GlobalSat BT-338, SD-502 and BC-337
8. Tests - Day 2
We tested all GlobalSat GPS devices with a Dell Axim X50v. We recorded all produced data for a pre-selected route with VisualGPSce (free edition) and later analyzed it with GPSLog. In order to measure the TTFF tests ("Time to First Fix" which is the time it takes for a GPS to determine its current position), we used the GPSInfo "Cold Start" function and measured the time with a chronometer. All tests ran continuously, under the same environmental conditions (night, cloudy weather, 6~8°) and all installed in an Audi, model A4 2004.
After the first day, our curiousity had been aroused and so, we performed new series of tests, including the BC-337's external antenna, which is supposed to increase the sensitivy and give better results than the originally attached antenna. We rested all three Globalsat GPS products, again with the same route and same enviromental conditions. Note, that there are three BC-337 results, the first with the attached antenna, the second with the external antenna installed on the car's dashboard and the PDA sitting in the passenger's seat, and lastly with the external antenna installed on the car's dashboard and the PDA situated so that the built-in antenna could also see the sky. The posted TTFF times are the average of the three measurements.
| BT-338 | SD-502 | BC-337 | BC-337 only antenna | BC-337 + antenna | ||
| Time to First Fix (TTFF) | Secs | 43.33sec | ? | 66.66 | 36 | 36.33 |
| Fix | Invalid | 0 | 0 | 0 | 0 | 0 |
| 2D | 0 | 5.1 | 0 | 0 | 0 | |
| 3D | 100 | 94.9 | 100 | 100 | 100 | |
| Satellites | Average (in view) | 10 | 9 | 9.98 | 9 | 9 |
| Average (in use) | 6.80 | 5.15 | 7.82 | 7.95 | 7.93 | |
| Average Signal Level (in dB) | Maximum per Satellite | 47.14 | 39.17 | 40.13 | 48.13 | 47.00 |
| Average per Satellite | 39.28 | 29.00 | 32.81 | 40.14 | 39.83 | |
The results are very interesting. Starting with the TTFF times, we notice that the SD-502 had problems acquiring satellites and long fix times, some were up to 120secs! The BT-338 delivered what it promises <45sec, while the BC-337 with the external antenna, really make a difference at 36secs!
The BT-338 may had the higher average in view satellites but average used less than BC-337 (with or without the external antenna).The SD-502 gets the last place with only 5.15 average in use satellites. Lastly, the BT-338 shows its teeth, it reached 47.14 dB maximum and 39.28 dB average per satellite. The BC-337 comes second and the SD-502 last. When we installed the external antenna, the BC-337 gave the best performance with 40.14 dB (average per satellite).
Looking at the altitude graphs, we can see that BT-338 and BC-337 gave similar numbers, while BC-337 with external antenna seems to further increase the detail of the course. The SD-502 reported rather higher altitudes...
Looking at the results of both days, we can say that the sensivity of each GPS receiver varies from day to day, hence weather conditions, but in general the BC-337 with external antenna, seems to be the most preferead solution. Of course the BT-338 is very close and will satisfy users with the ability to use Bluetooth connection interface :-)
