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How good should WAAS accuracy be on 76CSx?


jarras

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Just got my first GPS unit yesterday. Jumped in with both feet on the Garmin 76CSx. I've read and understand that the Sirf chips give me a better chance of locking more satellites, and that seems to be as advertised. But I'm not getting the advertised WAAS-enabled position errors of < 3m 95% of the time. I only get < 3m about 1% of the time. Through this forum I've stumbled on a great description of WAAS, and specifically how to get locked onto the right satellites, which I've done. I'm able to lock one of the WAAS satellites, and get 8-10 others locked in differential mode. But still the positional error is always >10ft.

 

So, is there something else I need to do, or are the Garmin claims totally bogus, or maybe my unit is just defective?

 

What kind of experience are other users having?

 

Thanks.

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My experience between the 60C and the 60Cx is that the 60C would often report accuracy better than 10', but it would also often show erroneous positions (usually attributed to poor reception and/or multipath errors). My 60Cx seldom reports accuracy of 10' or better (usually more like about 12' to 14'), but it is consistently better at showing accurate positions on the screen. I think that the Cx is just more conservative in calculating its EPE.

 

...just my 2¢

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I have the 76csx and am quite disappointed with all the float I get. Sometimes it gets me right there, but I can stand still and it will then tell me to go 25 feet in some direction.... Lots of wander... Seems best to follow it as I walk in and get to ground zero... if I walk around when I can't find it, I think I get more float. And even with the canopy gone in winter, it has not been that much better.

 

I am in CT and from what I've heard WAAS is not functioning here... and there was something about sattelite relocation going on.. I'm not sure why that would affect my unit if I have 8 sattelites, but then I still think it's magic anyway......

 

I like the unit, but it sure ain't perfect in that regard...

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You might want to download Trimble’s free Planning utility from their web site. This will allow you calculate the DOP for your position at any given day. You may be getting eight satellites, but if they are not in the best geometric position, you will not get good DOP position. I am extremely pleased with the accuracy of my 76CSx. The estimated error seems to be conservative. I lay a lot of my tracks on GIS maps, so if there is a lot of wandering it becomes very apparent. I got very poor results with the 76CS in heavy foliage but am happy with the 76CSx. It works so well four of my friends have bought identical units. I do not get the wandering you mention unless I carry the unit in my pocket which causes it to be in a non vertical position as I navigate under heavy brush. As always, make sure you have the latest firmware/software.

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I see the same as NeoGeo in regards to my new 60CSx in comparison to older Garmin units in that the x unit may report 14-18 ft epe while my Legend reports 9-10, but the position shown on both is the same. Plus, I don't know where you are quoting the accuracy ratings from, as standard consumer grade gps units will only give 3-5m accuracy at best in most situations. Even in reading the 76CSx manual specifications, it states for WAAS 3-5 meters(10-16 feet) 95% typical, not <3m. I tend to think that the newer units are reporting a more conservative, yet consistent position and epe.

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... I don't know where you are quoting the accuracy ratings from, as standard consumer grade gps units will only give 3-5m accuracy at best in most situations. Even in reading the 76CSx manual specifications, it states for WAAS 3-5 meters(10-16 feet) 95% typical, not <3m. I tend to think that the newer units are reporting a more conservative, yet consistent position and epe.

 

You're right about the spec in the manual that states 3-5m 95%. I found that this morning. However, I only received that manual and spec AFTER buying and receiving the unit. When shopping for the unit, I used Garmin's website. A link on the 76CSx page leads you to their "What is WAAS?" page where they say "A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time." So it looks like I was misled into setting my expectations too high.

 

Bottom line, if my unit is doing as well as it can and as well as what others experience, then I'm happy. It's really an incredible technology. My big concern was that maybe something was wrong and needed to be fixed.

 

Thanks for the feedback.

 

Here's the link to Garmin's WAAS explanation page. Note also that the manual says that the FAA confirmed WAAS accuracy to 1-2 meters throughout most of the USA. No promises, but again raising expectations.

http://www.garmin.com/aboutGPS/waas.html

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Here is my 2 cents worth. I believe that the new sirf chip technology is so sensitive ( hence better sat. coverage under adverse conditions ) that you will get more drift if you stand still too long but you are right in that it is more accurate when moving to the cache site. My accuracy never gets better than 12-14 feet either with either waas or without. I also think the claims from Garmin are the epa fuel mileage estimates for your car. Maybe once in a blue moon you will get those claimed mileage figures or for the gps accuracy results.

team sidewinder

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