[time-nuts] Upgrading TS2100 from TCXO to OCXO

[Robert Watzlavick.com]

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 <GDowd at symmetricom.com> 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: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] 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.
>> 
> 
> 
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