[time-nuts] I've designed a GPSDO, but how "good" is it?

Charles Steinmetz csteinmetz at yandex.com
Tue Aug 18 19:42:24 EDT 2015

Nick wrote:

>I believe I'm at or better than the stability I originally sought. 
>Part 1 of my question is whether that's actually true or whether my 
>naivety is presenting me with a delusion. Part 2 is whether the 
>price point at which I've arrived will support the level of 
>stability I've achieved, or am I delusional in thinking people would 
>or should pay what I'm asking for what I'm offering.
>      *     *     *
>10^-9 was the target all along. Question number two that I came with 
>was whether or not it was reasonable to ask $175 for 10^-9.

 From your description, I doubt that you have achieved 1e-9 from 1S 
to 1000S (the range of primary interest for frequency and TI 
counters) -- but I'll defer on that point until Tom reports on its performance.

As to question 2 (assuming that your GPSDO *does* exhibit stability 
of 1e-9 from 1S to 1000S):

There may be people who would pay $150 or even $175, but in my view 
that is only because they do not know how it performs and what other 
GPSDOs are available and how they perform.  For starters, consider these:

Jackson Labs LTE-Lite board-level GPSDO with TCXO ADEV <7e-11 at 
tau >/= 10S.  Brand new with warranty from an established GPSDO 
manufacturer.  $185

independent measurements at <http://www.ke5fx.com/gpscomp.htm>
GPSDO with OCXO, small production from hobbyist (BG7TBL).  Published 
Allan Deviation graph better than 3e-11 from 1S to 7kS; better than 
5e-12 at 100S.  Complete kit -- comes with PS and external antenna.  $149

Trimble commercial board-level GPSDO card with OCXO; includes power 
supply.  $119

Nortel by Trimble NTBW50AA packaged GPSDO with OCXO; kit with antenna 
and cables.  $159

Lucent by Symmetricom Z3810AS GPSDO timing system; two disciplined OCXOs.  $150

The OCXO units all have ADEVs in the low e-11s at 1S and generally 
get better at longer tau.  The Jackson Labs TCXO product is not far 
behind, owing to the careful selection and testing of the TCXOs by 
Jackson Labs.  With the parts that you have chosen based on your 
budget, you cannot expect to get near this level of performance even 
if you improve the disciplining algorithm.

So, to put it bluntly: Even if you hit your design goal, you have a 
nice learning project -- but not anything that justifies offering 
them for sale.

Best regards,


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