Posts by Colintd 25 publicly visible posts • joined 2 Dec 2016
Good to get an inside view, but the base station issue is only "easily" soluble if the government is prepared to pay for all the additional base stations, _and_ override the planning issues which have stopped masts being installed. There is no commercial justification for the additional investment to reach near 100% landmass coverage, and the government has just not been willing to foot the bill.
The fundamental issues is that our political leaders and most of the civil service have no idea when it comes to technology and engineering, and a disdain for those who do. The results is that the decision makers on engineering projects lack the ability to separate truth from sales BS, or to negotiable deliverable specifications. At best they are misled, at worse, in their ignorance they push for things that are just not viable.
With ESN, we have AirWave, as system incorporating from day-one specialist function (e.g. push-to-talk), using low frequencies to allow full coverage, and designed for very high availability, being "replaced" with a "service" built on top of a commercial phone system. The commercial system is designed to maximize profit from the infrastructure investment of mobile carriers, lacks push-to-talk (which is hard to retrofit), and uses high frequencies designed to maximize bandwidth at the expense of coverage.
Throwing money at the problem, and sticking their head in the sand, will not fix these fundamental issues, yet no-one will admit it is doomed.
Having spend the last 30 years working on mobile comms, this is an example of a government decision made by people who have no engineering knowledge, and a disdain for those who do.
They have taken a dedicated system, designed for reliability, specific function, and operating at a low frequency (which gives it wide range, good building penetration and requires a small number of base-stations), and are attempting to replace it with a "service" piggybacked on a commercial high frequency systems (so inherently poorer coverage, worse service indoors, and needing a massive number of base-stations to achieve the required universal coverage).
The underlying commercial infrastructure is understandably designed and optimized to maximize operator return on their spectrum and hardware investment _not_ emergency service availability. As such it is fundamentally incompatible with the desired operational characteristics of the emergency comms service.
The only way to make it work is by massively incentivizing the commercial operators to provide 100% cell coverage on their networks, and by overruling all the planning constraints which mean cell towers get rejected. Arguably 100% commercial cell coverage is a useful thing in its own right, but it would require a huge level of investment which makes no commercial sense, and which the government has never been willing to fund.
The shifts in frequency are used to managed production capacity vs load.
When the network load is less than instantaneous generation capacity, the excess energy increases the kinetic energy stored in the turbines and they speed up, increasing the frequency. The governers then decrease the amount of steam being fed in, balancing the power, and lowering the speed/frequency to the target. When the network load is higher than the generation capacity, the turbines are robbed of kinetic energy, slowing down and decreasing the frequency. More steam in added, and the system comes back to balance.
Hence short term balancing is dependent on the inertia of the turbine/generator sets. The problem when a large fraction of the generation comes for inverter systems (batteries and solar), is that there is minimal inertia in the system, and it becomes significantly more unstable, and prone to trip outs.
Are you sure your data is correct?
https://en.wikipedia.org/wiki/Energy_density (and other references) suggests Jet 1A has a specific energy density of around 43MJ/Kg whereas Lithium ion batteries are between 0.4 and 0.9 MJ/Kg... That is between 50-100 times worse.
Even lithium-air is only 9MJ/Kg, so 5 times worse, and they are unproven technology.
In addition, as a number of others have noted, fuel is burnt so not present at landing. For batteries this is not the case.
The best things were the MAU relay testers. A large connector with a 9v battery, that when inserted into a port powered the related relay and opened the ring to the new device. You knew the relay had operated when there was a clunk, and you knew it had worked right when the network kept going (as the tester had loopback wires). Except we had one where the tester had been damaged inserting a new battery, and it didn't correctly loop. Use the tester, open the ring, wait for people to start shouting!
I'm afraid you explanation is incorrect. A 3d fix needs 4 satellites as you need to solve for time and 3 spacial variables, which is why GPS receivers can typically provide very accurate time output, as they already solve for that.
The time/frequency references used for static telecoms start with a survey mode which removes 3 variables, and then allows you to get pretty accurate time with just one satellite (the ephemerides and an L2 receiver can give you a lot of ionospheric compensation).
Portable atomic clocks are great tech, but won't really help with GPS as even if you ignore relativistic drifts, you'd still need 3 sats for a 3d fix.
I suspect the default is static as otherwise the car would constantly undertake emergency brakeng when it fails to identify am object. This fits with the comment that the braking was disabled due to erratic behaviour. I'm not saying this is the right default, I'm just speculating about why it was set that way.
We had a mainframe room "upgraded" from high security key lock (which were good enough that I struggled to pick them) to an RF fob lock and one of those big magnetic latches. This was supposed to be for better security (with entry logs) for a high profile project. I demonstrated that I could open the new door either by flicking a mcb on the breaker panel (it was held shut with an active magnet, so fail open) or a really solid shoulder barge (once you opened up a small gap, the magnetic force drops off pretty sharply).
The new system was quickly replaced by some good high security physical locks...
Printing out email and dictating replies used to be 100% real in the time that you has physical circ folders for printed documents.
But then so did shared email accounts, where we did a daily download, via a modem, of email for our group, with was printed and circed, with batched sending of replies which had been prepared in text editors and transferred on crispy discs (crispies being the 3.5" followup to the 5.25" and 8" floppy)...
We also had "SneakerNet" for our first laserprinter, which meant you copied you file onto a disc, walked over to the machine with the printer attached, inserted the disc, and then did a local print.
I remember that halon system going off in the taperoom for the Cambridge university mainframe during the late 80s. Minor fire went out, but the level of dust raised meant all the tapes had to go through a special wash/cleaning machine (actual liquid bath with sponge pads). Extremely disruptive.
Rather than silence I can speak from personal experience about what happens if you hit the kill/field dump switch on an NMR/MRI machine. All the stored energy in the coil vaporises the liquid helium coolant, followed.by a very loud bang/woosh as several thousand pounds of now gaseous helium, with about x1000 volume goes up the vent pipe. Had to be done as some idiot had come in with a steel gas cylinder which was literally dragged off the trolley into the coil. Not an experience to be repeated. Try leaning near the kill switch if you go for an MRI and see the techs.reaction...
In the early 90's we had a Compaq 33MHz 386 as a main build server, with a hard disc (can't remember the vendor or size) where they had made a bad choice of spindle lubricant. It would run indefinitely if left on, but if you turned it off overnight, the next day the disc wouldn't spin up when you turned it back on. The "trick" was to turn on the power, then lift up the whole case and give it a sharp twist. The inertia of the disc meant you overcame the static friction and the disc would then startup. Over time the twist required became larger/more sudden, but it lasted until we upgraded to a shiny new 486.
Having worked on these, the chassis was normally hot 100% of the time, because the oncoming mains went through a bridge rectifier with no isolating transformer. The chassis was connected to the -ve side of the rectifier, so you have a nice half-wave 240V potential on the chassis.
I was taught to work on these beasts with one hand in your pocket, as it minimized the chance of through body contact. More exciting was using a scope on these units, as connecting the shield (grounded) to the chassis (with 240V half wave) was a big no-no. The exciting approach was to let your scope float (plastic knobs only), the more sensible approach to use an isolating transformer for the TV, and then ground the chassis.
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