For those of us who need accurate clocks and don't have $1500 to spend, highly stable temp controlled oscillator chips are cheap and common right now. (Search eBay for OXCO)
For example, this one (which I'm using) is accurate in the PPB range:
An OXCO has excellent phase noise and short term stability, but drifts. A Cs reference has better long term stability. An Rb device has pretty good long term stability once you factor out the linear "aging" (i.e., a constant change). GPS-DO combine GPS receivers with firmware and discipline another oscillator, usually a quartz crystal because of the low phase noise.
So the right way to compare these various references is with an Allan deviation plot, which rates the stability across different time scales.
For this new Symmetricom product, they list the following Stability in their Allan deviation chart (no plot, hmmm): Tau = 1s ADEV = 2e-10 Tau = 10s ADEV = 7e-11 Tau = 100s ADEV = 2e-11 Tau = 1000s ADEV = 7e-12
They similarly give phase noise, aging, initial calibration accuracy, etc.
FEI's 5680A Rb product at http://freqelec.com/rb_osc_fe5680a.html shows their ADEV plot, so I squinted at it and read these values: Tau = 1s ADEV ~ 3e-11 Tau = 10s ADEV ~ 3e-12 Tau = 100s ADEV ~ 7e-13 Tau = 1000S ADEV ~ 3e-13
Further than that (days) and you start running into aging corrections.
An Rb unit you buy off eBay isn't likely to perform like this; you'd need a temperature-controlled room, and need to keep it away from 60Hz fields (the magnetic field is used to "tune" the transition, I think due to the anomalous Zeeman effect, but I could be wrong). Also, a NIST scientist told me that gravity effects are strong as well, so it must be calibrated at the same altitude as use to get these 10^-12 and better numbers.
Still, for about $100 for either an Rb or a GPS-DO, they're pretty good. The OXCO is pretty good too, but beats the Rb or GPS-DO only in phase noise. (Oh, and cost and power consumption.)
You should try blocking the GPS signal in your region for a while and just have a look at how many things stop functioning like in this post to know that GPS might not be the wise solution here
It's also a way to get your precise location found by the FCC, at a cost of only $10,000!
Standard atomic clocks are a Cesium or Rubidium based standard.
Rb oscillators aren't used for primary standards, only Cs. Rb oscillators can be set from a primary standard and retain that calibration exceedingly well, but they aren't primary standards themselves. (I have three of them, and they didn't agree until I adjusted them.)
I wonder how much of the power capacity issues is due to Japan using a combination of 50Hz and 60Hz power preventing them from easily sending power between the two systems?
We have essentially 3 separate grids in the US, roughly East, West, and Texas. (Most of Texas is pretty much on its own.) Plus we have some long-distance high-voltage DC runs, both from Canada and up one down through Central California. NPR has a nice graphic, but in Flash: http://www.npr.org/templates/story/story.php?storyId=110997398
The 50/60 Hz 100/90v division line in Japan dates to the year 1600 and the battle of Seki-ga-hara
We don't need to beat the Russians into space anymore. It's not 1957. We need as much interest and capability in engineering, technology, and math as we do in science.
When I helped run the local elementary school science fair, I encouraged engineering projects. I find it depressing the number of kids who do dull, boring projects and get good marks because they followed the scientific method. Those kids are ones who will be turned off to all science and engineering related fields.
A kid who builds a radio or does a math proof is just as deserving, if not more.
The Coast Guard strongly urges mariners currently using LORAN-C for navigation to shift to a GPS navigation system and become familiar with its operation as soon as possible. Mariners will not be able to rely upon LORAN-C for navigation as of Feb. 8, 2010.
Buying on eBay, if done occasionally would be allowed. (The so called "pizza rule.") Selling would be allowed only if ham gear and occasionally, and not if it's your job. It's unlikely to be done on HF (but nobody really knows what the Pactor-3 users are doing that they ought to be doing with commercial SailMail). But over microwave links it could and does happen often, since several of the 802.11 2.4 GHz channels overlap with ham bands.
There's an interesting project, probably most closely related to this topic, at http://hsmm-mesh.org/ using Linksys routers and OSS mesh software.
The number of US amateur radio operators has been growing consistently since 2007. In fact, except for a period of a few years at the start of the web era, it's grown consistently since its inception.
A lot of nerdy people got into ham radio in the early 1990's because they wanted to do packet radio, which came from Aloha Net, the same project in the 1960's that begat packet networks and eventually TCP/IP and friends. When those folks moved over to the wired internet, and let their ham licenses lapse, the ham population declined. But in the past few years it's been growing again, partially due to crossover from DIY/MAKE people interested in everything from bouncing microwave signals off the moon to building their own radios out of a handful of transistors to GPS tracking with Arduino shields and RF transmitters.
Even though everyone's pain threshold is different, please mention tolerable duration of use. For me, I've got an iPhone 3 with Touch Term Pro. There are some idiosyncracies with its onscreen keyboards, but once learned, its decent. This is sufficient for short tasks, but I wouldn't want to use this setup for more than about 7 minutes. This is sufficient for checking service status and kicking off one or two things, but troubleshooting is right out.
OK, bring up Emacs. Now tell me how it works. (Or Vi, if that's your preference.)
Yes, it's pretty much downhill from the G1 as far as keyboards go. Only the Epic has 5-rows and the Evo Shift is presumably called that because you have to press the shift key to get numbers.
There's been a trend toward 4-row keyboards in the Android devices that even have them. The G1 had 5-rows of keys, so numbers are OK and you can type []{}`|. But the G2 is 4 rows and there's not even a soft key for backquote.
At least on the Hiptop you got a real control key, not a control prefix.
Maybe Nokia will see the light and support Android, or maybe Cyanogen will do the port.
but they just weren't quite up to the demands back in the eighties (yes, I'm old).
I lusted after the HP-55 an adult friend had but when the HP-25 came out I bought that with my own money, then sold it to buy an HP-29C. Then when the replacement for that came out, I was despondent: I remember wondering, when will it end?!?!
It's interesting to see how mobile phones are not only starting to encroach on netbooks/laptops, but also now on e-readers. How long until they encroach on home PCs?
I'm sold on my phone. It has VNC, SSH, and a slide out keyboard. I have a choice between sitting inside at work at a PC browsing the web, or sitting outside on my phone. Guess which one I pick every night?
You won't be picking up the G2 to use with SSH, that's for sure. No []{}`|\ keys, unless someone comes out with a hack to type them in some other way.
There's a small guard band of a few hertz, but that's not even wide enough to carry a dialup modem datalink (3000 hertz wide), much less a broadband internet connection.
Having made this same practical simplification on Slashdot before, I feel compelled to point out that it's incorrect. 3000 Hz is enough bandwidth for just about anything, if the signal to noise ratio is high enough, by the Shannon-Hartley theorem. To get 56K bits/sec out of a 3000 Hz channel, a 13 dB S/N ratio for the channel theoretically would be enough.
There are some coding techniques that approach the Shannon limit: Convolutional Codes, Turbo Codes, and LDPC Codes, the last of which can come arbitrarily close. Using one of these codes would allow you to get arbitrarily close to getting 56K bits/sec out of a 3000 Hz channel with 13 dB of S/N.
So, making a blanket statement about bandwidth-vs-bitrate is incorrect, though in practice, you're right that 3000 Hz isn't the whitespace that the FCC is talking about.
Slashdot Mirror
Actually, if you use Emacs, ^X-^F lena.png works fine.
For those of us who need accurate clocks and don't have $1500 to spend, highly stable temp controlled oscillator chips are cheap and common right now. (Search eBay for OXCO)
For example, this one (which I'm using) is accurate in the PPB range:
An OXCO has excellent phase noise and short term stability, but drifts. A Cs reference has better long term stability. An Rb device has pretty good long term stability once you factor out the linear "aging" (i.e., a constant change). GPS-DO combine GPS receivers with firmware and discipline another oscillator, usually a quartz crystal because of the low phase noise.
So the right way to compare these various references is with an Allan deviation plot, which rates the stability across different time scales.
For this new Symmetricom product, they list the following Stability in their Allan deviation chart (no plot, hmmm):
Tau = 1s ADEV = 2e-10
Tau = 10s ADEV = 7e-11
Tau = 100s ADEV = 2e-11
Tau = 1000s ADEV = 7e-12
They similarly give phase noise, aging, initial calibration accuracy, etc.
FEI's 5680A Rb product at http://freqelec.com/rb_osc_fe5680a.html shows their ADEV plot, so I squinted at it and read these values:
Tau = 1s ADEV ~ 3e-11
Tau = 10s ADEV ~ 3e-12
Tau = 100s ADEV ~ 7e-13
Tau = 1000S ADEV ~ 3e-13
Further than that (days) and you start running into aging corrections.
An Rb unit you buy off eBay isn't likely to perform like this; you'd need a temperature-controlled room, and need to keep it away from 60Hz fields (the magnetic field is used to "tune" the transition, I think due to the anomalous Zeeman effect, but I could be wrong). Also, a NIST scientist told me that gravity effects are strong as well, so it must be calibrated at the same altitude as use to get these 10^-12 and better numbers.
Still, for about $100 for either an Rb or a GPS-DO, they're pretty good. The OXCO is pretty good too, but beats the Rb or GPS-DO only in phase noise. (Oh, and cost and power consumption.)
IHFTP
You should try blocking the GPS signal in your region for a while and just have a look at how many things stop functioning like in this post to know that GPS might not be the wise solution here
It's also a way to get your precise location found by the FCC, at a cost of only $10,000!
Standard atomic clocks are a Cesium or Rubidium based standard.
Rb oscillators aren't used for primary standards, only Cs. Rb oscillators can be set from a primary standard and retain that calibration exceedingly well, but they aren't primary standards themselves. (I have three of them, and they didn't agree until I adjusted them.)
I wonder how much of the power capacity issues is due to Japan using a combination of 50Hz and 60Hz power preventing them from easily sending power between the two systems?
We have essentially 3 separate grids in the US, roughly East, West, and Texas. (Most of Texas is pretty much on its own.) Plus we have some long-distance high-voltage DC runs, both from Canada and up one down through Central California. NPR has a nice graphic, but in Flash: http://www.npr.org/templates/story/story.php?storyId=110997398
The 50/60 Hz 100/90v division line in Japan dates to the year 1600 and the battle of Seki-ga-hara
Although 70 cm isn't one of the major ham bands
It's quite heavily used. It's the most heavily used UHF ham band.
For example, take a look at this list of hand-held radios for sale by one vendor; 2/3 of them work on 70cm.
http://www.gigaparts.com/store.php?action=matrix&catcode=tx-ht
http://thehill.com/blogs/hillicon-valley/technology/143089-fcc-cracks-down-on-cell-phone-a-gps-jamming-devices
and more here
http://www.google.com/search?q=fcc+cell+phone+jammer+letter
http://www.google.com/search?q=fcc+gps+phone+jammer+letter
So if you're a theater owner or office manager and think one of these at $50 is a good bargain, think about $10,000 and two years in jail instead.
Right, just because there are absolutely no other chipsets that work with Sandy Bridge CPUs doesn't mean you can't go off and build your own at home!
Probably Jeri Ellsworth has made one out of some bits of an old wok and a satellite dish already.
We don't need to beat the Russians into space anymore. It's not 1957. We need as much interest and capability in engineering, technology, and math as we do in science.
When I helped run the local elementary school science fair, I encouraged engineering projects. I find it depressing the number of kids who do dull, boring projects and get good marks because they followed the scientific method. Those kids are ones who will be turned off to all science and engineering related fields.
A kid who builds a radio or does a math proof is just as deserving, if not more.
And the coast guard has been saying this for a year too: http://www.navcen.uscg.gov/?pageName=loranMain
Or use RFC1149 updated with wicker packets.
Buying on eBay, if done occasionally would be allowed. (The so called "pizza rule.")
Selling would be allowed only if ham gear and occasionally, and not if it's your job.
It's unlikely to be done on HF (but nobody really knows what the Pactor-3 users are doing that they ought to be doing with commercial SailMail).
But over microwave links it could and does happen often, since several of the 802.11 2.4 GHz channels overlap with ham bands.
There's an interesting project, probably most closely related to this topic, at http://hsmm-mesh.org/ using Linksys routers and OSS mesh software.
The number of US amateur radio operators has been growing consistently since 2007. In fact, except for a period of a few years at the start of the web era, it's grown consistently since its inception.
A lot of nerdy people got into ham radio in the early 1990's because they wanted to do packet radio, which came from Aloha Net, the same project in the 1960's that begat packet networks and eventually TCP/IP and friends. When those folks moved over to the wired internet, and let their ham licenses lapse, the ham population declined. But in the past few years it's been growing again, partially due to crossover from DIY/MAKE people interested in everything from bouncing microwave signals off the moon to building their own radios out of a handful of transistors to GPS tracking with Arduino shields and RF transmitters.
Here's a graph:
http://wa5znu.org/2011/01/ham-census/2005-2010-chart.png
Leigh/WA5ZNU
A lot of people laughed at Tesla too. Only took 100 years to prove the man right, for the most part.
No, it only took a few years to prove him right on the things he was right about. They're still working on the things he was wrong about.
Maybe the paper is a troll, like Mobile phone radiation linked to people jumping to conclusions.
Even though everyone's pain threshold is different, please mention tolerable duration of use. For me, I've got an iPhone 3 with Touch Term Pro. There are some idiosyncracies with its onscreen keyboards, but once learned, its decent. This is sufficient for short tasks, but I wouldn't want to use this setup for more than about 7 minutes. This is sufficient for checking service status and kicking off one or two things, but troubleshooting is right out.
OK, bring up Emacs. Now tell me how it works. (Or Vi, if that's your preference.)
Yes, it's pretty much downhill from the G1 as far as keyboards go. Only the Epic has 5-rows and the Evo Shift is presumably called that because you have to press the shift key to get numbers.
There's been a trend toward 4-row keyboards in the Android devices that even have them. The G1 had 5-rows of keys, so numbers are OK and you can type []{}`|.
But the G2 is 4 rows and there's not even a soft key for backquote.
At least on the Hiptop you got a real control key, not a control prefix.
Maybe Nokia will see the light and support Android, or maybe Cyanogen will do the port.
It's missing []{}|\`. All but ` you can type with a pop-up on-screen kbd.
I'd like to see something like the Samsung Epic 4G keyboard from Tmobile.
Now if they could only add another rows of keys I could type my password...
but they just weren't quite up to the demands back in the eighties (yes, I'm old).
I lusted after the HP-55 an adult friend had but when the HP-25 came out I bought that with my own money, then sold it to buy an HP-29C.
Then when the replacement for that came out, I was despondent: I remember wondering, when will it end?!?!
I'm sold on my phone. It has VNC, SSH, and a slide out keyboard. I have a choice between sitting inside at work at a PC browsing the web, or sitting outside on my phone. Guess which one I pick every night?
You won't be picking up the G2 to use with SSH, that's for sure. No []{}`|\ keys, unless someone comes out with a hack to type them in some other way.
Notable for the HTC G2 is that it has a modified hinge that opens up to a slide-out QWERTY keyboard.
That sounds to me like it has a physical keyboard.
It doesn't have [, ], `, and a few other keys. Geesh, even the first Sidekick had them.
There's a small guard band of a few hertz, but that's not even wide enough to carry a dialup modem datalink (3000 hertz wide), much less a broadband internet connection.
Having made this same practical simplification on Slashdot before, I feel compelled to point out that it's incorrect.
3000 Hz is enough bandwidth for just about anything, if the signal to noise ratio is high enough, by the Shannon-Hartley theorem. To get 56K bits/sec out of a 3000 Hz channel, a 13 dB S/N ratio for the channel theoretically would be enough.
There are some coding techniques that approach the Shannon limit: Convolutional Codes, Turbo Codes, and LDPC Codes, the last of which can come arbitrarily close. Using one of these codes would allow you to get arbitrarily close to getting 56K bits/sec out of a 3000 Hz channel with 13 dB of S/N.
So, making a blanket statement about bandwidth-vs-bitrate is incorrect, though in practice, you're right that 3000 Hz isn't the whitespace that the FCC is talking about.
But practically speaking, you're right.