[time-nuts] More ES100 WWVB Measurements

[Joseph Gwinn]

On Mon, 31 Dec 2018 12:00:02 -0500, time-nuts-request at lists.febo.com 
wrote:

>  time-nuts Digest, Vol 173, Issue 44

> Message: 7
> Date: Mon, 31 Dec 2018 04:04:22 -0800
> From: "Tom Van Baak" <tvb at LeapSecond.com>
> To: "Discussion of precise time and frequency measurement"
> 	<time-nuts at lists.febo.com>
> Subject: Re: [time-nuts] More ES100 WWVB Measurements
> Message-ID: <96BB388753294278A9CDE96C1EA7D9AE at pc52>
> Content-Type: text/plain;	charset="UTF-8"
> 
> Hi Graham,
> 
> That's very nice work. And you have uncovered several unusual effects 
> in the ES100. Bugs? Features? If we time nuts keep up the good work 
> to evaluate this chip, we are likely at some point to get an 
> informative response from the guys who designed it. They read 
> time-nuts.

I didn't see this mentioned, but I think I have found the relevant US 
patent application: US20130051184A1, Real-time clock integrated circuit 
with time code receiver, method of operation thereof and devices 
incorporating the same, Oren Eliezer et al, Oren Eliezer et al, filed 
2013-02-28.  

.<https://patents.google.com/patent/US20130051184>

Found this by chasing stuff from the EverSet website: 
.<http://everset-tech.com/wp-content/uploads/2014/11/ReceiverRadioClocks.pdf>.

Joe Gwinn

 
> So now both you and Tim have observed the off-by-one-second (or 
> off-by-N-seconds) effect in the ES100. I wonder if this explains why 
> some of my ES100-based La Crosse 1235UA Ultratomic wall clocks are 
> off by a second sometimes.
> 
> My main question: in your "Time Plot.PNG" plot, what is the cause of 
> the sawtooth pattern? The points are almost all on a clear negative 
> slope, though bounded by roughly +/- 75ms. Looking on the far left, I 
> see a time drift of +50 ms to -25 ms over an hour, which is 
> equivalent to a -20 ppm frequency offset; about -2 seconds/day.
> 
> Do you think this is due to the 16 MHz onboard xtal? If so, how about 
> changing the temperature of the eval board by a lot (say, several 
> tens of degrees) for an extended time (say, 4 hours) and see if the 
> sawtooth slope changes convincingly.
> 
> Also, just to be sure, can you put a known independent timing signal 
> (e.g., GPS/1PPS) into your complex BeagleBone Black / Debian 9.4 / 
> ntpd time server / Python 3 / Excel stack to establish the validity 
> of your measurement methodology? Very likely you did it right, but I 
> always cringe when I hear "Linux" or "NTP" and "precise time" in the 
> same sentence. Yes, sorry, forgive me; I grew up in the "trust, but 
> verify" generation [1]. It applies pretty well to metrology also ;-)
> 
> /tvb
> 
> [1] https://en.wikipedia.org/wiki/Trust,_but_verify
> 
> 
> End of time-nuts Digest, Vol 173, Issue 44
> ******************************************