Quirky GPS

Submitted: Thursday, Mar 30, 2006 at 17:40
ThreadID: 32354 Views:1582 Replies:6 FollowUps:14
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A while ago I was driving in a westerly direction one morning with some cloud about and the GPS could not locate any satellites. I posted here on EO and was told not to worry about it and see what happens next time I start it up. Sure enough it was working the next day.

Today I drove out in the same direction and the GPS once again could not locate any satellites. There was a bank of Cirrus Cloud quite high up in the sky and I recall that that was the case last time.

On my way home travelling east and with the cloud now moved away the GPS located its usual 9 to 12 satellites.

It seems that high cloud affects the GPS but low rain clouds do not as the GPS has worked well in pouring rain.

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Reply By: Footloose - Thursday, Mar 30, 2006 at 18:35

Thursday, Mar 30, 2006 at 18:35
Don't worry about it Willem. They are surwe to have blown away by the time you get started :))))))))))
AnswerID: 163921

Reply By: Member - Mike DID - Thursday, Mar 30, 2006 at 18:41

Thursday, Mar 30, 2006 at 18:41
Cloud has no effect on satellite availability.

Satellite availability does vary from hour to hour and day to day - they are in a 12 hour orbit and they do try try to have 8 satellites above the horizon in most of the world most of the time.

To get satellite lock when you first turn it on, it really helps to be stationary. Before each sat can be used for a position fix you need to receive the Ephemeris data. For this the GPS must receive from that sat for 30 seconds WITHOUT INTERRUPTION. Trees, buildings or body parts will interrupt the satellite signal.

It really helps if you have an external antenna, rather than one on the dashboard.

Mike
AnswerID: 163923

Follow Up By: Willem - Thursday, Mar 30, 2006 at 18:47

Thursday, Mar 30, 2006 at 18:47
Then it must be Ground Hog Day where the same scene repeats itself over and over again...lol

My dash board GPS works OK. Not worried about turning GPS on but like to check my speed( if you can call it speeding in a slow old 4.2 diesel).

Normally have no problems and can even get a signal when parked in my garage(with the door open ofcourse).

Thanks for the feedback

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Follow Up By: Member - Mike DID - Thursday, Mar 30, 2006 at 19:29

Thursday, Mar 30, 2006 at 19:29
The satellite availability repeats itself everyday with a shift - about half an hour per day I think.

Mike
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Follow Up By: Mad Dog (Australia) - Friday, Mar 31, 2006 at 08:23

Friday, Mar 31, 2006 at 08:23
If the clouds were laden with moisture maybe there could be some blocking effect?
Water will block/attenuate GPS signals. For example, you can't receive GPS signals underwater, although having a GPS receiver antenna very close to the water surface may allow some reception.
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Follow Up By: Member - Mike DID - Friday, Mar 31, 2006 at 09:00

Friday, Mar 31, 2006 at 09:00
"Does RAIN or SNOW or CLOUDS affect the reception of my GPS receiver?
Answer: No. Not so as the user can tell without instrumentation. "

- gpsinformation.net/gpsclouds.htm

Mike
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Reply By: Wayne (NSW) - Thursday, Mar 30, 2006 at 18:56

Thursday, Mar 30, 2006 at 18:56
Willem,

I have had a problem with my GPS. It first happened around the beginning of the year when I was in Victoria Snowy river area. For three days in a row the GPS failed to pick up any satellites for a couple of minutes at 11:45 am.

It happened again last week when I was down in the Dargo area (you know where that is :-)) ) and again at 11:45 am the GPS dropped out.

I have a external aerial mounted on top of the snorkel and the GPS has never dropped out until then

I asked Vic Widman and he said that if he told me what was going on he would have to shoot me.

I don't think that you are alone in the disappearing GPS signal.

Wayne
AnswerID: 163927

Follow Up By: Willem - Thursday, Mar 30, 2006 at 19:08

Thursday, Mar 30, 2006 at 19:08
Wayne

Yep it could have been around that time here (11.15am).

Maybe Bonz was right after all with his scrambled theory..lol
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Follow Up By: Member - ROTORD - Thursday, Mar 30, 2006 at 19:37

Thursday, Mar 30, 2006 at 19:37
Hello All

The US military have the ability to move satelites to cover areas of increasing operational interest .Keep a watch on international affairs and you may work out where they have gone .
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Follow Up By: StephenF10 - Friday, Mar 31, 2006 at 08:17

Friday, Mar 31, 2006 at 08:17
They may be able to move geostationary satellites around (within limits) but the GPS satellites are in 12hr orbits so are moving anyway. They cannot be made to cover any part of the earth more than any other as the plane of orbit passes through the centre of gravity of the earth.

Stephen.
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Follow Up By: Member - MrBitchi (QLD) - Friday, Mar 31, 2006 at 08:19

Friday, Mar 31, 2006 at 08:19
Rotord, the old conspiracy theory again :-))

The GPS satelittes are not manouverable like their spy satellites, they are set in a pre determined orbit.
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Reply By: Old Scalyback & denny - Thursday, Mar 30, 2006 at 20:08

Thursday, Mar 30, 2006 at 20:08
evening all
not working in buildings sounds like b/s to me as mine regulary hangs above my desk in the study with the switch board straight behind and it always picks up 5-6 sats (its an old magellan 310)and when travelling it either hangs in the back window or sits on the console lid

steve
AnswerID: 163954

Reply By: Pajman Pete (SA) - Friday, Mar 31, 2006 at 06:30

Friday, Mar 31, 2006 at 06:30
If you were heading west it must have been the coriolis force! :o)

Pete
Any mug can be uncomfortable out bush

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AnswerID: 164020

Follow Up By: Willem - Friday, Mar 31, 2006 at 08:00

Friday, Mar 31, 2006 at 08:00
YES!

F Coriolis = -2 m (w x vr)
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Follow Up By: Willem - Friday, Mar 31, 2006 at 08:03

Friday, Mar 31, 2006 at 08:03
And more!!!



This entry contributed by Leonardo Motta

The Coriolis force is a fictitious force exerted on a body when it moves in a rotating reference frame. It is called a fictitious force because it is a by-product of measuring coordinates with respect to a rotating coordinate system as opposed to an actual "push or pull."

As an example, suppose an observer is sitting on a carousel that appears to him to be stationary but, from the point of view of an outside observer standing on the ground, the carousel is rotating with angular velocity . Now suppose that the carousel rider moves a ball with mass m radially away from the center of the carousel. From the point of view of the observer outside, the ball moves in a curved path which is tangent to the center of rotation. Since the ball's path is curved in inertial space, there must be a force to accelerate it, and this force is called the Coriolis force. The Coriolis force can be observed directly in satellite tracking of hurricanes, whose paths can clearly be seen to curve to the right in the northern hemisphere and to the left in the southern hemisphere as their distances from the Earth's rotation changes.

To compute the Coriolis force, note that the ball moved by the carousel rider has angular velocity , so its angular momentum is

(1)

When the mass is close to the center, it has relatively little angular momentum, but as it moves farther out (increasing r), it has greater angular momentum. Therefore, a torque must be exerted in order to move it along the radius, and that torque is the rate of change of L with time as m moves along the radius. If m moves entirely radially, that stays constant and the torque is given by

(2)

where is the Coriolis force.

The Coriolis force is therefore the sidewise force that has to be exerted by the carousel rider to cause the ball to move outward at a radial speed which, upon solving (2), is

(3)

In vector notation, the Coriolis force is given by

(4)
(5)
(6)

where is the Coriolis acceleration. It can therefore be seen that The Coriolis force independent of radius, and is present even at the origin of the rotating coordinate system.

Coriolis Acceleration, Coriolis Frequency, Coriolis Parameter, Rossby Number



Coriolis, G.-G. "Sur les équations du mouvement relatif des systèmes de corps." J. de l'Ecole royale polytechnique 15, 144-154, 1835.

Feynman, R. P.; Leighton, R. B.; and Sands, M. The Feynman Lectures on Physics, Vol. 1. Redwood City, CA: Addison-Wesley, pp. 19-8-19-9, 1989.

French, A. P. Newtonian Mechanics. New York: W. W. Norton, pp. 528-529, 1971.

© 1996-2006 Eric W. Weisstein

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Follow Up By: Michael B - Friday, Mar 31, 2006 at 09:20

Friday, Mar 31, 2006 at 09:20
Willem,

WOW, all this just to see how fast you are going???...LOL

Regards
Michael B (SA)
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FollowupID: 418859

Follow Up By: Willem - Friday, Mar 31, 2006 at 19:16

Friday, Mar 31, 2006 at 19:16
Yes Michael

Silly isn't it?....lol
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Follow Up By: Member - Mike DID - Friday, Mar 31, 2006 at 22:07

Friday, Mar 31, 2006 at 22:07
"The Coriolis effect is an apparent deflection of a moving object in a rotating frame of reference. There are examples of this effect in everyday life, such as the direction of rotation of cyclones. "

"The Coriolis effect is NOT the fictitious Centrifugal force given by w x(w x r). However, the co-existence of Coriolis and centripetal forces makes simple explanations of the effect of Coriolis in isolation difficult. "

- from en.wikipedia.org/wiki/Coriolis_force

This could get hotter than debates on charging AGM batteries :-)

Mike
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Reply By: Member - JohnR (Vic)&Moses - Friday, Mar 31, 2006 at 09:12

Friday, Mar 31, 2006 at 09:12
Geez Bro, good to see you adding the references at the bottom of your dissertation above. Adds real value to our reading. We will confer the degree at the next graduation. DEO

One day when I was deciding the positioning of paddock boundaries my Meriplat when I had it, (now been stolen) continued at some considerable speed after I stopped driving. I turned it off and just as well I had set up the waypoints before hand as I was able to continue after I turned it on again.
Cheers,
Who?
John

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AnswerID: 164042

Follow Up By: Willem - Friday, Mar 31, 2006 at 19:19

Friday, Mar 31, 2006 at 19:19
Ahhh Young Mose

I did a good copy and paste there, but some of the computations did not appear. Weird looking algebra equations which left be rather cold(better go and put me socks on then)

You resting up after all the hard yakka at the games?

Cheers mate
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