The effect of an external antenna and another chip-set

In this test we will compare the performance of 3 systems under different field conditions. The systems are:
-a Garmin GPS 76
-a Garmin GPS 76 with external Mighty Mouse II active antenna
-a Falcom NAVI-S Smart antenna with a SiRFstar II/LP chip-set

Field Condition 1: half open sky.

To the North of our position was a tall building at only 5m distance, thus blocking satellites in the North. All around were trees, blocking the sight lower than 45 degrees above the horizon. In this winter period some satellites came through the branches, now without leaves. A low, but dense tree to the South blocked satellites in that direction.

For the first screen-shot we carried the GPS 76 as any-one does, when walking: at stomach height, 45 degrees up. We were faced North, building in front.

Picture 1

GPS 76, facing North

For the second picture, we simply turned 180 degrees, so facing South. GPSr still in exactly the same position in front of us.

Picture 2

GPS 76, facing South

The third shot is taken with the GPS76 in the pocket, but linked to a Mighty Mouse II active external antenna on our hat. We were facing South.

Picture 3

GPS 76 and Mighty Mouse 2

Still facing South, we replaced the Mighty Mouse II by a Falcom NAVI-S Smart GPS antenna and linked it to the pocketPC. Result is picture 4.

Picture 4

NAVI-S

The first thing that we remark is that the NAVI-S is aware of satellite 30, low in the SE, but does not seem to know about satellite 10, low in the NNE. As these satellites are just above or just below the horizon, this probably has no importance. The NAVI-S looks for satellite 6, much higher in the sky then the GPS76.

As all 4 results are almost identical (see hdop, pdop, vdop and Err), the only conclusion from this test, although not spectacular, is that as long as the sky is open enough and there are enough satellites in view, nothing is critical. The GPSr in front of you, with or without external antenna, or a GPSr with a SiRFstar II/LP chip-set, it does not really matter. Reception and accuracy are good.

For the next Field Condition, we will have to look for a much more covered sky, preferably in a pine forest.

For other useful programs for pocketPc or Palm, see our GPS Software page.