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Old May 6th 19, 04:08 PM posted to rec.aviation.soaring
Dan Marotta
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Posts: 4,601
Default Implausible Time Records

Yes, the GPS jamming usually centers around Alamogordo and ranges out to
about 400 nm.Â* Moriarty is well within that area.Â* I've asked other
local pilots and they don't report so many drop outs.

Maybe there are just too many GPS antennae in my ship.Â* I'll take a look
at a divider for everything except the ADS-B WAAS GPS.Â* Its antenna is
mounted aft of the engine in the Stemme.Â* The rest are on or under the
glare shield.

On 5/5/2019 7:42 PM, JS wrote:
On Sunday, May 5, 2019 at 3:43:24 PM UTC-7, Dan Marotta wrote:
Thanks Tim

I'll increase my time interval to 2 seconds and see if that helps.

Strange that the igc file does not show GPS drop outs since my ClearNav
screen went white with the caption (something like) No GPS.Â* Zero
satellites.Â* And the ClearNav vario said, "Warning no GPS".Â* The
PowerFlarm portable screen also went blank with a "Zero satellites" message.

On 5/5/2019 1:05 PM, Tim Newport-Peace wrote:
Dan,

Open your file with a text editor and search for "B190338"
This will put you in the right area.
In each record, after the letter B, the next six bytes are the time.

After B190339 the time jumps back to B190337, which is odd, and leads to
there being two records with a time of 190338, and also 190339.

Odd, but I have seen this before. Maybe you can avoid it in future by
setting a longer fix interval, even 2 seconds might help, but no promises.

I am not seeing any GPS outage around that time. This would be shown by the
Letter "A" in the 25th byte changing to a "V".

Although it does not help a lot, the sequence error seems to happen as you
left the ground, so I guess you were not reversing turns?

I'm not saying this is what OLC are complaining about, just that it is odd
and it might be.

Tim.

--
Dan, 5J

That smells of GPS jamming.
Check this page.
https://www.navcen.uscg.gov/pdf/gps/...terference.pdf
I did not have a problem with the vario file today. My antenna has a shortened cable to a MECA divider, then a short SMA-SMA link cable.
Jim


--
Dan, 5J