7. Tests - Day 1
We tested all of GlobalSat's 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 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.
|Satellites||Average (in view)||9||9.93||10.00|
|Average (in use)||7.14||5.43||5.61|
|Average Signal Level (in dB)||Maximum per Satellite||46.88||40.17||41.17|
|Average per Satellite||39.64||32.12||32.81|
The results speak for themselves. The best performance comes from the BT-338, which had the highest average satellites in use and the highest average signal level per satellite. Even though on average, it didn't "view" more than 9 satellites, it had the highest average in-use time (7.14). Even though the BC-337 had good signal levels, it needed an extra fix, possibly due to a bad reception. It managed an average of 10 satellites in view (we saw up to 12) but had an average satellite in use of only 5.61. Lastly, the SD-502 had the lowest overall performance, both in use and in average signal levels.
Using VisualGPSXP, we made several plots, mostly for the altitude. As you will see, the three GPS devices produced slightly different results:
Not all Globalsat GPS receivers reported the same altitude for the same course...
For all previous tests, all receivers were installed on the car's dashboard, in clear and direct view of the satellites. However, it is possible, especially with the BT-338, to have it installed in the front glove compartment. Should you expect any difference in the performance? The answer is yes, as the following table shows:
|Model||BT-338||BT-338 in glove box|
|Time to First Fix (TTFF)||Secs||<45sec||<45sec|
|Satellites||Average (in view)||9||9|
|Average (in use)||7.14||7.11|
|Average Signal Level (in dB)||Maximum per Satellite||46.88||39.25|
|Average per Satellite||39.64||30.00|
Apart from the slightly lower performance, there is also a change in the reported altitude...