Re: [time-nuts] GPSDO disciplining algorithms

[Charles Steinmetz]

Alan wrote:

I'm interested in GPSDO disciplining algorithms - presumably the 
good ones are really well thought out stochastic control algorithms.


There are two regimes a GPSDO must deal with -- normal operation, and holdover.

There is not a whole lot of mystery about normal, locked 
operation.  GPS is quite noisy at low tau -- e-8 or so at 1 second -- 
and improves steadily with increasing tau for many decades until 
reaching a floor in the e-13 to e-14 range.  By contrast, OCXOs are 
much better at low tau, falling off when tau reaches ~1000 seconds 
(typically) and their random-walk drift mechanisms take over.  So, 
you want a very slow loop to allow the local oscillator to determine 
the stability more or less by itself with little influence from the 
GPS at all tau where the LO is more stable than the GPS, crossing 
over to GPS dominance al longer tau.  The required time constant is 
longer than practicable for an analog loop, so the control loop must 
necessarily be digital.


For reasonably fast acquisition (and probably a necessity for 
acquisition at all), it is common practice to implement a loop with 
switchable or variable time constants, starting with a TC of a few 
seconds and, as lock is approached and then held, and the OCXO 
settles in, increases to the normal operating value (in the hundreds 
to thousands of seconds range, depending on the particular 
OCXO).  Frequency control is typically implemented by a DAC driving 
an EFC (varactor) input on the OCXO.  The DAC steps should be small 
enough to set the OCXO to the required accuracy, and numerous enough 
to provide a sufficient range for tracking significant temperature 
changes and crystal drift.


There really isn't much more to it than that (although "that" 
includes a mind-numbing number of details that need to be worked out 
and optimized -- I don't mean to imply that it is anything less than 
a lot of very hard work).


The holdover regime is clearly entered when the GPS loses 
lock.  However, it begins much earlier, when GPS stability is reduced 
due to link noise, multipath, poor antenna location, etc.  Some means 
must be used to determine when the GPS timing is compromised, and by 
how much, and measures taken to maintain the best possible stability 
from the GPSDO under the circumstances.  At some point, the best that 
can be done is to set an alarm indicating that the GPSDO output 
cannot be trusted.


The simplest thing to do is to hold the DAC output at the 
last-known-good value until normal locked operation is resumed.  In 
an effort to improve on this, many commercial GPSDOs use predictive 
algorithms to learn the drift characteristics of the OCXO over time 
and temperature while it is operating normally, and then adjust the 
DAC output in accordance with the learned patterns during 
holdover.  Kalman filtering is typically used for this.  (There is a 
large body of literature on Kalman filtering and other predictive algorithms.)


Unfortunately, as others have already said, there is very little in 
the literature about GPSDO disciplining algorithms.  It appears that 
most of the research has been done by GPSDO manufacturers and is 
considered proprietary.


Best regards,

Charles



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Re: [time-nuts] 10811 Alternatives

[Bob Camp]

Hi

I guess it comes down to what you expect from each level of the process. Each 
of us
may expect something different. Toss in language barriers and things can get 
even more
confused. Watching the commercials on TV can easily lead you to expectations 
that may not
be met :)

-

These base stations get a “fork lift upgrade” and the fork lift drops the old 
one onto a truck. They
are hauled to a depot where they pile up. The objective it to get rid of them, 
not to take care of them.
They then get shipped by rail to a port and tossed on a ship. Once in China, 
they are broken down.
That breakdown process involves multiple levels of sorting and transfers from 
site to site. By the 
time the board gets it’s OCXO pulled, it may have passed through a dozen hands. 
That’s a tough 
process for an OCXO. 

I see *lots* of OCXO’s at auction that have damaged labels, dings in the cans, 
rust on
the cans and leads, scratches all over the place. I guess that they spent time 
under water or at 
least in the rain. I take this as verification that the scrap process was not 
very gentle. 

---

Once they get to this point, there’s really not much you can do to correct the 
problem. The process
has nuked them. It’s just a matter of who will sell them and who will buy them. 

Once any OCXO has been beaten up, it’s a suspect part. Nobody builds them with 
a brutal
scrap process in mind. Even with a very extensive test process, one can only 
*guess* at it’s
condition. I have zero expectation of any surplus dealer on the planet carrying 
out more than a simple
“power on, lights work, outputs on the right connectors” sort of test. 

———

When I see a sale for "100% tested”, I expect an OCXO will have some sort of 
output and the controller
will cut back and not run away. I don’t expect that somebody aged it or ran 
ADEV. I also expect that
the seller has *some* vague idea of what he’s selling. I also accept that he 
may or may not have
done the test himself. 

What I *do* expect from a seller is that a “guarantee, 14 days to return” means 
I have a way of getting my
money back.. Of course this involves *me*testing the gizmo as soon as I got it. 
It also involves *me* being 
set up to test what ever the gizmo was. After that I have to go through what 
ever process the return / refund
requires. 



Some people have an expectation that a $15 board pull OCXO (that likely sold 
for > $200 a few years ago) 
can simply be plugged in and counted on to work 100% perfectly with no 
verification. In 50 years
of dealing with surplus gear, I can’t think of any time or any dealer from whom 
that’s ever been the case. 
The problem is not the dealer, it’s the expectation. 

There’s also an expectation that some dealer out there is “magic” in some way. 
Sorry, but they all get their
stuff in the same market. They all rely on information from “upstream” that may 
or may not be correct. They 
all are in business to sell what’s out there. Are some less honest than others 
- of course. Even the ones that
are totally honest are still limited (in this case) by the scrap process. 

———

What to do?

Don’t pay crazy prices for crazy claims. If the claim is to good to be true, it 
probably is. Plan on buying more
than one gizmo and sorting them out. This is surplus !!! Expect the worst and 
be happy when it goes better than that. 

Bob



> On Apr 13, 2015, at 1:28 PM, Charles Steinmetz  wrote:
> 
> Bob wrote:
> 
>> I've always found that building in performance / reliability is a lot 
>> cheaper than testing it in...
> 
> And if you are a surplus dealer, letting the customer test it for you is a 
> lot cheaper than testing it yourself
> 
> One of the defective MV89s I received ("guaranteed 100% tested and working") 
> came in a box the previous customer had used to return it, complete with that 
> customer's name and address, the seller's real name and address (different 
> from the name and address of the seller on file with ebay), and a note from 
> the previous buyer listing the faults with the unit.  Nobody could possibly 
> have tested that unit in even the most cursory way and deemed it to be 
> "working."
> 
> After 6 purchases from 6 different sellers (well, 6 different seller IDs -- I 
> suspect 2 or 3 of them might have been the same person), I never once 
> received an MV89 that came close to meeting spec.  I did open one up after 
> ebay refunded me without requiring me to return it, and I was shocked at the 
> crudeness of the construction and the poor build quality.  They may all leave 
> the factory meeting spec, but it wouldn't surprise me to find that many of 
> them never do.
> 
> Best regards,
> 
> Charles
> 
> 
> 
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Re: [time-nuts] Ultra High Stability Time Base Options for 53132A

[John Ackermann N8UR]

Among my group of ham project-building friends, the motto is "There is no 
problem so big or complicated that it cannot be over-engineered."


> On Apr 13, 2015, at 5:03 PM, Richard (Rick) Karlquist  
> wrote:
> 
> 
> 
>> On 4/13/2015 12:14 PM, Magnus Danielson wrote:
>> 
>> Oh yes. Some people say that you should not overcomplex things. My
>> experience is that oversimplifying them can cause a long stretch of
>> complex problems and complex workarounds making the total solution more
>> expensive in development, customer relations and more complex than
>> starting with a more advanced solution, that actually attempts to
>> address the design issues. Ah well.
>> 
> 
> This is extremely good advice.  The ultimate example of the
> oversimplified design is the Muntz TV set, where few parts are
> used, but they all interact with each other in mysterious
> ways that depend on unknown unspecified parameters.  The ultimate example of 
> the overcomplicated design is the Japanese VCR, circa 1980.
> Schematic looks like it was designed by committee.  The parts
> count has become bloated to the point of redundancy.  Neither
> is desirable.
> 
> Rick Karlquist N6RK
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Re: [time-nuts] Ultra High Stability Time Base Options for 53132A

[Richard (Rick) Karlquist]

On 4/13/2015 12:14 PM, Magnus Danielson wrote:


Oh yes. Some people say that you should not overcomplex things. My
experience is that oversimplifying them can cause a long stretch of
complex problems and complex workarounds making the total solution more
expensive in development, customer relations and more complex than
starting with a more advanced solution, that actually attempts to
address the design issues. Ah well.



This is extremely good advice.  The ultimate example of the
oversimplified design is the Muntz TV set, where few parts are
used, but they all interact with each other in mysterious
ways that depend on unknown unspecified parameters.  The ultimate 
example of the overcomplicated design is the Japanese VCR, circa 1980.

Schematic looks like it was designed by committee.  The parts
count has become bloated to the point of redundancy.  Neither
is desirable.

Rick Karlquist N6RK
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Re: [time-nuts] Ultra High Stability Time Base Options for 53132A

[Attila Kinali]

On Mon, 13 Apr 2015 01:16:08 -0400
Charles Steinmetz  wrote:

> >The faster the comparator, the greater its analog bandwidth.
> >Thus there is more total noise to cause jitter.  The DC to
> >daylight comparator is the opposite of the John Dick (JPL)
> >paper on zero crossing detectors in PTTI around 1990.  John
> >teaches that you use the MINIMUM bandwidth amplifier to
> >square up a sine wave.
> 
> For Dick's paper, see:

Charles, Rick, thanks for the list. I will work trough it :-)

Attila Kinali

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Re: [time-nuts] KS-24361 Power Module Repair

[Chuck Harris]

No, I meant exactly what I said.

When you are removing epoxy potting compound, put it in an oven
set to 140C, and let it cook until up to temperature.  The potting
epoxy will become about as soft as pencil eraser rubber.  You can
then pick at it, and get pretty big chunks to come off.  When the
epoxy starts to feel hard again, pop it back in the oven.

-Chuck Harris

OBTW, we are not talking about crystal ovens here, but rather unpotting
power supply modules.

Al Wolfe wrote:

This seems a bit toasty and is equivalent to 284F. Maybe meant 140F not C?


An oven set to 140C is your friend when doing jobs like
this.


FWIW, the GE Progress Line two-way radios oscillator crystal holders had an 
octal
base, held two crystals, and the heating element could be used on 6 volts or 12 
volts
depending on which way the holder was plugged in.  I have no idea of how well 
they
held the temperature. Always planned to use one with an external proportional
controller but never got around to it.

Al, k9si
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Re: [time-nuts] 10811 Alternatives

[Charles Steinmetz]

Bob wrote:

I've always found that building in performance / reliability is a 
lot cheaper than testing it in...


And if you are a surplus dealer, letting the customer test it for you 
is a lot cheaper than testing it yourself


One of the defective MV89s I received ("guaranteed 100% tested and 
working") came in a box the previous customer had used to return it, 
complete with that customer's name and address, the seller's real 
name and address (different from the name and address of the seller 
on file with ebay), and a note from the previous buyer listing the 
faults with the unit.  Nobody could possibly have tested that unit in 
even the most cursory way and deemed it to be "working."


After 6 purchases from 6 different sellers (well, 6 different seller 
IDs -- I suspect 2 or 3 of them might have been the same person), I 
never once received an MV89 that came close to meeting spec.  I did 
open one up after ebay refunded me without requiring me to return it, 
and I was shocked at the crudeness of the construction and the poor 
build quality.  They may all leave the factory meeting spec, but it 
wouldn't surprise me to find that many of them never do.


Best regards,

Charles



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Re: [time-nuts] Ultra High Stability Time Base Options for 53132A

[Magnus Danielson]

Rick,

On 04/13/2015 01:48 AM, Richard (Rick) Karlquist wrote:



On 4/12/2015 2:22 PM, Magnus Danielson wrote:

Hi,

The buffer transistors has not AC-bypass of the emitter resistance, so
that the DC current becomes large and thus contributes flicker noise.

The comparator at the bottom isn't doing a beutifull work of squaring
things up without contributing noise, considering the sine output of the
10811.

Was that it, Rick?

Cheers,
Magnus



The resolution of page 13 is poor, and it seems to be a bitmap instead
of a vector file.  The fuzzy thing in the lower right corner looks
like it might be a comparator.  I think this was the smoking gun.


I checked the component listing, which provided very good hints.


There was a saying by H.L. Menken to the effect that for every
complex problem, there is a simple, obvious, invalid solution.


Oh yes. Some people say that you should not overcomplex things. My 
experience is that oversimplifying them can cause a long stretch of 
complex problems and complex workarounds making the total solution more 
expensive in development, customer relations and more complex than 
starting with a more advanced solution, that actually attempts to 
address the design issues. Ah well.



Squaring up a 10811 with a comparator is a perfect example of this
principle.  Non-time-nuts always seem to gravitate to this design.


Oh, they defend their choice with that they use a schmitt-trigger.
*facepalm*


Of course you're right, any comparator will add jitter to a 10811.
The faster they are, the more jitter they add.


Indeed. Hello Noise-bandwidth.


I noticed that the standard 10 MHz oscillator is built with
an ECL line receiver.  Another example of Menken's saying.
This is a TERRIBLE oscillator design, but one that would appeal
to the non-initiated.  I built one of these oscillators in 1976
at the suggestion of my boss.  After seeing how bad it was, I
quietly designed it out and never used it again.


Go and check the HP5370A/B reference amplifier board. It has an ECL 
circuit to detect the presence of 10 MHz. It does this by producing a 5 
MHz 25% PWM signal... with ECL... with very good rise-time. ECL have 
never been known for its speed and rise-time (irony might have been 
used). So, it turns out that the board spewes out a wide spectrum of 5 
MHz spikes. All this to drive a LED that goes green if there is a 10 MHz 
to aid the fault analysis once you lift the lid. A bad design. Disabled 
the detector by grounding a base on a transistor, and got a much more 
quiet box. The Motorola ECL handbook warns about the rise-time issue, 
it's a standard signal integrity and EMC issue.


Cheers,
Magnus
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Re: [time-nuts] Distribution Amps

[Frank Schneider]

Agreed, no comparison of course. However, I just needed the signal for my 
signal generator, a frequency counter and a clock. So I have one output to 
spare. Besides, I don't have to worry about my pacemaker


Frank

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Perry Sandeen 
via time-nuts
Sent: 13 April 2015 00:05
To: time-nuts@febo.com
Subject: [time-nuts] Distribution Amps

List,


 
There has been a large exchangeof ideas for various home-brew or other video 
box alternatives which all wouldseem to work OK.


 
For me it was simpler to buy asurplus HP 5087A for best offer which turned out 
to be $300 delivered.


 
Besides having 12 outputs, youhave a choice of 3 inputs.  It alsoaccepts IIRC 
1, 5, and 10 MHz input signals.


 
I probably will never use all ofits capabilities but for my needs it was the 
best choice.


 
Also if your pacemaker isn’t intop-notch order, you may not want to look at the 
prices of its newerreplacement.


 
Regards,


 
Perrier


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Re: [time-nuts] GPSDO disciplining algorithms

[Attila Kinali]

On Mon, 13 Apr 2015 13:03:36 +
Alan Ambrose  wrote:

> I'm interested in GPSDO disciplining algorithms - presumably the good ones 
> are really well thought out stochastic control algorithms.
> 
> Is it possible to point me to the seminal references / papers / datasheets 
> that describe typical algorithms and the advantages and disadvantages of the 
> various approaches?
> 
> I can see, for example:
> 
> http://tycho.usno.navy.mil/papers/ts-2000/gpstime.steering.kmm.ion.sep00.pdf

The paper you refer to is a about how to generate UTC(GPS), ie how to
stear the clocks of the satellites in order to get a correct time
on the ground. It has nothing to do with stearing a GPSDO.

You are right that GPSDOs are nothing but control loops with
added noise. You can approach the whole thing by standard control
theory and ignore noise in a first approximation. The book by
Franklin et al.[1] is a good start, IMHO.

The next step is to model the system with all non-idealities that
affect the oscillator frequency (temperature, aging, retrace,..).
The field you want to have a look for this is called "System Identification".
For that you will also need to know how a quartz crystall oscillator
behaves under different conditions. A good place to start for
this is Vig's Crystall Oscillator Tutorial[2], as it contains
many references.

If you have done that, you can apply addaptive control, ie measure
the systems inputs and outputs and guess from that the internal
parameters for better control. The generic technique here is
called Kalman Filters. But fellow time-nut Marek Peca would tell
you that a Wiener filter is better suited[3]. Of course, the field
of adaptive control is vast and there are many more methods to have
a look at. "Model Predictive Control" might be one of the key words
you'd like to search for.

If you are asking yourself why I am not refering you to specifc
literature on GPSDOs, then I have to tell you that there is hardly
any. The best fit for you that I am aware of is [4], but this is
nothing other than what i have written above. And you will need
to understand these things to understand the paper.


Attila Kinali


[1] "Feedback Control of Dynamic Systems", by Franklin, DaPowell, Emami-Naeini

[2] "Quartz Crystal Resonators and Oscillators", by Vig, multiple versions
http://ko4bb.com/manuals/index.php?dir=02_GPS_Timing/John_Vig_Tutorials_on_Crystal_Oscillators

[3] "Clock composition by wiener filtering illustrated on two atomic clocks",
by Peca, Michalek, Vacek, 2013
http://dx.doi.org/10.1109/EFTF-IFC.2013.6702293 
https://rtime.felk.cvut.cz/~pecam1/eftf/

[4] "Adaptive OCXO Drift Correction Algorithm", by Nicholls, Carleton, 2004
http://dx.doi.org/10.1109/FREQ.2004.1418510

-- 
< _av500_> phd is easy
< _av500_> getting dsl is hard
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Re: [time-nuts] GPSDO disciplining algorithms

[Bob Camp]

Hi

That paper is addressing the task of keeping the cesium standards in the GPS
satellites on frequency. With the exception of a couple Ham designs, most 
GPSDO’s
are done commercial. The algorithms used are mostly proprietary. That’s not to 
say that they don’t use common control approaches (PID, PI etc).

There are more general papers about locking device A to source B where both
devices have a known noise profile. The answer there is to match the loop to
the crossover in the noise plots.

Bob

> On Apr 13, 2015, at 9:03 AM, Alan Ambrose  wrote:
> 
> Hi all,
> 
> I'm interested in GPSDO disciplining algorithms - presumably the good ones 
> are really well thought out stochastic control algorithms.
> 
> Is it possible to point me to the seminal references / papers / datasheets 
> that describe typical algorithms and the advantages and disadvantages of the 
> various approaches?
> 
> I can see, for example:
> 
> http://tycho.usno.navy.mil/papers/ts-2000/gpstime.steering.kmm.ion.sep00.pdf
> 
> Am I right in thinking that this subject area usually called 'GPS 
> disciplining' or 'GPS steering' in the literature?
> 
> TIA, Alan
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Re: [time-nuts] Ultra High Stability Time Base Options for 53132A

[Richard (Rick) Karlquist]

On 4/13/2015 3:11 AM, John Miles wrote:


A comparator with less open-loop gain was what they needed.  Somebody at HP 
really liked ECL line receivers, though.  Those were very noisy at HF, but this 
had little or nothing to do with their bandwidth (see my other post.)

To square up a 10 MHz signal from an OCXO it's hard to beat a simple diff amp 
with a pair of bipolars, a la Wenzel.

-- john, KE5FX
Miles Design LLC



The HP counters all used ECL line receivers for the A and B
channel to convert the input frequency signal to be counted
into a digital square wave.  Naive engineers then ape'd this
for use on the timebase clock.

Engineers at HP who actually knew what they were doing,
such as Tom Falkner, did use differential pairs.  However,
HP being a huge company, the word did not necessarily get
disseminated to all the other HP engineers.

Rick Karlquist N6RK
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Re: [time-nuts] GPSDO disciplining algorithms

[Tim Shoppa]

See especially Appendix A here:
http://www.jackson-labs.com/assets/uploads/main/HP_AppNote.pdf

The HP goal was specifically to meet telco 48-hour holdover specs. Others
here have had vastly different concepts of holdover length (sometimes just
seconds!)

Tim N3QE

On Mon, Apr 13, 2015 at 9:03 AM, Alan Ambrose 
wrote:

> Hi all,
>
> I'm interested in GPSDO disciplining algorithms - presumably the good ones
> are really well thought out stochastic control algorithms.
>
> Is it possible to point me to the seminal references / papers / datasheets
> that describe typical algorithms and the advantages and disadvantages of
> the various approaches?
>
> I can see, for example:
>
>
> http://tycho.usno.navy.mil/papers/ts-2000/gpstime.steering.kmm.ion.sep00.pdf
>
> Am I right in thinking that this subject area usually called 'GPS
> disciplining' or 'GPS steering' in the literature?
>
> TIA, Alan
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Re: [time-nuts] GPSDO disciplining algorithms

[Alan Ambrose]

Hi all,

I'm interested in GPSDO disciplining algorithms - presumably the good ones are 
really well thought out stochastic control algorithms.

Is it possible to point me to the seminal references / papers / datasheets that 
describe typical algorithms and the advantages and disadvantages of the various 
approaches?

I can see, for example:

http://tycho.usno.navy.mil/papers/ts-2000/gpstime.steering.kmm.ion.sep00.pdf

Am I right in thinking that this subject area usually called 'GPS disciplining' 
or 'GPS steering' in the literature?

TIA, Alan
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Re: [time-nuts] [Bulk] Re: Ultra High Stability Time Base Options for 53132A

[J. L. Trantham]

Fuzzy page 13 is the 53132-60011, with the extra components not found on the 
53132-60016, which is on page 45 and much clearer.  It is an LM361M and is on 
both boards. 

Now that I have the 53132-60011 board, I plan to start with page 45 and 
're-draw' a clear page 13.

Joe

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Richard (Rick) 
Karlquist
Sent: Sunday, April 12, 2015 6:49 PM
To: Discussion of precise time and frequency measurement
Cc: mag...@rubidium.se
Subject: [Bulk] Re: [time-nuts] Ultra High Stability Time Base Options for 
53132A


The resolution of page 13 is poor, and it seems to be a bitmap instead of a 
vector file.  The fuzzy thing in the lower right corner looks like it might be 
a comparator.  I think this was the smoking gun.

There was a saying by H.L. Menken to the effect that for every complex problem, 
there is a simple, obvious, invalid solution.

Squaring up a 10811 with a comparator is a perfect example of this principle.  
Non-time-nuts always seem to gravitate to this design.

Of course you're right, any comparator will add jitter to a 10811.
The faster they are, the more jitter they add.

I noticed that the standard 10 MHz oscillator is built with an ECL line 
receiver.  Another example of Menken's saying.
This is a TERRIBLE oscillator design, but one that would appeal to the 
non-initiated.  I built one of these oscillators in 1976 at the suggestion of 
my boss.  After seeing how bad it was, I quietly designed it out and never used 
it again.

Rick Karlquist N6RK
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Re: [time-nuts] 10811 Alternatives

[Bob Camp]

Hi

I probably should not rule out the MV89’s going through an exceptionally brutal 
salvage process. I’m sure there are a range of outfits doing this stuff and 
that 
some take more care than others. We may just have a lot of 10,000 MV-89’s 
that got nuked and now are forever floating around the world getting re-sold 
multiple 
times.

You could ask - why not test them fully? That’s not an easy task. The list I 
gave is
far from a full test process on an OCXO. One would at least add aging and some 
more detailed limits here and there to a proper test profile. If you are 
looking for 
damaged parts, there would be even more testing required past a normal testing 
profile. 
I’ve always found that building in performance / reliability  is a lot cheaper 
than testing it in …..

Bob

> On Apr 12, 2015, at 10:03 PM, Peter Bell  wrote:
> 
> I would personally consider those MV89s from Chinese sources as being extra
> suspect - a few years back, one of the Chinese surplus vendors had a big
> box of them (some removed from PCBs, and others apparently new) that were
> identified to me as containing bad ceramic caps and suffering from various
> problems ranging from poor phase noise performance to being completely
> inoperative.
> 
> The guy who had them (who I know quite well) volunteered this information
> and said that as far as he was concerned they could only be sold as scrap -
> but it's possible they have ended up in the hands of dealers that are not
> so scrupulous.
> 
> 
> On Mon, Apr 13, 2015 at 8:46 AM, Bob Camp  wrote:
> 
>> Hi
>> 
>> I don’t think there’s anything at all wrong with the MV-89A as an OCXO. In
>> fact, I believe that properly
>> handled they are a good part. The gotcha is the abuse they get in the
>> “recycling” process. I’m
>> willing to bet that any OCXO that sees the same sort of process will come
>> out with issues.
>> 
>> Bottom line - Don’t attack an OCXO with a torch, drop it down a flight of
>> stairs, leave it out in the rain
>> for a few years, and then really abuse it after that. They need to be
>> treated with some care ….
>> 
>> For what ever reason, parts like IC’s seem to be more tolerant of the
>> scrap out process than OCXO’s.
>> Rb’s seen to show up *with* PCB’s still attached, so they didn’t get the
>> torch process.
>> 
>> Because of all that, there’s not much way to pick a “good” OCXO model. The
>> thing you need to find
>> are parts that you are sure did not take a beating while being pulled off
>> of boards. With zero view into
>> that end of the sourcing process …. not much way to pick and choose.
>> 
>> About the only thing to do is to buy parts that never went on to pc
>> boards. That’s no guarantee, but
>> it ups the odds a bit. You may be buying test rejects. They could still
>> have been dropped down a
>> flight of stairs. They might be counterfeit parts.
>> 
>> Considering that you are buying a $250 to $400 OCXO for <$20, there *will*
>> always be some risk ….
>> 
>> Bob
>> 
>>> On Apr 12, 2015, at 6:02 PM, Perry Sandeen via time-nuts <
>> time-nuts@febo.com> wrote:
>>> 
>>> List,
>>> 
>>> 
>>> 
>>> It appears from Bob Camp’sexperience (and others) that the Chicoms
>> Morion oscillators are to be avoided.
>>> 
>>> 
>>> 
>>> My question is: Could Bob Camp,Rick K. and other gurus with experience
>> come up with a list of the Ebay 10 MHzsurplus oscillators that would be
>> worth buying as well as what would be a fairprice? Also some good vendor
>> names would be nice as well.
>>> 
>>> 
>>> 
>>> I realize that surplus listvaries quite a bit and it still a bit of a
>> crap shoot, but perhaps the odds arebetter from certain venders, makes, and
>> models.
>>> 
>>> 
>>> 
>>> Regards,
>>> 
>>> 
>>> 
>>> Perrier
>>> 
>>> 
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Re: [time-nuts] Ultra High Stability Time Base Options for 53132A

[John Miles]

> Squaring up a 10811 with a comparator is a perfect example of this
> principle.  Non-time-nuts always seem to gravitate to this design.
> 
> Of course you're right, any comparator will add jitter to a 10811.
> The faster they are, the more jitter they add.

A comparator with less open-loop gain was what they needed.  Somebody at HP 
really liked ECL line receivers, though.  Those were very noisy at HF, but this 
had little or nothing to do with their bandwidth (see my other post.) 

To square up a 10 MHz signal from an OCXO it's hard to beat a simple diff amp 
with a pair of bipolars, a la Wenzel.

-- john, KE5FX
Miles Design LLC


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Re: [time-nuts] Ultra High Stability Time Base Options for 53132A

[John Miles]

>The faster the comparator, the greater its analog bandwidth.
>Thus there is more total noise to cause jitter.  The DC to
>daylight comparator is the opposite of the John Dick (JPL)
>paper on zero crossing detectors in PTTI around 1990.  John
>teaches that you use the MINIMUM bandwidth amplifier to
>square up a sine wave.

Although you hear it a lot, I'm not so sure of the generality of this 
statement.  It would make sense if you were talking about a sampling process 
where noise from the entire system bandwidth is aliased irreversibly into the 
output signal, but I don't see a compelling reason to think of a ZCD that way.  
It's true that saturated logic is quieter than unsaturated logic, but during 
the critical zero crossing time, is it really saturated?  If the device is 
faster than the input signal, the answer is a definite "No," and that's where I 
think the conventional wisdom about fast comparators being bad for jitter comes 
from.  They aren't contributing more jitter, they're just failing to clean up 
the input jitter during the transition time.  

All other things being equal, it's desirable to minimize the time spent in that 
region of the waveform.  It doesn't necessarily hurt to choose a faster logic 
family, as long as the process noise and device gain are otherwise compatible 
with the decision.  Random jitter on the 7.5 GHz ADCLK905 is specified at 
around 60 femtoseconds, after all.  A residual PN test at 10 MHz on an ADCLK905 
ends up at around -135 dBc/Hz at 1 Hz just like many other slower comparators, 
a figure that's good for 1s ADEVs in the E-14s (see 
http://www.ke5fx.com/ADCLK905_ADEV.png and 
http://www.ke5fx.com/ADCLK905_PN.png).  

At lower carrier frequencies, the ADCLK905's apparent jitter is worse because 
the low slew rate of the input signal gives its open-loop gain more time to 
influence the outcome.  But it wouldn't be significantly better if the 
ADCLK905's bandwidth were a thousand times lower.  Of course, when the input 
signal is *much* slower, as in the JPL paper, a multistage shaper with 
optimized bandwidth and gain allocation is helpful.  But their situation at 1 
Hz is not directly applicable at 5/10 MHz.  An obsessive focus on bandwidth 
here is just going to make the phase tempco worse without improving the jitter.

> BTW: If anyone here has any good text to read on oscillator design,
> please let me know. I'm collecting those :-)

In addition to the ones Rick mentioned, you might look into Enrico Rubiola and 
Jeremy Everard.

-- john, KE5FX
Miles Design LLC

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Re: [time-nuts] Ultra High Stability Time Base Options for 53132A

[Charles Steinmetz]

Rick wrote:


The faster the comparator, the greater its analog bandwidth.
Thus there is more total noise to cause jitter.  The DC to
daylight comparator is the opposite of the John Dick (JPL)
paper on zero crossing detectors in PTTI around 1990.  John
teaches that you use the MINIMUM bandwidth amplifier to
square up a sine wave.


For Dick's paper, see:



The idea is clear from the block diagram, if you don't want to read 
the whole paper:




Oliver Collins published a paper expanding on this idea ("The Design 
of Low Jitter Hard Limiters," 1996).


Attila wrote:


If anyone here has any good text to read on oscillator design,
please let me know.


I concur with Rick's suggestions.  I would also suggest Edson's 1953 
text, "Vacuum-Tube Oscillators," which gives details on some concepts 
that are often glossed over in later texts:




Here is a selection of others I have found useful:























 
(esp. Chs. 5-6)





Best regards,

Charles


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