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 > availability 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.
