I don't think it would be as hard as you might think PROVIDED you really understood it yourself. Of course, this applies to anything you wish to teach to anyone.
The problem with relativity is that it is so counter intuitive to everyday experience and to the classical physics you've been taught that you have to unlearn much of it first. That may make it easier for younger people to understand -- they don't have as much to overcome as they would later.
Like most EEs, I was taught classical electromagnetism, first in high school, then in lower level undergraduate physics, and finally in much more detail in junior level EE school classes. We were also taught relativity, but as a separate topic within physics. Had I been taught relativity first, and then been taught electromagnetism in the relativistic way I think it would have actually have been easier and more satisfying. I would have learned that there really isn't such a thing as "magnetism"; what we see as magnetism is really just the electrostatic force as affected by special relativity (and some quantum mechanics). I would have readily understood why there are no magnetic monopoles, for example. And it would have shown me how every field in physics is related to every other, in fact that there really is only one "physics".
Actually no, it's not a straightforward calculation. That's why they want to conduct the test.
It's not a simple collision like we learned about in physics class, with the change in the asteroid's momentum coming entirely from the impactor. The impactor will hit at extremely high velocity (by earth standards), meaning that it will carry a lot of kinetic energy (one half mass times velocity squared) in a small volume. This kinetic energy will vaporize and blow off part of the asteroid, which because of the asteroid's small size, will completely escape.
The mass of the ejecta will greatly exceed the mass of the impactor, so even though it may move much more slowly than the impactor it will carry away considerably more momentum (mass times velocity). The momentum of this ejecta will have most of the effect on the asteroid's trajectory.
But it's unknown exactly how much momentum will be carried away by the ejecta as this depends on the makeup of the asteroid, its density, porosity, how quickly the impactor stops and releases its energy, etc. So that's why they want to try it.
A similar effect was at play in the JFK assassination that helped cause the counter-intuitive "back and to the right" motion of his head that had so many people incorrectly thinking there was a second shooter.
The main differences between it and the Funcube dongle are the same: the SDRPlay can sample at much higher rates, but only at 12 bits/sample, while the Funcube dongle samples at 192 kHz with 16 bits. The Funcube dongle therefore appears better suited to narrower modes, especially on HF and VHF where there may be strong interferers on nearby frequencies. The SDRPlay can do broadband modes too wide for the Funcube, such as HD Radio, ADS-B and digital TV, though many of those can also be done even more cheaply with 8-bit RTL-SDR dongles. The SDRPlay can also produce wideband waterfall displays.
Many hams today ARE using the Raspberry Pi and Arduino for their projects. Such as the local high school kids I help mentor. They build high altitude balloon payloads and fly them, and they all carried either an Arduino, a Pi, or both.
I/Q interfaces are vulnerable to ground loops only if the I/Q interface is analog. Why should it be, when we have excellent digital interfaces designed specifically for stereo digital audio? There are now several inexpensive SDRs (price range $100-$200) with USB interfaces, e.g., the Funcube Dongle Pro+ and the SDRPlay (there's now a second version). There's also the ultra-cheap RTL-SDR, but its narrow 8-bit A/D limits its use to VHF or UHF signals without strong adjacent channel interference. It's ideal for ADS-B (with a filter!) but I wouldn't recommend it for HF.
I've done most of my work so far with the Funcube dongle, which samples at 192 kHz and 16 bits/channel, feeding a USB interface. It looks just like a standard audio A/D to the OS, because that's what it is. The I&Q signals are produced at baseband so yes there are DC offsets and small gain and phase errors, but I found them easy to remove in software. Some phase noise is sometimes audible within a few hundred hertz of DC, but is easily swamped by typical input noise and gain settings.
Overall, this thing makes an excellent but inexpensive general coverage receiver. I sure wish I had something like this when I was a young ham without much money.
Hey, if you can read that disk, could you put it on the net somewhere? I didn't keep copies of all the earlier versions of my software. It'd be neat to see which one you got.
Probably the ultimate in QRP right now is WSPR (Weak Signal Propagation Reporter). This is a specially-designed very low speed (~1 bps) digital modulation and coding format designed for use as a propagation beacon, especially on the HF ("shortwave") bands. But it has recently been adapted for tracking ultra light weight (12.5 gram!) high altitude balloon payloads. One such payload, WB8ELK-2, has completed three complete trips around the world in the past month and is now on its fourth:
The tracker payload is powered directly by a pair of small thin-film solar panels. The weight budget is so extremely tight that there is no battery, so it transmits only during the day.
Well, not to toot my own horn too loudly, but in the mid 1980s I wrote a TCP/IP implementation. I intended it for ham radio use on low end PCs, as the only existing general purpose implementations were on commercial minicomputers far beyond a ham budget. (I actually began it on a dare by Terry Fox, WB4JFI, who insisted it was too complex to implement on anything a ham could afford.)
Before I knew it, my software was being widely used outside ham radio for dialup access to the Internet. Universities and companies set up banks of modems and PCs to give their students and employees access to their existing connections. Pretty soon commercial companies sprang up to do the same for the public, again using my software; I think we now call them "Internet Service Providers".
Meanwhile, the OSI world was continuing to produce large piles of paper, but no inexpensive (or free), usable software.
In the early 1990s, I went to Qualcomm where I ported my code onto their phones so it could be used to provide wireless Internet services.
Sure, my software is long obsolete now. When people still ask about it, I tell them to go look at Linux. But it once played a role that went well beyond ham radio, even though that's all I had originally meant it for. Perhaps this was an example of a butterfly flapping its wings; I don't know.
I was just trying to say exactly that, but Slashdot lost my edited comment when I changed an option. Argh.
I never said all hams should build their own radios. But all hams should be able to learn how their radios work, if they are so inclined, and to modify and experiment with them. That's what the hobby is supposed to be about. It's exactly the same philosophy behind the open source software movement, only we hams had it first.
Most ham manufacturers still make hardware schematics available for their equipment, but microcontroller firmware has always been a sore point, especially with more and more functionality moving into DSP (as it should).
Yes, I am working on open source DSP software for the Raspberry Pi (or any other Linux platform) and inexpensive software-defined radio (SDR) front ends like the Funcube Dongle and the SDRPlay. (All three products come from the UK. Not sure what that means, but I'm glad they're making them.)
But my biggest beef is with ham digital voice. There are not one, not two but THREE mutually incompatible digital voice "standards" in common use on the VHF/UHF bands here in soCal: Fusion (Yaesu), D-Star (Icom) and DMR (Motorola). All three modulation and coding designs are dated and inefficient, with disappointing performance. Worse, they all use the same proprietary digital voice codec (AMBE) that's patented out the wazoo. It must be purchased on a custom DSP when it could easily be implemented in software on the same DSPs that do everything else in the radio. This is despite the ready availability of a superior, un-encumbered ham-developed algorithm called CODEC2 (by Dave Rowe, VK5DGR). The manufacturers simply ignore it, and few of us hams are in the position to mass-market small hand-held radios.
Yes, ham radio is still very much a "thing". But to me, the one "thing" it never has been is the purchasing of closed, proprietary software that can be turned off at whim by the developer.
To me, ham radio has always been a unique hands-on opportunity to learn what's "behind the knobs" of a piece of communications hardware (or now, software). Even if you don't build (or write) your own stuff, even if you're primarily interested in using it to talk to others, it still gives you (or should give you) the opportunity to learn how it all works, to make technology just a little less mysterious and intimidating.
Ham radio still provides a creative outlet for hundreds of thousands of people. It helps STEM students learn about electronics, math, physics, or just about any other field of science and engineering even remotely associated with radio communications, such as computers and networking, satellites and remote sensing. When I got into it in high school nearly 50 years ago, it confirmed for me that I wanted to become an electrical engineer, a decision I have never regretted.
Even many who decide that a STEM career isn't for them are hams simply because it's an enjoyable hobby.
I had not heard this story, but that might be because I don't personally use Ham Radio Deluxe or any other proprietary ham software, certainly nothing that can be controlled in this way. Other hams are free to use whatever they want, but I personally consider proprietary software to be fundamentally incompatible with the nature and purpose of ham radio.
I don't like locked-down computers any more than you do. I hate ransomware even more; it's the single most despicable use of public key cryptography there is.
But consider that without public key cryptography Apple wouldn't even be in a position to stop the FBI from hacking the iPhone. Individuals wouldn't even have the option to secure their personal communications, at least not in practice. (Yes, I know all about one-time pads. That's why I said "in practice").
Nor would we have the Internet, or at least anything like the one we have now. And without the Internet, computers of all kinds (secure or non-secure boot) wouldn't be nearly as capable and available as they are now because the volume and demand would be vastly less.
I really can't think of more deserving recipients. I've never met Hellman, but I've met Diffie a few times, including when we testified to the Senate Commerce Committee during the 1990s Crypto Wars.
He's a national asset whenever the NSA and FBI get a little too far out of line. Which is most of the time.
Well, I've recently developed a machine to convert atmospheric CO2 into various simple organic molecules known as "sugars", which have the significant advantage over methanol of being relatively nontoxic. My design has been successfully tested for some time and it only requires sunlight, water and a few miscellaneous other inexpensive materials.
And best of all, my machine is self-replicating!
Telephone companies used to have this exact problem. (Maybe they still do). Central offices contain a "mainframe", essentially a huge patch panel that connects cable pairs coming in the building to the switches. Technicians activated a given local loop by running a cross-connect pair. When service was discontinued, they'd often just disconnect the pair but leave it in the mainframe to clog things up for the future.
I suspect this problem is decreasing with the growth of remote switching. E.g., AT&T U-verse terminates the customer loop in a VRAD cabinet in the local neighborhood instead of carrying it all the way to the central office.
I don't mean to denigrate her contribution in any way, but Lamarr's frequency-hopping spread spectrum is not the one used in CDMA mobile phones. It is used in Bluetooth.
Lamarr invented "frequency hopping" while CDMA cellular and GPS use "direct sequence". Frequency hopping is just what it sounds like: a narrowband transmitter is continually retuned to a different radio channel. Unless the receiver tuning follows the same sequence at the proper times it cannot receive the transmission.
Direct sequence XORs a narrowband signal with a high speed pseudorandom "chip" sequence, and the receiver undoes this operation by XORing it again by the same sequence properly synchronized in time. It closely resembles a keystream-type encryption system, though the "keystream" is not necessarily secret. The main difference is that direct sequence is a wideband signal while, at any instant, a frequency hopped signal is still narrowband.
Each method has advantages. Frequency hopping can be especially resistant to strong narrowband jamming, so it's a favorite of military systems (Lamarr's intended use). Direct sequence is easier to use with coherent modulation so it tends to use transmitter power more efficiently, and it can often provide precise timing and positioning as a side benefit. Or, in the case of GPS, as its primary purpose.
While CDMA mobile phones were very important in the 1990s and 2000s, it is now being replaced with LTE (Long Term Evolution), which uses OFDM - Orthogonal Frequency Division Multiplexing. So do many other modern terrestrial digital communication systems including DSL, HD Radio, DVB-T (but not ATSC), WiFi and DRM (Digital Radio Mondiale).
My guess is that the Metropolitan Police is far from gone from the area; they simply got tired of being an overt tourist attraction. The Ecuadorian Embassy is right around the corner from Harrod's and also the hotel where we stayed as tourists last summer. I got the definite impression that the police on duty were photographed a lot...
Yes. I think cooler heads will eventually prevail, and they'll reverse their knee-jerk decision to phase out nuclear.
One only has to look at German CO2 emissions over the past few years to see why.
Of course, until they do I'm sure the French and Czechs will be happy to sell Germany their surplus nuclear power.
Speaking of the horrific consequences of nuclear weapons testing in the Pacific, a big one that's still with us today is the knee-jerk phobia of nuclear power, often by people who can't distinguish between the two.
Along with wind and solar, nuclear power is one of our chief tools to mitigate global warming, which will in the long term prove to be far worse than weapons testing.
It sure doesn't help that the US government lied through its teeth about atmospheric testing. I've been trying to find a copy of Joseph Rotblat's paper deducing that most of the yield of the Ivy Mike and Castle Bravo tests came from the fast fission of the U-238 tamper, revealing as a lie the government's claim that fusion bombs were inherently clean. Anybody know where I can find a copy?
Slashdot Mirror
Part of the introduction is missing:
After "Plenty of cat owners will happily tell you their felines are capable of responding to their own names"
it should read "...they just choose not to."
There, fixed that for ya.
Ah, so *THIS* is how the Talosians kept Captain Pike from bouncing off the walls of his cage. I always wondered about that.
I don't think it would be as hard as you might think PROVIDED you really understood it yourself. Of course, this applies to anything you wish to teach to anyone.
The problem with relativity is that it is so counter intuitive to everyday experience and to the classical physics you've been taught that you have to unlearn much of it first. That may make it easier for younger people to understand -- they don't have as much to overcome as they would later.
Like most EEs, I was taught classical electromagnetism, first in high school, then in lower level undergraduate physics, and finally in much more detail in junior level EE school classes. We were also taught relativity, but as a separate topic within physics. Had I been taught relativity first, and then been taught electromagnetism in the relativistic way I think it would have actually have been easier and more satisfying. I would have learned that there really isn't such a thing as "magnetism"; what we see as magnetism is really just the electrostatic force as affected by special relativity (and some quantum mechanics). I would have readily understood why there are no magnetic monopoles, for example. And it would have shown me how every field in physics is related to every other, in fact that there really is only one "physics".
Actually no, it's not a straightforward calculation. That's why they want to conduct the test.
It's not a simple collision like we learned about in physics class, with the change in the asteroid's momentum coming entirely from the impactor. The impactor will hit at extremely high velocity (by earth standards), meaning that it will carry a lot of kinetic energy (one half mass times velocity squared) in a small volume. This kinetic energy will vaporize and blow off part of the asteroid, which because of the asteroid's small size, will completely escape.
The mass of the ejecta will greatly exceed the mass of the impactor, so even though it may move much more slowly than the impactor it will carry away considerably more momentum (mass times velocity). The momentum of this ejecta will have most of the effect on the asteroid's trajectory.
But it's unknown exactly how much momentum will be carried away by the ejecta as this depends on the makeup of the asteroid, its density, porosity, how quickly the impactor stops and releases its energy, etc. So that's why they want to try it.
A similar effect was at play in the JFK assassination that helped cause the counter-intuitive "back and to the right" motion of his head that had so many people incorrectly thinking there was a second shooter.
The largest estimate for the size of Psyche is 253 km across. Mars is about 6800 km in diameter, enormously larger.
Yes, I just picked up a SDRPlay 2 last weekend.
The main differences between it and the Funcube dongle are the same: the SDRPlay can sample at much higher rates, but only at 12 bits/sample, while the Funcube dongle samples at 192 kHz with 16 bits. The Funcube dongle therefore appears better suited to narrower modes, especially on HF and VHF where there may be strong interferers on nearby frequencies. The SDRPlay can do broadband modes too wide for the Funcube, such as HD Radio, ADS-B and digital TV, though many of those can also be done even more cheaply with 8-bit RTL-SDR dongles. The SDRPlay can also produce wideband waterfall displays.
Many hams today ARE using the Raspberry Pi and Arduino for their projects. Such as the local high school kids I help mentor. They build high altitude balloon payloads and fly them, and they all carried either an Arduino, a Pi, or both.
I/Q interfaces are vulnerable to ground loops only if the I/Q interface is analog. Why should it be, when we have excellent digital interfaces designed specifically for stereo digital audio? There are now several inexpensive SDRs (price range $100-$200) with USB interfaces, e.g., the Funcube Dongle Pro+ and the SDRPlay (there's now a second version). There's also the ultra-cheap RTL-SDR, but its narrow 8-bit A/D limits its use to VHF or UHF signals without strong adjacent channel interference. It's ideal for ADS-B (with a filter!) but I wouldn't recommend it for HF.
I've done most of my work so far with the Funcube dongle, which samples at 192 kHz and 16 bits/channel, feeding a USB interface. It looks just like a standard audio A/D to the OS, because that's what it is. The I&Q signals are produced at baseband so yes there are DC offsets and small gain and phase errors, but I found them easy to remove in software. Some phase noise is sometimes audible within a few hundred hertz of DC, but is easily swamped by typical input noise and gain settings.
Overall, this thing makes an excellent but inexpensive general coverage receiver. I sure wish I had something like this when I was a young ham without much money.
You're welcome!
Hey, if you can read that disk, could you put it on the net somewhere? I didn't keep copies of all the earlier versions of my software. It'd be neat to see which one you got.
Probably the ultimate in QRP right now is WSPR (Weak Signal Propagation Reporter). This is a specially-designed very low speed (~1 bps) digital modulation and coding format designed for use as a propagation beacon, especially on the HF ("shortwave") bands. But it has recently been adapted for tracking ultra light weight (12.5 gram!) high altitude balloon payloads. One such payload, WB8ELK-2, has completed three complete trips around the world in the past month and is now on its fourth:
https://tracker.habhub.org/#!m...
The tracker payload is powered directly by a pair of small thin-film solar panels. The weight budget is so extremely tight that there is no battery, so it transmits only during the day.
Well, not to toot my own horn too loudly, but in the mid 1980s I wrote a TCP/IP implementation. I intended it for ham radio use on low end PCs, as the only existing general purpose implementations were on commercial minicomputers far beyond a ham budget. (I actually began it on a dare by Terry Fox, WB4JFI, who insisted it was too complex to implement on anything a ham could afford.)
Before I knew it, my software was being widely used outside ham radio for dialup access to the Internet. Universities and companies set up banks of modems and PCs to give their students and employees access to their existing connections. Pretty soon commercial companies sprang up to do the same for the public, again using my software; I think we now call them "Internet Service Providers".
Meanwhile, the OSI world was continuing to produce large piles of paper, but no inexpensive (or free), usable software.
In the early 1990s, I went to Qualcomm where I ported my code onto their phones so it could be used to provide wireless Internet services.
Sure, my software is long obsolete now. When people still ask about it, I tell them to go look at Linux. But it once played a role that went well beyond ham radio, even though that's all I had originally meant it for. Perhaps this was an example of a butterfly flapping its wings; I don't know.
Thanks. It was actually TCP/IP (the Internet protocols) over packet radio.
I was just trying to say exactly that, but Slashdot lost my edited comment when I changed an option. Argh.
I never said all hams should build their own radios. But all hams should be able to learn how their radios work, if they are so inclined, and to modify and experiment with them. That's what the hobby is supposed to be about. It's exactly the same philosophy behind the open source software movement, only we hams had it first.
Most ham manufacturers still make hardware schematics available for their equipment, but microcontroller firmware has always been a sore point, especially with more and more functionality moving into DSP (as it should).
Yes, I am working on open source DSP software for the Raspberry Pi (or any other Linux platform) and inexpensive software-defined radio (SDR) front ends like the Funcube Dongle and the SDRPlay. (All three products come from the UK. Not sure what that means, but I'm glad they're making them.)
But my biggest beef is with ham digital voice. There are not one, not two but THREE mutually incompatible digital voice "standards" in common use on the VHF/UHF bands here in soCal: Fusion (Yaesu), D-Star (Icom) and DMR (Motorola). All three modulation and coding designs are dated and inefficient, with disappointing performance. Worse, they all use the same proprietary digital voice codec (AMBE) that's patented out the wazoo. It must be purchased on a custom DSP when it could easily be implemented in software on the same DSPs that do everything else in the radio. This is despite the ready availability of a superior, un-encumbered ham-developed algorithm called CODEC2 (by Dave Rowe, VK5DGR). The manufacturers simply ignore it, and few of us hams are in the position to mass-market small hand-held radios.
Yes, ham radio is still very much a "thing". But to me, the one "thing" it never has been is the purchasing of closed, proprietary software that can be turned off at whim by the developer. To me, ham radio has always been a unique hands-on opportunity to learn what's "behind the knobs" of a piece of communications hardware (or now, software). Even if you don't build (or write) your own stuff, even if you're primarily interested in using it to talk to others, it still gives you (or should give you) the opportunity to learn how it all works, to make technology just a little less mysterious and intimidating. Ham radio still provides a creative outlet for hundreds of thousands of people. It helps STEM students learn about electronics, math, physics, or just about any other field of science and engineering even remotely associated with radio communications, such as computers and networking, satellites and remote sensing. When I got into it in high school nearly 50 years ago, it confirmed for me that I wanted to become an electrical engineer, a decision I have never regretted. Even many who decide that a STEM career isn't for them are hams simply because it's an enjoyable hobby.
I had not heard this story, but that might be because I don't personally use Ham Radio Deluxe or any other proprietary ham software, certainly nothing that can be controlled in this way. Other hams are free to use whatever they want, but I personally consider proprietary software to be fundamentally incompatible with the nature and purpose of ham radio.
I don't like locked-down computers any more than you do. I hate ransomware even more; it's the single most despicable use of public key cryptography there is. But consider that without public key cryptography Apple wouldn't even be in a position to stop the FBI from hacking the iPhone. Individuals wouldn't even have the option to secure their personal communications, at least not in practice. (Yes, I know all about one-time pads. That's why I said "in practice"). Nor would we have the Internet, or at least anything like the one we have now. And without the Internet, computers of all kinds (secure or non-secure boot) wouldn't be nearly as capable and available as they are now because the volume and demand would be vastly less.
Where you see eccentricity, I see genius, insight and long hair. And I couldn't care less about the long hair.
I really can't think of more deserving recipients. I've never met Hellman, but I've met Diffie a few times, including when we testified to the Senate Commerce Committee during the 1990s Crypto Wars. He's a national asset whenever the NSA and FBI get a little too far out of line. Which is most of the time.
Well, I've recently developed a machine to convert atmospheric CO2 into various simple organic molecules known as "sugars", which have the significant advantage over methanol of being relatively nontoxic. My design has been successfully tested for some time and it only requires sunlight, water and a few miscellaneous other inexpensive materials. And best of all, my machine is self-replicating!
Telephone companies used to have this exact problem. (Maybe they still do). Central offices contain a "mainframe", essentially a huge patch panel that connects cable pairs coming in the building to the switches. Technicians activated a given local loop by running a cross-connect pair. When service was discontinued, they'd often just disconnect the pair but leave it in the mainframe to clog things up for the future. I suspect this problem is decreasing with the growth of remote switching. E.g., AT&T U-verse terminates the customer loop in a VRAD cabinet in the local neighborhood instead of carrying it all the way to the central office.
Lamarr invented "frequency hopping" while CDMA cellular and GPS use "direct sequence". Frequency hopping is just what it sounds like: a narrowband transmitter is continually retuned to a different radio channel. Unless the receiver tuning follows the same sequence at the proper times it cannot receive the transmission.
Direct sequence XORs a narrowband signal with a high speed pseudorandom "chip" sequence, and the receiver undoes this operation by XORing it again by the same sequence properly synchronized in time. It closely resembles a keystream-type encryption system, though the "keystream" is not necessarily secret. The main difference is that direct sequence is a wideband signal while, at any instant, a frequency hopped signal is still narrowband.
Each method has advantages. Frequency hopping can be especially resistant to strong narrowband jamming, so it's a favorite of military systems (Lamarr's intended use). Direct sequence is easier to use with coherent modulation so it tends to use transmitter power more efficiently, and it can often provide precise timing and positioning as a side benefit. Or, in the case of GPS, as its primary purpose.
While CDMA mobile phones were very important in the 1990s and 2000s, it is now being replaced with LTE (Long Term Evolution), which uses OFDM - Orthogonal Frequency Division Multiplexing. So do many other modern terrestrial digital communication systems including DSL, HD Radio, DVB-T (but not ATSC), WiFi and DRM (Digital Radio Mondiale).
My guess is that the Metropolitan Police is far from gone from the area; they simply got tired of being an overt tourist attraction. The Ecuadorian Embassy is right around the corner from Harrod's and also the hotel where we stayed as tourists last summer. I got the definite impression that the police on duty were photographed a lot...
Yes. I think cooler heads will eventually prevail, and they'll reverse their knee-jerk decision to phase out nuclear. One only has to look at German CO2 emissions over the past few years to see why. Of course, until they do I'm sure the French and Czechs will be happy to sell Germany their surplus nuclear power.
Speaking of the horrific consequences of nuclear weapons testing in the Pacific, a big one that's still with us today is the knee-jerk phobia of nuclear power, often by people who can't distinguish between the two. Along with wind and solar, nuclear power is one of our chief tools to mitigate global warming, which will in the long term prove to be far worse than weapons testing. It sure doesn't help that the US government lied through its teeth about atmospheric testing. I've been trying to find a copy of Joseph Rotblat's paper deducing that most of the yield of the Ivy Mike and Castle Bravo tests came from the fast fission of the U-238 tamper, revealing as a lie the government's claim that fusion bombs were inherently clean. Anybody know where I can find a copy?
Direct quote from "The View" regarding her quack beliefs on vaccines and autism: "The University of Google is where I got my degree from."