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Baud Rate Question - GPS 18x and iGuidance
jkurtz11
Hi,

I recently purchased a garmin gps 18x serial receiver and am successfully using it with iguidance 4.0. Generally I am very happy with the performance of this combination. I have one minor problem which pops up occasionally though. It is quite minor, but I'm curious if anyone has any insight. Sometimes the indication of my traveling speed in iGuidance will go to 0 mph for an instant, and then return to showing my correct speed. I've checked the gps info page in iGuidance and it shows I have very good reception with 8 to 9 green bars, so I don't think it's a satellite problem. My hunch was that it has something to do with the baud rate. By default the gps 18x is set to 4800 baud. I have the choice to increase it using the Garmin utlity program, but don't know if there is any advantage to doing so. Is the baud rate simply a measure of the speed of the data transfer? Would a faster one necessarily result in better performance? I guess I could just try experimenting but just thought I would ask here first.

Thanks,

Justin
Ken in Regina
It's unlikely that increasing the data transfer rate would make any difference. The GPS data is usually sampled every second. There is very little data in the NMEA data messages from the GPS receiver so 4800 should be more than fast enough to transfer the data.

Calculating the speed is simply the straight-line distance between the most recent data point and the one immediately before it, the time between the two data points and those two numbers are used to compute the speed. Those are not complex calculations. Even the smaller handhelds, which are relatively underpowered compared to your average laptop, can do it quite quickly. So with the small amount of data transfered at 4800 bps there will still be lots of time left between each data message to do the calculation.

It sounds more like something is causing the occasional data message to be corrupted so it gets tossed and no speed calculation can be done until another couple of good data messages are received.

But that's just a guess. Of course it should be dead easy to simply bump the data transfer rate to 9600 and see if it makes any difference. If you do, let us know please.

...ken...
jkurtz11
Thanks for the info Ken. After updating the unit's software and enabling the nmea 2.0 option, the problem has gone away. I'm still running it at 4800 baud, and everything is fine. I'm not sure exactly what the problem was, but everything works great now.
Ken in Regina
I'm glad it's working now. There was probably something in the older combination that was causing the occasional data message to be corrupted or misunderstood. I guess we don't care as long as it works.

...ken...
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