FR935 GPS cut-offs

I think the real issue is Garmin has no clue here. This could have been a one off issue where the way the sattelites were located combined with the tree cover caused the problems. Maybe it was some kind of interference that threw it off. Given what I saw in the file, where the signal seemed to cut in and out before going out for a long period, my guess is it was a software or firmware issue (maybe even in the GPS chip). Unfortunately cases like this are not easily reproducible and almost certainly not enough info in the file to analyze what actually went on. Signal strength for each sattelite isn't recorded. So unless this starts happening regularly with numerous devices, I would expect Garmin to just brush it aside. Not much else they really could do other than try to add debug code to record suspected causes.

I've tried to do some additional analysis of your activity but none of the tools I'm using (mygpsfile, Sporttracks) seem to be able to absorb a fit file in the 2.x format so I'm not much help.

When you say that you're losing 10K of the track are you referring to the actual distance measured or just the map track between the points where GPS is dropping out? Just curious since you stated that you're using Stryd for distance/pace. Is the overall distance recorded within reason?

Your trace certainly appears outstanding except for the dropout sections. That seems to tell me that your signal on the trail was functional and so I'd suspect some aboration in the course navigation capabilities. I've done lots of trail running without GPS dropouts but have never used navigation so can't offer any useful observations there.

Thanks all for the comments. I was using Stryd for pace, distance and power. That's why I ended up having the distance right, or close enough for me. Stryd got it maybe 1.5km too much, but I was using calibration fact. of 100. The track was cut in two separate places, the first drop out lasting approx an hour! Second drop out was also long, but being mobile right now and cannot really check. Settings were gps only and smart recording with navigation...

Distance will usually be pretty close even when you lose GPS signal, even without a footpod, because the watch itself has accelerometers it uses to compute speed/distance. I had a similar thing happen 3 years ago with my 620 and didn't realize it had lost GPS half way through a 50k because the distance was still pretty accurate.

The entire issue here is that it stopped recording GPS signal for a period, likely due to loss of signal. Unknown is whether it was a software bug or bad reception. Only Garmin could help answer that.

Strava will be more off as it ignores distance in the file and recomputes it from GPS.

I also thought that Strava would behave as you mentioned, but interestingly no. The distance is the same on Strava. This also leaves me wondering what is happening.

Getting even more interesting. Today I tested the Ultratrac mode. Settings: ultratrac, Stryd Datafield but no Stryd pod with me, 1-sec rec, no navigation. I think I managed to reproduce the problem. In track there is now approx 10min cut off of the track/signal. Looking at GC, I also see the elevation being flatlined at the same time on altitude graph. As 935 is not using GPS elevation I don't understand why the altitude also flatlined at the same time? Another side note about Ultratrac: I had about same battery consumption 4.5%/hr than normally with GPS only mode. And the track, apart from the cut off, doesn't look that bad which is also a suprise.
But if one would jump into conclusions, it could be assumed that smart rec or navigation has no play in this problem. But could the altitude (barometer) have something odd going on? Or is just that the GPS freaks out for whatever reason and takes really long time to get the signal back? GPS sw/fw issue?

Heidstocker: what settings do you have on your watch (gps, smart, etc.)?

ciq.forums.garmin.com/.../1252156.png

Heidstocker: what settings do you have on your watch (gps, smart, etc.)?

I've 1s-GPS only
Glonass has a tendency to make things worse for me.

Beside that: I have no external component connected (not even HR-strap or phone, BT is turned off). Navigation is sometimes on but most of the times I don't use navigation.
And I've never seen an altimeter-lock like on your screenshot. I wonder if the Stryd/ConnectIQ thing might cause your symptoms (just remember the optical HR issues we just survived ;-) )

Thanks, I will make note of your settings and see how that would play for me. Can I also ask what is your barometer setting: auto or fixed to alti/baro?

I looked again the previous problematic cut off track and I see the same altitude freeze/lock as with my latest example. So it seem that when the GPS signal is lost or the GPS module is frozen, the altitude gets frozen as well. Pls see the screenshot.
I have now set the barometer setting to manual for altitude. I also want to see if this help with the altitude drifting I have been seeing, where training starting and ending at the same point will have very different altitude.
I really hope Garmin would nebale native running power support e.g. with Stryd, so I would not need to use additional app or datafield for power. Other vendors have been doing this for quite some time already and it would also be great to have more than one power value during training, i.e. avg, lap, 30-sec etc.ciq.forums.garmin.com/.../1253104.png

I've barometer setting at auto. As a side note: the longest runs I do are 30k trails (usually around 3h, 4h if it contains technical climbs). So usually I'm already done when your problems start ;-)