Relative values & GPS

[jimi]

you are locked in a a cabin in a ship travelling at a constant speed with an atomic clock, and a sophisticated computer capable of receiving a land based atomic clock signal. Could you calculate the speed you are travelling at? If so could you not triangulate your position accurately using land based atomic clocks, thus doing away with reliance on GPS?

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[ParaHandy]

is this a DOS 3.1 function? can't seem to find it ....

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[wooslehunter]

Yes, you'd effectively do exactly what GPS does anyway. i.e. calculate the distance to you from a fixed point. Each fixed station sends out a signal. Since you have an accurate clock & know when it's sent, by measuring when it's received you know the distance. Only problem is, that you'd have to guarentee that the signal is line of sight and not subject to multi-path or bouncing off the atmosphere. Therefore, you'd need 1000s of stations to cover a small area unless they're vey high up - like satellites.

Guess what, you can do exactly that with the cell phone infrastructure on land. The technique was proved years ago. A technician in the US was working on a cell when he heard an emergency call from a driver who'd driven off the road & crashed. The car wasn't visible from the road & the driver didn't know his exact position. The techy had the bright idea to check on the parameters he could measure on the cell & then worked out the position by trilateration.

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[Aja]

Is this not more or less what Decca and Loran did - a timed pulse?

Donald



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[Superstrath]

You would then be dependent on the supplier of the transmitted signal - I expect we'd leave this to the USA - so you're back to square one.
A lot of research and development went into Loran, Decca and so on and they still fell by the wayside to satnav anyway.
I hope you weren't planning to make your fortune from this idea!


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[Steve Clayton]

It's all to do with the phase relationship of the transmit and receive pulse and the comparisons of one pulse to the other at the receiver end (which needs a coho oscillator). If you you know the frequency then you know the wavelength which has a measured distance. Your boat system would need calibrating - even the length of the coax from antenna to receiver will affect the accuracy of the fix.

All good in theory; one major problem is that the wavelength is affected via the media it is progating though; over dry land and then over a humid atmosphere such as water caused this wavelength to change ever so slightly. Accuracy of the systems I used to work with (ARGO and Autotape from Brown & Root) was +/- 3metres and this was on barges laying gas and oil lines.

Do I pass the interview: anybody got a job for an old radar technician???



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[Sans Bateau]

It might be a Windows function, I've not gone over to windows yet, I want to see if it catches on before I make a commitment, but I have upgraded to DOS 4.0

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[BlueSkyNick]

Maybe you could call yourself a Formerly Active Radar Technician, or old FART for short !!

(PS only joking, mate!)

<hr width=100% size=1>Never be afraid to try something new.
Amateurs built the ark, professionals built the Titanic

 

[Keen_Ed]

Don't see how you could, actually. As the clock in your cabin is a super-accurate atomic clock, all it will do is keep time with the signal received from the land based clock (assuming they were set equally to start with). As you are locked in your cabin, you have no way of finding out local time, and working out your position from that.

If you are trying to calculate your position by calculating the time it takes for the atomic clock signal to reach you, then I'm not sure about that either. How is the signal reaching you? If it's by HF, how do you calculate the exact length of the path taken - how many times has the signal bounced, and from what altitude?

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[claymore]

Before the panel answers this I think we should know why you have been locked in your cabin. Obviously - being the phantom kipper that you are there really ws no need to lock you into the cabin - merely to show you the bunk would normally suffice and as most of those who have sailed with you can testify, the zzz's would emanate forthwth. So we can obnly assume that again, you have been up to no good.
As you haven't been up to any good why should we help you - obviously those who have detained you had good reason to so, I think its time for you to come clean on this

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Claymore
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[jimi]

mmm .. but if two clocks start off the same, one is kept static and the other moved don't the times start to differ?

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[Keen_Ed]

Trying to remember A level physics here - but IIRC, that only kicks in to a measurable extent when speeds are a significant fraction of light speed.

GPS can do what it does because the receiver is receiving signals from the satellites on line of sight.


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[cameronke]

Hi Jimi

I had been holding back on this one as I had suspected that you were refering to Einsteins Theory of Relativity, namely that time experienced by an observer moving closer to the speed of light (say 5 kts???????) is different from a (relatively) stationary observer. This was confirmed by one of the most inexpensive experiments ever carried out in physics. Two atomic clocks were synchronised and one was taken for a tourist class flight round the world. Upon its return it was found to be out of synch with its brother. However when the traveling clock was taken round the world the OTHER way it was found to be back in synch. Ie one way it has the speed of the aircraft PLUS the speed of rotation of the earth whereas the other way was the speed of the earth MINUS the speed of the aircraft. Each time the stationary clock was only going at the speed of the earths rotation. There possibly lies the problem with your proposal, the speed of the earth. (I think)

Does that fertile mind of yours ever rest?

Regards

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[jimi]

I've been locked up cos I've been a naughty boy! However I do notice I feel a bit lighter than I did 10 minutes ago!

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[claymore]

Are they starvin ye shun? - Para's no busy jes noo - ef ye work oot where yez are - he'll come tae yer rescue

<hr width=100% size=1>regards
Claymore
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[jimi]

Far from it, I wiz locked in ra pantry .. nae pants but loads o' food! Couple of minutes ago I suddenly felt extremely heavy though but now am sort of floating in a state of weightlessness.. wonder what the time is?

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[duncan]

hah - DOS 6.2 here!

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[jimi]

Dearie me, I must have travelled to a parallel universe .. no longer is time in AD or BC,gregorian or augustinian... it measured in windows operating system versions .. no thats a good idea .. unless you've got a red hat!

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[Rowana]

<<unless you've got a red hat! >>

Or a white sheepskin yin!

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[ParaHandy]

.. all this blether aboot his bunnet but he's so attached to it, he leaves it behind. mind, of course, none of us yins have experienced being woken from interplanetary hyper warp drive clutching ones atomic clock ....

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