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

Mon Aug 25 00:19:14 UTC 2014

Bob which Efratom are you talking about?
Bert

In a message dated 8/24/2014 6:33:12 P.M. Eastern Daylight Time,  
kb8tq at n1k.org writes:

Hi

It is not what is done in the Efratom Rb’s. Their pps  input is set up to 
get things on frequency / on time quickly. The assumption  is that you plug 
it into a pps to get it “right” and then take off on your  mission. That 
takes them into the short (for a Rb) time constant region.  

Bob

On Aug 24, 2014, at 5:56 PM, Brooke Clarke  <brooke at pacific.net> wrote:

> Hi Bob:
> 
> I think  that's what's done in the SRS PRS10
>  http://www.prc68.com/I/PRS10.shtml
> 
> Have Fun,
> 
>  Brooke Clarke
> http://www.PRC68.com
>  http://www.end2partygovernment.com/2012Issues.html
>  http://www.prc68.com/I/DietNutrition.html
> 
> Bob Camp  wrote:
>> Hi
>> 
>> If you lock an Rb to GPS, you  need / want / should do it with a *very* 
long time constant. Numbers in the  one day to several days range are 
commonly seen. If you lock it up with a  tighter (shorter time constant) loop, it 
will just wander around as it follows  the GPS input. That’s what would 
happen if you hook your Rb to your Trimble  and turn on the disciplining on the 
Rb. It will significantly degrade the  stability of the Rb.
>> 
>> If you have a temperature stable  environment (or create one) you can 
get some very good results with an (good)  Rb locked to a (good) GPS via a 
proper long time constant setup. It’s not  easy, but it can be done.
>> 
>> Bob
>>  
>> 
>> On Aug 23, 2014, at 6:31 PM, Ed Palmer  <ed_palmer at sasktel.net> wrote:
>> 
>>> 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
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> 
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