[ntp:questions] Re: Good GPS for attic?

John Pettitt jpp at cloudview.com
Thu Mar 10 06:17:56 UTC 2005

Brad Knowles wrote:
> At 6:26 PM -0800 2005-03-09, roy wrote:
>>  Isn't this a bit misrepresented?  The way I read his web page, he
>>  replaced the standard, 39 cent crystal with a $1,500 rubidium frequency
>>  standard.  No wonder it keeps time so well!
>     No, the real key to PHK's work was taking one of the most accurate
> off-the-shelf/kit GPS units designed to provide accurate time, combining
> that with a host that had very low latency to servicing the necessary
> interrupts, and only then did he add the Rubidium clock.  He would not
> have lost too much by going with an OCXO or even a TCXO.
>     If you want that same level of accuracy and precision in a
> commercial unit, you probably won't be able to get it.  If you can,
> you'll spend enough money that you could have bought at least one decent
> car or made a down payment on a house.

That said for $85 you can get a Garmin GPS18 lvc which claims +/- 1us
(modulo the stability of your system and the latency of your PPS drivers).


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