Accuracy Problems????

[Tightlines01]

Hey all, on a recent hunt I started to experience some accuracy problems that I haven't noticed on my previous caches.

 

When arriving roughly at the destination, my gps started to vary the distance by what seems like more than acceptable amounts. It would tell me that I was anywhere from 5 feet to 125 feet away from the destination. My first thoughts pertained to the territory I was in but I wouldn't consider it cavernous or heavily forrested. To be fair I was down following a creek in a wooded park.

 

Even if that was the reason for the accuracy problems while sitting here typing this I had accuracy readings from 4 feet to 155 feet. The majority of the time it read from 15 to 50 but the swings to the extreems happened alot.

 

I am currently using a Garmin Map 76S, with some mapsource info downloaded into it. I am new to the GPS world and am wondering if I'm missing something, do you have any suggestions?

 

Thanks

Andy

[+Renegade Knight]

If you were in a canyon with steep walls that can impact the accuracy.

 

Wherever you go there you are.

[Team Sidewinder]

Well there is the common problem with all gpsr that when you moving really slow due to terrain or just looking for the cache or come to a stop or while you are sitting there typing a post to this thread your accuracy readings are going vary alot. That is just my guess as to what the problem might be. My garmin 12XL and my 76S both do the same thing under these same conditions.

sidewinder

 

LOST AND FOUND DEPT.

[Tightlines01]

Sidewinder,

 

On the first couple of hunts I went on I didn't notice this nearly as much. Does this problem "come and go"? On some of the hunts I went on it would hardly vary at all making it much easier to track in on where the exact co-ordinates are. Would an external antenna help to correct this problem? If so what type would you recommend.

 

Thanks

Andy

[Team Sidewinder]

Well the only time it comes and goes is when is if a cache is in such a area as you have to creep along for or stand still for a couple of minutes or so. Caches where you can keep moving right up until you are within the range your gps is telling you are right on top of it then I don't have this happen. It isn't really that much of a problem but just the nature of the beast as far as I can tell. I am using a Might Mouse II external antenna and that will help some if tree cover or mountains obscure a good view of the sky and cause sat. lock to be lost and I do stress SOME. I don't use my external antenna much since I got my 76S as the internal antenna seems to be so much better than the garmin 12XL I had before. I will admit that I haven't had my 76S all that long either and haven't had it on nearly as many cache hunts as my old reliable gps so maybe I am not your best source of info on this either. Hope this helps but am sure there are people on this forum that could give you a better reason why this might be happening.

sidewinder

 

LOST AND FOUND DEPT

[+Rich in NEPA]

The quad-helix antenna that is found in the GPSmap76 series has a signal reception pattern that is biased more towards the horizontal, as opposed to a patch-type antenna that has a signal reception pattern biased toward the vertical.

 

In general, the more "spread out" the SV's are that you're locked on to, the more accurate the position being calculated. This means a preference (satellite geometry) for those SV's that are nearest the horizon. When you can only see those SV's that are clustered overhead, the position calculation gives the poorest accuracy. (The reverse is true for calculating elevation. However, accurate elevation values are not normally as important as better horizontal position accuracy.)

 

So, depending on your surroundings (say, heavy woods but not necessarily a heavy canopy), the patch antenna can indeed appear to (and sometimes does) provide better reception. (I have a 12XL in addition to a map76 so I can speak from experience. In my car, for example, the 12XL often acquires a faster lock and displays higher signal strength than the map76. For this reason I carry my remote patch-type antenna with me in the woods when signals are sketchy.)

 

Cheers ...

 

~Rich in NEPA~

 

 

=== A man with a GPS receiver knows where he is; a man with two GPS receivers is never sure. ===