PA6H GPS constantly changing course reading?

I just got an ultimate gps from Adafruit and am reading the GPS data from it with a valid fix with an external gps antenna plugged in.

It’s sitting on the desk next to me, but I’m noticing that the direction and speed are constantly changing. The course will jump 100 degrees in an instant, then be +/- 10 degrees of that reading then make another massive jump. The speed is constantly reading just under 1 knots.

It is using the PA6H GPS chip and I was curious if anyone else has had issues with the GPS or if this is expected behavior for this GPS? (I’ve asked this over on adafruit’s forum as well, but figured the people over here might be just as familiar with this GPS chip)

If you are not moving, the calculated course direction and speed are not meaningful. Take it out for a walk!

The random jumps are due to the position errors, which change from time to time, and can be many meters.

Its not an issue with that ‘particular chip’, all GPSs will have the same ‘issue’

You have it working indoors, so you will have noted reception is likley poor and the position\location is changing around quite a bit.

Now think, how does a GPS know its course and speed ?

@Srnet, I get what you’re saying yes, however the GPS units I have used in the past have either been more precise or have had filtering to ignore low speeds. Either way, my previous units didn’t have this issue when sitting still.

However, as it turned out, there was an issue with the board. Outside with no tall buildings even after getting fixes from 8 satellites it reported a host of incorrect data even after several hours. Using an external antenna on my car I tried to observe speed an directional data at lower speeds and higher speeds all of which reported garbage data. Such as no speed, no direction, and random position jumps.

I swapped it out for a ZOE-M8Q from sparkfun and have been getting much better data. It still does the heading jitter, but knowing that this is common behavior for GPS units I can filter that out when not moving, thanks.

That is certainly not expected. I suspect you had a bad antenna connection.

Yeah, I tried with several different (including the integrated one). The integrated one gave me the worst data, by far and connected to the least amount of satellites, but the external ones gave bad results as well. It happens, every so often you just get that lucky bad board, lol. Fortunately, I did get a new one and had some older ones that I could test with to keep me moving.

I would suggest that all the differences you are seeing are down to the strength\quality of signals received, which can vary between GPSs and the type of antennas that are in use and the exact location of course.

I dont see how a GPS, since it cannot know where it is, can tell the difference between apparent ‘movements’ that are real and those caused by propagation and reception issues, any suggestions ?

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