DL1 GPS accuracy issues?

[Kenton]

Please bear with me, I'm a new DL1 user...

I recently got a new DL1 and have been using it to log SCCA autocross runs.

When compare my logged runs with runs logged on other units, my runs don't line up compared to the others (at least 2 different units, runs within 60 minutes of each other). When I try to compare the GPS position or GPS speed accuracy in an XY window vs. distance between the various runs, I see the other unit's data to have a much lower value in the graph (whatever the units are). The other units show up as very consistent data and mine is all over. We are comparing same model car (Corvette), runs within 60 min. of each other, antenna attached to same spot (top of roof) using the same attachment (blue masking tape).

One thing I noticed are that my data files are much larger than the other units (length of recording was twice as long in the sample I looked at, but the size of the file was an order of magnitude larger). Will a noisy GPS signal cause the size of the .run file to be larger?

Only thing I know is that I initially tried to attach the antenna using velcro, and had some difficulties. When I tried to remove the velcro from the back of the antenna, the sticker on the bottom of the antenna came of and got mutilated to the point that I couldn't put it back on (seemed to have some kind of mylar coating on it). Could that affect the GPS antenna operation?

Sorry for the long posting...
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Kenton Cabiness

[faraday]

Your new DL1 is probably a raw data capable unit that can provide a more accurate software based 20Hz GPS solution.
The Run Manager details the logger's firmware and serial number. 11-6 is a raw capable firmware. The feature is hardware dependent, the firmware must suit the hardware...
I'm not sure what the serial number break point is for raw capable units, but it is around 3000. The raw data (carrier phase and pseudorange) takes considerable storage space. This is probably the reason for files larger than those of your colleagues with older units.
The accurate post-processing algorithms that use the raw data are built into Analysis, but you must purchase a coded licence file that is specific to your logger serial number to enable all this.
Nevertheless, the accuracy of the standard solution is not degraded.
Something else is plagueing you.
I doubt that it is simple GPS accuracy or drift, or the antenna's damaged label. Try to swap antennas (or prefferably loggers) with one of your buddies to isolate the causal component or installation issue. Perhaps, one of the Support gents will volunteer to examine some data. This might shorten your diagnostic efforts.

[Kenton]

Thanks for the info. Given that I'm running 11-6 firmware, my serial # is 2976, and the size of my .run files, I'd say I've got the latest and greatest...

I'll try swapping antennas with a friend this weekend to see if I can isolate the source of the problem.

If I want to experiment with trying to create a ground plane on my fiberglass bodied car to increase the signal, anyone know how large it would need to be? I'm thinking a suction cup camera mount with a metal plate that is grounded to the body should act as a ground plane, just not sure how large it would need to be...
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Kenton Cabiness

[faraday]

Kenton the keen one!
Your desire, perhaps even desperation for a better result is commendable, but I think it is unlikely that the apparent lack of a ground plane is the problem or that providing one will improve performance. I think I have read that these antennae don't need more than what is built in to them. I wish I could recall where, to cite it and state facts with total confidence.
There have been many problem free installations with R-T and similar GPS loggers on f.g. bodied vehicles and with antennae on roll bar tubing. I would put some effort into researching the ground plane issue with a GPS hardware expert if adequate literature can't be found online before making something.
If you can swap the logger, leaving antenna and power supply as is, you will test your installation. Have you an RPM connection? Noise can be introduced there, but many installations have failed to get a proper RPM trace because of noise without harming GPS performance. It sounds as though you will be systematic...


Hope you resolve matters soon.