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Comment: No high speed Internet? (Score 5, Interesting) 490

by Strider- (#46586055) Attached to: Are DVDs Inconvenient On Purpose?

I work with a number of locations that lack any form of high speed internet. They have enough internet to facebook, order the DVDs, etc... but nowhere near enough bandwidth to actually stream the movies. The DVD-by-mail option is their only option, if netflix et al were to shut down this service, they would be very unhappy.

Comment: Re:Doppler data? (Score 1) 491

by Strider- (#46570481) Attached to: How Satellite Company Inmarsat Tracked Down MH370

"Stationary" satellites aren't really. They drift around within an approximately 30km x 30km x 30km box, and these movements are very well known. This isn't much, but is enough that you can locate an earth station to within a few miles if you have enough time. IN this case, they only have a few pieces of data, hence the larger solution.

Comment: Re:Some questions (Score 1) 491

by Strider- (#46568737) Attached to: How Satellite Company Inmarsat Tracked Down MH370

It should also be noted that much, if not all, signal generation on the satellite is going to be traceable to an atomic clock.

There's often very little signal generation being done on the spacecraft itself. Putting complex electronics in the radiation environment of space, where it can't be repaired, and electrical power is at a premium, is generally a bad idea. With certain exceptions (Iridium et al), all the intelligence is done on the ground, where it can be maintained and repaired. Most satellites are just dumb bent pipes.

Years ago, I assisted a major satellite operator with geo-locating an interfering uplink. Based on the doppler shift caused by the motion of the satellite, and about 72 hours of repeated sensing and passes, they were able to narrow down the offending dish to within a 1 mile by 5 mile ellipse. That's small enough that they can go and "mow the lawn" with equipment on a helicopter or other aircraft to find the offender. As I recall, in the end the offender was a failed credit card clearing system on a gas station west of Detroit.

Comment: Re:Some questions (Score 5, Informative) 491

by Strider- (#46565455) Attached to: How Satellite Company Inmarsat Tracked Down MH370

How come the frequency information of the signal received by the satellite was saved? What is the purpose of saving all that data in normal operations?

The communications system in question is likely based on TDMA (Time Division Multiple Access). While I have not worked with Inmarsat systems, all the other satcom systems I have worked with log each connection, and various pieces of information regarding the connection. One of these parameters that is logged is the frequency offset (ie the difference between the expected and actual frequency). This is useful from a troubleshooting perspective as it allows you to spot transmitter and receiver components that are drifting out of specification. Some of the more advanced satellite systems (iDirect) will actually log the geographic coordinates of the uplink site, as this plays into the timing requirements for the network. Unfortunately, Inmarsat isn't this aggressive with their timing, so time of flight isn't an issue).

And why did it take three weeks to do that analysis?

This is pure speculation on my part, but I would wager they had to go back through significant amounts of logs in order to characterize the transmitter and receiver components on that particular aircraft. The doppler effect is going to be subtle compared to the thermal drift of the transmitter, so they need to factor that out before they can get at the thermal drift. Also every oscillator and transmitter is different, so they would need to characterize the transmitter that is on that specific aircraft (which is now of course missing).

Comment: Re:If no decay, why a fire risk? (Score 2) 167

by Strider- (#46495669) Attached to: Forests Around Chernobyl Aren't Decaying Properly

The place is isolated.... what is the ignition source; if there is no heat produced by decay of materials?

Every so often, especially in certain times of a year, you get these massive natural electrical discharges called "lightning" that does quite a good job of starting forest fires.

Comment: Re:Does it really cost $100k? (Score 1) 461

by Strider- (#46464103) Attached to: The $100,000 Device That Could Have Solved Missing Plane Mystery

Most jet fuel supplied to large municipal airports is piped in directly from refineries so the cost is much lower, about half of your $6. Source: http://www.eia.gov/dnav/pet/pe... [eia.gov]

Uhmm, not necessarily true. YVR, the second busiest airport in Canada, has all of its jet fuel trucked in from the Cherry Point refinery in Washington State. There is a proposal to lay a pipeline, but NIMBY is proving a pain to overcome. I'm sure this is the case for many other airports as well.

Comment: Re:Does it really cost $100k? (Score 1) 461

by Strider- (#46464045) Attached to: The $100,000 Device That Could Have Solved Missing Plane Mystery

GPS tracking of the flight? Unlikely. Flight arrival information was likely taken off an ATC feed from secondary surveillance radar.

Actually, most flight tracking at least over land, is done via ACARS, which is a VHF radio system that beacons the aircraft position, altitude, etc... as well as allows sending of short messages. This is in addition to the radar transponder system.

Comment: Re:Solution: Duct tape one of these on top (Score 1) 461

by Strider- (#46464003) Attached to: The $100,000 Device That Could Have Solved Missing Plane Mystery

1. That works with GSM signals. Aint gonna work over the ocean.

Actually, the SPOT uses the Iridium Short Burst Data system, so it goes out via satellite, and will work anywhere on the planet, other than those where it's explicitly prohibited by local laws.

Comment: Re:Horrible coffee (Score 1) 769

by Strider- (#46392099) Attached to: The Next Keurig Will Make Your Coffee With a Dash of "DRM"

Cleaning the grounds out of a french press is awful. The aeropress completely fixes that problem.

Eh? take press, partly refill with water, swish around, and down the garburator (or if on a boat, over the side!). Easy peasy, takes all of 30 seconds. Might need to run the plunger under the tap for a few seconds, but again, no big deal.

Comment: There are some good reasons for global menu bar (Score 1, Informative) 255

by Strider- (#46301591) Attached to: Ubuntu 14.04 Brings Back Menus In Application Windows

There actually are some good reasons for going with a global menu bar. When developing the original interface for the Mac, Apple studied the various options for the menus in depth. What they found is that when the menus are at the top of the screen, they are significantly faster to access, as they have infinite depth, thus you do not have to be anywhere near as accurate in your pointing to access them. In effect, you only need to have to worry about the left-right position of the cursor, as you can just fling it to the top of the screen and not be precise in that dimension. If the menu bar is attached to the window, you have to position the the cursor in both dimensions. The ultimate of this is the screen corners, which is also the reason for the Apple Menu being up there. This is a subtle effect, but is backed up by some good hard data.

Comment: Re:no, storage is NOT nececery. (Score 1) 551

by Strider- (#46168535) Attached to: Should Nuclear and Renewable Energy Supporters Stop Fighting?

Correct me if I'm wrong but 'DC' is terrible at long distances, you lose vast amounts of the energy put in to push it the whole way. This is why AC is used today.

Consider this your correction. With modern technologies, High Voltage DC is actually the preferred method for long-distance power transmission. In the past, the issue was always the AC/DC conversion at either end of the line.

HVDC has a number of things to recommend it.

1) Uses the entirety of the conductor for power transmission. When you push AC through a conductor, it exhibits what's called the "Skin Effect." In the case of 60Hz AC, the power is actually only using about the outer 7mm of the conductor. Power companies actually do make use of this, using a steel core for tensile strength, and a copper sheath for high conductivity, but it also puts a limit on how much current a given conductor can actually carry. At DC, the power will flow through the entirety of the conductor, and since resistance is proportional to the cross-section area of the conductor, you get less loss for a given piece of cable.
2) AC loses significant amounts of power to the ground through capacitive losses. In effect, the transmission line forms a very large capacitor with the earth. For long transmission lines this becomes a significant effect. Again, because this is due to frequency, DC solves the problem.
3) Isolates and relaxes the frequency requirements of the grid. After they lost most of the power grid to an ice storm in 1998, Quebec Hydro rebuilt their grid using HVDC transmission lines and interconnects to the eastern grid. Because of this, they were isolated from the frequency instability that caused the large north-east blackout in 2003 and thus the lights stayed on.

Anyhow, the main reason why AC has been used for long haul transmission is because when the grid was built out, there was no efficient way to convert power between AC and DC or to change the voltage once it was in the DC domain. With the advent of modern power electronics, it's quite possible to build megawatt and/or gigawatt scale inverter/rectifiers that will do this more efficiently than the AC losses for long distance power transmission. As with all of our crumbling infrastructure, the main problem is that no one is willing to invest in the capital expenditures to make it happen.

A LISP programmer knows the value of everything, but the cost of nothing. -- Alan Perlis

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