff Glave Vancouver, Canada The window holes are much too small to let the much longer wavelengths of the 'AM' signals through. The body of the plane is a very effective screen. The 'FM' signals can squeeze in, but it helps if you have a window seat. I've also listened to SW in the middle of the Atlantic. Flying from the UK to Florida, on the other side of the Atlantic the first FM stations you hear are usually speaking French (from Quebec) It's quite alarming! Ian. -- If you stretch a string on a globe from London to Florida, it will show the 'great circle' route that's the shortest, and that should be your plane's path, barring storme, hurricanes, etc. You'll see that it comes really close to the eastern Canadian provinces. |
"Richard Clark" wrote in message ... On Sat, 11 Dec 2004 14:11:44 -0800, "Ed Price" wrote: You are asking him to allow a potentially dangerous device to be operated just for your convenience and entertainment. Switch roles for just a minute. Hi Ed, This would make sense (to switch roles) if the administration hadn't trumped that call. Reports recently indicate that the FAA may soon allow anyone, anytime, to make cell phone calls while in flight. Anything goes for a price. The FDA has proven that it is no longer the watchdog of medicine, and the FCC is the gateway for spectrum bargains and marketplace sweeps. With these acronyms, one may well wonder what the "F" stands for. 73's Richard Clark, KB7QHC If you make your own TRF receiver, with no LO, it won't interfere with anything. In fact, you can then put an AM detector in it, and also listen to the aircraft chatter. Another way is to listen to stations at or below 97.3 MHz, which would keep the LO at 108 MHz or below. |
"Some Guy" wrote in message ... What a load of horse ****. You guys are acting as if the engines and flight control surfaces of an aircraft are intimately tied to the plane's radio receiver, and the slightest odd or out-of-place signal that it receives is enough to send any plane into a tail spin. No, the laws say that you can be arrested for breaking them, and one way to break them is to use a FM radio while the aircraft is flying. All this while the air travel industry is considering allowing passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT by adding cell-phone relay stations to the planes and allowing any such calls to be completed via satellite. So I guess the feeble radiation by my FM radio (powered by 2 AAA batteries) is enough to cause a plane to dive into the ocean, but the guy next to me putting out 3 watts of near-microwave energy is totally safe. You don't know what you're talking about. With the attitudes of the air marshals nowadays, making airliners turn around and go back to their departure point just because a passenger is unruly, there is a high probability that one of them is flying along on your flight, and if he sees an earphone hanging out of your ear, you might be that unruly passenger they arrest at the departure point. Especially with your nasty attitude! What about my hand-held GPS unit? Any chance me using it (during all phases of a flight, which I do routinely) will result in a one-way ticket to kingdom come? Geez, what a TWERP! You can't add two and two without jumping to conclusions! A rational conversation with you is nearly impossible. Getting back to the original question (poor to non-existant AM reception), I understand the idea of aperature and long wavelenths of AM radio and the size of airplane windows - but what about the effect of ALL the windows on a plane? Don't they create a much larger effective apperature when you consider all of them? And since the plane isin't grounded, isin't the exterior shell of a plane essentially transparent to all RF (ie it's just a re-radiator) because it's not at ground potential? You're even dumber than I had thought. Look up Faraday Shield. Here, try this: http://www.physlink.com/Education/AskExperts/ae176.cfm You don't have to worry about a ground for it to work. Duh. |
"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message ... "Richard Clark" wrote in message ... On Sat, 11 Dec 2004 14:11:44 -0800, "Ed Price" wrote: You are asking him to allow a potentially dangerous device to be operated just for your convenience and entertainment. Switch roles for just a minute. Hi Ed, This would make sense (to switch roles) if the administration hadn't trumped that call. Reports recently indicate that the FAA may soon allow anyone, anytime, to make cell phone calls while in flight. Anything goes for a price. The FDA has proven that it is no longer the watchdog of medicine, and the FCC is the gateway for spectrum bargains and marketplace sweeps. With these acronyms, one may well wonder what the "F" stands for. 73's Richard Clark, KB7QHC If you make your own TRF receiver, with no LO, it won't interfere with anything. In fact, you can then put an AM detector in it, and also listen to the aircraft chatter. Another way is to listen to stations at or below 97.3 MHz, which would keep the LO at 108 MHz or below. Like maybe putting the LO at about 80 MHz, so that the 3rd harmonic of the LO drops into the UHF navcom band? Ed wb6wsn |
"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message ... "Some Guy" wrote in message ... What a load of horse ****. You guys are acting as if the engines and flight control surfaces of an aircraft are intimately tied to the plane's radio receiver, and the slightest odd or out-of-place signal that it receives is enough to send any plane into a tail spin. No, the laws say that you can be arrested for breaking them, and one way to break them is to use a FM radio while the aircraft is flying. All this while the air travel industry is considering allowing passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT by adding cell-phone relay stations to the planes and allowing any such calls to be completed via satellite. So I guess the feeble radiation by my FM radio (powered by 2 AAA batteries) is enough to cause a plane to dive into the ocean, but the guy next to me putting out 3 watts of near-microwave energy is totally safe. You don't know what you're talking about. With the attitudes of the air marshals nowadays, making airliners turn around and go back to their departure point just because a passenger is unruly, there is a high probability that one of them is flying along on your flight, and if he sees an earphone hanging out of your ear, you might be that unruly passenger they arrest at the departure point. Especially with your nasty attitude! What about my hand-held GPS unit? Any chance me using it (during all phases of a flight, which I do routinely) will result in a one-way ticket to kingdom come? Geez, what a TWERP! You can't add two and two without jumping to conclusions! A rational conversation with you is nearly impossible. Getting back to the original question (poor to non-existant AM reception), I understand the idea of aperature and long wavelenths of AM radio and the size of airplane windows - but what about the effect of ALL the windows on a plane? Don't they create a much larger effective apperature when you consider all of them? And since the plane isin't grounded, isin't the exterior shell of a plane essentially transparent to all RF (ie it's just a re-radiator) because it's not at ground potential? You're even dumber than I had thought. Look up Faraday Shield. Here, try this: http://www.physlink.com/Education/AskExperts/ae176.cfm You don't have to worry about a ground for it to work. Duh. He's not dumber than "I" thought! Ed wb6wsn |
Ed Price wrote:
"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message ... "Richard Clark" wrote in message ... On Sat, 11 Dec 2004 14:11:44 -0800, "Ed Price" wrote: You are asking him to allow a potentially dangerous device to be operated just for your convenience and entertainment. Switch roles for just a minute. Hi Ed, This would make sense (to switch roles) if the administration hadn't trumped that call. Reports recently indicate that the FAA may soon allow anyone, anytime, to make cell phone calls while in flight. Anything goes for a price. The FDA has proven that it is no longer the watchdog of medicine, and the FCC is the gateway for spectrum bargains and marketplace sweeps. With these acronyms, one may well wonder what the "F" stands for. 73's Richard Clark, KB7QHC If you make your own TRF receiver, with no LO, it won't interfere with anything. In fact, you can then put an AM detector in it, and also listen to the aircraft chatter. Another way is to listen to stations at or below 97.3 MHz, which would keep the LO at 108 MHz or below. Like maybe putting the LO at about 80 MHz, so that the 3rd harmonic of the LO drops into the UHF navcom band? Ed wb6wsn It is official; i just read in one of my electronigs mags i get that the FAA indeed has ruled that airlines can allow use of computers over the net when flying. But it is up to each given airline to modify their own giudelines (as they see fit). |
Ed Price wrote:
"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message ... "Some Guy" wrote in message ... What a load of horse ****. You guys are acting as if the engines and flight control surfaces of an aircraft are intimately tied to the plane's radio receiver, and the slightest odd or out-of-place signal that it receives is enough to send any plane into a tail spin. No, the laws say that you can be arrested for breaking them, and one way to break them is to use a FM radio while the aircraft is flying. All this while the air travel industry is considering allowing passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT by adding cell-phone relay stations to the planes and allowing any such calls to be completed via satellite. So I guess the feeble radiation by my FM radio (powered by 2 AAA batteries) is enough to cause a plane to dive into the ocean, but the guy next to me putting out 3 watts of near-microwave energy is totally safe. You don't know what you're talking about. With the attitudes of the air marshals nowadays, making airliners turn around and go back to their departure point just because a passenger is unruly, there is a high probability that one of them is flying along on your flight, and if he sees an earphone hanging out of your ear, you might be that unruly passenger they arrest at the departure point. Especially with your nasty attitude! What about my hand-held GPS unit? Any chance me using it (during all phases of a flight, which I do routinely) will result in a one-way ticket to kingdom come? Geez, what a TWERP! You can't add two and two without jumping to conclusions! A rational conversation with you is nearly impossible. Getting back to the original question (poor to non-existant AM reception), I understand the idea of aperature and long wavelenths of AM radio and the size of airplane windows - but what about the effect of ALL the windows on a plane? Don't they create a much larger effective apperature when you consider all of them? And since the plane isin't grounded, isin't the exterior shell of a plane essentially transparent to all RF (ie it's just a re-radiator) because it's not at ground potential? You're even dumber than I had thought. Look up Faraday Shield. Here, try this: http://www.physlink.com/Education/AskExperts/ae176.cfm You don't have to worry about a ground for it to work. Duh. He's not dumber than "I" thought! Ed wb6wsn "Faraday shield" to some degree is a myth. I have seen radars inside quonset huts track a *bird* flying a few miles away (thru the metal wall)! |
"Robert Baer" wrote in message ... Ed Price wrote: "Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message ... "Some Guy" wrote in message ... What a load of horse ****. You guys are acting as if the engines and flight control surfaces of an aircraft are intimately tied to the plane's radio receiver, and the slightest odd or out-of-place signal that it receives is enough to send any plane into a tail spin. No, the laws say that you can be arrested for breaking them, and one way to break them is to use a FM radio while the aircraft is flying. All this while the air travel industry is considering allowing passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT by adding cell-phone relay stations to the planes and allowing any such calls to be completed via satellite. So I guess the feeble radiation by my FM radio (powered by 2 AAA batteries) is enough to cause a plane to dive into the ocean, but the guy next to me putting out 3 watts of near-microwave energy is totally safe. You don't know what you're talking about. With the attitudes of the air marshals nowadays, making airliners turn around and go back to their departure point just because a passenger is unruly, there is a high probability that one of them is flying along on your flight, and if he sees an earphone hanging out of your ear, you might be that unruly passenger they arrest at the departure point. Especially with your nasty attitude! What about my hand-held GPS unit? Any chance me using it (during all phases of a flight, which I do routinely) will result in a one-way ticket to kingdom come? Geez, what a TWERP! You can't add two and two without jumping to conclusions! A rational conversation with you is nearly impossible. Getting back to the original question (poor to non-existant AM reception), I understand the idea of aperature and long wavelenths of AM radio and the size of airplane windows - but what about the effect of ALL the windows on a plane? Don't they create a much larger effective apperature when you consider all of them? And since the plane isin't grounded, isin't the exterior shell of a plane essentially transparent to all RF (ie it's just a re-radiator) because it's not at ground potential? You're even dumber than I had thought. Look up Faraday Shield. Here, try this: http://www.physlink.com/Education/AskExperts/ae176.cfm You don't have to worry about a ground for it to work. Duh. He's not dumber than "I" thought! Ed wb6wsn "Faraday shield" to some degree is a myth. I have seen radars inside quonset huts track a *bird* flying a few miles away (thru the metal wall)! You must have some strange buddies. Who in the world would set up a radar within a metal hut? And even if they did, who would think it's a good idea to stay inside with it if it were on? There's nothing mythical about the Faraday shield; it works really well, so long as there are no discontinuities (apertures) and sufficient thickness and conductivity. Under real-world conditions, steel works pretty good, and any thickness sufficient to support itself will yield great shielding effectiveness. So the only real performance variable left is the holes in the conductive surface. How many, maximum dimension, proximity of radiating source to the shield, etc. While I would expect a Quonset hut to really mess up the accuracy of a radar, it likely wouldn't be a good shield, as the floor isn't metal, I don't think the ends are metal, and the various skin panels are rather poorly RF bonded. Ed wb6wsn |
"Robert Baer" wrote in message ... Ed Price wrote: "Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message ... "Some Guy" wrote in message ... What a load of horse ****. You guys are acting as if the engines and flight control surfaces of an aircraft are intimately tied to the plane's radio receiver, and the slightest odd or out-of-place signal that it receives is enough to send any plane into a tail spin. No, the laws say that you can be arrested for breaking them, and one way to break them is to use a FM radio while the aircraft is flying. All this while the air travel industry is considering allowing passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT by adding cell-phone relay stations to the planes and allowing any such calls to be completed via satellite. So I guess the feeble radiation by my FM radio (powered by 2 AAA batteries) is enough to cause a plane to dive into the ocean, but the guy next to me putting out 3 watts of near-microwave energy is totally safe. You don't know what you're talking about. With the attitudes of the air marshals nowadays, making airliners turn around and go back to their departure point just because a passenger is unruly, there is a high probability that one of them is flying along on your flight, and if he sees an earphone hanging out of your ear, you might be that unruly passenger they arrest at the departure point. Especially with your nasty attitude! What about my hand-held GPS unit? Any chance me using it (during all phases of a flight, which I do routinely) will result in a one-way ticket to kingdom come? Geez, what a TWERP! You can't add two and two without jumping to conclusions! A rational conversation with you is nearly impossible. Getting back to the original question (poor to non-existant AM reception), I understand the idea of aperature and long wavelenths of AM radio and the size of airplane windows - but what about the effect of ALL the windows on a plane? Don't they create a much larger effective apperature when you consider all of them? And since the plane isin't grounded, isin't the exterior shell of a plane essentially transparent to all RF (ie it's just a re-radiator) because it's not at ground potential? You're even dumber than I had thought. Look up Faraday Shield. Here, try this: http://www.physlink.com/Education/AskExperts/ae176.cfm You don't have to worry about a ground for it to work. Duh. He's not dumber than "I" thought! Ed wb6wsn "Faraday shield" to some degree is a myth. You use weasel words like 'to some degree' to avoid talking about the truth. Radio waves don't go thru a sheet of metal. I have seen radars inside quonset huts track a *bird* flying a few miles away (thru the metal wall)! No, not thru a metal wall. I saw the radar go thru the wooden walls of the bldg when I was in radar repair school in the army. But that was wood. Your so-called metal quonset hut was probably wood or fiberglass. If you saw anything, it was probably your own reflection off the metal walls, IF it didn't fry you like a porkchop in a microwave oven! |
Ed Price wrote:
"Robert Baer" wrote in message ... Ed Price wrote: "Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message ... "Some Guy" wrote in message ... What a load of horse ****. You guys are acting as if the engines and flight control surfaces of an aircraft are intimately tied to the plane's radio receiver, and the slightest odd or out-of-place signal that it receives is enough to send any plane into a tail spin. No, the laws say that you can be arrested for breaking them, and one way to break them is to use a FM radio while the aircraft is flying. All this while the air travel industry is considering allowing passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT by adding cell-phone relay stations to the planes and allowing any such calls to be completed via satellite. So I guess the feeble radiation by my FM radio (powered by 2 AAA batteries) is enough to cause a plane to dive into the ocean, but the guy next to me putting out 3 watts of near-microwave energy is totally safe. You don't know what you're talking about. With the attitudes of the air marshals nowadays, making airliners turn around and go back to their departure point just because a passenger is unruly, there is a high probability that one of them is flying along on your flight, and if he sees an earphone hanging out of your ear, you might be that unruly passenger they arrest at the departure point. Especially with your nasty attitude! What about my hand-held GPS unit? Any chance me using it (during all phases of a flight, which I do routinely) will result in a one-way ticket to kingdom come? Geez, what a TWERP! You can't add two and two without jumping to conclusions! A rational conversation with you is nearly impossible. Getting back to the original question (poor to non-existant AM reception), I understand the idea of aperature and long wavelenths of AM radio and the size of airplane windows - but what about the effect of ALL the windows on a plane? Don't they create a much larger effective apperature when you consider all of them? And since the plane isin't grounded, isin't the exterior shell of a plane essentially transparent to all RF (ie it's just a re-radiator) because it's not at ground potential? You're even dumber than I had thought. Look up Faraday Shield. Here, try this: http://www.physlink.com/Education/AskExperts/ae176.cfm You don't have to worry about a ground for it to work. Duh. He's not dumber than "I" thought! Ed wb6wsn "Faraday shield" to some degree is a myth. I have seen radars inside quonset huts track a *bird* flying a few miles away (thru the metal wall)! You must have some strange buddies. Who in the world would set up a radar within a metal hut? And even if they did, who would think it's a good idea to stay inside with it if it were on? There's nothing mythical about the Faraday shield; it works really well, so long as there are no discontinuities (apertures) and sufficient thickness and conductivity. Under real-world conditions, steel works pretty good, and any thickness sufficient to support itself will yield great shielding effectiveness. So the only real performance variable left is the holes in the conductive surface. How many, maximum dimension, proximity of radiating source to the shield, etc. While I would expect a Quonset hut to really mess up the accuracy of a radar, it likely wouldn't be a good shield, as the floor isn't metal, I don't think the ends are metal, and the various skin panels are rather poorly RF bonded. Ed wb6wsn I do not think your objections concerning the floor or the bonding of the panels are too relevant. The ends are metal and not relevant either. The radar was pointing right at the wall (no windows nearby); any presumed leakage via remote holes that you assumed might allow the transmitted signal to leak, but would then not be focused on the bird(s) and the path lengths would vary. But the reflected signal from the bird or birds would be rather weak and could not possibly be received via the same wild path(s) to a very directional antenna. My point is that a Farady shield is a good attenuator, but not "perfect" as ASSuMEd. And it sure is not "flat" in attenuation characteristic as a function of frequency. |
"Watson A.Name - \"Watt Sun, the Dark Remover\"" wrote:
"Robert Baer" wrote in message ... Ed Price wrote: "Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message ... "Some Guy" wrote in message ... What a load of horse ****. You guys are acting as if the engines and flight control surfaces of an aircraft are intimately tied to the plane's radio receiver, and the slightest odd or out-of-place signal that it receives is enough to send any plane into a tail spin. No, the laws say that you can be arrested for breaking them, and one way to break them is to use a FM radio while the aircraft is flying. All this while the air travel industry is considering allowing passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT by adding cell-phone relay stations to the planes and allowing any such calls to be completed via satellite. So I guess the feeble radiation by my FM radio (powered by 2 AAA batteries) is enough to cause a plane to dive into the ocean, but the guy next to me putting out 3 watts of near-microwave energy is totally safe. You don't know what you're talking about. With the attitudes of the air marshals nowadays, making airliners turn around and go back to their departure point just because a passenger is unruly, there is a high probability that one of them is flying along on your flight, and if he sees an earphone hanging out of your ear, you might be that unruly passenger they arrest at the departure point. Especially with your nasty attitude! What about my hand-held GPS unit? Any chance me using it (during all phases of a flight, which I do routinely) will result in a one-way ticket to kingdom come? Geez, what a TWERP! You can't add two and two without jumping to conclusions! A rational conversation with you is nearly impossible. Getting back to the original question (poor to non-existant AM reception), I understand the idea of aperature and long wavelenths of AM radio and the size of airplane windows - but what about the effect of ALL the windows on a plane? Don't they create a much larger effective apperature when you consider all of them? And since the plane isin't grounded, isin't the exterior shell of a plane essentially transparent to all RF (ie it's just a re-radiator) because it's not at ground potential? You're even dumber than I had thought. Look up Faraday Shield. Here, try this: http://www.physlink.com/Education/AskExperts/ae176.cfm You don't have to worry about a ground for it to work. Duh. He's not dumber than "I" thought! Ed wb6wsn "Faraday shield" to some degree is a myth. You use weasel words like 'to some degree' to avoid talking about the truth. Radio waves don't go thru a sheet of metal. I have seen radars inside quonset huts track a *bird* flying a few miles away (thru the metal wall)! No, not thru a metal wall. I saw the radar go thru the wooden walls of the bldg when I was in radar repair school in the army. But that was wood. Your so-called metal quonset hut was probably wood or fiberglass. If you saw anything, it was probably your own reflection off the metal walls, IF it didn't fry you like a porkchop in a microwave oven! Nope; it was a metal quonset hut; Army Signal Corps Fort Huachuca AridZona. |
"Robert Baer" wrote in message ... Ed Price wrote: "Robert Baer" wrote in message ... Ed Price wrote: "Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message ... "Some Guy" wrote in message ... What a load of horse ****. You guys are acting as if the engines and flight control surfaces of an aircraft are intimately tied to the plane's radio receiver, and the slightest odd or out-of-place signal that it receives is enough to send any plane into a tail spin. No, the laws say that you can be arrested for breaking them, and one way to break them is to use a FM radio while the aircraft is flying. All this while the air travel industry is considering allowing passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT by adding cell-phone relay stations to the planes and allowing any such calls to be completed via satellite. So I guess the feeble radiation by my FM radio (powered by 2 AAA batteries) is enough to cause a plane to dive into the ocean, but the guy next to me putting out 3 watts of near-microwave energy is totally safe. You don't know what you're talking about. With the attitudes of the air marshals nowadays, making airliners turn around and go back to their departure point just because a passenger is unruly, there is a high probability that one of them is flying along on your flight, and if he sees an earphone hanging out of your ear, you might be that unruly passenger they arrest at the departure point. Especially with your nasty attitude! What about my hand-held GPS unit? Any chance me using it (during all phases of a flight, which I do routinely) will result in a one-way ticket to kingdom come? Geez, what a TWERP! You can't add two and two without jumping to conclusions! A rational conversation with you is nearly impossible. Getting back to the original question (poor to non-existant AM reception), I understand the idea of aperature and long wavelenths of AM radio and the size of airplane windows - but what about the effect of ALL the windows on a plane? Don't they create a much larger effective apperature when you consider all of them? And since the plane isin't grounded, isin't the exterior shell of a plane essentially transparent to all RF (ie it's just a re-radiator) because it's not at ground potential? You're even dumber than I had thought. Look up Faraday Shield. Here, try this: http://www.physlink.com/Education/AskExperts/ae176.cfm You don't have to worry about a ground for it to work. Duh. He's not dumber than "I" thought! Ed wb6wsn "Faraday shield" to some degree is a myth. I have seen radars inside quonset huts track a *bird* flying a few miles away (thru the metal wall)! You must have some strange buddies. Who in the world would set up a radar within a metal hut? And even if they did, who would think it's a good idea to stay inside with it if it were on? There's nothing mythical about the Faraday shield; it works really well, so long as there are no discontinuities (apertures) and sufficient thickness and conductivity. Under real-world conditions, steel works pretty good, and any thickness sufficient to support itself will yield great shielding effectiveness. So the only real performance variable left is the holes in the conductive surface. How many, maximum dimension, proximity of radiating source to the shield, etc. While I would expect a Quonset hut to really mess up the accuracy of a radar, it likely wouldn't be a good shield, as the floor isn't metal, I don't think the ends are metal, and the various skin panels are rather poorly RF bonded. Ed wb6wsn I do not think your objections concerning the floor or the bonding of the panels are too relevant. The ends are metal and not relevant either. The radar was pointing right at the wall (no windows nearby); any presumed leakage via remote holes that you assumed might allow the transmitted signal to leak, but would then not be focused on the bird(s) and the path lengths would vary. But the reflected signal from the bird or birds would be rather weak and could not possibly be received via the same wild path(s) to a very directional antenna. My point is that a Farady shield is a good attenuator, but not "perfect" as ASSuMEd. And it sure is not "flat" in attenuation characteristic as a function of frequency. Those weren't objections, they were speculations on my part as to how you boys could have been finessing the generally applicable laws of physics. But truly, the story stinks. So you and your army buddies are in this metal hut, with a fairly high-power radar, and somebody comes up with the bright idea to turn the thing on. Apparently no thought about RF personnel hazards and no concern about strong reflections cooking your detector. Did you test your M16's in a Quonset hut too? Next point. "The radar was pointing right at the wall..." Now tell me, in a semi-circular Quonset hut, how do you point anything "right at the wall"? Maybe straight up? Now, a bird doesn't have a very big radar cross section, maybe only about 0.01 square meters, so the return loss is really big. And to resolve a single bird, I'm gonna guess that you had an X or K band radar. So let's run some numbers. Let's say you had a 100kW radar, with a 30 dBi antenna of 1 square meter aperture. At 1500 meters, your detector power would be about 1 picowatt, or -60 dBm. Well hey, that's pretty decent, I'll bet you could see a bird at one mile. But that's assuming no loss at all due to the metal hut skin. Let's see what happens if we say that the metal hut walls give us only 40 dB of shielding (by absorption or reflection, it doesn't matter). That bites 80 dB out of your path budget, putting your detector signal down to -140 dBm. I think your story just ran out of luck. Now you can argue about the 40 dB shielding effectiveness of the metal wall, but I'll say that I was being very generous about that. At 10 GHz, I know (How? Easy, I do it everyday. Just 3 days ago, I was keeping some 1.3 GHz from radiating off of some cables, and it was common old Reynolds Wrap to the rescue.), I can get 100 dB out of a sheet of aluminum foil. The SE is so damn high from the material that the only significant factor is when the energy finds a path around the shield. Don't try to argue that a Faraday cage leaks; you appear to be trying to build a general case based on your experience of always having observed leaky structures. Sure, I know that shielding varies with lots of factors, conductivity, permeability, thickness, frequency, angle of incidence, distance from source, and then there's the problem of apertures. But your hut, with plain old galvanized steel about 1/16" thick, would make a great shielded enclosure, as long as the joints didn't leak. BTW, I don't like using the term "Faraday cage". Despite all due respect to Mr. Faraday, calling it a shielded enclosure is a clearer description. Ed wb6wsn |
Robert Baer wrote:
"So the only real performance variable left is the holes in the conductive surface." A plane window, like the fuselage itself, acts as apipe below cutoff frequency. Minimum size for low attenuation is 1/2-wavelength. The thicker the window frame, the longer the waveguide and the greater the attenuation at frequencies below cutoff. See page 277 of "Transmission Lines, Antennas, and Wave Guides" by King, Mimno, and Wing to quantify the attenuation. It`s big below cutoff. Best regards, Richard Harrison, KB5WZI |
Ed Price wrote:
"Robert Baer" wrote in message ... Ed Price wrote: "Robert Baer" wrote in message ... Ed Price wrote: "Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message ... "Some Guy" wrote in message ... What a load of horse ****. You guys are acting as if the engines and flight control surfaces of an aircraft are intimately tied to the plane's radio receiver, and the slightest odd or out-of-place signal that it receives is enough to send any plane into a tail spin. No, the laws say that you can be arrested for breaking them, and one way to break them is to use a FM radio while the aircraft is flying. All this while the air travel industry is considering allowing passengers to use their own cell phones WHILE THE PLANES ARE IN FLIGHT by adding cell-phone relay stations to the planes and allowing any such calls to be completed via satellite. So I guess the feeble radiation by my FM radio (powered by 2 AAA batteries) is enough to cause a plane to dive into the ocean, but the guy next to me putting out 3 watts of near-microwave energy is totally safe. You don't know what you're talking about. With the attitudes of the air marshals nowadays, making airliners turn around and go back to their departure point just because a passenger is unruly, there is a high probability that one of them is flying along on your flight, and if he sees an earphone hanging out of your ear, you might be that unruly passenger they arrest at the departure point. Especially with your nasty attitude! What about my hand-held GPS unit? Any chance me using it (during all phases of a flight, which I do routinely) will result in a one-way ticket to kingdom come? Geez, what a TWERP! You can't add two and two without jumping to conclusions! A rational conversation with you is nearly impossible. Getting back to the original question (poor to non-existant AM reception), I understand the idea of aperature and long wavelenths of AM radio and the size of airplane windows - but what about the effect of ALL the windows on a plane? Don't they create a much larger effective apperature when you consider all of them? And since the plane isin't grounded, isin't the exterior shell of a plane essentially transparent to all RF (ie it's just a re-radiator) because it's not at ground potential? You're even dumber than I had thought. Look up Faraday Shield. Here, try this: http://www.physlink.com/Education/AskExperts/ae176.cfm You don't have to worry about a ground for it to work. Duh. He's not dumber than "I" thought! Ed wb6wsn "Faraday shield" to some degree is a myth. I have seen radars inside quonset huts track a *bird* flying a few miles away (thru the metal wall)! You must have some strange buddies. Who in the world would set up a radar within a metal hut? And even if they did, who would think it's a good idea to stay inside with it if it were on? There's nothing mythical about the Faraday shield; it works really well, so long as there are no discontinuities (apertures) and sufficient thickness and conductivity. Under real-world conditions, steel works pretty good, and any thickness sufficient to support itself will yield great shielding effectiveness. So the only real performance variable left is the holes in the conductive surface. How many, maximum dimension, proximity of radiating source to the shield, etc. While I would expect a Quonset hut to really mess up the accuracy of a radar, it likely wouldn't be a good shield, as the floor isn't metal, I don't think the ends are metal, and the various skin panels are rather poorly RF bonded. Ed wb6wsn I do not think your objections concerning the floor or the bonding of the panels are too relevant. The ends are metal and not relevant either. The radar was pointing right at the wall (no windows nearby); any presumed leakage via remote holes that you assumed might allow the transmitted signal to leak, but would then not be focused on the bird(s) and the path lengths would vary. But the reflected signal from the bird or birds would be rather weak and could not possibly be received via the same wild path(s) to a very directional antenna. My point is that a Farady shield is a good attenuator, but not "perfect" as ASSuMEd. And it sure is not "flat" in attenuation characteristic as a function of frequency. Those weren't objections, they were speculations on my part as to how you boys could have been finessing the generally applicable laws of physics. But truly, the story stinks. So you and your army buddies are in this metal hut, with a fairly high-power radar, and somebody comes up with the bright idea to turn the thing on. Apparently no thought about RF personnel hazards and no concern about strong reflections cooking your detector. Did you test your M16's in a Quonset hut too? Next point. "The radar was pointing right at the wall..." Now tell me, in a semi-circular Quonset hut, how do you point anything "right at the wall"? Maybe straight up? Now, a bird doesn't have a very big radar cross section, maybe only about 0.01 square meters, so the return loss is really big. And to resolve a single bird, I'm gonna guess that you had an X or K band radar. So let's run some numbers. Let's say you had a 100kW radar, with a 30 dBi antenna of 1 square meter aperture. At 1500 meters, your detector power would be about 1 picowatt, or -60 dBm. Well hey, that's pretty decent, I'll bet you could see a bird at one mile. But that's assuming no loss at all due to the metal hut skin. Let's see what happens if we say that the metal hut walls give us only 40 dB of shielding (by absorption or reflection, it doesn't matter). That bites 80 dB out of your path budget, putting your detector signal down to -140 dBm. I think your story just ran out of luck. Now you can argue about the 40 dB shielding effectiveness of the metal wall, but I'll say that I was being very generous about that. At 10 GHz, I know (How? Easy, I do it everyday. Just 3 days ago, I was keeping some 1.3 GHz from radiating off of some cables, and it was common old Reynolds Wrap to the rescue.), I can get 100 dB out of a sheet of aluminum foil. The SE is so damn high from the material that the only significant factor is when the energy finds a path around the shield. Don't try to argue that a Faraday cage leaks; you appear to be trying to build a general case based on your experience of always having observed leaky structures. Sure, I know that shielding varies with lots of factors, conductivity, permeability, thickness, frequency, angle of incidence, distance from source, and then there's the problem of apertures. But your hut, with plain old galvanized steel about 1/16" thick, would make a great shielded enclosure, as long as the joints didn't leak. BTW, I don't like using the term "Faraday cage". Despite all due respect to Mr. Faraday, calling it a shielded enclosure is a clearer description. Ed wb6wsn I was not alluding to leakage; a more accurate term would be re-radiation. Take an ordinary transformer; it radiates a magnetic field, despite the fact that the core is a closed loop. In fact, one could get nasty and say the same thing about a toroid transformer. Now add a shorted copper turn around the outside of the ordinary transformer's core (i have seen this on many TV power transformers and others as well). What happens? That magnetic field induces a current in that shorted turn, making an opposing magnetic field - thereby reducing the net radiated magnetic field greatly - but not to zero. Now, instead of using that closely wrapped copper shoted turn, put that transformer inside that shielded room you love. Results: great reduction, but not to zero. Increase the frequency to something one might consider RF. Now one has an RF transmitter inside that shielded room, inducing currents in the wall(s). Those currents create opposing fields, and greatly attenuate the signal outside the walls. But they are not zero. BW, radar is usually pulsed, and in the megawatt to multi-megawatt region for the pulse. Also, the quonset huts i saw had relatively vertical walls; the rounded curvature was more so near the top. And it might help to ask the bird(s); they even dislike those pesky jets getting in their way. |
FAR more likely that the antenna for the radar was outside the hut.
There may have been one slaved to it, inactive, inside the hut to demonstrate what's going on upstairs. There are plenty of good reasons why such a demo wouldn't work as described, from killing the detector with strong reflections, to massive re-re-reflections inside the building, to the fact that radar relies on a "pencil" beam that wouldn't survive through those walls in any rational way, and so on. |
"Robert Baer" wrote in message ... SNIP "Faraday shield" to some degree is a myth. I have seen radars inside quonset huts track a *bird* flying a few miles away (thru the metal wall)! You must have some strange buddies. Who in the world would set up a radar within a metal hut? And even if they did, who would think it's a good idea to stay inside with it if it were on? There's nothing mythical about the Faraday shield; it works really well, so long as there are no discontinuities (apertures) and sufficient thickness and conductivity. Under real-world conditions, steel works pretty good, and any thickness sufficient to support itself will yield great shielding effectiveness. So the only real performance variable left is the holes in the conductive surface. How many, maximum dimension, proximity of radiating source to the shield, etc. While I would expect a Quonset hut to really mess up the accuracy of a radar, it likely wouldn't be a good shield, as the floor isn't metal, I don't think the ends are metal, and the various skin panels are rather poorly RF bonded. Ed wb6wsn I do not think your objections concerning the floor or the bonding of the panels are too relevant. The ends are metal and not relevant either. The radar was pointing right at the wall (no windows nearby); any presumed leakage via remote holes that you assumed might allow the transmitted signal to leak, but would then not be focused on the bird(s) and the path lengths would vary. But the reflected signal from the bird or birds would be rather weak and could not possibly be received via the same wild path(s) to a very directional antenna. My point is that a Farady shield is a good attenuator, but not "perfect" as ASSuMEd. And it sure is not "flat" in attenuation characteristic as a function of frequency. Those weren't objections, they were speculations on my part as to how you boys could have been finessing the generally applicable laws of physics. But truly, the story stinks. So you and your army buddies are in this metal hut, with a fairly high-power radar, and somebody comes up with the bright idea to turn the thing on. Apparently no thought about RF personnel hazards and no concern about strong reflections cooking your detector. Did you test your M16's in a Quonset hut too? Next point. "The radar was pointing right at the wall..." Now tell me, in a semi-circular Quonset hut, how do you point anything "right at the wall"? Maybe straight up? Now, a bird doesn't have a very big radar cross section, maybe only about 0.01 square meters, so the return loss is really big. And to resolve a single bird, I'm gonna guess that you had an X or K band radar. So let's run some numbers. Let's say you had a 100kW radar, with a 30 dBi antenna of 1 square meter aperture. At 1500 meters, your detector power would be about 1 picowatt, or -60 dBm. Well hey, that's pretty decent, I'll bet you could see a bird at one mile. But that's assuming no loss at all due to the metal hut skin. Let's see what happens if we say that the metal hut walls give us only 40 dB of shielding (by absorption or reflection, it doesn't matter). That bites 80 dB out of your path budget, putting your detector signal down to -140 dBm. I think your story just ran out of luck. Now you can argue about the 40 dB shielding effectiveness of the metal wall, but I'll say that I was being very generous about that. At 10 GHz, I know (How? Easy, I do it everyday. Just 3 days ago, I was keeping some 1.3 GHz from radiating off of some cables, and it was common old Reynolds Wrap to the rescue.), I can get 100 dB out of a sheet of aluminum foil. The SE is so damn high from the material that the only significant factor is when the energy finds a path around the shield. Don't try to argue that a Faraday cage leaks; you appear to be trying to build a general case based on your experience of always having observed leaky structures. Sure, I know that shielding varies with lots of factors, conductivity, permeability, thickness, frequency, angle of incidence, distance from source, and then there's the problem of apertures. But your hut, with plain old galvanized steel about 1/16" thick, would make a great shielded enclosure, as long as the joints didn't leak. BTW, I don't like using the term "Faraday cage". Despite all due respect to Mr. Faraday, calling it a shielded enclosure is a clearer description. Ed wb6wsn I was not alluding to leakage; a more accurate term would be re-radiation. Take an ordinary transformer; it radiates a magnetic field, despite the fact that the core is a closed loop. In fact, one could get nasty and say the same thing about a toroid transformer. Now add a shorted copper turn around the outside of the ordinary transformer's core (i have seen this on many TV power transformers and others as well). What happens? That magnetic field induces a current in that shorted turn, making an opposing magnetic field - thereby reducing the net radiated magnetic field greatly - but not to zero. Now, instead of using that closely wrapped copper shoted turn, put that transformer inside that shielded room you love. My shielded enclosure only asks that I respect it; I don't think it would provide better SE even if I told it that I loved it. Results: great reduction, but not to zero. Nothing ever goes to zero; I'll usually settle for "great" reductions. Increase the frequency to something one might consider RF. Now one has an RF transmitter inside that shielded room, inducing currents in the wall(s). Those currents create opposing fields, and greatly attenuate the signal outside the walls. You're getting a little fuzzy here. The propagating wave induces surface currents on the metal barrier. The currents "sink" into the metal, decreasing to about 37% (1/e) in what's called a "skin depth". At 10 GHz, a "skin depth" in steel is really thin. After even 10 skin depths, the current is down to only about 1/100,000 of what was on the surface. And there's a whole lot of more skin depths to go before the current is presented to the far surface of the steel barrier. And only then does the surface current on the far side of the barrier get to launch a propagating wave. Note that the "opposing fields" you mentioned are on the INSIDE, the near surface, of the barrier. The reflected field is 180 degrees out of phase with the incident field, so, real close to the metal surface, the E-field nulls. OTOH, that reflected wave now goes marching back at you, creating lots of fun with out-of-phase energy pumped back into the original radiating element. Everybody sees bad, bad VSWR. And, since you guys were inside a metal hut, there's even more fun in store for you. Not all that energy goes back into the originating antenna. A lot of it just keeps bouncing around inside the hut, creating 3-D variations in power density. Think of yourself as a potato, slowly cooking. So, to keep this straight, the current that survives Ohmic losses to make it to the far side of the barrier doesn't "greatly attenuate the signal outside the walls". It actually creates the signal (the propagating wave) on the far side of the barrier. We can talk about aperture leakage and re-radiation from barrier impedance discontinuities some other time. But they are not zero. BW, radar is usually pulsed, and in the megawatt to multi-megawatt region for the pulse. Multi-megawatt? Hmm, 10 MW? OK, and maybe a duty cycle of 0.01%? Isn't that 1 kW average? I own a 250 kW X-band radar that will do up to 0.1% duty cycle. I sure wouldn't sit in a metal box with that thing running! I wouldn't even want to be in the boresight of the antenna within a few hundred feet. I was trying to be charitable in assuming that nobody would be so dumb as to fire up a multi-megawatt radar INSIDE a metal hut. Looks like you guys proved me wrong! Ed wb6wsn Ed wb6wsn |
What's with all the recipe bull**** posts?
Who's posting these? Ed Price wrote: oil. Add a little water, season, then add the carcass. Simmer for half an hour keeping the stock thick. Remove the carcass and add the vegetables slowly to the stock, so that it remains boiling the whole time. Cover the pot and simmer till vegetables are tender (2 hours approximately). Continue seasoning to taste. Before serving, add butter and pasta, serve piping with hot bread and butter. |
On Tue, 28 Dec 2004 09:32:21 -0500, Julia Child
wrote: ignore What's with all the recipe bull**** posts? Who's posting these? Well, this is the info I received. I don't really understand it, but this is what I was told: Hello, this message is never sent unsolicited. Don't panic. You - or more precisely someone using your mail address - have posted a test message to the following Newsgroups: de.alt.test,bit.listserv.test,rec.radio.amateur.an tenna Your message was sent Sat, 25 Dec 2004 21:01:30 GMT travelling from your location to the news.karlvalentin.de (Germany). Your article arrived here at Sun Dec 26 2004 00:40:05 +0100 (CET) and this is the way it went (read from back to front): news.karlvalentin.de!news.qymp.de!tarantoga!auth.d e.news.easynet.net!spool3.bllon.news.easynet.net!e asynet-quince!easynet.net!news.glorb.com!transit1.nntp.hc cnet.nl!transit.nntp.hccnet.nl!transit2.nntp.hccne t.nl!feeder.news-service.com!psinet-eu-nl!news.satx.rr.com!149.52.149.150.mismatch Reflector Mail is sent to anybody posting into a group ending with the word ".test". If you don't want to receive reflector mails, include e.g. the words 'ignore' at the top of your articles. For obvious reasons, mails to are directed into /dev/null. If you feel to write us, send your mail to instead. Full headers plus the first 20 lines of your original message we | Path: news.karlvalentin.de!news.qymp.de!tarantoga!auth.d e.news.easynet.net!spool3.bllon.news.easynet.net!e asynet-quince!easynet.net!news.glorb.com!transit1.nntp.hc cnet.nl!transit.nntp.hccnet.nl!transit2.nntp.hccne t.nl!feeder.news-service.com!psinet-eu-nl!news.satx.rr.com!149.52.149.150.mismatch | From: Bob Miller | Subject: Modification of G5RV - need help on this | Approved: Bob Miller | Newsgroups: de.alt.test,bit.listserv.test,rec.radio.amateur.an tenna | References: | Date: Sat, 25 Dec 2004 21:01:30 GMT | Message-ID: | X-Newsposter: AtomicPost/32 (http://149.52.149.150) Registered | NNTP-Posting-Host: 149.52.149.150 | X-Trace: satx.rr.com 5830402087 149.52.149.150 (25 Dec 2004 21:01:30 GMT) | Followup-To: news.admin.net-abuse.email | Lines: 49 | Xref: news.karlvalentin.de de.alt.test:11560 | | soften. | In skillet, brown the meat in a little olive oil, | then add onions, peppers, and celery (all chopped finely) | and season well. | Place in a large bowl and cool. | Add seasoned breadcrumbs and a little of the tomato gravy, | enough to make the mixture pliable. | Divide the stuffing among the cabbage leaves then roll. | Place seam down in a baking pan. | Ladle tomato gravy on top, | and bake at 325¦ for 30 - 45 minutes. | | | | Umbilical Cordon Bleu | | Nothing is so beautiful as the bond between mother and child, | so why not consume it? | Children or chicken breasts will work wonderfully also. | Ed Price wrote: oil. Add a little water, season, then add the carcass. Simmer for half an hour keeping the stock thick. Remove the carcass and add the vegetables slowly to the stock, so that it remains boiling the whole time. Cover the pot and simmer till vegetables are tender (2 hours approximately). Continue seasoning to taste. Before serving, add butter and pasta, serve piping with hot bread and butter. |
Bob Miller wrote:
Julia Child wrote: What's with all the recipe bull**** posts? Who's posting these? Well, this is the info I received. I don't really understand it, but this is what I was told: this message is never sent unsolicited. Don't panic. You - or more precisely someone using your mail address - have posted a test message to the following Newsgroups: de.alt.test,bit.listserv.test,rec.radio.amateur.an tenna That's just a side-effect of the message having been posted to a 'test' newsgroup - basically irrelevant to the real issue. Look up 'hipcrime' in google for more info about what went on with the baby recipes. miguel -- Hit The Road! Photos from 32 countries on 5 continents: http://travel.u.nu |
The term Faraday screen, sield, or cage, has been applied to perforated
continuous sheets of metal in this thread. That`s generally wrong. A Faraday screen, shield, or cage is a network of parallel wires or strips connected together at one end but disconnected from each other at their opposite ends. I`ve worked at several broadcast stations which used Faraday screens at every tower to magnetically couple the tower to the feedline while eliminating all capacitive coupling. The purpose is to disadvantage harmonic coupling to the tower in which capacitance favors due to lowered capacitive reactance at the harmonic frequencies. At the stations, two coupled coils are used. They are close together and share the same axis. Between the two coil forms is erected a heavy plate sliced with parallel cuts. These start at one edge of the plate but end before reaching quite to the other edge. The purpose is to eliminate capacitive coupling between the coils but to allow tight magnetic coupling between the coils. In the broadcast station they also have another salutary effect. The tower`s lightning strikes nearly all are terminated on the Faraday screen and kept out of the radio equipment. A Faraday screen, shield, or cage is a network of parallel wires or strips connected on one end but disconnected from each other at their opposite ends. It`s similar to a conductive comb. The connected ends of the wires are usually grounded. The open-circuit wires prohibit circulating current from wire to wire. Fields of the induced current would cancel the field of the inducing current thus canceling inductive coupling. Due to the gaps, the screen is transparent to the magnetic field but the wires capture the electrostatic lines of force and eliminate capacitive coupling through the screen. A screen properly grounded at both ends of the wires sliminates magnstic and electrostatic coupling. It is a shield but not a Faraday shield. A continuous conducting shield is not a Faraday shield, even if perforated with small holes. A lot of screened rooms have been constructed from copper window screen. It decouples the contentents of the room from the whole world when done correctly. Best regards, Richard Harrison, KB5WZI |
Richard Harrison wrote:
A Faraday screen, shield, or cage is a network of parallel wires or strips connected together at one end but disconnected from each other at their opposite ends. I`ve worked at several broadcast stations which used Faraday screens The special comb-like structure that Richard describes, which is deliberately constructed to block electric fields but transmit magnetic fields, is normally called a Faraday "screen" - but not a cage. The term Faraday "cage" is reserved for a complete conducting enclosure that blocks both electric and magnetic fields from entering the interior. The rest of the discussion is about how well an incomplete or penetrated enclosure might work as a Faraday cage. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Ian White, G3SEK wrote:
"---but not a cage." A cage according to my American dictionary is: "A boxlike receptacle or enclosure for confining birds or other animals, made with openwork of wires, bars, etc." Ian sent me to my dictionary of electronics which reads: "Faraday cage-See Faraday Shield" Usage varies from place to place. I don`t know if I`m vindicated or stand corrected. Best regards, Richard Harrison, KB5WZI |
In message , Richard
Harrison writes Ian White, G3SEK wrote: "---but not a cage." A cage according to my American dictionary is: "A boxlike receptacle or enclosure for confining birds or other animals, made with openwork of wires, bars, etc." Ian sent me to my dictionary of electronics which reads: "Faraday cage-See Faraday Shield" Usage varies from place to place. I don`t know if I`m vindicated or stand corrected. Best regards, Richard Harrison, KB5WZI Was it not an Ice Bucket which Faraday used to demonstrate the fact that the electrostatic charges repelled each other as far as possible, and therefore stayed on the outside of the bucket? The inside was electrically dead. Ian. -- |
On Tue, 28 Dec 2004 21:46:06 +0000, Ian Jackson
wrote: Was it not an Ice Bucket which Faraday used to demonstrate the fact that the electrostatic charges repelled each other as far as possible, and therefore stayed on the outside of the bucket? The inside was electrically dead. Hi Ian, Maybe it was part of an office party. Anyway, Gauss demonstrated that electric charge FIELD LINES prefer as much separation as possible (which conforms to your charges being repelled). With a curvature, the field line normal to the surface will either cause line crowding or line spreading depending upon the geometry. With a positive curvature (the outside of a conducting shell) the lines spread; with a negative curvature (the inside of a conducting shell) the lines converge. Given that the bucket is conductive inside and out, he demonstrated that line proximity within the bucket drove the charges outside. This is not quite an issue of charges being repelled as far as possible, or they would be uniformly distributed inside and out. By the same logic (and experience), charge will accumulate on the surface at the smallest radius - hence the points on lightning rods. By extension, this is also the source of capacitor failure at either the edges (smallest radius of a plate) or in surface burrs. HCJB, in Quito, suffered from corona discharge and converted to loops (misnomer, actually box), they still suffered when the corners (smallest radius) supported the same discharge (being corner fed). They shifted to a center feed point and put the hi voltage nodes at the middle of a wire span. 73's Richard Clark, KB7QHC |
In message , Richard Clark
writes By the same logic (and experience), charge will accumulate on the surface at the smallest radius - hence the points on lightning rods. By extension, this is also the source of capacitor failure at either the edges (smallest radius of a plate) or in surface burrs. Again scraping the very bottom of the memory banks, I seem to recall that when lightning rods were first used (in the late 1700s), the British used sharp points. The French, in the spirit of one-upmanship, decided that theirs should have brass balls. DOH!!! Ian. -- |
"Ian Jackson" wrote , Richard Clark writes By the same logic (and experience), charge will accumulate on the surface at the smallest radius - hence the points on lightning rods. By extension, this is also the source of capacitor failure at either the edges (smallest radius of a plate) or in surface burrs. Again scraping the very bottom of the memory banks, I seem to recall that when lightning rods were first used (in the late 1700s), the British used sharp points. The French, in the spirit of one-upmanship, decided that theirs should have brass balls. DOH!!! Ian. -- Very interesting! However the American Benjamin Franklin's pointed lightning rods (it was not a British design) was never scientifically challenged until a couple of years ago. Scientists have now shown that blunt-tipped air terminals are attached by lightning with significantly higher frequency than sharp tipped rods are. Pretty amazing that it took over 230 years to "discover" this! So scrap the concept that a sharp edge attracts charges, at least it does not attract lighting, the ultimate charge. http://www.usatoday.com/weather/reso...-rod-tests.htm http://www.esdjournal.com/articles/f...n/franklin.htm http://www.mikeholt.com/news/archive...tningblunt.htm etc, etc Jack Painter Virginia Beach VA |
On Tue, 28 Dec 2004 18:56:13 -0500, "Jack Painter"
wrote: "Ian Jackson" wrote , Richard Clark writes By the same logic (and experience), charge will accumulate on the surface at the smallest radius - hence the points on lightning rods. By extension, this is also the source of capacitor failure at either the edges (smallest radius of a plate) or in surface burrs. Again scraping the very bottom of the memory banks, I seem to recall that when lightning rods were first used (in the late 1700s), the British used sharp points. The French, in the spirit of one-upmanship, decided that theirs should have brass balls. DOH!!! Ian. -- Very interesting! However the American Benjamin Franklin's pointed lightning rods (it was not a British design) was never scientifically challenged until a couple of years ago. Scientists have now shown that blunt-tipped air terminals are attached by lightning with significantly higher frequency than sharp tipped rods are. Pretty amazing that it took over 230 years to "discover" this! So scrap the concept that a sharp edge attracts charges, at least it does not attract lighting, the ultimate charge. http://www.usatoday.com/weather/reso...-rod-tests.htm http://www.esdjournal.com/articles/f...n/franklin.htm http://www.mikeholt.com/news/archive...tningblunt.htm etc, etc Jack Painter Virginia Beach VA Jack, All three references are of the same article. Note the rebuttals at the end of one of them. I would also find it hard to believe that ANY rods on a 12000 foot mountain were not hit in 7 years! That study would suggest that pointed rods were excellent lightning repellers and would protect things from being struck. Exactly what Franklin first thought. If not excellent repellers then it would be highly suspect of the placement of the pointed rods on the mountain. 73 Gary K4FMX |
Gary, K4FMX wrote:
"I would find it hard to believe that ANY rods on a 12,000 foot mountain were not hit in seven years." I saw a PBS program tonight on people scaling the highest peak in Antarctica. It may never have been struck by lightning in modern times. I spent two six-month hitches for my company on Tierra del Fuego. Not quite Antarctica, but still so cold that lightnning is unknown on the island. Best regards, Richard Harrison, KB5WZI |
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