[time-nuts] time-nuts Digest, Vol 78, Issue 67

Tue Jan 18 01:45:55 UTC 2011

Thanks Said.  I must have missed the link.
Jim
----- Original Message ----- 
From: <time-nuts-request at febo.com>
To: <time-nuts at febo.com>
Sent: Sunday, January 16, 2011 03:27 PM
Subject: time-nuts Digest, Vol 78, Issue 67


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> Today's Topics:
>
>   1. Fwd:  CS reservoir depletion (SAIDJACK at aol.com)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sun, 16 Jan 2011 15:27:23 EST
> From: SAIDJACK at aol.com
> Subject: [time-nuts] Fwd:  CS reservoir depletion
> To: time-nuts at febo.com
> Message-ID: <29bb9.3544d403.3a64aeab at aol.com>
> Content-Type: text/plain; charset="us-ascii"
>
>
> Hello Bob,
>
> very nice summary. Here is a plot to support your list:
>
> In terms of ADEV performance, a good GPSDO can come very close to and in
> some areas exceed the performance of a good Cs significantly.
>
> See the attached plot, this was created by super-imposing two typical
> plots available on a prominent Time-Nuts members' website, and shows a 
> 5071A
> compared to one of our Fury GPSDO units. Both compared against an even 
> better
> standard I believe.
>
> The red plot is the 5071A, the black plot is the Fury GPSDO.
>
> We can see that the Fury actually out-performs the 5071A between 0.1s to
> 10s with quite a bit of margin. Then it is less than one order of 
> magnitude
> difference between the two from 10s to about 40Ks, at which time the Fury
> seems  to "catch up" to the 5071A. The GPSDO likely also out-performs the
> 5071A in  terms of phase noise performance.
>
> There is about a 33x price difference between the two units new,  and as
> you mentioned the GPSDO is maintenance-free, whereas the 5071A requires 
> care
> from time to time. There is also a massive difference in power-consumption
> and thus operating costs.
>
> bye,
> Said
>
>
>
> From: Bob Camp <_lists at rtty.us_ (mailto:lists at rtty.us) >
> Date: January 16,  2011 12:00:50 PST
> To: Discussion of precise time and frequency  measurement
> <_time-nuts at febo.com_ (mailto:time-nuts at febo.com) >
> Subject:  Re: [time-nuts] CS reservoir depletion
> Reply-To: Discussion  of precise time and frequency measurement
> <_time-nuts at febo.com_ (mailto:time-nuts at febo.com) >
>
>
>
>
>
> Hi
>
> While I agree with the idea of  a "super GPS" as being a good standard,
> there are some reasons for needing  something else:
>
> 1) You need something to  compare *your* GPS gizmo to in your setting.
> Knowing that it might be working  ok is not as good as knowing that it is
> working  ok.
>
> 2) Without some fancy corrections, GPS  can indeed drift. The period might
> be hours, it could be days. The net effects  will cancel over a long 
> enough
> time, but that time may be longer than your  loop can suppress.
>
> 3) Anything that  creates a "fast" change in your local fly wheel 
> standards
> will still show up  on the output. It will walk out with time. Things in
> this category are stuff  like a step change in the supply voltage creating 
> a
> change in your OCXO  output.
>
> All of that can be worked on. Much  of it applies equally to having a
> single Cs in the basement.
>
> There are a couple of things the GPS gives  you that the Cs will not:
>
> 1) It will tell you  what time it is to within a few ns. Most of us
> "frequency guys" don't realize  quite how hard that is to do without GPS.
>
> 2)  The long term stability (because it's steered) of the GPS is going to
> eventually beat anything else out there. If you do really long data runs
> (months, years) the GPS will always win.
>
> 3)  Low cost to run. Even if you have a working Cs, how long until the 
> tube
> goes?  The GPS has essentially no wear out mechanisms. The Cs is full of
> strange  stuff. The parts in the GPS are pretty cheap / easy to find.
>
> 4) Easy to duplicate. Everything you are  likely to use in a fancy GPS
> setup is commonly available in quantity. The  components are "known good" 
> and
> cheap. No gamble on a tube or other hard to  replace stuff.
>
> 5) Easy to run. There's not  much mystery about what's going on. Nothing 
> is
> hidden in a vacuum bottle. No  hidden numbers in a rom. Everything is
> pretty much right in front of you. The  only exception would be the 
> disciplining
> software in the GPSDO if you choose  to use it.
>
> I admit that the GPS makes a  *lot* of sense. I sure wouldn't turn down a
> nice shinny new HP cesium if one  showed up on my doorstep.
>
> Bob
>
>
>
>
> On  Jan 16, 2011, at 7:01 AM, _EWKehren at aol.com_ (mailto:EWKehren at aol.com)
> wrote:
>
>
> Having two HP CBT's minus enclosure sitting on  my window sill, allow me 
> to
>
>
>
> ad my two cents worth. Looking at the  assemblies I see more art than
>
>
> science and duplicating something like that  would most likely end in
> failure.
>
>
> Comparing that to the previous H Maser  discussions the collective know
> how
>
>
> and resources of the list could maybe result  in a  Maser.
>
>
> As to refurbishing tubes some of us have  discussed that off line and  in
>
>
> my opinion with proper tools and equipment  cleaning and replacing  cesium
> is
>
>
> doable. Cynics say the manufacturers of tubes  could do it but rather 
> sell
>
>
> only new ones since they are the only source  of the much more expensive
> new
>
>
> tube. I think that is only half the  story.
>
>
> The reason in my opinion why refurbishing the  tube is commercially not
>
>
> viable is you have to ask: when done what do  you really have? You have 
> not
>
>
>
> eliminated some of the failure modes, in the  case of the 5071 the data in
> the
>
>
> EPROM does not necessarily reflect the tube  and who could say how long 
> the
>
>
> tube  would last? A crap  shoot.
>
>
> I have a HP 5061 B and a HP 5062 C but  eventually want to replace them
>
>
> totally with a Tbolt-Rb-HP 10811 combination  using two digital loops that
> are
>
>
> tailored to  the devices. I am now  focusing  on the thermal management 
> in
>
>
> order to get maximum performance. There is  work going on by some members
> of
>
>
> the list to develop more sophisticated digital  loops. Lets face it, with
> GPS
>
>
> properly  used, having a Cesium Standard  will give you the warm feeling
>
>
> that you have a primary  standard.
>
>
> By the way that is why I repeatedly have asked  the list if there is any
>
>
> long term Tbolt data out there comparing the 1  PPS or the 10 MHz with a
> Maser.
>
>
> I hope this is worth two  cents.
>
>
> Bert Kehren
>
>
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