Implausible Time Records

On 5/20/19 2:42 PM, wrote:
I’ve not heard back from Lxnav yet, but I had a private email from a very smart person that pointed out that both the October 2 and October 4 flights had the clock jump after takeoff but before soaring began. The flight this week had the clock jump a minute or so after soaring began, and thus is likely why OLC flagged this one and not the other two. It appears that the clock jump is 7 to 8 minutes after the unit is turned on. Since I generally do not turn the system on until just before takeoff, it is believed that the system is using an internal clock until it syncs with the gps satellites and then resets the clock which may be different by a couple of seconds. My plan is to turn the 9070 on a few minutes before launch to allow it to sync clocks to see if that helps. It is not clear to me if Dan’s issue is similar to mine or different.

MS


They do have clocks to help achieve lock on the satellites, but I've
seen the reported time jump immediately after lock was achieved. Don't
know why the 9070 would wait minutes after achieving lock before
correcting the time. Maybe an issue of 2D vs 3D lock. If you're
turning on the logger immediately before takeoff, you're risking losing
the early part of the flight entirely, not just having time problems.

Dan was having lots of gps altitude dropouts during flights, that might
just be jamming. He did have a time jump just at liftoff, so that fits
in with switching the clocks.

If you're turning on the logger immediately before takeoff, you're risking losing
the early part of the flight entirely, not just having time problems.

Good point. I’m not usually worried about the igc file much for casual flights which is what these all were. Or at least I wasn’t worried until the OLC problem.
Of course for record, badge, or contest flights; I turn the computer and backup loggers on long before takeoff since tasks have to be entered and checked.
You may be on the right track with the 2D vs 3D lock. I will try to look at the gps satellite status page before takeoff in the future.

At 21:27 20 May 2019, kinsell wrote:
On 5/20/19 2:42 PM, wrote:
I’ve not heard back from Lxnav yet, but I had a private email from a
very smart person that pointed out that both the October 2 and October 4
flights had the clock jump after takeoff but before soaring began. The
flight this week had the clock jump a minute or so after soaring began,
and
thus is likely why OLC flagged this one and not the other two. It
appears
that the clock jump is 7 to 8 minutes after the unit is turned on. Since
I
generally do not turn the system on until just before takeoff, it is
believed that the system is using an internal clock until it syncs with
the
gps satellites and then resets the clock which may be different by a
couple
of seconds. My plan is to turn the 9070 on a few minutes before launch
to
allow it to sync clocks to see if that helps. It is not clear to me if
Dan’s issue is similar to mine or different.

MS


They do have clocks to help achieve lock on the satellites, but I've
seen the reported time jump immediately after lock was achieved. Don't
know why the 9070 would wait minutes after achieving lock before
correcting the time. Maybe an issue of 2D vs 3D lock. If you're
turning on the logger immediately before takeoff, you're risking losing
the early part of the flight entirely, not just having time problems.

Dan was having lots of gps altitude dropouts during flights, that might
just be jamming. He did have a time jump just at liftoff, so that fits
in with switching the clocks.

I've looked at Dan's trace, and the dropouts are in the latter part of the
flight,
nowhere near the time when the clock problem occurs, so probably not
jamming. Micheal's flight shows no GPs dropouts at all, but still
experienced
the problem.

So...Â* Does having a 3D fix with, say 8 satellites, constitute good GPS
time?Â* I would think so.

On 5/20/2019 3:27 PM, kinsell wrote:
On 5/20/19 2:42 PM, wrote:
I’ve not heard back from Lxnav yet, but I had a private email from a
very smart person that pointed out that both the October 2 and
October 4 flights had the clock jump after takeoff but before soaring
began.Â* The flight this week had the clock jump a minute or so after
soaring began, and thus is likely why OLC flagged this one and not
the other two.Â* It appears that the clock jump is 7 to 8 minutes
after the unit is turned on.Â* Since I generally do not turn the
system on until just before takeoff, it is believed that the system
is using an internal clock until it syncs with the gps satellites and
then resets the clock which may be different by a couple of seconds.
My plan is to turn the 9070 on a few minutes before launch to allow
it to sync clocks to see if that helps.Â* It is not clear to me if
Dan’s issue is similar to mine or different.

MS


They do have clocks to help achieve lock on the satellites, but I've
seen the reported time jump immediately after lock was achieved.Â*
Don't know why the 9070 would wait minutes after achieving lock before
correcting the time.Â* Maybe an issue of 2D vs 3D lock.Â* If you're
turning on the logger immediately before takeoff, you're risking
losing the early part of the flight entirely, not just having time
problems.

Dan was having lots of gps altitude dropouts during flights, that
might just be jamming.Â* He did have a time jump just at liftoff, so
that fits in with switching the clocks.

--
Dan, 5J