[time-nuts] Adjusting HP 5065A frequency

EWKehren at aol.com EWKehren at aol.com
Mon Oct 22 10:46:32 EDT 2012


Tom
A good place to start is with a manual of the Austron 2055 delay if there  
is real interest. Does any one have it in PDF form?
As to the disciplining a Rb or specifically a HP5065A, the filter part is  
the challenge. Having worked on it for the last ten years always using 
Brooks  loop and developing work around's it will do every thing except 
temperature  control and barometric pressure. I have done temperature analog but rely 
mainly  on holding the Rb temperature stable within a tenth degree C.
Bob recently put things in perspective when there was talk about a 32 bit  
DAC. On one side you have GPS and time averaging is required to get full use 
of  it. That is why a Rb is uniquely qualified for it. The original Shera 
input  implemented on a 1 $ G/A is more than enough for time capture wether 
using a  sawtooth corrected GPS receiver or a Tbolt.  On the other end a 
LTC1655 is  again more than enough in an Rb application. You can use it 16 bit 
direct or  dither two or 4 bits. Filter is  easy and do not forget that the 
Rb has an  additional filter between cell and OCXO. Brooks V402NE will do the 
job, how ever  others and I have not been able to buy some in the last nine 
month. Any one  knows what is going on?
What is needed is some one in the group be willing and able to step up to  
the plate and develop the filter on a PIC with all the things learned, and  
believe me, we are still learning as we adapt a M100/8600 via a Tbolt . 
I will be willing to help with every thing except the PIC.
If you bring out the C field coil directly you have full isolation and do  
not have to worry about ground loops.
A complete unit would cost less than $ 40 and more important be assembled  
by any one. I brought it up before but no one responded. If no response I 
will  still be able to do every thing with the HP5065A RVFR that was given to 
me. 
Bert Kehren
 
 
 
In a message dated 10/22/2012 7:33:08 A.M. Eastern Daylight Time,  
tvb at LeapSecond.com writes:

Hi  Bert,

Not sure about the range/resolution. That would depend on how the  standard 
is used and what its frequency drift rate is. The stability doesn't  have 
to be too much better than the standard itself.
The Austron 2055  resolution is 1e-14, IIRC. The Symmetricom AOG is 1e-19  
(overkill).

What I've found in some GPSDO and passive atomic standards  (e.g., Rb or 
Cs) is that as soon as you turn on the DAC and enable the loop,  you get more 
short-term noise, say in the range of 1 to 100 seconds. That's  why for best 
stability you always switch off the loop during a sensitive  measurement. 
Many older Cs had a "Cs off" switch for this. Not only did it  conserve 
cesium but it also means you're running straight off the high-quality  OCXO. This 
is also true for GPSDO, like the TBolt which allows you to turn off  
disciplining with a s/w command.

In general, when you discipline a OCXO  you get that characteristic ADEV 
"hump". This is expected, a natural byproduct  of combining two unknowns, one 
that's assumed to be better at short tau and  worse at long tau (e.g., OCXO) 
and one that's assumed to be better at long tau  and worse at short tau 
(e.g., Rb cell, or Cs beam, or GPS receiver). At some  point there is a 
cross-over and you know/assume that at that point each must  be contributing 
1/sqrt(2) of the noise.

To see the humps in living  color, refer to: 
http://www.leapsecond.com/pages/gpsdo/

To answer your  question about short/medium/long, I guess in this case 
short is tau left of  the hump; medium is the hump, and long is tau to the right 
of the  hump.

/tvb

----- Original Message ----- 
From:  <EWKehren at aol.com>
To: <time-nuts at febo.com>
Sent: Monday,  October 22, 2012 4:04 AM
Subject: Re: [time-nuts] Adjusting HP 5065A  frequency


Tom
I have two questions what should the range,  resolution and stability   of 
the delay generator be and how  much do you think a digital loop driven by 
a  
Tbolt would degrade  short and medium precision. What is your definition of 
short  and  medium?
Bert Kehren


In a message dated 10/22/2012 12:25:08 A.M.  Eastern Daylight Time,  
tvb at LeapSecond.com writes:

Three   companies come to mind for phase microsteppers. A popular one 
decades ago  was  made by Austron (model 2055A). I got mine on eBay but 
they are  
not as common  now as ten years ago.

The current models by  Symmetricom and Spectra  Dynamics are extremely 
high-end (expensive)  and overqualified for use with a  vintage rubidium 
oscillator. If you  visit NIST or USNO you will see these  impressive units.

It would  be a very fun project to make your own. I  suspect other group  
members could either help you or would eagerly employ your  design  for 
their 
own use.

But -- before you decide on a hardware   solution see if you can do it in 
software.

An analogy is what we  do  with GPS 1PPS sawtooth errors. There are two 
ways 
to deal with  this. One is to  capture the correction message over RS232, 
measure  the DUT vs. GPS 1PPS with a  TIC, and then numerically apply the  
sawtooth correction with one line of code.  Several of the popular  GPS 
monitor 
programs do this automatically for you  (TBoltmon and  TAC32, for example). 
The 
software solution is perfect to the   granularity of the sawtooth message, 
typically 1 ns.

The  hardware  implementation usually involves a PIC and a programmable  
delay generator. The  PIC listens for the correction message over  RS232 
and then 
has plenty of time  (up to one second) to program the  delay chip. When the 
hardware 1PPS arrives  it is delayed to  compensate for the aforementioned 
sawtooth error. The result  is a  hardware 1PPS that's quite close to the 
ideal 
1PPS, limited again by  the  granularity of the message, as well as offset 
or linearity  errors in the delay  chip.

So that's the analogy. To apply this to  your rubidium, ask  yourself which 
instruments or measurements or  users are downstream of your  5065A 10 MHz 
output. Can they deal with  daily software corrections to a stable  but 
slightly imprecise  frequency, or do they really need the frequency to be  
as 
accurate as  possible at all times.

There's a third alternative as  well. You  might consider using your 5065A 
as the LO in a GPSDO. This will   sacrifice some short- and mid-term 
precision 
due to additive noise, but  it  will guarantee the best possible long-term  
accuracy.

/tvb

----- Original Message ----- 
From:  Edgardo Molina 
To:  Tom Van Baak ; Discussion of precise time and  frequency measurement 
Sent: Sunday, October 21, 2012 8:49 PM
Subject:  Re: [time-nuts]  Adjusting HP 5065A frequency


Dear  Tom,


Good evening. In relation to your last comments on this and  other 
subjects, 
I  am sharing some thoughts and experience about it.  I took the liberty to 
 
separate the topics as to ease the interested  parties to follow up  
accordingly. TNX.




a.  Information you kindly provided  and the index for  newbies:


Thank you! You just provided me  with lots of new  ideas and information on 
the subject. You have very valuable   information in your web site. As Hal 
was saying, an index should be  done  anywhere so it could be easier for 
the 
rest of us to locate the  information. I  am planning soon to build a web 
page 
for my lab. In  english of course for  everybody to share my experiences. I 
could  work on an index to point out to  the various sources of information 
 
and topics that are difficult to find. That  I think could expedite  things 
a 
little bit. 


b. Phase Micro   steppers:


I saw the phase micro steppers working at CENAM   time scale. I was 
wondering that the technique could be translated to  my  5065As and not 
trying to 
touch them so often. If I am assuming  correctly and  the technique could 
be 
used with the HP Rb standards.  Are those phase micro  steppers easy to 
find? I 
mean, affordable in  the second market? If there is  one of course. I saw 
the 
ones used at  CENAM are produced by SpectraDynamics in  Colorado. According 
to Mike  Lombardi it is a small highly specialized company  with a small  
market to serve. I could translate it as "expensive and   exotic"  : ) Am I 
correct?


c. Thunderbolt and my  will  to share initial experiences:


I am gathering a lot  of  information on the Thunderbolts as I am using 
them 
in my thesis  work. I bought  a couple of them. If my information or novice 
 
experience with these receivers  is good for anybody, I would be more  than 
glad to share it.


Thank you.


Kind  regards,






Edgardo Molina
Dirección  IPTEL


www.iptel.net.mx


T : 55 55 55202444
M :  04455  20501854


Piensa en Bits SA de   CV






Información   anexa:








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On Oct 21, 2012, at 7:29   PM, "Tom Van Baak" <tvb at LeapSecond.com> wrote:


Hi  Edgardo,

What you'll find is that many labs do not  periodically  adjust the C-field 
of their 5061A or 5065A at all.

Instead, any  phase or frequency adjustment is done with phase  
microsteppers or  simply done in software with time and rate adjustments to 
the  raw  
data. These methods avoid all possible physical side-effects of  changing  
voltages, currents, and fields. It also makes it possible  to gather 
long-term  
data to show how the standard is operating (if  you make mechanical rate  
adjustments it complicates data that you  have already  collected).

The other point is that when making  stability  measurements, there is no 
requirement that the reference  (e.g., 5065A) be  perfectly on-frequency. 
So 
this removes motivation  for physically touching and  possibly perturbing 
the 
operation of the  reference.

Please also take the time to read these pages.

"HP  5065A  Rubidium C-Field  Resolution"
http://leapsecond.com/pages/hp-5065a-cfield/

"Rubidium   Oscillator  Stability"
http://leapsecond.com/images/4rb.gif

"Stability and  Noise  Performance of Various Rubidium  Standards"
http://www.ke5fx.com/rb.htm

"Performance of  Low-Cost  Rubidium  Standards"
http://febo.com/pages/oscillators/rubes/

"A close look  at  a drifting HP 5065A Rubidium Frequency  Standard"
http://leapsecond.com/pages/doug-rb/

/tvb


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