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side by side unit accuracy


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Posted

A friend and I both have the etrex Legend. We recently took a trip and had both units side by side.

 

My friends would get pegged at 6-7 feet of accuracy (with waas on), but mine would never get below 14 (also waas enabled).

 

Any thought as to why there would be such a difference? Our elevation was regularly 30-50 feet different, but our speeed would be exactly the same.

 

Just got off with a guy at garmin and he didn't have any answers for me other then "different conditions, yadda, yadda". But being right next to eachother the condiditions thing doesn't fly with me.

 

Any ideas?

Posted

Did you both have locks on exactly the same satellites? Did you both have WAAS data collected for exactly the same satellites (the "D" indicators)? If the answer to both of those questions is Yes, then I would think it a bit unusual. Otherwise, it's pretty much as I would expect.

 

PS_sig.gif

Posted

Hubby and I both have Garmins....he a III+ and I a V....He had thought of selling his when mine arrived but no way now.....each seems to have an area that it is better at......

 

III+ because of smaller memory.....the screen is easier to read. Keeps it's signal longer... Basically zeros in on cache same as mine.

 

V way best for road trips although it frequently says that you are "off road" when you are still on the thruway or other desginated main roads... You can leave the cache area and it will still track behind you, beeps just before and at turns...for me a reall plus as I am accustom to getting lost.....

 

Last weekend I was out on a whale watch....in a boat on the ocean with WAAS.....I pulled in 14 sats..........

 

anyway

 

DxChallenged

 

"Have you no news on your travels?" the Book of fairy & folk tales of Ireland (1888)

Posted

I have wondered about this since I got my Garmin V. Enabling the WAAS and giving it time to lock onto one of the WAAS birds, then motionless for an hour or so, I never get better than 11-12 feet of indicated accuracy. I have upgraded from firmware v2.02 up through v2.03 to v2.04 - no version did any different. I did the 3 finger system reset after each upgrade. I have had the unit on for an extended time in both Oklahoma and New Mexico. I figured at around 6000 ft elevation in NM I would have a great signal and get the sub 3 meter accuracy reflected on the estimated position error. The signal is great with 5 or 6 satellites nearly maxed out on the signal strenght meter, and the rest at better than 50%.

 

Any thoughts? If I switch from WAAS enabled to disabled, the EPE number doesnt change, it just says 3D GPS instead of 3D differential GPS.

Switching back to WAAS enabled, the EPE is initially about twice as big, then fairly quickly drifts down to the 11-12 number.

 

I wouldnt wonder about this if the spec for WAAS wasnt 3 meters or less 95% of the time. I never get my unit to indicate an EPE of under 3 meters.

Posted

I read in another forum that WAAS is sending no useful signal. I have turned on and off the WAAS on my V and get better accuracy with WAAS off! So maybe the WAAS is of no use yet. How come?

Do you have the amplified antannae attachment? The one with the mag mount? The signal strength will be peaked on all sats and accuracy has been better, but the best accuracy I have had is 11 feet. Anyone had any better on the V?

 

nscaler

"Anyone not here, raise your hand!".

Posted

When I tried running a comparison test between different GPS models, I encountered RF interferance between the different models. My vista did bad things when placed against a maggi 330 and a Handspring Visor GPS Companion.

 

The best way I got a good measurement was to keep all other GPS's that I was going to test at least 30 feet from the test point. Once I did that, the little Garmin 48 got better results then anything else I tested under a clear sky.

Posted

Keep in mind that shadowing a sattelite will change accuracy. I will set mine down and if I walk around it, the accuracy will change as I block certain salttelites.

 

Steve Bukosky N9BGH

Waukesha Wisconsin

Posted

kinda off topic but DARC do you like your handspring visor companian or not why and why not and what are the ups and downs of it im thinking about getting one SOON hopefully also what visor do you have? thanks in advance

 

Support Open Source

Posted

The smallest number for the EPE I've seen on my Vista is four meters. That's equivalent to 13 feet. That was in normal mode, since the European counterpart to the American WAAS, EGNOS, isn't operational yet. They do transmit, but with a "no use" signal, which Garmin's units interprets as don't care about this signal. I've heard that Magellan units do use the signal, when available, in spite of the status signal.

 

I've received WAAS in France, but that's of no use there, since all differential corrections reflect the situation over North America, not over Europe.

 

The four meter EPE I had with twelve satellites received at the same time.

 

There is another thing. It seems to me that where I live (N 57), I can more frequently get many sats at the same time, compared to if I travel south to, say, N 50. Does anyone know if that's because the satellites turn around and starts going back south again about where I live, so that I can receive them more often than if I was closer to the equator? That seems logical to me, but I'm not sure if I'm correct in my assumption.

 

Anders

Posted

quote:
Originally posted by Anders:

 

There is another thing. It seems to me that where I live (N 57), I can more frequently get many sats at the same time, compared to if I travel south to, say, N 50. Does anyone know if that's because the satellites turn around and starts going back south again about where I live, so that I can receive them more often than if I was closer to the equator? That seems logical to me, but I'm not sure if I'm correct in my assumption.


 

Basically there are no satellites over either of the poles or even close to the poles. As one goes further north (or south) one also sees satellites over the poles (other side of the world).

 

Cheers, Kerry.

 

I never get lost icon_smile.gif everybody keeps telling me where to go icon_wink.gif

Posted

quote:
Originally posted by Anders:

 

There is another thing. It seems to me that where I live (N 57), I can more frequently get many sats at the same time, compared to if I travel south to, say, N 50. Does anyone know if that's because the satellites turn around and starts going back south again about where I live, so that I can receive them more often than if I was closer to the equator? That seems logical to me, but I'm not sure if I'm correct in my assumption.


 

Basically there are no satellites over either of the poles or even close to the poles. As one goes further north (or south) one also sees satellites over the poles (other side of the world).

 

Cheers, Kerry.

 

I never get lost icon_smile.gif everybody keeps telling me where to go icon_wink.gif

Posted

Anders, some figures.

 

Based on current constellation (today) at N50 you should have a 12 satellites in view (down to horizon) 11.7% over a 24 hour period.

 

At N60 you'll see 12 for 12.4% over a 24 hour period.

 

Now if one had a receiver with more than 12 channels at N60 there would be a max of 15 sats in view for 4.1% of the time but at N50 the maximum numbers one could see is 14 (5.5% of the time)

 

Cheers, Kerry.

 

I never get lost icon_smile.gif everybody keeps telling me where to go icon_wink.gif

Posted

Anders, some figures.

 

Based on current constellation (today) at N50 you should have a 12 satellites in view (down to horizon) 11.7% over a 24 hour period.

 

At N60 you'll see 12 for 12.4% over a 24 hour period.

 

Now if one had a receiver with more than 12 channels at N60 there would be a max of 15 sats in view for 4.1% of the time but at N50 the maximum numbers one could see is 14 (5.5% of the time)

 

Cheers, Kerry.

 

I never get lost icon_smile.gif everybody keeps telling me where to go icon_wink.gif

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