legendcx vs. 60cx

[ericlink]

I was geocaching today for the first time and had my legend cx and my dads 60cx. When I compared the distance to the cache that each unit was displaying the legend showed 50 feet more then what the 60cx showed. I checked that the legend had the same projection as the 60cx as well as waas enabled. The 60cx was only off by about 5 feet and my legend was about 50 ft off. Can anyone explain to me as to why this may be. Any suggestions welcome. Thanks to all that reply!! Eric

[QuigleyJones]

The most likely answer is that the units use different GPS Chips, with the 60cx having a more powerful one.

[+ergomaniac]

Perhaps the cache was placed with a 60cx, which doesn't mean it's more accurate, it's just taking you back to where the 60cx determines the coords to be.

 

I have a 60cx and my son has a venture cx (identical GPS to the Legend) and on some caches he is closer and others I am closer. Some older caches were placed with GPS's that were really bad at holding a signal under tree cover. The drift on the older units would be significant so neither of your GPS's will read the location accurately. The best way to test them is to find a known survey monument where you have a clear sky view and see how they do. I've done this several times with our GPS's and they are both amazingly accurate.

 

I've actually observed that the sensitivity of the SIRF chip (combined with the quad helix antennae) can add a bit of error when I'm under heavy tree cover. My theory is that the unit is able to pick up really poor signals from under the canopy and unfortunately, uses these signals as part of the calculation. I've found that the Venture (with the patch antennae) is often more accurate under these circumstance (if it can get a signal that is...) because it is looking almost straight up and doesn't pick up the weaker signals.

 

I'd be interested in hearing if other "SIRF" users have observered this behaviour or is it just my imagination?

Edited May 20, 2007 by ergomaniac

[+Prime Suspect]

I've actually observed that the sensitivity of the SIRF chip (combined with the quad helix antennae) can add a bit of error when I'm under heavy tree cover. My theory is that the unit is able to pick up really poor signals from under the canopy and unfortunately, uses these signals as part of the calculation. I've found that the Venture (with the patch antennae) is often more accurate under these circumstance (if it can get a signal that is...) because it is looking almost straight up and doesn't pick up the weaker signals.

 

I'd be interested in hearing if other "SIRF" users have observered this behaviour or is it just my imagination?

My experience has been the opposite.

[Hertzog]

 

I've actually observed that the sensitivity of the SIRF chip (combined with the quad helix antennae) can add a bit of error when I'm under heavy tree cover. My theory is that the unit is able to pick up really poor signals from under the canopy and unfortunately, uses these signals as part of the calculation. I've found that the Venture (with the patch antennae) is often more accurate under these circumstance (if it can get a signal that is...) because it is looking almost straight up and doesn't pick up the weaker signals.

 

I'd be interested in hearing if other "SIRF" users have observered this behaviour or is it just my imagination?

I had a similar experience last summer. The 60CSx was still tracking, but only getting 4 or 5 satellites at the time, and I got some large deviations from the trail I was on. Also, as an experiment I have taken the 60CSx into movie theaters; it will maintain track, but the "blob" of tracks will usually be all over the theater!

 

It's something to be aware of, but remember that when the SiRF unit is tracking under these conditions, other units will have lost track completely. It's better to have a less accurate track than no track at all, but you need to keep in mind that it IS less accurate than normal.

[+CheshireFrog]

When I compared the distance to the cache that each unit was displaying the legend showed 50 feet more then what the 60cx showed. I checked that the legend had the same projection as the 60cx as well as waas enabled. The 60cx was only off by about 5 feet and my legend was about 50 ft off.

 

Well, all other things being equal, the 60CX is expected to be more accurate, but there's not enough information in your post. What did the EPE read for both units? Taking the error into account might reveal that the two readings weren't so different. Also, remember that your GPS is not taking you to the cache, it's taking you to the posted coords; we also don't know what the EPE was for the person who hid the cache.

 

Find a benchmark placed in the last few years and place them both on the ground with a clear view of the sky and leave them lay for 10 minutes. Then compare the readings.

 

I've actually observed that the sensitivity of the SIRF chip (combined with the quad helix antennae) can add a bit of error when I'm under heavy tree cover. My theory is that the unit is able to pick up really poor signals from under the canopy and unfortunately, uses these signals as part of the calculation.

 

No, I've never seen this. The only thing I've seen that degrades the accuracy of my 60, (other than lack of a signal), is signal reflection, and that's true of all GPSr's.

[+Hynr]

My caching partner has a 60CS (without SiRF); I have a 60CSx (with SiRF); most of the time the two GPSrs agree as to position to within the accuracy limits of the two devices (the accuracy spec is the same). But when things get flaky (canyons, dense trees,...) 95% of the time the 60CSx is less flaky. (There are numerous times when my caching partner beats me to the cache despite that).

[+ergomaniac]

My caching partner has a 60CS (without SiRF); I have a 60CSx (with SiRF); most of the time the two GPSrs agree as to position to within the accuracy limits of the two devices (the accuracy spec is the same). But when things get flaky (canyons, dense trees,...) 95% of the time the 60CSx is less flaky. (There are numerous times when my caching partner beats me to the cache despite that).

 

I would expect this to be the case with the 60cs and the 60csx because they both have the quad helix antennae which I believe, has a better ability to pick up signals that are lower on the horizon (which is not necessarily a good thing if you want accuracy). My original observation was regarding the different accuracy that ericlink reported between the Legend cx and the 60 cx. The Legend cx has a patch antennae that looks directly overhead and presumably would get less signal bounce than the super sensitive Quad Helix/SIRF combination. I've noticed that under moderate tree cover, the Venture cx (patch antennae) will often have a better accuracy reading than my 60cx. It does however, struggle to maintain it's lock under heavy tree cover.

 

There is certainly no question that the SIRF receiver will behave much better under a thick canopy or in city canyons... that's why we paid the big bucks for them! (I also agree that when caching it's a keen (trained) eye that scores the most caches not the GPS accuracy!)

[+imajeep]

I've actually observed that the sensitivity of the SIRF chip (combined with the quad helix antennae) can add a bit of error when I'm under heavy tree cover. My theory is that the unit is able to pick up really poor signals from under the canopy and unfortunately, uses these signals as part of the calculation. I've found that the Venture (with the patch antennae) is often more accurate under these circumstance (if it can get a signal that is...) because it is looking almost straight up and doesn't pick up the weaker signals.

I've noticed the same thing about my 60 Csx. I can pull in a signal under lousy conditions, but I get forty-foot accuracy, rather than fifteen-feet. I check the satellite page when I'm under heavy canopy to see what king of accuracy I'm getting.

[ericlink]

Howdy all! Thanks for all of your coments. I understand that the 60cx has a better antenna but the funny thing was when I was comparing the two they both had the same amount of locked satellites, however the legend had a 50 ft difference as stated in my first post. Also I was not under any tree canopy or in a deep ravine.

 

In response to CheshireFrog I am not sure exactly what is meant by EPE. Can anyone tell me what it stands for?

 

Ergomaniac, I agree with you that a good trained eye will find more caches. I'm sure that is why I found more when I never had a gps. HaHa.

 

Thanks again to all!

[ericlink]

Oops Double Posted.

Edited May 22, 2007 by ericlink

[Brakeless1]

Do you have legend upgraded to latest firmware? as alot of people had that problem before last update.

[vtmtnman]

Check your map datum on both units.Make sure they're both set to WGS84.Consult user's manual to learn how if you don't know how to do this already.

[+CheshireFrog]

Howdy all! Thanks for all of your coments. I understand that the 60cx has a better antenna but the funny thing was when I was comparing the two they both had the same amount of locked satellites, however the legend had a 50 ft difference as stated in my first post. Also I was not under any tree canopy or in a deep ravine.

 

In response to CheshireFrog I am not sure exactly what is meant by EPE. Can anyone tell me what it stands for?

 

Ergomaniac, I agree with you that a good trained eye will find more caches. I'm sure that is why I found more when I never had a gps. HaHa.

 

Thanks again to all!

 

EPE is Estimated Postitional Error, it's the readout that people use as a guess as to how accurate their readings are.

 

For example, let's say you have both GPSr's sitting on top of the cache under a light tree canopy. The 60CSx reads that it is 5 feet away from the cache with an EPE of 10 feet, and the Legend reads that it's 12 feet away from the cache with an EPE of 15 feet. In actuality, both of thesde receivers are spot on, well within the expected range of accuracy.

 

A second example: let's say that you found the cache, but your 60CSx reads that its current position is 25 feet off from the coords, and again has an EPE of 10 feet. Is this a problem with the accuracy of your receiver? No, remember, your receiver is not looking for the cache, it's looking for the coords. In this case it would be nice to know what the hider had for an EPE when he placed the cache.