[time-nuts] HP-5065A frequency adjustment advise and Common (all in) view GPS comparisons proposal.

Sun Oct 21 15:50:03 UTC 2012

Dear Magnus,

Good morning. Welcome back! I hope you are enjoying typing at home again.

a. I just downloaded TimeLab. What a nice pice of software! Now I am ready for some action. 

b. Regarding your comment on the TBolt as a close UTC source, I just finished my first approach for my thesis GPSDO using the TBolt module. I still have to master the use of Lady H. to get the best out of it. I have only been using TBolt monitor software while I gain experience with it.

c. As per our last comments on instrumentation for phase and time interval measurements, I decided first to get an affordable unit such as the 53132A with the Prologix GPIB adapter. Afterwards I am not moving my finger from pointing to an SR-620 as a dedicated unit for time interval and phase measurements. Until now I feel blind in terms of measuring resources and technics. I must put some attention to it.

d. Your clarification of the use of Phase Shifters is welcome. I can see the need for them to work with time scales and the differences among the old and new Cs and Rb standards. 

e. Yes, you are right. They are currently using the Novatel antenna. How different in performance is the Novatel 700 pin-wheel GPS antenna compared for a regular amplified GPS unit such as the Symmetricom 52532A or the legacy HP units? Is it a matter of gain? Or radiation pattern characteristics? Regarding the VP Oncore receivers I recall a comment from them praising those receivers for both amateur and pro work. I haven't got one yet, but certainly planning to do so. Dr. Levine commented that the older units are better made and so, better performing. How can I tell the difference? I have seen several variations on the used market. 

f. A warm welcome to the new Atlanta member. Has he posted yet?

Thank you as always.

Regards,

Edgardo Molina
Dirección IPTEL

www.iptel.net.mx

T : 55 55 55202444
M : 04455 20501854

Piensa en Bits SA de CV

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On Oct 20, 2012, at 3:08 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

> Dear Edgardo,
> 
> On 10/19/2012 11:06 PM, Edgardo Molina wrote:
>> Dear Group,
>> 
>> Good afternoon. I just realized that my two HP 5065As have been
>> running for about a month and their operation has been closely
>> monitored. Now I assume both clocks are stabilized. I want to
>> start doing some phase and time comparisons between them and
>> with respect of a TrueTime 5 MHz GPS receiver signal. I only
>> have an old Tracor 895A linear phase/time comparator for this
>> purpose. Luckily it has 5 MHz as a frequency input.  At least
>> it will allow me to get close to a decent synchronization as I
>> continue searching for better measurement instruments. Next week
>> I will be receiving my first HP 53132A and Prologix GPIB-USB
>> interface to start characterising my clocks and doing
>> Allan Deviation work.
> 
> You should have a good starting-point then. Pull in TimeLab!
> 
>> My question here is how to finely adjust the 5065A frequency
>> to bring it in phase to the 5 MHz GPS derived signal. I read
>> somewhere that it can be fine tuned using the C Field control,
>> but I am afraid of moving it as both controls have been set
>> to each instrument's factory values. My oscillator fine
>> frequency adjustment pots are set to 250 and locked there as
>> per manual recommendation.
> 
> This is a fine recommendation when you use them as stand-alone instruments. However, it will limit their ability to achieve SI second (UTC second back in the days when you intentionally frequency offset it) to be the current instruments properties and long term drift.
> 
> If you use a UTC source of sufficient quality (i.e. GPS clock such as Thunderbolt) you can remove systematic frequency offsets to within a much tighter specification.
> 
>> May I get some advise as which is the best procedure to adjust
>> these clocks to start matching them regularly to GPS reference?
>> I just don't want to mess with the clocks during the process.
> 
> The manual gives a good description of how to coarse tune the HP5065A into a state where the OCXO is close to correct frequency, locks, has good signal properties to maintain lock over time and not add to much noise. You have a stable frequency source, but not "on mark". The C-field correction is to get the final touch, to correct the frequency to be very near what the SI second should give you.
> 
> For manual trimming, straight frequency measurement is a good start for things like oven oscillators, but then you better start to use Time Interval (TI) mode. Recall that you want to measure over such lengths that the systematic error dominates over the noise. TimeLab is a good tool to do this, as it's phase and frequency plots will do linear or quadratic estimates, draw the trend curves and you can get a good feel for it. You can also get the Allan Deviation and Time Deviation to see how your phase and frequency drift compares to the noises.
> 
>> Also related to my previous question, is it common to use phase
>> shifters with the 5065A not to touch the frequency standard adjustments?
>> I saw NMIs using them to adjust Cs clock time scales without touching
>> the Cs adjustments.
> 
> You are comparing apples and oranges.
> 
> Good Caesium atomic beam clocks does auto-trimming with a separate control loop to steer the C-field. Old caesiums, such as HP5060A and HP5061A is in this sense "open loop" (the term has been used in this context before) and need C-field corrections. With such auto-trimming, the systematic error due to C-field error can be significantly reduced, if not effectively eliminated. Other systematic effects is still there, but quality clocks take care to handle them one way or another.
> 
> Even good Rubidium gas cell clocks does not have this C-field locking, as the C-field correction is used to overcome the systematic effects of wall-collisions, buffert gas pulling (which is used to coarse-correct the wall-collision effect), cavity pulling and ligth amplitude pulling.
> 
> I'm not talking about other standards using caesium and rubidium, but most of the effects is dues to the standard type rather than atom type.
> 
> So, old Caesiums and Rubidiums require the C-field corrections to align up, taking out their systematic effects, and also to compensate drift in them, which comes natural from aging.
> 
> Good quality modern Caesium clocks on the other hand doesn't need this correction to the same degree, but it is also trouble some to measure the clock if you measure it after corrections, so by monitoring the non-corrected clock and then create a corrected variant for the time-scale realization is the preferred variant.
> 
>> I would like to explore some interesting possibilities as a
>> byproduct of this enterprise. Is anybody interested in common
>> (all in) view GPS clock comparisons with me? I just learned the pro
>> way of doing it at CENAM over the last couple of days during the
>> symposia of time and frequency that I had the luck to attend. With
>> some coordination there has to be a way to reproduce those
>> experiences here, not only as isolated comparisons, but continuous
>> periodic measurements. Probably automated in the future. I am
>> afraid we will not be able to achieve legal traceability to UTC,
>> as we are not doing this directly with an NMI or following a legal
>> traceability chain to it. Or am I wrong? Does anybody has direct
>> legal traceability using common view GPS with an NMI? Despite this,
>> we could still build a network of inter comparisons using GPS as a
>> way to continuously monitor our labs performance, just as the SIM
>> network headed by NIST, NRC and CENAM do across the american
>> continent NMIs.
> 
> What for instance NIST do in their system as a service is nothing very secret, it is just taking off the shelf components (VP Oncore), some measurement infrastructure and some software and apply many of the principles covered in a whole range of articles. GPS common view as such isn't all that hard to do. Some of the trick is to do coordinated logging and to steer which satellites is being used. Some others is trivial stuff as using a good quality antenna (they now use the Novatel 700 pin-wheel antenna if I recall correctly).
> 
> It would be nice to set up such a thing, cook up the software to run it and operate it continuously.
> 
>> If the idea is welcome, please answer to the thread. I am more than
>> enthusiastic. If there are currently efforts to achieve this, please
>> accept my apologies for the lack of knowledge in the group's work.
>> Still I would like to cooperate if possible. Other comments regarding
>> feasibility and technical implications are surely welcome.
> 
> I haven't seen anyone do it with such systematic rigour, but it would be a nice little lab to do. :)
> 
>> By the way, while attending the symposia, I noticed with pride that
>> the Time-Nuts community is highly regarded among the crème de la crème
>> Time and Frequency circles. Thank you all for allowing me to
>> participate with the group.
> 
> We all contribute with information, questions, answers, experience, tinkering and experiments. Nice to hear that they have taken notice.
> 
> I always take the opportunity to talk warmly about the group. I think I may have recruited yet another guy while being in Atlanta this week.
> 
>> Thank you!
> 
> Thank you.
> 
> Cheers,
> Magnus - just home from a loooong travel
> 
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