[ntp:questions] SNTP server + ntpd 4.2.4 client

Unruh unruh-spam at physics.ubc.ca
Wed Mar 19 17:16:03 UTC 2008

"Richard B. Gilbert" <rgilbert88 at comcast.net> writes:

>Steve Kostecke wrote:
>> On 2008-03-19, Noob <root at localhost> wrote:
>>>Does the GPS18LVC provide an oscillator to serve time even when there 
>>>are not enough satellites in sight?
>> No. You'll have to pay (much) more than $70-$80 if you want a good
>> hold-over oscillator.

>With something like 27 NAVSTAR (GPS) satellites aloft, there should 
>almost always be seven or eight above the horizon.  Satellites more than 
>ten degrees above the horizon are preferred!

>I've never used the GPS18LVC (I have a Motorola M12+T) but if you know 
>your exact location you only need one satellite to get the time.  There 
>are four equations in four unknowns (lattitude, longitude, elevation, 
>and time).  Not knowing any of these variables, you need four 
>satellites.  Once you know your location a single satellite is 
>sufficient to solve for time.

Yes, but the internals of the receiver are not available to the user. Thus
the 18LVC uses a minimum of 4 since it is quite possible that it is
moving-- it is designed for OEM truck operations. Thus the 18LVC claim, if
I recall correctly, that it needs 4 If less than 4 for a few 10s of seconds
it stops delivering a PPS. On the other hand, as you say, if you have any
view of the sky at all, that should not be a problem.

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