[time-nuts] GPSDO Component Selection

Jerry jsternmd at att.net
Sun Sep 9 22:10:28 UTC 2012


Sounds like the Heisenberg Uncertainty principle at work :-)

jerry

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bob Camp
Sent: Sunday, September 09, 2012 5:53 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] GPSDO Component Selection

Hi

Position accuracy and timing accuracy are two very different things.
Firmware is optimized to improve either one. "Position" firmware is often
pretty poor for timing. 

Bob

On Sep 9, 2012, at 5:05 PM, Chris Albertson <albertson.chris at gmail.com>
wrote:

> On Sun, Sep 9, 2012 at 1:14 PM,  <bg at lysator.liu.se> wrote:
> 
>> True for a cheap oem navigation receiver. Not true for a geodetic 
>> quality receiver, who usually have some options (external frequency 
>> input, PPS_in) to make them the best timing receivers available. 
>> However they are much more expensive than the typical single frequency
timing reciver.
> 
> I looked at every link and can't see where they give a timing accuracy
> spec on the PPS with respect to UTC.   Possition accurracy is very
> good and we might assume the timing is as good.  But they don't say it 
> is.  What's interesting is these GPSes will accept an accurate clock
> input in order to give better location data.   That is the opposite of
> a timing GPS where you tell it accurate location data so that it can
> get better timing.   Cutting down the unknown in one lets you do
> better in the other.   I assume these all cost well over $50.  You can
> get a pretty good timing GPS for $30 and it WILL have the PPS error 
> specified.
> 
> To the OP.  None of this matters a lot because PPS is a standard input 
> signal.  It is easy to swap out a GPS receiver later.  Same with the 
> OCXO.  From a control point of view they are all pretty much the same.
> You can swap them out later
> 
> 
> Chris Albertson
> Redondo Beach, California
> 
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