[time-nuts] Symmetricom TS2100-GPS - 1PPS has 10uS offset

Greg Dowd gdowd at symmetricom.com
Mon May 20 18:13:30 EDT 2013

Hi Esa,
	Sorry, I haven't tracked this group for a while.  Too much work :-)  You are intuitive.  I expect that the TS21 is triggering on the wrong edge.  Way, way back when the TS21 was invented, we were using an external Acutime antenna that had an open collector pps, hence falling edge trigger.  When we added support for an onboard gps, they muxed the two 1pps sources together and we had an incompatible trigger logic problem.  The way I fixed it at the time was to empirically measure the pulse width and use the antenna delay compensation field to "correct" the pps.  This value was stored in e2 at mfg time based on gps receiver module.  At some point, your unit must have not been set or been set to incorrect value or had its gps receiver replaced.  Is there an antenna prop delay command available you can use?

Greg Dowd | Symmetricom®, Inc.
Staff Scientist 
2300 Orchard Parkway, San Jose, CA 95131
Direct:  408.964.7643 
gdowd at symmetricom.com  |  www.symmetricom.com
Symmetricom.  Leading the world in precise time solutions.

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Esa Heikkinen
Sent: Friday, May 10, 2013 11:06 AM
To: time-nuts at febo.com
Subject: [time-nuts] Symmetricom TS2100-GPS - 1PPS has 10uS offset


I bought Symmetricom Tymserve TS2100-GPS some time ago. When comparing 
it's 1PPS with Thunderbolt they are not in sync:

Symmetricom seems to be always about 10 uSec ahead. If I turn of the 
power and then on again, it will be in sync very short moment after the 
tracking led is turned in. But then it will always roll itself at 10 
uSec ahead and lock there, when the locked led turns on.

It seems that it has somehow wrong GPS PPS offset or maybe it's 
folloring the 1PPS signal from it's internal GPS from the wrong edge 
(this is just my guess; Thunderbolt has 10 uSec long PPS signal, maybe 
the internal GPS as well?)

I understand that TS2100 is not as accurate PPS source as Thunderbolt. 
But it's manual claims that 1PPS accuracy should be 1 uS. So this is 
clearly out of spec. This is strange because the Symmetricom seems to be 
high quality product. Obviously not?

Is there any way to fix this by adjusting some offset with telnet etc? 
If not, maybe I try to invert the 1PPS from internal GPS. Or if someone 
knows how to use Thunderbolt as a time source, I could use that and 
remove the internal GPS...

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