[time-nuts] time-nuts Digest, Vol 121, Issue 65

[Ed Palmer]

Hi Dave,

On 8/23/2014 3:51 PM, Dave M wrote:
> Thanks for that suggestion, Ed.  After a bit of reading in the X72 
> Reference Guide, it appears that the X72 does have a 1PPS input.  That 
> would be considerably easier than trying to interface the Rb into the 
> GPSDO.  Still trying to understand what the manual is telling me. Next 
> thing is to determine if my unit has that option enabled (firmware 
> option).  That will be a chore for after the holiday... really busy 
> next week.
>
> What would that (1PPS disciplining) do for me... in terms of 
> maintaining the Rb frequency accurately set?  Would it be as accurate 
> as having the Rb disciplined via the EFC input?

It's kind of overkill, but by connecting the 1 PPS from the NTBW50AA to 
the X72, the X72 will be disciplined to the 1 PPS so the frequency will 
be accurate.  The question is how well will it be disciplined, i.e. what 
will the Allen Deviation graph look like.  I have a few X72 and SA-22c 
(X72's cousin), but none of them have that option.  I don't know of any 
published data on it.  Maybe you can tell us how well it performs.

In general, I just don't see the point of disciplining a Rb standard to 
GPS.  I don't understand what will be gained by doing it.  I have a 
Z3801A and a Tbolt plus a free-running FRK as a house standard.  I 
occasionally compare the FRK to the Z3801A but the drift is so low 
(~1e-12 per month over 9 months) that I see no reason to link them.

One exception that I recently discussed on another forum was a guy who 
lives in a ground floor, north-facing condo.  He might need to have a 
disciplined Rb standard due to poor GPS visibility.

Ed

>
> Thanks,
> Dave M
>
>
>> Message: 5
>> Date: Fri, 22 Aug 2014 16:19:45 -0600
>> From: Ed Palmer <ed_palmer at sasktel.net>
>> To: Discussion of precise time and frequency measurement
>> <time-nuts at febo.com>
>> Subject: Re: [time-nuts] EFC info on Trimble 34310-T OXCO
>> Message-ID: <53F7C201.5070206 at sasktel.net>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>> Have you checked your X72 to see if it has the 1 PPS discipline
>> option?
>> That would be a lot easier (and probably better) than your proposed
>> transplant.
>>
>> Ed
>>
>> On 8/22/2014 12:39 PM, Dave M wrote:
>>> Does anyone have any info on the OXCO in the Nortel/Trimble
>>> NTBW50AA-17 GPSTM receiver?  The OXCO is labeled as Trimble 34310-T.
>>> I see some Trimble 34310-T oscillators on Ebay with pinouts labeled,
>>> but no other info.
>>>
>>> Specifically, I'd like to know the EFC characteristics for it.  I'm
>>> thinking of the possibility of pulling the OXCO out of the GPSTM and
>>> subbing in a 10 MHz Rubidium, and using the GPSTM to discipline the
>>> Rubidium.  My Rubidium is a Symmetricom X72, recently purchased.  It
>>> seems to be working well.
>>> Does anyone know the differences between the three OXCOs used in the
>>> GPSTM receivers ("T", "T2" and "Oak")?
>>>
>>> Thanks for some insight,
>>> Dave M