[hpsdr] GPS 1PPS board

[Chris Salinas]

John,

I just read a website on this TU00 model and that they measured the accuracy of +/- .000001 Hz at the 10 Khz pin. Too me it sounds stable enough for a majority of work.
 
I ordered one yesterday just too play with and do some measurements. Can always use it for APRS if it doesn't hold water.
 
I'll let you all know what I find.
 
Chris N0TTW

--- On Mon, 4/6/09, John Ackermann N8UR <jra at febo.com> wrote:


From: John Ackermann N8UR <jra at febo.com>
Subject: Re: [hpsdr] GPS 1PPS board
To: "Henry Vredegoor" <henry.vredegoor at gmail.com>
Cc: "'Graham / KE9H'" <KE9H at austin.rr.com>, "'Chris Salinas'" <n0ttw at yahoo.com>, "'HPSDR discussion list'" <hpsdr at lists.hpsdr.org>
Date: Monday, April 6, 2009, 3:09 PM


I'd put it a little differently:  the 10kHz signal does not make it possible to get *better* performance than a GPS with a 1 PPS signal, but it allows much simpler circuitry since filtering a 10 kHz signal is much easier than filtering 1 PPS, particularly if using analog components.

However it's important to realize that the GPS part of any GPSDO affects only the long term frequency stability.  When measuring over time periods shorter than around 1000 seconds, the performance of the XO is paramount.  One of the problems with building a cheap GPSDO is that good XOs are expensive, and therefore the short term stability is pretty much  tied to the builder's budget or scrounging skills.

The control loop should (a) optimize the "cross-over" point where the XO stability matches the GPS system stability; and (b) avoid messing up the short term stability through excess noise applied to the XO's tuning voltage.

John
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