GPS

[thewalleyeguy]

Is there a difference in accuracy and quality between a GPS with an internal or external antannae.

[Fish Head]

Someone can feel free to correct me, but I don't believe there is any difference in accuracy. They have had some problems with the internal antennas, however lowrance say that they have that all ironed out now.

[uglystick007]

Depends on your application. Are you looking for streets, fishing hot spots or geocaches? I have used a garmin Emap for several years with Roads and Recreation maps. For the most part it always was accuarate enough to navigate streets and return to fishing hot spots. I just aquired a LMS332-C sonar/gps with the navionics premium chip. On a high Definition lake it will zoom to 1/17 nm which is accurate enough to navigate to the mouth of a 20 ft channel. The navionics only zooms to 1/8 nm on non high definition lakes which is not very good. The Garmin always let me zoom in and find my latest track or waypoint. So just to confuse you some more it depends more on which specific application you want to use it for. Lowrance is winning the fishing applications and Garmin still has an edge on basic navigation. I'm still getting used to the Lowrance GPS functions but it sure seems like the Garmin is simpler or easier to use. The Lowrance functions/menus just seem harder to use.

[PerchJerker]

There is no difference in accuracy, as long as each unit has a clear view of the satellites the accuracy should be the same. The question is do you get a better view of the sats with an external or internal antenna.

I have both external and internal antenna gps in my boat, I prefer the external antenna.

[Team Otter]

You covered the essentials. I, too, prefer the external antenna but in most cases, the internal antenna works just fine.

[Mike Walerak]

Both my handheld with and internal antenna and my Lowrance with an external are very comparable in accuracy.

I feel the nearly alll quality units are as accurate as they can be with the governments installation of selective availability.

mw

[PierBridge]

Quote:

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with the governments installation of selective availability.

mw

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Thanks for the info guys......they turned of selective availability in May of 2000......

[Mike Walerak]

I believe they had turned it back on to some degree due to all the things going on around the world. I may be wrong though. Any GPS experts out there?

mw

[computerboy]

I'm far from a GPS expert, but I was researching this very issue a while back. The U.S. Military has apparently developed the capability to alter the accuracy of GPS in specific areas. This capability is known as Regional Denial. So rather than degrade all GPS signals with SA, they can degrade the signal around sensitive "areas of interest".

As far as accuracy is concerned with internal vs. external antennas, it really doesn't matter as long as they utilize the same technology (i.e. WAAS vs. non-WAAS). In my experience, the ability to obtain/maintain a GPS signal is the primary advantage of an external antenna (there are always exceptions of course).

Hope that helps.

[iffwalleyes]

You know what amazes me is that your GPS can estimate how much error it has in position. If it can do that why can't it just tell you where you are at? Something I have thought about on occation.

[onemagnum]

What is the deal with that (correction location)?

[Fishin4Life]

Quote:

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You know what amazes me is that your GPS can estimate how much error it has in position. If it can do that why can't it just tell you where you are at? Something I have thought about on occation.

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It probably can calculate error easily. But finding the exact position may be difficult. By giving you a 5 foot error (just for example) That 5 feet could go in any directions and the gps prolly doesn't know which one. I could be wrong, its just a guess

[countryboy9799]

Just another guess here,

I would think it is taking into account how many and also how well it is locked onto the satalittes. The more satt's and stronger signal's it's recieving is one way they determine how accurate they are.

[JollyT]

I know a guy that travels around the country quite a bit and uses his GPS in his rental vehicles to find his way around. He was in D.C. and said when you get near certain areas (Whitehouse, pentagon, etc.) it will read a block or two off randomly on his mapping software. Something degrading the signal perhaps?

[computerboy]

Actually, there was a similar post some time ago about this very subject which is how I found out about Regional Denial to begin with. An FM'er posted a thread about a buddy of his that noticed some odd behavior when driving by the Mall of America. Well after many a conspiracy theory and scores of Google searches later, it turned out to be nothing more than how the GPS software worked. From what I remember, the software mapped the city into a grid rather than by streets. When you crossed a certain point, the map would shift and appear to move the position.

Now, considering the sensitivity of the two locations you've mentioned....I'd actually be surprised if you DIDN'T see some anomalies in those areas.

[SpecialK]

The US gov't restricts the abilty of the current units to get exact readings. In the next 5 - 10 years the europeans will have enough of their sats in the air with fewer restrictions but, I believe, it will mean having to buy a new unit if you want to use them.