[time-nuts] Nav Receiver Sawtooth Correction?

[Bob Stewart]

Random noise or not, wouldn't a position error in a nav receiver cause a corresponding displacement of the 1PPS pulse?

Also there's a bit more to it than just minor noise.  It's probably multipath, or perhaps even jammers passing on the freeway about a mile away.  Whatever the cause, take a look at this screen capture of "foxtrotgps" over about 40 minutes of elapsed time.  The red is the GPS movement around my house that I periodically mention.  I judge it to be about 15 ft on the diagonal.  Sometimes it is much much worse.  Likewise I would expect the 1PPS to move by that amount.

http://www.evoria.net/AE6RV/Nav/NavWander.png

Bob




>________________________________
> From: Chris Albertson <albertson.chris at gmail.com>
>To: Bob Stewart <bob at evoria.net>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
>Sent: Sunday, March 23, 2014 9:24 PM
>Subject: Re: [time-nuts] Nav Receiver Sawtooth Correction?
> 
>
>What you are seeing in position error is a random noise.  There is no
>pattern to it and it is not predictable.  A sawtooth error is very
>nice and regular looking.  It's not "noisy" and can be predicted in
>advance.    Possition error is not at all like sawtooth.
>
>I think what you CAN do is look at the size of the error.  Then you
>adjust the gain on the loop control based of the measured error sigma.
>
>
>
>
>On Sun, Mar 23, 2014 at 6:30 PM, Bob Stewart <bob at evoria.net> wrote:
>> Hi Ignacio,
>>
>> Thanks for the response.  I've got a UT+ in the parts box.  But that's not the problem I'm trying to solve.  I'm trying to make the best GPSDO that I can make using a nav receiver at the moment.  Call it an obsession if you like.  It's OK if I don't have corrections to the nanosecond for each PPS.  But I can see the nav receiver wandering around; especially on cloudy days, (the antenna is in the attic, so that's about the best I can do for that) and it just seems to me that I should be able to do a general correction for nav position errors.  Sorry if my naive posts are starting to get on people's nerves.
>>
>> Bob
>>
>>
>>
>>
>>>________________________________
>>> From: EB4APL <eb4apl at cembreros.jazztel.es>
>>>To: time-nuts at febo.com
>>>Sent: Sunday, March 23, 2014 7:35 PM
>>>Subject: Re: [time-nuts] Nav Receiver Sawtooth Correction?
>>>
>>>
>>>Bob,
>>>
>>>The sawtooth is generated by the granularity of the GPS receiver clock
>>>not being synchronous with the recovered PPS.  The receiver program can
>>>calculate the correction to be applied to the next PPS and outputs it in
>>>a message, bu only in timing receivers, this is not a useful thing in
>>>navigation receivers and I think that it cannot be calculated using the
>>>satellites' position, it is a receiver "defect".
>>>Why don't you buy a timing receiver?  An used Motorola Encore M12+
>>>timing receiver can be bought by $35 or less (ebay items 290656401551 or
>>>301131583613.  The seller is a known Time Nuts supplier).  An UT+ or GT+
>>>even for quite less.
>>>
>>>Regards,
>>>Ignacio EB4APL
>>>
>>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
>
>
>-- 
>
>Chris Albertson
>Redondo Beach, California
>
>