Radio Luxembourg is, however, most famous as the source of the "Luxembourg effect." In 1933, shortly after these powerful transmissions started, its modulation was heard in the Netherlands, mixed with that of a German station on another frequency (1). It was soon proposed that this occurred because Radio Luxembourg's signal was so powerful it was heating the ionosphere, producing a nonlinear condition that mixed the two AM signals (2). This effect has since been studied by the HAARP (High Frequency Active Auroral Research Program) in Alaska.
As an aside, B. D. H. Telegen, the discoverer of the Luxembourg effect, was quite an interesting guy. He also invented the pentode vacuum tube (valve).
(1) Telegen, B. D. H., Interaction between radio waves? , Nature, 6, 369, 1933
(2) Bailey, V.A. and D.F. Martyn, Influence of electric waves on the ionosphere, Phil. Mag., 23, 369, 1934
Unlikely as it may seem, William Duddell's singing arc has an important place in wireless history. It was based on the carbon arc lamp, invented by Sir Humphrey Davy in the 1840s and which became popular in the 1850s, prior to the invention of the incandescent lamp. The arc lamp employed two carbon rods which, when brought together and then separated, produced a brilliant white light.
Unfortunately, it also produced a lot of audio noise (hissing, spitting, and whistling), which limited its use to outdoor lighting. Tesla and JJ Thompson independently designed high-frequency ac alternators to try to overcome this noise, with limited success (although the alternator technology became useful later for long wave wireless transmitters).
Duddell found that, by placing a capacitor in parallel to the arc, he could change the noise into a more-or-less pure tone, and he could adjust the pitch of the tone by adjusting the value of the capacitor. He created a musical instrument by connecting several of these oscillators to a keyboard, and toured Europe as a travelling novelty act.
The Dane Valdemar Poulsen began experimenting with Duddell's arc in 1902. He found that the frequency of oscillation could be greatly increased by operating the arc in a hydrogen atmosphere (!), and that both the frequency of oscillation and the efficiency could be improved by placing a magnetic field perpendicular to the arc. He was able to move the frequency high enough to make Duddell's singing arc a useful wireless transmitter; in fact, it was the first negative resistance, continuous-wave oscillator ever made. (Spark transmitters produce a damped wave.)
The U.S. rights to Poulsen's arc transmitter were purchased in 1909 and were used by the Federal Telegraph Company to make extremely powerful wireless transmitters--1 megawatt transmitters were delivered to the U.S. Navy by 1918. However, by that time short waves, which the arc transmitter could not make efficiently, became more practical for long-distance communication, and the vacuum tube led to the demise of arc transmitter technology. There were, however, several interesting threads that continued on:
--Valdemar Poulsen also invented the "telegraphone," the first magnetic wire recorder
--The Federal Telegraph Company hired Lee DeForest to work on receivers for its stations; while there, he invented the triode vacuum tube
--Peter V. Jensen left Federal to invent the loudspeaker; formed the Magnavox Corporation
--In the 1930s, unused magnetic pole pieces from a scrapped 1 megawatt arc transmitter were scavenged by Prof. Ernest O. Lawrence at the University of California at Berkeley, and used to make the first cyclotron subatomic particle accelerator.
So William Duddell's singing arc had quite a legacy!
The problem is in the definition of "better." Read "The Innovator's Dilemma" by Clayton M. Christensen.
The basic idea is that your present customers value a certain set of features or parameters of your product, which leads you to continue to make the same product, only "better", defining "better" to be "the same as your present product, only with [the parameter(s) they care about] improved." Significant numbers of new customers, however, can only be attracted by a new technology that, while perhaps scoring lower with your present customers, has some other feature that is not in your present product. Christensen uses the example of disk drives, which have been placed in smaller and smaller form factors, even though that hurts the existing customers of disk drive manufacturers, by reducing their storage capacity (which is the parameter the present customers care about). Smaller disk drives, however, enable the drives to be used in minicomputers instead of big iron, then in desktops instead of minicomputers, then in laptops and PDAs, etc., increasing their sales volume each time--the new customers at each transition value physical size over absolute storage capacity. The larger sales volume in turn led to R&D that enabled the new generation to eventually surpass the old in the original performance metric, storage capacity.
Existing customers resisted the change each time because, for example, the first 3.5-inch drives had less capacity than 5.25-inch drives, and who wants less capacity in a hard drive? But the manufacturer that listened to his present customers, keeping to the 5.25-inch format and not making 3.5-inch drives, found his market, and his business, disappearing quickly. Christensen used the term "incremental change" to describe the capacity improvements made in a given drive form factor (which made existing customers happier), and "distruptive change" to describe the move from one form factor to another (which brought in new customers).
Yes, but your reputation is established by making a giant stride in your field, and establishing a reputation is vitally important for a young researcher, leading to research money, subordinates, fame and power--all useful, even if all you want is to continue your research. Schoen claimed to be the first to work out how to make several things that are the major goals in their areas, including single-molecule transistors and organic field-effect transistors, and to discover fundamental physical properties of avant-garde materials, such as superconductivity in polymers and fullerines. Had he reported that he had just concluded a series of experiments that did *not* produce superconductive tetracene, for example, no one would know of, or care about, him. If he could get the paper published at all, it would be in some second-tier publication, not on the cover of Nature.
Wow, what a spectacularly, ah, interesting translation--no offense intended to those associated with the writing of the translation engine. One of the machine translation pitfalls I hadn't previously considered was the problem of identifying and handling proper names that are also in the dictionary of the original language. Schoen == beautiful, or beautifully, so "Jan Hendrik Schoen" gets translated to "January Hendrik beautiful," and multiple references to "Schoen" in the text get morphed into, well, "beautiful" phrases. I guess he's fortunate, to some extent; we can all think of less complementary examples....
This thread discusses a common misconception about loss vs. frequency. It is not true, in general, that path loss increases with frequency, as the grandparent poster suggests, nor is it true that the path loss decreases with frequency, as the parent poster posits.
Path loss is independent of frequency. Think about it--if path loss were proportional to frequency, no light would reach the Earth from the sun, due to the incredible path loss at that high frequency.
However, "apparent" path loss depends on the type of antenna used. "Constant gain" antennas, like the resonant dipoles and loops commonly used for WLANs, get smaller with increasing frequency, since their size is proportional to a wavelength. They therefore intercept proportionally less of the radiated signal at higher frequencies, and a "loss" is apparent. Parabolic dishes, on the other hand, are of the "constant aperture" antenna type; as the parent poster correctly points out, the gain of these antennas increases with frequency. Users of these antennas see a "path loss" increase at lower frequencies.
Interestingly, if one were to transmit with a dipole and receive that signal with a parabolic dish (so that one side of the link had a constant gain antenna and the other side had a constant aperture antenna), the apparent "path loss" of this system would be independent of frequency.
That's the whole reason it works--the frequency of resonance is a function of the physical size (and shape) of the resonantor, just like in acoustics, where the larger bell has a lower pitch. The frequency of resonance of the earth-ionosphere cavity is largely (but not completely) determined by the circumference of the Earth.
Schumann resonance-lightning from around the world
on
Listen to the Sky
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· Score: 5, Interesting
You're probably referring to the Schumann resonance, the resonance of the earth-ionosphere resonant cavity. Energy from lightning around the world excites this resonance, which then rings--much as hitting a bell with a hammer causes the bell to ring.
Also like an acoustic bell, there is a fundamental frequency of resonance and many overtones that grow fainter as you go up in frequency. The fundamental Schumann resonance is approximately 7.8 Hz; the first few overtones are usually given as 13.8, 19.7, 25.7, and 31.7 Hz. There is a slight variation in the frequencies involved over long periods of time, as the ionosphere changes in response to solar activity.
Check the link I provide, pal--even the 1994 paper I cite isn't online, just the citation for it. If there were there an earlier paper, it has not been recorded in any article database google searches, nor has it been cited by any electronic article published since. The article doesn't provide a citation to the paper it mentions; I'm pointing out that, with the information provided, it seems likely that the 1994 reference is the correct citation and that the original author is in error.
A quick google search reveals evidence of only one paper (but not the paper itself, unfortunately) entitled, "Performance, Beliefs, and the Illusion of Control", see, e.g., here:
Kottemann, J.E., Davis, F.D., & Remus, W.R. (1994). Computer-assisted decision making: Performance, beliefs, and the illusion of control. Organizational Behavior and Human Decision Processes, 57, 26-37.
Note that this paper was published in 1994; it's not a "1980s paper" as cited in the article. Careless errors like this make one wonder what else in the author's train of thought is similarly researched. Perhaps he's just incorporating incertainty into his references, too--or, maybe he considers 1994 to be statistically similar to the 1980s?
It has to do with the relative length of time it takes to send morse characters. (Note in the following that "dahs" are three times as long as "dits".)
For example, "AND" is di-dah dah-dit dah-di-dit, while "ES" is dit di-di-dit. "AND" takes more than three times as long to send as "ES", so "ES" has become popular. Similar logic leads to the use of "FB" over "OK", although both are heard.
The letter "O", dah-dah-dah, is particularly troublesome, since it is a popular vowel in English, yet it is very long; other letters are often substituted for it when possible. On the other hand, "E", dit, is the shortest letter; it is often used to to substitute for other vowels. "FER" for "FOR" is the result.
I agree completely. Reading about this system made me marvel at the salesmanship involved. You'd think anyone past high school would recognize such obvious pseudoscience, but I guess the saying about fools being born every minute is a great truism. People don't realize how rare hail damage is, statistically, and so they can be led to believe that systems like this work, when it's just very likely that hail hasn't fallen on that 100-acre plot of land in the last three years because, well, hail wasn't going to fall there in the first place.
Unless Nissan got a better deal, even the company's guarantee is worthless, viz.:
[...]
Anti-Hail clause
In order to respect its obligation of fully satisfied or money back warranty, Hail Stop Equipment inc. warrants to the users of its product a protection against hail on a 500 meters (1650 pi.) radius. If the customer had damages caused by hail inside the protected zone, then Hail Stop Equipment inc. will compensate the customer's losses. The refund value is limited to the lesser of both amounts; either to the value of the losses or the amount that the customer paid to buy its Ollivier Hail Suppression system(R). The customer requests are subjected to a $5,000US exemption. A preheating delay of 20 minutes must occure to give the time to the Ollivier system to reaches optimal efficiency.
In order to keep your guarantee your 3 years warranty effective, Hail Stop Equipment inc. require a complete annual audit of the system to deliver a yearly certificate of conformity attesting that the system has been inspected (and adjusted if need be) and Hail Stop Equipment inc. takes back its warranty for another year until the end of the third year from the date of installation. The certificate also confirms the eligibility to the service contract renewal. The yearly certification assures the customer that its system is always functional, safe and efficient. If you are covered by an optional service contract, then the manpower required for the works of yearly certification is free. [emphasis added]
So, even if hundreds of acres of cars are hail-damaged while the system is in use (after the 20-minute warmup period), the company is only liable for the cost of the "hail suppression system", minus $5000! However, you have to pay, either directly or via a service contract, for an annual inspection to keep the 3-year warrranty in force--price undisclosed.
The only way this makes any economic sense for Nissan is if they got the system for free, so that the shyster company can use them as a showcase customer, for the publicity value. Even then, you'd think the public embarassment at being associated with such a scam would be intolerable.
The whole thing reminds me of the story about the guy jumping up and down in the middle of the street, blowing a whistle. Someone walks up and says,
Thanks for the link to MBco--actually, they list the EIRP in Table 1 here. 67 dBW EIRP at S band! And a 4.1-ton satellite, 22 m by 31 m in size! Wow! The other thing they've done is gone to 15 fps and a QVGA screen, so they've reduced the data rate significantly--it's only 512 kb/s. That geatly helps sensitivity over a conventional full-screen, full-motion video stream.
I said I wanted to see the satellite design--I didn't doubt that the Japanese had done the design work; I just couldn't see how they could do it. (A 12-meter dish will have a gain of about 48 dB at 2.8 GHz, BTW.)
The handset design is one thing, but I'd really like to see the design of the satellite.
Since the article discusses the use of a single satellite, for use by Korea and Japan only, one concludes that the satellite must be in geosynchronous orbit (otherwise there would be service outages as it passed behind the earth). That puts it 22,300 miles up (in the Clarke Belt).
Since the Clarke Belt is so far away, a combination of
high transmitter power in the satellite,
good sensitivity (low noise figure) in the receiver back on Earth, and
high antenna gain at both transmitter and receiver
are typically used to make the link work. Modern satellite television (e.g., DirecTV) uses a relatively high frequency of operation (12 GHz) so that high antenna gain can be achieved in a physically small (i.e., less than two foot diameter) package. However, the article says that the proposed system operates at 2.6 GHz. This would seriously kill any hope of significant antenna gain at the receiver, even if one could design a gain antenna that could track a satellite in a mobile, handheld system.
Said another way, in the DirecTV system, the typical Earthside antenna has a gain of about 33.5 dBi. The handheld antenna gain will be doing well to reach 0 dBi. Since the DirecTV receiver has a noise figure of only 1 dB, no receiver sensitivity improvement is possible there. The only way to get back the 33.5 dB of link margin is to either increase the satellite's antenna gain by an additional 33.5 dB (which would make it impractically large, especially given the low frequency of operation, and give it a very small footprint on the Earth's surface) or increase the transmitter power by 33.5 dB (or 2239x).
How is the system to work?? Does anyone have a link margin calculation for this system?
While direct reception of Spirit and Opportunity is probably beyond the capabilities of single-amateur equipment, reception of a continuous wave (unmodulated carrier) beacon transmitted by the Mars Relay Radio System aboard the Mars Global Surveyor on the way to Mars was achieved by amateurs in 1996. At the time, the 1.3 Watt transmitter was approximately 5 million km away from Earth.
The Mars Express probe that launched the ill-fated Beagle 2 lander, and the Mars Orbiter in orbit around Mars, were both detected by this station in November last year, although it stretches the definition of "amateur" quite a bit; also by these guys with much more modest equipment.
For a real challenge, the New Horizons spacecraft, scheduled for launch in 2006 to Pluto and the Kuiper Belt beyond, will employ beacon cruise mode, in which it will send a fixed tone (see page 42), designed for easier reception by amateurs, while cruising in deep space.
Additional information on amateur deep space reception is available here.
laches, n: Negligence or undue delay in asserting a legal right or privilege.
As the judge noted in his ruling, "...the Supreme Court held that a person 'may forfeit his rights as an inventor by a willful or negligent postponement of his claims, or by an attempt to withhold the benefit of his improvement from the public until a similar or the same improvement should have been made and introduced to others'". Lemelson was found to have delayed the prosecution of his patents--albeit within the rules and procedures of the USPTO--and Symbol and Cognex were able to use the defense of prosecution laches to defend themselves from Lemelson's request for license fees by getting the claims of the relevant patents ruled unenforceable. The judge noted that
More than five million United States patents have issued from 1914 through 2001. Lemelson's own exhibits demonstrate that of the 325 patents that issued in that period with a prosecution pendency of longer than eleven years, Lemelson holds the top thirteen positions for the longest prosecutions. Some of the claims asserted by Lemelson in this case will not expire until 2011, fifty-five years after the 1956 application was filed and forty-eight years after the application issued as a patent...If the defense of prosecution laches does not apply under the totality of circumstances presented here, the Court can envision very few circumstances under which it would.
In addition, the judge ruled that the claims were "not infringed by Symbol and Cognex because use of the accused products does not satisfy one or more of the limitations of each and every asserted claim [i.e., Lemelson's patent does not cover the products for which Lemelson was trying to get license fees]; and that the claims are invalid for lack of written description and enablement even if construed in the manner urged by Lemelson...." This last point refers to the so-called "enablement" requirement of a patent: A patent should enable one of ordinary skill in the art to duplicate the invention from the patent document. The judge ruled that "one of ordinary skill in the art to which it pertains" would be unable to make a functional machine vision system as described by Lemelson's patents.
Since Spirit is rebooting sixty times per day, a problem that started when an electric motor moving its spectrometer "conked out", one thinks first of a hardware failure, possibly leading to software corruption.
I don't know the boot sequence of Spirit, but in most battery-powered embedded systems with which I am familiar, an elaborate state machine design is made to ensure that, when the boot sequence is complete, the system has sufficient power to perform any task that may be requested of it. Since the power supply is limited, an unexpectedly heavy load on the primary supply could cause the supply voltage to the microcomputer to fall below its specified lower limit, leading to a system reset.
Now imagine that there is a hardware failure associated with some process that runs during the boot sequence--a voltage regulator turn-on, a heating system initialization, an electric motor activation, whatever--that results in excessive current drain. When this part of the boot sequence is reached, the supply voltage falls, and the microcomputer resets. This disables the problem-causing hardware, unloading the power supply. When the supply voltage recovers, the microcomputer reboots (either automatically, with a power-on reset, via a watchdog timer, or via some other means) and, when the critical part of the boot sequence is reached, the supply voltage falls again. The system is now in a continuous loop, in which it can remain indefinitely. (Or at least 60 times per day....)
Note that this situation can also arise due to a defect in the power supply--if the output impedance of the power supply has risen for some reason, its output voltage under lightly loaded conditions can be acceptable, but it may not be able to supply heavier loads.
One expects the Spirit power supply to be complex, with separate regulators for the microcomputer, radio transceiver, and electric motors, so looking for common circuits and systems would be the first thing to do when troubleshooting for this type of failure. Looking for system conditions that can cause a system reset would be another; the JPL people have lived with their systems for years now, and would have had many design reviews to identify possible system failure scenarios--I'm not telling them anything new here. I understand that the system telemetry received yesterday indicates that the power supply is within specification, so that seems to eliminate that possiblility.
The second alternative is a soft memory failure of some kind, either caused by a supply failure as the parent suggests or perhaps by a radiation event of some kind.
Note that these problems can be multi-disciplinary; for example, the problem could be caused by some vibration when a motor runs that loosens a broken connection created by a chemical reaction to something on the surface (to take an extreme example).
Helen, Georgia (also here) is a fascinating place in its own right. You drive along the highway through dozens of nondescript small Georgia towns (each fading into obscurity in its own way) then come around a curve in the road to find an alpine villiage from Bavaria! In the late 1960's, with the town's major industries gone, the citizens decided that they needed a new industry if the town was to survive, and went with tourism. To separate themselves from their neighbors, they went with a "theme": The entire town was rebuilt with cobblestone alleyways, bavarian-style buildings, etc.--everything from doghouses to government buildings is done in the same style. The effect is quite dramatic and has been a great economic success; far from fading into obscurity, their biggest problem now is controlling the town's growth.
When I was younger, and before my brains were fully developed, I climbed radio towers for a living. Right up the side, several hundred feet, replacing light bulbs, installing antennas, etc.
One morning my partner and I were packing the truck to go climb a tower at a pulp mill (where wood pulp is boiled to--eventually--produce paper) in a nearby town. Just as we were starting the truck, the boss comes running out, waiving his arms and telling us to stop--he'd just received a phone call from the mill; the tower collapsed the night before! Apparently, the corrosive exhaust of the the mill had weakened the tower to the point that it wouldn't support its own weight.
My partner and I told ourselves that we would have spotted the weakness in the tower once we got there, and wouldn't have climbed it anyway; nevertheless, our usual pre-climb tower inspections were done with significantly more attention to detail after that.
The problem with this solution is that the crystal is now physically 32.768/10.000 = 3.2768 times as large as the original, and won't fit in the watch. As I mentioned, the frequency chosen is a compromise between physical size of the crystal and power consumption; that's why the original watch design didn't use a 2^13 = 8.192 kHz crystal, for example.
Because all things digital are not programmable. To minimize power consumption, the counting logic in your average wristwatch is fixed in hardware, and is not adjustable. There's no software running in it.
Hacking a digital watch is nontrivial, especially if you have the same size and power consumption requirements as the original watch. The power budget of digital watches is austere, to say the least; typical drain of the entire watch, including oscillator, divider chain, and display driver, is 500 nA at 1.5 V, or 750 nW (a nanowatt is one billionth of a Watt).
Watches use 32.768 kHz AT-strip (tuning fork-style) quartz crystals (like these) as a compromise between size and low power consumption. The smaller the size of a crystal operating in a given mode of oscillation, the higher the frequency of oscillation. However, the power consumption of a digital switching circuit increases directly with the switching frequency (it is P (Watts) = CV^2f, where C is the capacitance of the switching device in Farads, V is the difference in volts between a logical 1 and a logical 0, and f is the frequency of switching in Hz). Having a higher oscillation frequency requires a longer frequency divider to divide the oscillator's output down to the required 1 Hz output, which raises the power consumption of the divider (mostly due to the higher switching frequency of the first few stages).
Having the crystal oscillate at a binary multiple of the desired output (32768 = 2^15) makes the divider circuits especially simple (15 divide-by-two stages in series). Having a non-binary multiple would require more switching circuitry and add to power consumption.
To hack such a system to Mars time would require either changing the crystal frequency or the divider string. Changing the divider string would require modifying the watch chip, a design task that would be relatively simple, digital design tools being what they are, but expensive and time-consuming, since a new IC mask set would have to be generated and a new lot of chips run through the fab--say, $250k and 3-6 months, if you started today. Not very desirable if you're a JPL guy funding this out of your own pocket (which is how this was done).
The alternative is to modify the crystal frequency. AT-strip tuning-fork watch crystals are cheap because they're made in a lithographic manner not dissimilar to that of IC production--a mask is made, resist is printed over a quartz blank, the blank is etched, etc. This produces nearly-identical parts in bulk, making them cheap. This is different from the standard AT-cut crystals with which most amateurs are familiar; AT-cut crystals are individually cut and polished to frequency. Since AT-strip crystals are made in bulk, one cannot get a small lot of them inexpensively, as one can AT-cut crystals; the manufacturer must make a new mask set for the new frequency, a relatively expensive task if one will only purchase, say, a hundred crystals. Modifying the crystal frequency is less expensive than making a new watch chip; however, neither option is suitable for the volumes and price points the JPL guys were trying to hit. Ergo, the mechanical watch.
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Radio Luxembourg is, however, most famous as the source of the "Luxembourg effect." In 1933, shortly after these powerful transmissions started, its modulation was heard in the Netherlands, mixed with that of a German station on another frequency (1). It was soon proposed that this occurred because Radio Luxembourg's signal was so powerful it was heating the ionosphere, producing a nonlinear condition that mixed the two AM signals (2). This effect has since been studied by the HAARP (High Frequency Active Auroral Research Program) in Alaska.
As an aside, B. D. H. Telegen, the discoverer of the Luxembourg effect, was quite an interesting guy. He also invented the pentode vacuum tube (valve).
(1) Telegen, B. D. H., Interaction between radio waves? , Nature, 6, 369, 1933
(2) Bailey, V.A. and D.F. Martyn, Influence of electric waves on the ionosphere, Phil. Mag., 23, 369, 1934
Unlikely as it may seem, William Duddell's singing arc has an important place in wireless history. It was based on the carbon arc lamp, invented by Sir Humphrey Davy in the 1840s and which became popular in the 1850s, prior to the invention of the incandescent lamp. The arc lamp employed two carbon rods which, when brought together and then separated, produced a brilliant white light.
Unfortunately, it also produced a lot of audio noise (hissing, spitting, and whistling), which limited its use to outdoor lighting. Tesla and JJ Thompson independently designed high-frequency ac alternators to try to overcome this noise, with limited success (although the alternator technology became useful later for long wave wireless transmitters).
Duddell found that, by placing a capacitor in parallel to the arc, he could change the noise into a more-or-less pure tone, and he could adjust the pitch of the tone by adjusting the value of the capacitor. He created a musical instrument by connecting several of these oscillators to a keyboard, and toured Europe as a travelling novelty act.
The Dane Valdemar Poulsen began experimenting with Duddell's arc in 1902. He found that the frequency of oscillation could be greatly increased by operating the arc in a hydrogen atmosphere (!), and that both the frequency of oscillation and the efficiency could be improved by placing a magnetic field perpendicular to the arc. He was able to move the frequency high enough to make Duddell's singing arc a useful wireless transmitter; in fact, it was the first negative resistance, continuous-wave oscillator ever made. (Spark transmitters produce a damped wave.)
The U.S. rights to Poulsen's arc transmitter were purchased in 1909 and were used by the Federal Telegraph Company to make extremely powerful wireless transmitters--1 megawatt transmitters were delivered to the U.S. Navy by 1918. However, by that time short waves, which the arc transmitter could not make efficiently, became more practical for long-distance communication, and the vacuum tube led to the demise of arc transmitter technology. There were, however, several interesting threads that continued on:
--Valdemar Poulsen also invented the "telegraphone," the first magnetic wire recorder
--The Federal Telegraph Company hired Lee DeForest to work on receivers for its stations; while there, he invented the triode vacuum tube
--Peter V. Jensen left Federal to invent the loudspeaker; formed the Magnavox Corporation
--In the 1930s, unused magnetic pole pieces from a scrapped 1 megawatt arc transmitter were scavenged by Prof. Ernest O. Lawrence at the University of California at Berkeley, and used to make the first cyclotron subatomic particle accelerator.
So William Duddell's singing arc had quite a legacy!
The problem is in the definition of "better." Read "The Innovator's Dilemma" by Clayton M. Christensen.
The basic idea is that your present customers value a certain set of features or parameters of your product, which leads you to continue to make the same product, only "better", defining "better" to be "the same as your present product, only with [the parameter(s) they care about] improved." Significant numbers of new customers, however, can only be attracted by a new technology that, while perhaps scoring lower with your present customers, has some other feature that is not in your present product. Christensen uses the example of disk drives, which have been placed in smaller and smaller form factors, even though that hurts the existing customers of disk drive manufacturers, by reducing their storage capacity (which is the parameter the present customers care about). Smaller disk drives, however, enable the drives to be used in minicomputers instead of big iron, then in desktops instead of minicomputers, then in laptops and PDAs, etc., increasing their sales volume each time--the new customers at each transition value physical size over absolute storage capacity. The larger sales volume in turn led to R&D that enabled the new generation to eventually surpass the old in the original performance metric, storage capacity.
Existing customers resisted the change each time because, for example, the first 3.5-inch drives had less capacity than 5.25-inch drives, and who wants less capacity in a hard drive? But the manufacturer that listened to his present customers, keeping to the 5.25-inch format and not making 3.5-inch drives, found his market, and his business, disappearing quickly. Christensen used the term "incremental change" to describe the capacity improvements made in a given drive form factor (which made existing customers happier), and "distruptive change" to describe the move from one form factor to another (which brought in new customers).
And that's what Negroponte meant.
Yes, but your reputation is established by making a giant stride in your field, and establishing a reputation is vitally important for a young researcher, leading to research money, subordinates, fame and power--all useful, even if all you want is to continue your research. Schoen claimed to be the first to work out how to make several things that are the major goals in their areas, including single-molecule transistors and organic field-effect transistors, and to discover fundamental physical properties of avant-garde materials, such as superconductivity in polymers and fullerines. Had he reported that he had just concluded a series of experiments that did *not* produce superconductive tetracene, for example, no one would know of, or care about, him. If he could get the paper published at all, it would be in some second-tier publication, not on the cover of Nature.
Wow, what a spectacularly, ah, interesting translation--no offense intended to those associated with the writing of the translation engine. One of the machine translation pitfalls I hadn't previously considered was the problem of identifying and handling proper names that are also in the dictionary of the original language. Schoen == beautiful, or beautifully, so "Jan Hendrik Schoen" gets translated to "January Hendrik beautiful," and multiple references to "Schoen" in the text get morphed into, well, "beautiful" phrases. I guess he's fortunate, to some extent; we can all think of less complementary examples....
This thread discusses a common misconception about loss vs. frequency. It is not true, in general, that path loss increases with frequency, as the grandparent poster suggests, nor is it true that the path loss decreases with frequency, as the parent poster posits.
Path loss is independent of frequency. Think about it--if path loss were proportional to frequency, no light would reach the Earth from the sun, due to the incredible path loss at that high frequency.
However, "apparent" path loss depends on the type of antenna used. "Constant gain" antennas, like the resonant dipoles and loops commonly used for WLANs, get smaller with increasing frequency, since their size is proportional to a wavelength. They therefore intercept proportionally less of the radiated signal at higher frequencies, and a "loss" is apparent. Parabolic dishes, on the other hand, are of the "constant aperture" antenna type; as the parent poster correctly points out, the gain of these antennas increases with frequency. Users of these antennas see a "path loss" increase at lower frequencies.
Interestingly, if one were to transmit with a dipole and receive that signal with a parabolic dish (so that one side of the link had a constant gain antenna and the other side had a constant aperture antenna), the apparent "path loss" of this system would be independent of frequency.
That's the whole reason it works--the frequency of resonance is a function of the physical size (and shape) of the resonantor, just like in acoustics, where the larger bell has a lower pitch. The frequency of resonance of the earth-ionosphere cavity is largely (but not completely) determined by the circumference of the Earth.
You're probably referring to the Schumann resonance, the resonance of the earth-ionosphere resonant cavity. Energy from lightning around the world excites this resonance, which then rings--much as hitting a bell with a hammer causes the bell to ring.
Also like an acoustic bell, there is a fundamental frequency of resonance and many overtones that grow fainter as you go up in frequency. The fundamental Schumann resonance is approximately 7.8 Hz; the first few overtones are usually given as 13.8, 19.7, 25.7, and 31.7 Hz. There is a slight variation in the frequencies involved over long periods of time, as the ionosphere changes in response to solar activity.
Check the link I provide, pal--even the 1994 paper I cite isn't online, just the citation for it. If there were there an earlier paper, it has not been recorded in any article database google searches, nor has it been cited by any electronic article published since. The article doesn't provide a citation to the paper it mentions; I'm pointing out that, with the information provided, it seems likely that the 1994 reference is the correct citation and that the original author is in error.
A quick google search reveals evidence of only one paper (but not the paper itself, unfortunately) entitled, "Performance, Beliefs, and the Illusion of Control", see, e.g., here:
Kottemann, J.E., Davis, F.D., & Remus, W.R. (1994). Computer-assisted decision making: Performance, beliefs, and the illusion of control. Organizational Behavior and Human Decision Processes, 57, 26-37.
Note that this paper was published in 1994; it's not a "1980s paper" as cited in the article. Careless errors like this make one wonder what else in the author's train of thought is similarly researched. Perhaps he's just incorporating incertainty into his references, too--or, maybe he considers 1994 to be statistically similar to the 1980s?
It has to do with the relative length of time it takes to send morse characters. (Note in the following that "dahs" are three times as long as "dits".)
For example, "AND" is di-dah dah-dit dah-di-dit, while "ES" is dit di-di-dit. "AND" takes more than three times as long to send as "ES", so "ES" has become popular. Similar logic leads to the use of "FB" over "OK", although both are heard.
The letter "O", dah-dah-dah, is particularly troublesome, since it is a popular vowel in English, yet it is very long; other letters are often substituted for it when possible. On the other hand, "E", dit, is the shortest letter; it is often used to to substitute for other vowels. "FER" for "FOR" is the result.
You may have been prescient: The new Lexus LS-430 has golf ball dimples on the underside.
I agree completely. Reading about this system made me marvel at the salesmanship involved. You'd think anyone past high school would recognize such obvious pseudoscience, but I guess the saying about fools being born every minute is a great truism. People don't realize how rare hail damage is, statistically, and so they can be led to believe that systems like this work, when it's just very likely that hail hasn't fallen on that 100-acre plot of land in the last three years because, well, hail wasn't going to fall there in the first place.
Unless Nissan got a better deal, even the company's guarantee is worthless, viz.:
So, even if hundreds of acres of cars are hail-damaged while the system is in use (after the 20-minute warmup period), the company is only liable for the cost of the "hail suppression system", minus $5000! However, you have to pay, either directly or via a service contract, for an annual inspection to keep the 3-year warrranty in force--price undisclosed.
The only way this makes any economic sense for Nissan is if they got the system for free, so that the shyster company can use them as a showcase customer, for the publicity value. Even then, you'd think the public embarassment at being associated with such a scam would be intolerable.
The whole thing reminds me of the story about the guy jumping up and down in the middle of the street, blowing a whistle. Someone walks up and says,
"Why are you blowing the whistle?"
"To scare the elephants away."
"Elephants? There are no elephants around here!"
"See? It's working!"
Thanks for the link to MBco--actually, they list the EIRP in Table 1 here. 67 dBW EIRP at S band! And a 4.1-ton satellite, 22 m by 31 m in size! Wow! The other thing they've done is gone to 15 fps and a QVGA screen, so they've reduced the data rate significantly--it's only 512 kb/s. That geatly helps sensitivity over a conventional full-screen, full-motion video stream.
I said I wanted to see the satellite design--I didn't doubt that the Japanese had done the design work; I just couldn't see how they could do it. (A 12-meter dish will have a gain of about 48 dB at 2.8 GHz, BTW.)
Very impressive.
The handset design is one thing, but I'd really like to see the design of the satellite.
Since the article discusses the use of a single satellite, for use by Korea and Japan only, one concludes that the satellite must be in geosynchronous orbit (otherwise there would be service outages as it passed behind the earth). That puts it 22,300 miles up (in the Clarke Belt).
Since the Clarke Belt is so far away, a combination of
high transmitter power in the satellite,
good sensitivity (low noise figure) in the receiver back on Earth, and
high antenna gain at both transmitter and receiver
are typically used to make the link work. Modern satellite television (e.g., DirecTV) uses a relatively high frequency of operation (12 GHz) so that high antenna gain can be achieved in a physically small (i.e., less than two foot diameter) package. However, the article says that the proposed system operates at 2.6 GHz. This would seriously kill any hope of significant antenna gain at the receiver, even if one could design a gain antenna that could track a satellite in a mobile, handheld system.
Said another way, in the DirecTV system, the typical Earthside antenna has a gain of about 33.5 dBi. The handheld antenna gain will be doing well to reach 0 dBi. Since the DirecTV receiver has a noise figure of only 1 dB, no receiver sensitivity improvement is possible there. The only way to get back the 33.5 dB of link margin is to either increase the satellite's antenna gain by an additional 33.5 dB (which would make it impractically large, especially given the low frequency of operation, and give it a very small footprint on the Earth's surface) or increase the transmitter power by 33.5 dB (or 2239x).
How is the system to work?? Does anyone have a link margin calculation for this system?
While direct reception of Spirit and Opportunity is probably beyond the capabilities of single-amateur equipment, reception of a continuous wave (unmodulated carrier) beacon transmitted by the Mars Relay Radio System aboard the Mars Global Surveyor on the way to Mars was achieved by amateurs in 1996. At the time, the 1.3 Watt transmitter was approximately 5 million km away from Earth.
The Mars Express probe that launched the ill-fated Beagle 2 lander, and the Mars Orbiter in orbit around Mars, were both detected by this station in November last year, although it stretches the definition of "amateur" quite a bit; also by these guys with much more modest equipment.
For a real challenge, the New Horizons spacecraft, scheduled for launch in 2006 to Pluto and the Kuiper Belt beyond, will employ beacon cruise mode, in which it will send a fixed tone (see page 42), designed for easier reception by amateurs, while cruising in deep space.
Additional information on amateur deep space reception is available here.
Care to tell the rest of us what the URL is?
As the judge noted in his ruling, "...the Supreme Court held that a person 'may forfeit his rights as an inventor by a willful or negligent postponement of his claims, or by an attempt to withhold the benefit of his improvement from the public until a similar or the same improvement should have been made and introduced to others'". Lemelson was found to have delayed the prosecution of his patents--albeit within the rules and procedures of the USPTO--and Symbol and Cognex were able to use the defense of prosecution laches to defend themselves from Lemelson's request for license fees by getting the claims of the relevant patents ruled unenforceable. The judge noted that
In addition, the judge ruled that the claims were "not infringed by Symbol and Cognex because use of the accused products does not satisfy one or more of the limitations of each and every asserted claim [i.e., Lemelson's patent does not cover the products for which Lemelson was trying to get license fees]; and that the claims are invalid for lack of written description and enablement even if construed in the manner urged by Lemelson...." This last point refers to the so-called "enablement" requirement of a patent: A patent should enable one of ordinary skill in the art to duplicate the invention from the patent document. The judge ruled that "one of ordinary skill in the art to which it pertains" would be unable to make a functional machine vision system as described by Lemelson's patents.
Whew.
Since Spirit is rebooting sixty times per day, a problem that started when an electric motor moving its spectrometer "conked out", one thinks first of a hardware failure, possibly leading to software corruption.
I don't know the boot sequence of Spirit, but in most battery-powered embedded systems with which I am familiar, an elaborate state machine design is made to ensure that, when the boot sequence is complete, the system has sufficient power to perform any task that may be requested of it. Since the power supply is limited, an unexpectedly heavy load on the primary supply could cause the supply voltage to the microcomputer to fall below its specified lower limit, leading to a system reset.
Now imagine that there is a hardware failure associated with some process that runs during the boot sequence--a voltage regulator turn-on, a heating system initialization, an electric motor activation, whatever--that results in excessive current drain. When this part of the boot sequence is reached, the supply voltage falls, and the microcomputer resets. This disables the problem-causing hardware, unloading the power supply. When the supply voltage recovers, the microcomputer reboots (either automatically, with a power-on reset, via a watchdog timer, or via some other means) and, when the critical part of the boot sequence is reached, the supply voltage falls again. The system is now in a continuous loop, in which it can remain indefinitely. (Or at least 60 times per day....)
Note that this situation can also arise due to a defect in the power supply--if the output impedance of the power supply has risen for some reason, its output voltage under lightly loaded conditions can be acceptable, but it may not be able to supply heavier loads.
One expects the Spirit power supply to be complex, with separate regulators for the microcomputer, radio transceiver, and electric motors, so looking for common circuits and systems would be the first thing to do when troubleshooting for this type of failure. Looking for system conditions that can cause a system reset would be another; the JPL people have lived with their systems for years now, and would have had many design reviews to identify possible system failure scenarios--I'm not telling them anything new here. I understand that the system telemetry received yesterday indicates that the power supply is within specification, so that seems to eliminate that possiblility.
The second alternative is a soft memory failure of some kind, either caused by a supply failure as the parent suggests or perhaps by a radiation event of some kind.
Note that these problems can be multi-disciplinary; for example, the problem could be caused by some vibration when a motor runs that loosens a broken connection created by a chemical reaction to something on the surface (to take an extreme example).
Helen, Georgia (also here) is a fascinating place in its own right. You drive along the highway through dozens of nondescript small Georgia towns (each fading into obscurity in its own way) then come around a curve in the road to find an alpine villiage from Bavaria! In the late 1960's, with the town's major industries gone, the citizens decided that they needed a new industry if the town was to survive, and went with tourism. To separate themselves from their neighbors, they went with a "theme": The entire town was rebuilt with cobblestone alleyways, bavarian-style buildings, etc.--everything from doghouses to government buildings is done in the same style. The effect is quite dramatic and has been a great economic success; far from fading into obscurity, their biggest problem now is controlling the town's growth.
When I was younger, and before my brains were fully developed, I climbed radio towers for a living. Right up the side, several hundred feet, replacing light bulbs, installing antennas, etc.
One morning my partner and I were packing the truck to go climb a tower at a pulp mill (where wood pulp is boiled to--eventually--produce paper) in a nearby town. Just as we were starting the truck, the boss comes running out, waiving his arms and telling us to stop--he'd just received a phone call from the mill; the tower collapsed the night before! Apparently, the corrosive exhaust of the the mill had weakened the tower to the point that it wouldn't support its own weight.
My partner and I told ourselves that we would have spotted the weakness in the tower once we got there, and wouldn't have climbed it anyway; nevertheless, our usual pre-climb tower inspections were done with significantly more attention to detail after that.
The problem with this solution is that the crystal is now physically 32.768/10.000 = 3.2768 times as large as the original, and won't fit in the watch. As I mentioned, the frequency chosen is a compromise between physical size of the crystal and power consumption; that's why the original watch design didn't use a 2^13 = 8.192 kHz crystal, for example.
Because all things digital are not programmable. To minimize power consumption, the counting logic in your average wristwatch is fixed in hardware, and is not adjustable. There's no software running in it.
Nope. It needs to be more than 2% slower, which is far more than one can pull such an oscillator. It'd stop.
Hacking a digital watch is nontrivial, especially if you have the same size and power consumption requirements as the original watch. The power budget of digital watches is austere, to say the least; typical drain of the entire watch, including oscillator, divider chain, and display driver, is 500 nA at 1.5 V, or 750 nW (a nanowatt is one billionth of a Watt).
Watches use 32.768 kHz AT-strip (tuning fork-style) quartz crystals (like these) as a compromise between size and low power consumption. The smaller the size of a crystal operating in a given mode of oscillation, the higher the frequency of oscillation. However, the power consumption of a digital switching circuit increases directly with the switching frequency (it is P (Watts) = CV^2f, where C is the capacitance of the switching device in Farads, V is the difference in volts between a logical 1 and a logical 0, and f is the frequency of switching in Hz). Having a higher oscillation frequency requires a longer frequency divider to divide the oscillator's output down to the required 1 Hz output, which raises the power consumption of the divider (mostly due to the higher switching frequency of the first few stages).
Having the crystal oscillate at a binary multiple of the desired output (32768 = 2^15) makes the divider circuits especially simple (15 divide-by-two stages in series). Having a non-binary multiple would require more switching circuitry and add to power consumption.
To hack such a system to Mars time would require either changing the crystal frequency or the divider string. Changing the divider string would require modifying the watch chip, a design task that would be relatively simple, digital design tools being what they are, but expensive and time-consuming, since a new IC mask set would have to be generated and a new lot of chips run through the fab--say, $250k and 3-6 months, if you started today. Not very desirable if you're a JPL guy funding this out of your own pocket (which is how this was done).
The alternative is to modify the crystal frequency. AT-strip tuning-fork watch crystals are cheap because they're made in a lithographic manner not dissimilar to that of IC production--a mask is made, resist is printed over a quartz blank, the blank is etched, etc. This produces nearly-identical parts in bulk, making them cheap. This is different from the standard AT-cut crystals with which most amateurs are familiar; AT-cut crystals are individually cut and polished to frequency. Since AT-strip crystals are made in bulk, one cannot get a small lot of them inexpensively, as one can AT-cut crystals; the manufacturer must make a new mask set for the new frequency, a relatively expensive task if one will only purchase, say, a hundred crystals. Modifying the crystal frequency is less expensive than making a new watch chip; however, neither option is suitable for the volumes and price points the JPL guys were trying to hit. Ergo, the mechanical watch.