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Re: [gpsd-users] Garmin 18X-5Hz

From: Robin Schwab
Subject: Re: [gpsd-users] Garmin 18X-5Hz
Date: Tue, 16 Aug 2016 22:23:22 +0200
User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0

Dear Gary

Am 16.08.2016 um 20:39 schrieb Gary E. Miller:
On Tue, 16 Aug 2016 09:32:37 +0200
Miroslav Lichvar <address@hidden> wrote:
I mean frequency of the oscillator on which is based the system clock.
As the temperature increases the clock slows down and ntpd/chronyd has
to tell the kernel to speed up the system clock to compensate for that

The temp is no gonna take a steap jump for 10 seconds.  That is the length
of my spike.

I think you're right when you say you're stubborn. ;-) You tell the list there is a random jump roughly every two weeks in your system. But when I tell you to try to correlate it with GPS signal quality (in particular TDOP) you tell me I must prove my theory to you. I just tried to help. If there would be a strong correlation of TDOP with your problem (bird sitting on the antenna) then you could find a way to discard the bad TDOP data. Otherwise you would at least know that GPS signal quality in your case is not the problem and you could focus on software bugs and other possible theories.

I was once doing a map survey with expensive Trimble DGPS equipment. Even with the super expensive stuff we had a DOP forecast telling us which time of the day we could trust the data most. As others said the Trimble will even give you a fix inside a metal enclosing. But precision will drop.

From a signal theory point of view I would like to know wether I have the metal encasing/bird on the antenna or not. This is what DOP provides.


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