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domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 01:16pm 13 Jan 2014

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Pity, the many tablets, smartphones with GPS do not have this jack. Dependent on the location it may be a gamble to get a good GPS signal without antenna.

As a technical aside: During a cruise I spoke to a Concorde captain re navigation and he told me that they still use ring-laser inertial navigation + GPS as the GPS is not too great in the polar regions due to the equatorial sats. I studied astro navigation and had my own bubble sextant and believed the GPS meant the end of the gyro driven inertial nav systems.

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

paceman
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Joined: 07/10/2011
Location: Australia
Posts: 1329

Posted: 02:17pm 13 Jan 2014

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Vic,

DX.com seem to be a pretty big crowd (they used to call themselves 'Deal Extreme"), a lot of Back Shed members on the microcontroller forum have bought stuff from them over the last couple of years - I've probably bought a dozen things from them in that time without any trouble.

One thing to remember though is the flip-side of having zero freight costs - their delivery can be slow... My deliveries have ranged from a pretty good ten days to a pretty bad thirty-five days. Typically it's about two and a half weeks.

Greg

yahoo2

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Joined: 05/04/2011
Location: Australia
Posts: 1166

Posted: 04:28pm 13 Jan 2014

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domwild said As a technical aside: During a cruise I spoke to a Concorde captain re navigation and he told me that they still use ring-laser inertial navigation + GPS as the GPS is not too great in the polar regions due to the equatorial sats. I studied astro navigation and had my own bubble sextant and believed the GPS meant the end of the gyro driven inertial nav systems.

If you are on the ground or sea and moving slowly or stopped then you only need accuracy in two dimensions and simple predictive algorithms, poor signal and bad angle satellites for your position can be shed from the data stream before any differential correction is applied giving superb accuracy.

Adding the vertical axis lowers the accuracy by a factor of 10, add to that the speed of an aircraft and the visibility of satellites that offer very poor triangulation due to the height of the aircraft and no reliable ground based differential signals over the Southern ocean. The GPS can be relatively accurate but not 24/7 so the inertia system fills in the holes. There are small windows of poor triangulation that repeat for 10 -15 minutes every 11 and 3/4 hours for about 3 weeks most years at certain points on the earth (I live on one of them) You cant park a plane and wait for the PDOP (positional degree of probability) to come back to good levels.

Combining GPS with cheap electronic gyro's is pretty common on boats auto pilot and roll prevention systems and agricultural machinery's autosteer systems.

I'm confused, no wait... maybe I'm not...

domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 01:00am 14 Jan 2014

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Interesting, yahoo2, do you have a pilot license or surveyor? My senior comms expired 30 years back!

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

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