[ntp:questions] Questions about joining pool.ntp.org

unruh unruh at wormhole.physics.ubc.ca
Mon Aug 29 21:38:16 UTC 2011


On 2011-08-29, NPG <nathan at cmpublishers.com> wrote:
> On 8/27/2011 1:16 PM, unruh wrote:
>> On 2011-08-27, NPG <nathan at cmpublishers.com> wrote:
>>> Long range plans.
>>> Does anyone know the current price of a meinberg M300 with WWVB receiver.
>>> I've asked them for a quote, but haven't heard back yet.
>>> My guess ~ $1,000 - $2,000.
>> 
>> Why would you want to do that? 
>
> Why not?
> Seriously, because I don't know any better, so I'll ask stupid
> questions, consider the answers, and hopefully avoid making stupid mistakes.


> Their hardware, seems to be well designed.
> I figured, that I'd build the best plan that I could ( another way to
> say serious overkill ), then adjust it down to reality.

First ask what your requirements are and then you can buy the equipment
to meet those.  You do not want to find yourself in the position of the
car buyer who drives his car to the shopping mall every Fri, but goes
out and buys himself a Lotus.

>
>> Get a Sure gps receiver for $50 do a bit
>> of wiring, and get far greater accuracy than from WWV 
>
> Stupid noob question alert.
> Does GPS provide better accuracy?

Yes. The gps receiver knows exactly how far away you are from the GPS
sattelite ( that is what gps is for primarily) and can therefore
calculate the time it takes the signal to propagate from the sattelite
to your receiver, and add that time to the time stamp that the
satteliate sends. Thus it knows ( to better than a few ns ) exactly what
time it is at the gps receiver. A WWV receiver on the other hand has no
way of knowing how far from the transmitter you are, and thus has no way
of calculating the propagation delay. Meinberg also makes GPS receivers
which are probably very reliable and robost-- probably more so than the Sure
device. On the other hand you can buy something like 20 or more Sure
units for one Meinberg. 

Now if you are worried about keeping good time even in the face of a
nuclear war, than it is quite possible that the WWV transmitter will
remian on air longer than the GPS system will. 
Thus your accuracy may be poorer but your reliability in such cases
higher. 


>




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