Accuracy with External Antenna

[+jonboy]

I have just started using a Gilsson External Amplified Antenna with my Garmin 76S, and while I am picking up many more satellites, it appears to be less accurate. When I download my track to a my TOPO mapping program, the track seems to deviate slightly from the route I actually walked. Also, when I obtain a new set of ten coordinates for my caches, the averaged result seems to differ significantly from those I obtained with just the unit. I used an external antenna several years ago to try and get more accurate coordinates for my caches, and other cachers compained my coordinates were off. Does anyone have any idea why this might be happening?

[planewood]

I have just started using a Gilsson External Amplified Antenna with my Garmin 76S, and while I am picking up many more satellites, it appears to be less accurate. When I download my track to a my TOPO mapping program, the track seems to deviate slightly from the route I actually walked. Also, when I obtain a new set of ten coordinates for my caches, the averaged result seems to differ significantly from those I obtained with just the unit. I used an external antenna several years ago to try and get more accurate coordinates for my caches, and other cachers compained my coordinates were off. Does anyone have any idea why this might be happening?

 

I have no idea?? That runs absolutely counter to my experiences with an Gillson antenna on my 60cx. But, that said, the antenna has no effect on the reported EPE. The reported coordinates are still closer, on average, to the actual coordinates.

 

Also, download the Trimble Planning software and try it out. Maybe you have just been out when the DOP was high. www.trimble.com

[BacktrailJitters]

I sometimes use an external antenna with my 76s. But, the only thing that seemed to increase accuracy was d/l the latest sw version, doing a master reset, and acquiring the latest satellite almanac for WASS. It agrees more with my 76CSx now.

[+NightPilot]

It's possible to pick up reflected signals which you wouldn't without the external antenna, depending on the environment. Reflected signals can adversely affect accuracy. It depends greatly on what is around the antenna - buildings, cars, trees, or whatever.

[+PFF]

It's possible to pick up reflected signals which you wouldn't without the external antenna, depending on the environment. Reflected signals can adversely affect accuracy. It depends greatly on what is around the antenna - buildings, cars, trees, or whatever.

 

NightPilot is exactly right. Reflections can cause unexpected, unpredictable results. Use the built-in antenna for ordinary circumstances and save the amplified antenna for cases when reception is poor. Other tips:

 

*Remember that the unit is reading the location of the antenna. Keep it oriented to the target.

 

*Unless an external antenna comes with a mounting system, you must provide a "ground plane" for it to work property. This can be any piece of metal--even an old auto license plate. I've found it convenient to use a large, right-angle, metal shelf bracket from the hardware store. One side, positioned horizontally, provides the metallic surface needed by the antenna, while the vertical portion becomes the "handle" with which to carry it.

 

-Paul-