I'll try to take a look and see if there is a way to set an arbitrary value that is stored across boot cycles. I would have thought it would work that way already but if it's not, I'll have to check.
And you are correct that any offset you program into the offset field should show up if you compare a baseline GPS pps against the output 1pps from the device. I would caution against using the lock light if you are playing with different control values. The lock light is a simple aggregation indicator of signal source available + phase offset < x microseconds + phase offset / time < x nanoseconds / second. I think the values of x and y were set based on reference source but there isn't much in the way of hysteresis and I've occasionally had tests where I tweaked variables which resulted in large overshoot and the lock light toggling for a while. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Robert Watzlavick.com Sent: Thursday, March 31, 2011 9:58 AM To: Discussion of precise time and frequency measurement Cc: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Upgrading TS2100 from TCXO to OCXO Thanks-that explains it. But I can't make an arbitrary offset value stick across a power cycle. Is that what the info field does? I was trying to compare the 1 PPS from my ts2100 to the Thunderbolt but my HP 5316 only has 100 ns resolution. I would think the offset should show up as a skew on the PPS output. -Bob On Mar 31, 2011, at 11:44 AM, Greg Dowd <[email protected]> wrote: > The offset command in the TS2100 is just a phase stepper in 100ns steps. > Usage was originally targeted at compensating for the GPS antenna cable > length (~ns/ft). As it turned out, we used it for another purpose as well. > The very first models of the 2100 used an external GPS receiver (Trimble > Acutime) which had an open collector 1PPS. Because of that, we triggered the > phase capture on the falling edge of the input signal. When we migrated the > design to support an internal receiver (CM3 IIRC), somebody forgot that and > we didn't have an extra inverter available at the right spot. What I ended > up doing was some conniptions inside the box where we would still trigger on > the falling edge and I would use the different default values of offset as > compensation for the pulse width. Unfortunately, as we changed GPS modules > (CM3->Ace->AceII), the pulse width changed and I don't think anyone ever went > back and fixed it. So, between all the different models, and due to the > availa bility of add-on GPS conversion kits, many of these units ended up with different values of info which corresponded to difference GPS receivers and some phase offsets. I'd say just set it to whatever works. > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Robert Watzlavick > Sent: Thursday, March 31, 2011 6:24 AM > To: Discussion of precise time and frequency measurement > Cc: Jason Rabel > Subject: Re: [time-nuts] Upgrading TS2100 from TCXO to OCXO > > I changed the root/eng/timing/offset parameter from -100 to 0 on my unit > and let it sit overnight. This morning, it is locked and without a > frequency offset. So I wonder why my unit would have had a 100 ns > offset programmed into it? I cannot figure out how to get the 0 value > to stick though. When I power cycle it, it returns back to -100. > > I programmed various values into to the info field, restarted the unit, > and read the following results for the offset parameter: > > 0x00000000 -5 > 0x00000010 -5 > 0x00000021 -5 > 0x00000022 -5 > 0x00000024 -100 > 0x00000028 -5 > > This is interesting for a couple of reasons. First, it matches what > Jason is seeing in his units with the -5 ns value for offset. However, > a different TS2100-IRIG unit I looked had an info value of 0 and its > offset was also 0. Maybe the presence of the GPS unit makes it think it > needs an extra offset? We know that bit 6 is used for GPS vs. UTC for > the NTP time (from the manual). I suspect bits 2 and 5 are for GPS > since my unit was delivered that way. I would think at least 2 bits > would be for the osc type but which ones? And if Jason's unit came > delivered as an OCXO, why aren't any bits set to signify that? Maybe > the TCXO/OCXO is one configuration and the Rubidium is another. It > someone had a factory configured Rubidium unit, it would be interesting > to know if there are any bits that correspond to it. > > -Bob > > On 03/30/2011 08:40 PM, Robert Watzlavick wrote: >> My unit (TCXO/GPS originally) has the root/eng/timing/offset set to >> -100. A TCXO-IRIG unit that I looked at has an offset value of 0. >> When I was first bringing up my unit with the OCXO, I was comparing >> the 10 MHz output against a stabilized Thunderbolt and I noticed the >> TS2100 EFC voltage seemed to stabilize but there was an offset in the >> 10 MHz output. The lock LED wasn't turning on either. I got >> impatient and started poking around and that's when I noticed the >> "offset" parameter was set to -100. I changed it to 0 and the lock >> LED immediately turned on but then the EFC started heading the other >> direction. I put it back at -100, let it sit for a few hours, and it >> eventually locked without a frequency offset. I'll set my offset back >> to 0 and see where it ends up overnight. >> > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
