Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Eric Scace]

Au contraire. My backgrounds lay scattered around in other fields, each of 
which have their own parallel tales where art, personalities, business, and 
legacy technologies/processes combine to produce unanticipated results.

I learn something from every one of the “uninteresting” stories about the 
details of electronic engineering and metrology — and hopefully retain enough 
to know when to ask for help in order to avoid a major pitfall when it comes to 
time lab stuff.

> On 2020 Apr 11, at 20:09 , Hal Murray  wrote:
> 
> 
> rich...@karlquist.com  said:
>> By now, few people besides Bob are still reading this. :-) 
> 

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Re: [time-nuts] OCXO and fluctuations after EFC adjustment (Ben Bradley)

[Bob kb8tq]

Hi

Electrolytic caps have a lot of leakage. That’s the bad news. The good news is 
that if you maintain a stable voltage on a tantalum part, the leakage decays 
( = drops off) with time. In a system with a fixed EFC, you probably can get 
away
with a tantalum part. You will have to wait a bit for it to “settle down”. 

Of course, if the Vref is quiet enough and the EFC narrow enough, there is no 
need for a big bypass on the EFC in the first place. 

If you dig into film caps, they have the same sort of decaying leakage …. 

All these caps are rated for leakage at some voltage after some time on
power. To keep the test easy, the time often is pretty short. Thus the data 
sheet numbers *should* give you a pretty good idea what the max leakage
will be. 

Bob

> On Apr 12, 2020, at 2:01 PM, Leon Pavlovic  wrote:
> 
> Speaking of high-performance crystal oscillators, EFC inputs and Tantalum
> capacitors, how to select a good decoupling capacitor for its EFC input?
> 
> I'm attaching two PN measurements made yesterday on a HP3048A. There are
> two 100MHz crystal oscillators in the setup, (1) a XCO made by myself,
> which I know from previous measurements on a E5052 that has a stable! PN of
> -130dBc/Hz at 100Hz and below (Vtune from HP3048A is connected to this
> XCO). The other one (2) is a commercial Connor-Winfield OCXO, specified as
> -125dBc/Hz at 100Hz. I'm not sure if this one has a stable PN. The EFC
> input is decoupled by a 1uF ceramic in parallel to 33uF/16V Tantal and 10kR
> to ground, and connected by another 10kR to its Vref output.
> 
> So where's the problem? The two measurements attached were taken only some
> minutes apart. The first one is expected, the second one is a disaster
> below 1kHz offset. Is it possible that the heated Connor-Winfield OCXO
> affected the Tantal capacitor on its EFC node after some minutes (both are
> in close proximity on a PCB), increasing the leakage or whatever phenomenon
> that corrupted its PN (modulation of the EFC voltage)?
> 
> Possible reasons for a fluctuating/unstable PN to consider:
> - one of the oscillators has unstable PN
> - the Tantalum capacitor should be replaced by a film or a ceramic 10uF?
> - broadcast FM stations influenced the second measurement
> - ?
> 
> Thanks for any advice where to look at the problem ;)
> Leon
> 
> 
> -- Forwarded message --
> From: Ben Bradley 
> To: Discussion of precise time and frequency measurement <
> time-nuts@lists.febo.com>
> Cc:
> Bcc:
> Date: Sat, 11 Apr 2020 23:22:29 -0400
> Subject: Re: [time-nuts] OCXO and fluctuations after EFC adjustment
> Despite my interest in the precision high-end of electronic design
> (and thus being a subscriber to this list), I have very little
> experience with such high-fallutin' designs. Still, I've done and seen
> some "interesting" things in my career. It's amazing how the minutiae
> of even jelly bean components can cause product failures.
> 
> A few decades ago (many of my jobs were engineering positions at
> companies that made equipment for the POTS phone line), the company I
> was with had some rather large surface-mount ceramic capacitors that
> were failing short in a new product that used them across the phone
> line (they were RATED for this application right there on the data
> sheet).  The concern was our product would some day short out the
> phone line and someone with another phone on the line would have an
> emergency and wouldn't be able to call 911 to get help. The possible
> legal liability to the company was obvious. In a discussion with other
> engineers and managers, someone wondered if it was the way the board
> was manufactured, maybe the solder process caused some caps to crack,
> or whether the failures were strictly the fault of the capacitor
> manufacturer. I volunteered to test the caps in an environmental
> chamber that wasn't being used at the time, putting them near the edge
> of, but still within, specs. I made a jig that put a bias voltage on
> many in parallel (using a mechanical spring connection, not soldered)
> and left them for a few days/weeks. Out of 100 to 150 devices, about 5
> or 10 became unacceptably leaky. I wrote up my report and emailed it
> to the other engineers and managers involved, and didn't hear back
> anything more about it. The good news (!) is the product wasn't in
> production for very long for several reasons, more recently of course
> that the POTS phone line is no longer the most common form of
> telecommunications. The bad news is it's no longer helpful to have
> POTS product design on my resume.
> 
> More recently, I saw this Kemet presentation on Digikey about tantalum
> capacitors. Certainly for aluminum electrolytic capacitors, the rated
> voltage is "th

Re: [time-nuts] OCXO and fluctuations after EFC adjustment (Ben Bradley)

[Leon Pavlovic]

Speaking of high-performance crystal oscillators, EFC inputs and Tantalum
capacitors, how to select a good decoupling capacitor for its EFC input?

I'm attaching two PN measurements made yesterday on a HP3048A. There are
two 100MHz crystal oscillators in the setup, (1) a XCO made by myself,
which I know from previous measurements on a E5052 that has a stable! PN of
-130dBc/Hz at 100Hz and below (Vtune from HP3048A is connected to this
XCO). The other one (2) is a commercial Connor-Winfield OCXO, specified as
-125dBc/Hz at 100Hz. I'm not sure if this one has a stable PN. The EFC
input is decoupled by a 1uF ceramic in parallel to 33uF/16V Tantal and 10kR
to ground, and connected by another 10kR to its Vref output.

So where's the problem? The two measurements attached were taken only some
minutes apart. The first one is expected, the second one is a disaster
below 1kHz offset. Is it possible that the heated Connor-Winfield OCXO
affected the Tantal capacitor on its EFC node after some minutes (both are
in close proximity on a PCB), increasing the leakage or whatever phenomenon
that corrupted its PN (modulation of the EFC voltage)?

Possible reasons for a fluctuating/unstable PN to consider:
- one of the oscillators has unstable PN
- the Tantalum capacitor should be replaced by a film or a ceramic 10uF?
- broadcast FM stations influenced the second measurement
- ?

Thanks for any advice where to look at the problem ;)
Leon


-- Forwarded message --
From: Ben Bradley 
To: Discussion of precise time and frequency measurement <
time-nuts@lists.febo.com>
Cc:
Bcc:
Date: Sat, 11 Apr 2020 23:22:29 -0400
Subject: Re: [time-nuts] OCXO and fluctuations after EFC adjustment
Despite my interest in the precision high-end of electronic design
(and thus being a subscriber to this list), I have very little
experience with such high-fallutin' designs. Still, I've done and seen
some "interesting" things in my career. It's amazing how the minutiae
of even jelly bean components can cause product failures.

A few decades ago (many of my jobs were engineering positions at
companies that made equipment for the POTS phone line), the company I
was with had some rather large surface-mount ceramic capacitors that
were failing short in a new product that used them across the phone
line (they were RATED for this application right there on the data
sheet).  The concern was our product would some day short out the
phone line and someone with another phone on the line would have an
emergency and wouldn't be able to call 911 to get help. The possible
legal liability to the company was obvious. In a discussion with other
engineers and managers, someone wondered if it was the way the board
was manufactured, maybe the solder process caused some caps to crack,
or whether the failures were strictly the fault of the capacitor
manufacturer. I volunteered to test the caps in an environmental
chamber that wasn't being used at the time, putting them near the edge
of, but still within, specs. I made a jig that put a bias voltage on
many in parallel (using a mechanical spring connection, not soldered)
and left them for a few days/weeks. Out of 100 to 150 devices, about 5
or 10 became unacceptably leaky. I wrote up my report and emailed it
to the other engineers and managers involved, and didn't hear back
anything more about it. The good news (!) is the product wasn't in
production for very long for several reasons, more recently of course
that the POTS phone line is no longer the most common form of
telecommunications. The bad news is it's no longer helpful to have
POTS product design on my resume.

More recently, I saw this Kemet presentation on Digikey about tantalum
capacitors. Certainly for aluminum electrolytic capacitors, the rated
voltage is "the rated voltage" and as long as the capacitor never goes
ABOVE that voltage (and has no overcurrent that would heat it up,
etc.), the cap is good for its combination of temperature and lifetime
rating. I (and as far as I know, everone I've known) assumed this was
the same for tantalums, but it appears that's not the case (this
presentation mentions several failure causes and shows how they are
multiplicative). As you go from 1/2 rated voltage to full rated
voltage, the chances of a tantalum failing goes up substantially. The
implied rule seems to be for maximum reliability, don't operate a
tantalum above HALF the rated voltage. I'd heard a lot of anecdotal
things about tantalums suddenly shorting out for this or that reason,
but hadn't heard of this, and here it is straight from the
manufacturer.
https://www.digikey.com/en/ptm/k/kemet/derating-guidelines-for-surface-mount-tantalum-capacitors/tutorial
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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Donald E. Pauly]

Unwind a foot or so of wire and measure the resistance to figure the wire
size.  If possible, then unwind the entire choke to find its proper
resistance.  This will determine the original value from the inductor data
sheet. If not calculate the resistance from the volume of the winding.

On Saturday, April 11, 2020, ed breya  wrote:

> Rick said:
> "In the case of the 10811, I have already posted about the reference diode
> of special characteristics. I don't remember all the exact details of how
> it was chosen, but it was based on proprietary knowledge."
>
> This reminds me of something unusual I found in a Vectron 10 MHz OCXO many
> years ago. It was busted, and it was a soldered-shut type. I had nothing to
> lose in taking it apart, hoping to find the problem and restore it if
> possible. It came apart OK, and I found in the densely packed circuitry, a
> small RF choke that was burned up. I traced the circuitry enough to figure
> out that it was in series with the internal reference regulator diode - a
> 1N82X 6.2V TC type. This added some small DC voltage drop to the Zener
> voltage, and that's what went to the internal circuitry, and also out to an
> external pin. This pin was intended to supply an external pot for tweaking
> the EFC line in stand-alone applications, and apparently sometime in its
> past, it had been faulted to an excessive voltage, causing the choke to
> burn out, and maybe damage to other parts.
>
> The only things I could figure were that the choke maybe served as a small
> copper resistance (+3000 ppm/K or so) to provide some extra degree of
> temperature compensation for some reason, or that it was to suppress
> possible oscillations from the Zener's negative R in avalanche.
>
> The choke was one of those little molded types, about the size of a 1/4 W
> resistor, and unfortunately burned up and apart too much to read any color
> bands. I guessed it to be around maybe up to a few uH, and a few ohms, but
> that's as far as I got. I set it aside, thinking someday I'll dig into it
> some more, but it still sits in pieces in a box somewhere, remaining a
> mystery to me. All I know is, there must have been a reason for it.
>
> Ed
>
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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Bob kb8tq]

Hi

Well….. 

Once upon a time, there was a design review on a space part. There
was an tantalum  cap used in a couple of places in the design. It was 
a 50V part and running at 12V. 

We got dinged for it. Turns out if you over derate electrolytics (of any sort)
there is a failure mechanism that creeps in. 

How was that discovered? Well NASA (or the military or ….)  sponsored 
severals studies at several universities. They did a bunch of testing and 
published a number of papers on the topic. Quick summary: "tested
a whole bunch and these failed". 

A good librarian with a week or two on their hands probably can track 
them down. I very much doubt you can find them outside a pay wall. 

Bob

> On Apr 12, 2020, at 5:52 AM, Gerhard Hoffmann  
> wrote:
> 
> 
> Am 12.04.20 um 05:22 schrieb Ben Bradley:
>> More recently, I saw this Kemet presentation on Digikey about tantalum
>> capacitors. Certainly for aluminum electrolytic capacitors, the rated
>> voltage is "the rated voltage" and as long as the capacitor never goes
>> ABOVE that voltage (and has no overcurrent that would heat it up,
>> etc.), the cap is good for its combination of temperature and lifetime
>> rating. I (and as far as I know, everone I've known) assumed this was
>> the same for tantalums, but it appears that's not the case (this
>> presentation mentions several failure causes and shows how they are
>> multiplicative). As you go from 1/2 rated voltage to full rated
>> voltage, the chances of a tantalum failing goes up substantially. The
>> implied rule seems to be for maximum reliability, don't operate a
>> tantalum above HALF the rated voltage. I'd heard a lot of anecdotal
>> things about tantalums suddenly shorting out for this or that reason,
>> but hadn't heard of this, and here it is straight from the
>> manufacturer.
>> https://www.digikey.com/en/ptm/k/kemet/derating-guidelines-for-surface-mount-tantalum-capacitors/tutorial
> For a space project, I was surprised that ESA required derating
> of tantalum working voltage only to 50%, where I was used to
> derate down to 1/3 as was proposed in a NEC data sheet from
> 30 years ago. But then, the only allowed Ta caps had 6 times
> the volume of commercial ones, so the first round of derating
> probably was already built-in.
> 
> 
> Those fat capacitors did really hurt, esp. when the proposed
> SEU mitigation of the regulators consisted of providing large
> enough load capacitance so that the regulators could go
> Berserk for a millisecond or two without blowing up the FPGA.
> 
> 
> cheers, Gerhard
> 
> 
> 
> 
> 
> 
> 
> 
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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[jimlux]

On 4/11/20 8:22 PM, Ben Bradley wrote:
=

More recently, I saw this Kemet presentation on Digikey about tantalum
capacitors. Certainly for aluminum electrolytic capacitors, the rated
voltage is "the rated voltage" and as long as the capacitor never goes
ABOVE that voltage (and has no overcurrent that would heat it up,
etc.), the cap is good for its combination of temperature and lifetime
rating. I (and as far as I know, everone I've known) assumed this was
the same for tantalums, but it appears that's not the case (this
presentation mentions several failure causes and shows how they are
multiplicative). As you go from 1/2 rated voltage to full rated
voltage, the chances of a tantalum failing goes up substantially. The
implied rule seems to be for maximum reliability, don't operate a
tantalum above HALF the rated voltage. I'd heard a lot of anecdotal
things about tantalums suddenly shorting out for this or that reason,
but hadn't heard of this, and here it is straight from the
manufacturer.
https://www.digikey.com/en/ptm/k/kemet/derating-guidelines-for-surface-mount-tantalum-capacitors/tutorial



reading the data sheet and ap notes very carefully is important. A lot 
of times, the ratings are for a situation which actually doesn't occur 
in the application.  That is, you have some current, which leads to some 
heating, which puts the internal temperature at some number other than 
25C, at which the rating is specified.


When it comes to pulse capacitors with polypropylene dielectric, the 
ratings go as V^7.5  - that is, doubling the voltage reduces the life by 
a factor of 181.


tungsten filaments go as something like the 12th power.





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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Ben Bradley]

Despite my interest in the precision high-end of electronic design
(and thus being a subscriber to this list), I have very little
experience with such high-fallutin' designs. Still, I've done and seen
some "interesting" things in my career. It's amazing how the minutiae
of even jelly bean components can cause product failures.

A few decades ago (many of my jobs were engineering positions at
companies that made equipment for the POTS phone line), the company I
was with had some rather large surface-mount ceramic capacitors that
were failing short in a new product that used them across the phone
line (they were RATED for this application right there on the data
sheet).  The concern was our product would some day short out the
phone line and someone with another phone on the line would have an
emergency and wouldn't be able to call 911 to get help. The possible
legal liability to the company was obvious. In a discussion with other
engineers and managers, someone wondered if it was the way the board
was manufactured, maybe the solder process caused some caps to crack,
or whether the failures were strictly the fault of the capacitor
manufacturer. I volunteered to test the caps in an environmental
chamber that wasn't being used at the time, putting them near the edge
of, but still within, specs. I made a jig that put a bias voltage on
many in parallel (using a mechanical spring connection, not soldered)
and left them for a few days/weeks. Out of 100 to 150 devices, about 5
or 10 became unacceptably leaky. I wrote up my report and emailed it
to the other engineers and managers involved, and didn't hear back
anything more about it. The good news (!) is the product wasn't in
production for very long for several reasons, more recently of course
that the POTS phone line is no longer the most common form of
telecommunications. The bad news is it's no longer helpful to have
POTS product design on my resume.

More recently, I saw this Kemet presentation on Digikey about tantalum
capacitors. Certainly for aluminum electrolytic capacitors, the rated
voltage is "the rated voltage" and as long as the capacitor never goes
ABOVE that voltage (and has no overcurrent that would heat it up,
etc.), the cap is good for its combination of temperature and lifetime
rating. I (and as far as I know, everone I've known) assumed this was
the same for tantalums, but it appears that's not the case (this
presentation mentions several failure causes and shows how they are
multiplicative). As you go from 1/2 rated voltage to full rated
voltage, the chances of a tantalum failing goes up substantially. The
implied rule seems to be for maximum reliability, don't operate a
tantalum above HALF the rated voltage. I'd heard a lot of anecdotal
things about tantalums suddenly shorting out for this or that reason,
but hadn't heard of this, and here it is straight from the
manufacturer.
https://www.digikey.com/en/ptm/k/kemet/derating-guidelines-for-surface-mount-tantalum-capacitors/tutorial

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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Alex Pummer]

Taka,
it was possible, to do without computer, although the computer is a very 
big help particularly for routine works, but it is possible not just 
trouble shoot but design, very complicated circuits to, and there are 
out there areas where computers still do not help today, Bob Peasa even 
cached the computer, that it is  lied to him, -- look here: 
https://www.autodesk.com/products/eagle/blog/whats-all-this-bob-pease-stuff-anyhow/ 
-- but it is fun, it is still fun I am doing it for the last 60 years. I 
just for that OCXO thema,  I cleaned up the output of the DDS with out 
VCO, but the principle is usable for any spectrum cleaning, I filed for 
patent thus could talk about it, but it would not fit into the tread. 
Engineering or as we spell it in German Ingenieur -ing, since the 
Franco-German word is derived from ingenuity, not from the 
engine.And yes over there we figured out how to make the "thinking 
machine", but we still using our own head to think.

73
KJ6UHN  ex DL6QF

On 4/11/2020 7:05 PM, Taka Kamiya via time-nuts wrote:

I'm STILL reading this, with interest.
I want to know the method of fault discovery, thought process that ensued, 
analysis conducted, testing process, and eventual root cause analysis.  We rely 
too much on automated processes and computers.  I want to know how engineers 
did more with less.  Before they are forever lost, we got to document it, or 
better yet, pass it on to newcomers.
I care more about how it was done before, not how it can be done better with 
this or that million dollar tool.

---
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
  


 On Saturday, April 11, 2020, 8:59:32 PM EDT, Bob kb8tq  
wrote:
  
  Hi




On Apr 11, 2020, at 8:10 PM, Richard (Rick) Karlquist  
wrote:



On 4/11/2020 2:25 PM, Bob kb8tq wrote:

Hi
Would you *really* want to read a book about how from August of 1986 to
January of 1993 AVX NPO’s had some sort of issue ( not that the issue is
clearly known, just that they are flakey) and that by 1994 the parts with
values below 220 pf in 0805 seemed to be fixed?
Again, the task was never to *fix* a component, simply to sort out the parts
that worked from the parts you didn’t want to use. The only feedback to the
manufacturer was via the (lack of) purchase orders.
Somehow I doubt anybody would make it past the first page ….
Bob

Back when before HP broke up into pieces, capacitor vendors considered
it a computer company and assumed that all capacitor orders were for
"computer grade" capacitors.  This envisioned huge motherboards with
thousands of bypass capacitors.  Like monitor specs where it is OK
for so many pixels to be bad, as long as 99% of the capacitors were
good ... ship them.  As long as the average leakage current met some
spec, it didn't matter if a few of them were very leaky.  The current
wouldn't be noticed.  Tempco and dissipation factor didn't matter.

We did actually give the manufacturer feedback, but it was not accepted
because we as an instrument division were not in their target market.
They didn't support repurposing.  It didn't matter than we were owned
by HP; we were using them for the wrong end use.  It's like those
disclaimers that say "We do not authorize for the life support
market" etc.

Some vendors flat out would not sell to our division although they
were fine with the computer divisions.

By now, few people besides Bob are still reading this. :-)

Rick N6RK

Indeed over the years, our experience was that feedback on components was
at best unwelcome and at worst a major waste of everybody’s time. Lots of
“dialog” and very little benefit. Unless you are a precision crystal company,
oscillator companies are *not* a big customer for any component outfit ….

Bob
   
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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Hal Murray]

kb...@n1k.org said:
> Somehow I doubt anybody would make it past the first page …. 

rich...@karlquist.com said:
> By now, few people besides Bob are still reading this. :-) 

But this time nuts.

I would enjoy hearing stories about how you figured out that batch X or part Y 
didn't work and/or why.

--

rich...@karlquist.com said:
> We did actually give the manufacturer feedback, but it was not accepted
> because we as an instrument division were not in their target market.

> Some vendors flat out would not sell to our division although they were fine
> with the computer divisions. 

Interesting.  Were there any vendors interested in your market area?

With my software hat on, I really appreciate feedback from smart users, and 
even the users who are not so geeky in your area as long as they are 
good/smart (and polite) about asking for help.  You can learn a lot from where 
they went wrong.  I think there used to be a usenet FAQ page about how to ask 
good questions.

I'm a bit surprised that you didn't connect with somebody at one of the 
vendors who really valued your feedback.  It sounds like the sort of thing 
that would help a company tune their process to make better parts.




-- 
These are my opinions.  I hate spam.




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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Bob kb8tq]

Hi


> On Apr 11, 2020, at 8:10 PM, Richard (Rick) Karlquist  
> wrote:
> 
> 
> 
> On 4/11/2020 2:25 PM, Bob kb8tq wrote:
>> Hi
>> Would you *really* want to read a book about how from August of 1986 to
>> January of 1993 AVX NPO’s had some sort of issue ( not that the issue is
>> clearly known, just that they are flakey) and that by 1994 the parts with
>> values below 220 pf in 0805 seemed to be fixed?
>> Again, the task was never to *fix* a component, simply to sort out the parts
>> that worked from the parts you didn’t want to use. The only feedback to the
>> manufacturer was via the (lack of) purchase orders.
>> Somehow I doubt anybody would make it past the first page ….
>> Bob
> 
> Back when before HP broke up into pieces, capacitor vendors considered
> it a computer company and assumed that all capacitor orders were for
> "computer grade" capacitors.  This envisioned huge motherboards with
> thousands of bypass capacitors.  Like monitor specs where it is OK
> for so many pixels to be bad, as long as 99% of the capacitors were
> good ... ship them.  As long as the average leakage current met some
> spec, it didn't matter if a few of them were very leaky.  The current
> wouldn't be noticed.  Tempco and dissipation factor didn't matter.
> 
> We did actually give the manufacturer feedback, but it was not accepted
> because we as an instrument division were not in their target market.
> They didn't support repurposing.  It didn't matter than we were owned
> by HP; we were using them for the wrong end use.  It's like those
> disclaimers that say "We do not authorize for the life support
> market" etc.
> 
> Some vendors flat out would not sell to our division although they
> were fine with the computer divisions.
> 
> By now, few people besides Bob are still reading this. :-)
> 
> Rick N6RK

Indeed over the years, our experience was that feedback on components was
at best unwelcome and at worst a major waste of everybody’s time. Lots of 
“dialog” and very little benefit. Unless you are a precision crystal company, 
oscillator companies are *not* a big customer for any component outfit ….

Bob


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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Adrian Godwin]

On Sun, Apr 12, 2020 at 1:11 AM Richard (Rick) Karlquist <
rich...@karlquist.com> wrote:

>
> By now, few people besides Bob are still reading this. :-)
>
>
>
On the contrary :)

Personally I'd love to read about the problems seen, debugged and fixed in
the manufacture of any generation of high quality equipment, whether
technical or otherwise. I'm sure there are areas with nothing interesting
to write and I'm very glad to be out of manufacturing support myself, but
am happy to hear of other's successes and workarounds.

-adrian
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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Richard (Rick) Karlquist]

On 4/11/2020 2:25 PM, Bob kb8tq wrote:

Hi

Would you *really* want to read a book about how from August of 1986 to
January of 1993 AVX NPO’s had some sort of issue ( not that the issue is
clearly known, just that they are flakey) and that by 1994 the parts with
values below 220 pf in 0805 seemed to be fixed?

Again, the task was never to *fix* a component, simply to sort out the parts
that worked from the parts you didn’t want to use. The only feedback to the
manufacturer was via the (lack of) purchase orders.

Somehow I doubt anybody would make it past the first page ….

Bob



Back when before HP broke up into pieces, capacitor vendors considered
it a computer company and assumed that all capacitor orders were for
"computer grade" capacitors.  This envisioned huge motherboards with
thousands of bypass capacitors.  Like monitor specs where it is OK
for so many pixels to be bad, as long as 99% of the capacitors were
good ... ship them.  As long as the average leakage current met some
spec, it didn't matter if a few of them were very leaky.  The current
wouldn't be noticed.  Tempco and dissipation factor didn't matter.

We did actually give the manufacturer feedback, but it was not accepted
because we as an instrument division were not in their target market.
They didn't support repurposing.  It didn't matter than we were owned
by HP; we were using them for the wrong end use.  It's like those
disclaimers that say "We do not authorize for the life support
market" etc.

Some vendors flat out would not sell to our division although they
were fine with the computer divisions.

By now, few people besides Bob are still reading this. :-)

Rick N6RK

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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Bob kb8tq]

Hi

Would you *really* want to read a book about how from August of 1986 to 
January of 1993 AVX NPO’s had some sort of issue ( not that the issue is 
clearly known, just that they are flakey) and that by 1994 the parts with 
values below 220 pf in 0805 seemed to be fixed? 

Again, the task was never to *fix* a component, simply to sort out the parts
that worked from the parts you didn’t want to use. The only feedback to the
manufacturer was via the (lack of) purchase orders. 

Somehow I doubt anybody would make it past the first page ….

Bob

> On Apr 11, 2020, at 4:48 PM, Taka Kamiya via time-nuts 
>  wrote:
> 
> I wish such persons would write a book about the subject.  Audience will be 
> small that it probably wouldn't make it a profitable venture.
> As to coding, I wonder why it's a "touchy" subject  In assembly time, 
> porting one architecture to another was a major undertaking.  One didn't 
> "port", but one would have to basically re-architect and re-code.  Also, 
> engineers did all kinds of odd things to get job done.  It's only recently 
> that we have almost unlimited amount of memory and more than enough speed 
> that many of us became lazy.  If lazy isn't the right word, reusability, 
> self-documenting, etc became more important than write a smallest and most 
> efficient code.
> Myself, I once participated in a project (just two of us  my boss and me) 
> where we had to use Z80 to read the data a large industrial machine puts out. 
>  It was coming out so fast, we couldn't code to read them.  So we had to use 
> DMA to write directly write to memory, and when there is a break in stream, 
> switch it over to CPU control and read them out.
> I also recall Sun Microsystem used two 68000 CPU because certain interrupt 
> didn't work right and it was essential for multi-tasking.  So they used two, 
> one executing ahead of the other.  Somehow, they coded OS to back track and 
> made multi-tasking work.  I thought it was very clever.
> As to EFC, an odd man out is SRS PRS10.  It gives you 3 ways to do it.  An 
> EFC input from outside, a 10 turn trimmer built into the box, or a 
> programmatic control via DAC.  As far as I know, there is no trimmer.  At 
> least it's not user accessible.  This is a very timely discussion as I am 
> working on PRS-10 project and 11081 project.  (two separate projects)
> 
> --- 
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
> 
> 
>On Saturday, April 11, 2020, 3:02:13 PM EDT, Richard (Rick) Karlquist 
>  wrote:  
> 
> 
> 
> On 4/11/2020 12:15 AM, John Moran, Scawby Design wrote:
> 
>> During my 50 years in the electronics industry I have always been puzzled 
>> about one aspect of crystal oscillators. They go to great lengths to use a 
>> precise piece of quartz as the heart, because of its unique properties, and 
>> then add standard external components - capacitors, varactors, Zeners, etc. 
>> to tweak its frequency. All these components vary far more than the original 
>> piece of quartz ... hence my confusion.
>> 
>> I know it is practically impossible to grind a crystal to exactly the 
>> frequency you want, and it then drifts over time, but what is the logic of 
>> using relatively wildly varying components to adjust the quartz? Are their 
>> temperature and ageing characteristics swamped by the superior crystal?
>> 
>> In all the papers I have ever read, the subject is never mentioned ... you 
>> just add a variable capacitor and/or an EFC circuit and job done.
>> 
>> I guess this is showing my total ignorance here, but I would like to know.
>> 
>> Maybe this is at the heart of Rick's usual speech?
>> 
>> John
>> 
>> 
> 
> For non-oven oscillators of ordinary precision (say 10 PPM over 0 to 
> 50°C), the low pullability of the crystal is such that adding
> adjustment capacitors is not a big hazard.  An EFC circuit that
> is inside some PLL of course is only at risk of adding some noise
> from the drive circuit.  I can't remember ever seeing an EFC'ed
> oscillators where the EFC was driven by, say, a pot.
> 
> In the case of the 10811, I have already posted about the
> reference diode of special characteristics.  I don't remember
> all the exact details of how it was chosen, but it was based
> on proprietary knowledge.
> 
> Another anecdote of interest is that when the first 10811's were
> being tested, they exhibited very bad aging.  It was eventually
> determined after a lot of investigation that oil in the piston
> trimmer was migrating around and tweaking the frequency.  I
> don't remember whether the fix was using a different type of
> oil, or having the vendor apply it selectively, or if they
> deleted the oil completely.
> 
> This type of knowledge can basically only be learned by getting
> a job working with the top experts in the field.  Before I worked
> for HP, it became clear that I needed to get a job there in order
> to figure out how their stuff worked.  I read HP manuals as much
> as I could, but 

Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Richard (Rick) Karlquist]

That caught my attention.  Could you please say more.

A DDS introduces spurs.  They move around as you change the adjustment
parameters.

Are the spurs small enough that they are not a problem with most applications?
  What applications do/don't get along with spurs?

What do spurs look like on an ADEV plot?

I think of a "DDS on a chip" as having a VCO/PLL up to some fairly high
frequency and some digital logic that brings that down to the target
frequency.  The high frequency means that the time step from N to N+1 cycles
is smaller.  But VCOs are noisy relative to a good crystal.  So in addition to
spurs, I'd expect more phase noise.

Am I on the right track?  What should I have asked?


The last part of your post is way off track.  The first "D" in DDS
stands for direct.  PLL's are INdirect.  An architecture I
frequently see and do not recommend is to try to "clean up" a
DDS by using it to phase lock a VCXO.  As you say, the VCXO, etc
adds noise.  And it doesn't clean up close in spurs within
the loop bandwidth.

I presented a paper at FCS in 1995 or 1996 about combining
a DDS with a "direct synthesizer" derived from the famous
HP5100 architecture.  This multi stage system reduces DDS spurs
by 20 dB or so per stage.

The 5071A has a DDS designed from scratch by the brilliant
physicist Robin Giffard that produced a very clean spectrum.
He went beyond the commercial DDS's.

Keysight sells a very high end Arbitrary Waveform Generator
that is essentially a DDS that goes up to 5 or 10 GHz.  It
is all on one custom chip.  When I retired, they were still
planning to add an 8 GHz whispering gallery oscillator as
a time base.  BTW, that oscillator did have EFC so it could
be locked to a 10 MHz reference.  However, the way it worked
was that they changed the temperature of the resonator oven.
So it doesn't break my "rule".

Rick

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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Taka Kamiya via time-nuts]

I wish such persons would write a book about the subject.  Audience will be 
small that it probably wouldn't make it a profitable venture.
As to coding, I wonder why it's a "touchy" subject  In assembly time, 
porting one architecture to another was a major undertaking.  One didn't 
"port", but one would have to basically re-architect and re-code.  Also, 
engineers did all kinds of odd things to get job done.  It's only recently that 
we have almost unlimited amount of memory and more than enough speed that many 
of us became lazy.  If lazy isn't the right word, reusability, 
self-documenting, etc became more important than write a smallest and most 
efficient code.
Myself, I once participated in a project (just two of us  my boss and me) 
where we had to use Z80 to read the data a large industrial machine puts out.  
It was coming out so fast, we couldn't code to read them.  So we had to use DMA 
to write directly write to memory, and when there is a break in stream, switch 
it over to CPU control and read them out.
I also recall Sun Microsystem used two 68000 CPU because certain interrupt 
didn't work right and it was essential for multi-tasking.  So they used two, 
one executing ahead of the other.  Somehow, they coded OS to back track and 
made multi-tasking work.  I thought it was very clever.
As to EFC, an odd man out is SRS PRS10.  It gives you 3 ways to do it.  An EFC 
input from outside, a 10 turn trimmer built into the box, or a programmatic 
control via DAC.  As far as I know, there is no trimmer.  At least it's not 
user accessible.  This is a very timely discussion as I am working on PRS-10 
project and 11081 project.  (two separate projects)

--- 
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
 

On Saturday, April 11, 2020, 3:02:13 PM EDT, Richard (Rick) Karlquist 
 wrote:  
 
 

On 4/11/2020 12:15 AM, John Moran, Scawby Design wrote:

> During my 50 years in the electronics industry I have always been puzzled 
> about one aspect of crystal oscillators. They go to great lengths to use a 
> precise piece of quartz as the heart, because of its unique properties, and 
> then add standard external components - capacitors, varactors, Zeners, etc. 
> to tweak its frequency. All these components vary far more than the original 
> piece of quartz ... hence my confusion.
> 
> I know it is practically impossible to grind a crystal to exactly the 
> frequency you want, and it then drifts over time, but what is the logic of 
> using relatively wildly varying components to adjust the quartz? Are their 
> temperature and ageing characteristics swamped by the superior crystal?
> 
> In all the papers I have ever read, the subject is never mentioned ... you 
> just add a variable capacitor and/or an EFC circuit and job done.
> 
> I guess this is showing my total ignorance here, but I would like to know.
> 
> Maybe this is at the heart of Rick's usual speech?
> 
> John
> 
>

For non-oven oscillators of ordinary precision (say 10 PPM over 0 to 
50°C), the low pullability of the crystal is such that adding
adjustment capacitors is not a big hazard.  An EFC circuit that
is inside some PLL of course is only at risk of adding some noise
from the drive circuit.  I can't remember ever seeing an EFC'ed
oscillators where the EFC was driven by, say, a pot.

In the case of the 10811, I have already posted about the
reference diode of special characteristics.  I don't remember
all the exact details of how it was chosen, but it was based
on proprietary knowledge.

Another anecdote of interest is that when the first 10811's were
being tested, they exhibited very bad aging.  It was eventually
determined after a lot of investigation that oil in the piston
trimmer was migrating around and tweaking the frequency.  I
don't remember whether the fix was using a different type of
oil, or having the vendor apply it selectively, or if they
deleted the oil completely.

This type of knowledge can basically only be learned by getting
a job working with the top experts in the field.  Before I worked
for HP, it became clear that I needed to get a job there in order
to figure out how their stuff worked.  I read HP manuals as much
as I could, but actually being there was the real secret.  I
asked as many people as possible about their particular expertise
in an effort to learn as much as possible.  The right approach is
necessary to get these experts to open up.  I was careful not to
wear out my welcome.

Every person is an expert in their particular field, and there
is always something to be learned from them.  A couple of ground
rules I formulated from experience:

1.  If they tell me something that I know is wrong, I usually just
thank them for the advice and then ignore it, rather than arguing.
Or "correcting" them!  Let them continue to believe what they
want to believe.  Sometimes I find out later that actually the
person was correct and I was wrong.

2.  Be extremely careful about asking "why 

Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Bob kb8tq]

Hi

Spurs on an ADEV plot look like ripples in the curve. If you have a part
with good close in phase noise / good short tau ADEV, you probably
can see effects from spurs that  120 db down in the vicinity of 10 Hz. 

Bob

> On Apr 11, 2020, at 4:22 PM, Hal Murray  wrote:
> 
> 
> rich...@karlquist.com said:
>> At this time, I will give my usual speech about IMHO the fact that since the
>> invention of the DDS on a chip, EFC should no longer be used  for high
>> performance oscillators. 
> 
> That caught my attention.  Could you please say more.
> 
> A DDS introduces spurs.  They move around as you change the adjustment 
> parameters.
> 
> Are the spurs small enough that they are not a problem with most 
> applications? 
> What applications do/don't get along with spurs?
> 
> What do spurs look like on an ADEV plot?
> 
> I think of a "DDS on a chip" as having a VCO/PLL up to some fairly high 
> frequency and some digital logic that brings that down to the target 
> frequency.  The high frequency means that the time step from N to N+1 cycles 
> is smaller.  But VCOs are noisy relative to a good crystal.  So in addition 
> to 
> spurs, I'd expect more phase noise.
> 
> Am I on the right track?  What should I have asked?
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[ed breya]

Rick said:
"In the case of the 10811, I have already posted about the reference 
diode of special characteristics. I don't remember all the exact details 
of how it was chosen, but it was based on proprietary knowledge."


This reminds me of something unusual I found in a Vectron 10 MHz OCXO 
many years ago. It was busted, and it was a soldered-shut type. I had 
nothing to lose in taking it apart, hoping to find the problem and 
restore it if possible. It came apart OK, and I found in the densely 
packed circuitry, a small RF choke that was burned up. I traced the 
circuitry enough to figure out that it was in series with the internal 
reference regulator diode - a 1N82X 6.2V TC type. This added some small 
DC voltage drop to the Zener voltage, and that's what went to the 
internal circuitry, and also out to an external pin. This pin was 
intended to supply an external pot for tweaking the EFC line in 
stand-alone applications, and apparently sometime in its past, it had 
been faulted to an excessive voltage, causing the choke to burn out, and 
maybe damage to other parts.


The only things I could figure were that the choke maybe served as a 
small copper resistance (+3000 ppm/K or so) to provide some extra degree 
of temperature compensation for some reason, or that it was to suppress 
possible oscillations from the Zener's negative R in avalanche.


The choke was one of those little molded types, about the size of a 1/4 
W resistor, and unfortunately burned up and apart too much to read any 
color bands. I guessed it to be around maybe up to a few uH, and a few 
ohms, but that's as far as I got. I set it aside, thinking someday I'll 
dig into it some more, but it still sits in pieces in a box somewhere, 
remaining a mystery to me. All I know is, there must have been a reason 
for it.


Ed

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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Hal Murray]

rich...@karlquist.com said:
> At this time, I will give my usual speech about IMHO the fact that since the
> invention of the DDS on a chip, EFC should no longer be used  for high
> performance oscillators. 

That caught my attention.  Could you please say more.

A DDS introduces spurs.  They move around as you change the adjustment 
parameters.

Are the spurs small enough that they are not a problem with most applications? 
 What applications do/don't get along with spurs?

What do spurs look like on an ADEV plot?

I think of a "DDS on a chip" as having a VCO/PLL up to some fairly high 
frequency and some digital logic that brings that down to the target 
frequency.  The high frequency means that the time step from N to N+1 cycles 
is smaller.  But VCOs are noisy relative to a good crystal.  So in addition to 
spurs, I'd expect more phase noise.

Am I on the right track?  What should I have asked?


-- 
These are my opinions.  I hate spam.




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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Taka Kamiya via time-nuts]

Funny you should mention this.
During testing, I noticed an odd repetitive and modulated signal on ALL DC 
lines.  It looked like a typical AM modulated signal of 100KHz carrier and 
somewhere around 1KHz signal.  It was around 40mV p-p.

Long story short, it was the oscilloscope probe that was picking up the signal. 
 Different scope and different probe showed there are no such signal on any of 
my power lines.

--- 
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
 

On Saturday, April 11, 2020, 12:56:26 PM EDT, Joseph Gwinn 
 wrote:  
 
 On Sat, 11 Apr 2020 00:24:45 -0400, time-nuts-requ...@lists.febo.com 
wrote:
Re: time-nuts Digest, Vol 189, Issue 18

> 
> Message: 4
> Date: Fri, 10 Apr 2020 13:23:22 -0400
> From: Bob kb8tq 
> To: Taka Kamiya , Discussion of precise time and
>     frequency measurement 
> Subject: Re: [time-nuts] OCXO and fluctuations after EFC adjustment
> Message-ID: <99642a49-8cdf-42d4-9039-7a5e7ff23...@n1k.org>
> Content-Type: text/plain;    charset=us-ascii
> 
> Hi
> 
> EFC changes by themselves are pretty much instantaneous. If you are seeing
> post tune drift, it likely is from the pot or from things like a 
> temperature change (or draft) when you go near the part. 
> 
> If your grounds are a bit intertwined, the change in oven current will give 
you
> a delta voltage on the ground. That can get into the EFC. Taking care of 
this 
> is harder than it seems. The 10811 has an independent ground return for the 
> oven, so it at least is *possible* to do in this case.
> 
> A good starting point is to hook up a DVM on your pot. Watch the voltage 
after
> you do a tune adjustment. If the drift you are after is in the parts 
> in 10^-12 range, that may take a pretty good DVM. 

Note that that many DVMs inject noise back into whatever they are 
measuring.  This could be interesting if one is measuring a 
frequency-control voltage.  A RC low pass filter may be useful.

Joe Gwinn

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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[jimlux]

On 4/11/20 6:04 AM, Bob kb8tq wrote:

Hi

Bottom line is that, as long as one is careful about *which* vendors supply 
which
parts, normal parts do the job. Nobody is going to publish that selection 
process
or the results. They very much want the “other guy” to have to do it on their 
own.


This is like low noise, low leakage FETs in high Z charge amplifiers - 
sure, it has a JEDEC 2N number and lots of people sell them, but the 
only ones worth buying are from that supplier in the UK, who "have the 
recipe".  And heavens forbid that they're sold or "lose the recipe".


(CSAC from Symmetricom vs Microsemi, comes to mind)





The 78L12 might look just like one from 5 other vendors. It also might work 10X
better than the others. Those caps may look pretty normal. They came from
“this guy” and not “those guys”. That cheap looking thermistor might have spent
a few years in evaluation before it was approved for use.

There is a lot of work that goes into component selection. It simply does not
result in $20 bulk metal film parts with 0.2 ppm/ C specs getting used. It is a
lot more difficult to spot in the finished product.


And I suspect this is very much more so with "mass production" than 
one-off artisanal hand crafting. If you're building one or two or three, 
you can "hand select" or build 10 to yield 3 good ones.


This is the peril of "build to print" in the space business. The print 
describes the one you built in the lab, but there's no guarantee that 
the next 5 will perform the same.






Bob



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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Joseph Gwinn]

On Sat, 11 Apr 2020 00:24:45 -0400, time-nuts-requ...@lists.febo.com 
wrote:
Re: time-nuts Digest, Vol 189, Issue 18

> 
> Message: 4
> Date: Fri, 10 Apr 2020 13:23:22 -0400
> From: Bob kb8tq 
> To: Taka Kamiya , Discussion of precise time and
>   frequency measurement 
> Subject: Re: [time-nuts] OCXO and fluctuations after EFC adjustment
> Message-ID: <99642a49-8cdf-42d4-9039-7a5e7ff23...@n1k.org>
> Content-Type: text/plain; charset=us-ascii
> 
> Hi
> 
> EFC changes by themselves are pretty much instantaneous. If you are seeing
> post tune drift, it likely is from the pot or from things like a 
> temperature change (or draft) when you go near the part. 
> 
> If your grounds are a bit intertwined, the change in oven current will give 
you
> a delta voltage on the ground. That can get into the EFC. Taking care of 
this 
> is harder than it seems. The 10811 has an independent ground return for the 
> oven, so it at least is *possible* to do in this case.
> 
> A good starting point is to hook up a DVM on your pot. Watch the voltage 
after
> you do a tune adjustment. If the drift you are after is in the parts 
> in 10^-12 range, that may take a pretty good DVM. 

Note that that many DVMs inject noise back into whatever they are 
measuring.  This could be interesting if one is measuring a 
frequency-control voltage.  A RC low pass filter may be useful.

Joe Gwinn

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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Taka Kamiya via time-nuts]

What I noticed over years of taking things apart is that manufacturers use 
precision parts when its needed and use ordinary parts elsewhere.  

For me, selecting parts is often not a possible proposition.  I do not own 
ultra precision test equipment and/or environmental chamber.  With intrusion of 
counterfeit and/or out-of-spec parts in market, it is getting very difficult to 
ensure what I have is what I think I have.  An only thing I can do is to buy 
from reputable sources when it counts and bite the bullet and buy well spec'd 
parts.  Even that does not guarantee genuine parts depending on where 
fakes/remarks are getting in.

--- 
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
 

On Saturday, April 11, 2020, 11:11:56 AM EDT, Bob kb8tq  
wrote:  
 
 Hi

Well, if you make OCXO’s that way, you will not be in business 
for very long. At least not selling to the major OEM’s ( or to any
customer who actually checks the parts).

Bob

> On Apr 11, 2020, at 10:26 AM, David C. Partridge 
>  wrote:
> 
> Well, that's how it's supposed to be done, but these days the usual (and 
> often only) criterion other than part value (e.g. 15V 200uF +/- 10%) seems to 
> be cost (cheapest == best).
> 
> Sad isn't it.
> 
> David
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@lists.febo.com] On Behalf Of Bob 
> kb8tq
> Sent: 11 April 2020 14:05
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] OCXO and fluctuations after EFC adjustment
> 
> Hi
> 
> Bottom line is that, as long as one is careful about *which* vendors supply 
> which
> parts, normal parts do the job. Nobody is going to publish that selection 
> process 
> or the results. They very much want the “other guy” to have to do it on their 
> own. 
> 
> The 78L12 might look just like one from 5 other vendors. It also might work 
> 10X 
> better than the others. Those caps may look pretty normal. They came from 
> “this guy” and not “those guys”. That cheap looking thermistor might have 
> spent 
> a few years in evaluation before it was approved for use. 
> 
> There is a lot of work that goes into component selection. It simply does not 
> result in $20 bulk metal film parts with 0.2 ppm/ C specs getting used. It is 
> a 
> lot more difficult to spot in the finished product. 
> 
> Bob
> 
> 
> 
> 
> 
>> On Apr 11, 2020, at 3:15 AM, John Moran, Scawby Design 
>>  wrote:
>> 
>> On Fri, 10 April 2020 14:31:53 -0700 Rick wrote:
>> 
>> 
>>> At this time, I will give my usual speech about IMHO the fact that
>> 
>>> since the invention of the DDS on a chip, EFC should no longer be used
>> 
>>> for high performance oscillators.
>> 
>> During my 50 years in the electronics industry I have always been puzzled 
>> about one aspect of crystal oscillators. They go to great lengths to use a 
>> precise piece of quartz as the heart, because of its unique properties, and 
>> then add standard external components - capacitors, varactors, Zeners, etc. 
>> to tweak its frequency. All these components vary far more than the original 
>> piece of quartz ... hence my confusion.
>> 
>> I know it is practically impossible to grind a crystal to exactly the 
>> frequency you want, and it then drifts over time, but what is the logic of 
>> using relatively wildly varying components to adjust the quartz? Are their 
>> temperature and ageing characteristics swamped by the superior crystal?
>> 
>> In all the papers I have ever read, the subject is never mentioned ... you 
>> just add a variable capacitor and/or an EFC circuit and job done.
>> 
>> I guess this is showing my total ignorance here, but I would like to know.
>> 
>> Maybe this is at the heart of Rick's usual speech?
>> 
>> John
>> 
>> 
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> 
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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Bob kb8tq]

Hi

Well, if you make OCXO’s that way, you will not be in business 
for very long. At least not selling to the major OEM’s ( or to any
customer who actually checks the parts).

Bob

> On Apr 11, 2020, at 10:26 AM, David C. Partridge 
>  wrote:
> 
> Well, that's how it's supposed to be done, but these days the usual (and 
> often only) criterion other than part value (e.g. 15V 200uF +/- 10%) seems to 
> be cost (cheapest == best).
> 
> Sad isn't it.
> 
> David
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@lists.febo.com] On Behalf Of Bob 
> kb8tq
> Sent: 11 April 2020 14:05
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] OCXO and fluctuations after EFC adjustment
> 
> Hi
> 
> Bottom line is that, as long as one is careful about *which* vendors supply 
> which
> parts, normal parts do the job. Nobody is going to publish that selection 
> process 
> or the results. They very much want the “other guy” to have to do it on their 
> own. 
> 
> The 78L12 might look just like one from 5 other vendors. It also might work 
> 10X 
> better than the others. Those caps may look pretty normal. They came from 
> “this guy” and not “those guys”. That cheap looking thermistor might have 
> spent 
> a few years in evaluation before it was approved for use. 
> 
> There is a lot of work that goes into component selection. It simply does not 
> result in $20 bulk metal film parts with 0.2 ppm/ C specs getting used. It is 
> a 
> lot more difficult to spot in the finished product. 
> 
> Bob
> 
> 
> 
> 
> 
>> On Apr 11, 2020, at 3:15 AM, John Moran, Scawby Design 
>>  wrote:
>> 
>> On Fri, 10 April 2020 14:31:53 -0700 Rick wrote:
>> 
>> 
>>> At this time, I will give my usual speech about IMHO the fact that
>> 
>>> since the invention of the DDS on a chip, EFC should no longer be used
>> 
>>> for high performance oscillators.
>> 
>> During my 50 years in the electronics industry I have always been puzzled 
>> about one aspect of crystal oscillators. They go to great lengths to use a 
>> precise piece of quartz as the heart, because of its unique properties, and 
>> then add standard external components - capacitors, varactors, Zeners, etc. 
>> to tweak its frequency. All these components vary far more than the original 
>> piece of quartz ... hence my confusion.
>> 
>> I know it is practically impossible to grind a crystal to exactly the 
>> frequency you want, and it then drifts over time, but what is the logic of 
>> using relatively wildly varying components to adjust the quartz? Are their 
>> temperature and ageing characteristics swamped by the superior crystal?
>> 
>> In all the papers I have ever read, the subject is never mentioned ... you 
>> just add a variable capacitor and/or an EFC circuit and job done.
>> 
>> I guess this is showing my total ignorance here, but I would like to know.
>> 
>> Maybe this is at the heart of Rick's usual speech?
>> 
>> John
>> 
>> 
>> ___
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>> To unsubscribe, go to 
>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>> and follow the instructions there.
> 
> 
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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[David C. Partridge]

Well, that's how it's supposed to be done, but these days the usual (and often 
only) criterion other than part value (e.g. 15V 200uF +/- 10%) seems to be cost 
(cheapest == best).

Sad isn't it.

David
-Original Message-
From: time-nuts [mailto:time-nuts-boun...@lists.febo.com] On Behalf Of Bob kb8tq
Sent: 11 April 2020 14:05
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] OCXO and fluctuations after EFC adjustment

Hi

Bottom line is that, as long as one is careful about *which* vendors supply 
which
parts, normal parts do the job. Nobody is going to publish that selection 
process 
or the results. They very much want the “other guy” to have to do it on their 
own. 

The 78L12 might look just like one from 5 other vendors. It also might work 10X 
better than the others. Those caps may look pretty normal. They came from 
“this guy” and not “those guys”. That cheap looking thermistor might have spent 
a few years in evaluation before it was approved for use. 

There is a lot of work that goes into component selection. It simply does not 
result in $20 bulk metal film parts with 0.2 ppm/ C specs getting used. It is a 
lot more difficult to spot in the finished product. 

Bob





> On Apr 11, 2020, at 3:15 AM, John Moran, Scawby Design 
>  wrote:
> 
> On Fri, 10 April 2020 14:31:53 -0700 Rick wrote:
> 
> 
>> At this time, I will give my usual speech about IMHO the fact that
> 
>> since the invention of the DDS on a chip, EFC should no longer be used
> 
>> for high performance oscillators.
> 
> During my 50 years in the electronics industry I have always been puzzled 
> about one aspect of crystal oscillators. They go to great lengths to use a 
> precise piece of quartz as the heart, because of its unique properties, and 
> then add standard external components - capacitors, varactors, Zeners, etc. 
> to tweak its frequency. All these components vary far more than the original 
> piece of quartz ... hence my confusion.
> 
> I know it is practically impossible to grind a crystal to exactly the 
> frequency you want, and it then drifts over time, but what is the logic of 
> using relatively wildly varying components to adjust the quartz? Are their 
> temperature and ageing characteristics swamped by the superior crystal?
> 
> In all the papers I have ever read, the subject is never mentioned ... you 
> just add a variable capacitor and/or an EFC circuit and job done.
> 
> I guess this is showing my total ignorance here, but I would like to know.
> 
> Maybe this is at the heart of Rick's usual speech?
> 
> John
> 
> 
> ___
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> To unsubscribe, go to 
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[John Moran, Scawby Design]

On Fri, 10 April 2020 14:31:53 -0700 Rick wrote:


>At this time, I will give my usual speech about IMHO the fact that

>since the invention of the DDS on a chip, EFC should no longer be used

>for high performance oscillators.

During my 50 years in the electronics industry I have always been puzzled about 
one aspect of crystal oscillators. They go to great lengths to use a precise 
piece of quartz as the heart, because of its unique properties, and then add 
standard external components - capacitors, varactors, Zeners, etc. to tweak its 
frequency. All these components vary far more than the original piece of quartz 
... hence my confusion.

I know it is practically impossible to grind a crystal to exactly the frequency 
you want, and it then drifts over time, but what is the logic of using 
relatively wildly varying components to adjust the quartz? Are their 
temperature and ageing characteristics swamped by the superior crystal?

In all the papers I have ever read, the subject is never mentioned ... you just 
add a variable capacitor and/or an EFC circuit and job done.

I guess this is showing my total ignorance here, but I would like to know.

Maybe this is at the heart of Rick's usual speech?

John


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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[jimlux]

On 4/10/20 2:31 PM, Richard (Rick) Karlquist wrote:







At this time, I will give my usual speech about IMHO the fact that
since the invention of the DDS on a chip, EFC should no longer be used 
for high performance oscillators.


Rick N6RK


Yes..

The only case I can think of is where the oscillator is being directly 
multiplied up and one cannot tolerate the spurs from a DDS.  There are 
folks who believe that this is the case for generating the downlink 
carrier in a deep space transponder.


However, I believe that even in that incredibly niche application, one 
can design a DDS to have minimal spurs in the area close to the carrier. 
In fact, just today, a transponder on Bepi Colombo makes a close 
approach to Earth on its way to Mercury that implements just such a scheme.


I can conceive that there might be an application where the "move the 
spurs around" approach wouldn't work or would be too complex.


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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[Richard (Rick) Karlquist]

On 4/10/2020 12:51 PM, ed breya wrote:

looking for. Also, moving the frequency far away from "ideal" changes 
the tempco, since it's no longer at the ideal center of the turnover 
point. In reality, this may not matter much, since after all these 
years, things may have drifted and aged way out of ideal-ness anyway.


SC cut crystals:

1.  Do not necessarily have a turnover
2.  Individual oven set points are not precisely at the
turnover if any.
3.  The crystals without a turnover, instead have a broad
range over which their tempco is extremely small

FWIW, the E1938A oscillators were manufactured using
a procedure whereby the oven set points were individually
set for each oscillator to be exactly on the turnover.
IIRC, the crystal blanks were tweaked slightly to assure
that all E1983A crystals had turnovers.  BTW, we used the
UPPER turnover on the E1938A, as opposed to the lower
turnover on the 10811.



The EFC bias (varactor leakage) current changes too, which interacts 
with the external driving voltage source impedance. For lowest noise and 
loading effects, keep the EFC driving resistance as low as possible.


It is easy to see from the 10811 schematic that the cathode of the EFC
varactor is connected to an avalanche/Zener diode of the temperature
compensated type with a conventional diode in series to do the
compensation.  The voltage of the diode (which is something like
6.2V is a "magic" voltage where the tempco goes to zero).  According
to the 10811 designers, this particular model of diode is particularly
well behaved in terms of noise due to the process by which it was made,
at least 40 years ago.

If you want to do anything serious with EFC, you probably need to bring
out both ends of the diode, etc.

At this time, I will give my usual speech about IMHO the fact that
since the invention of the DDS on a chip, EFC should no longer be used 
for high performance oscillators.


Rick N6RK

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Re: [time-nuts] OCXO and fluctuations after EFC adjustment

[ed breya]

This sort of behavior shouldn't be surprising at all. When you change 
the EFC (especially by a fairly large amount to move it a few Hz), you 
change the (transient and steady-state) operating points of the 
circuitry, so it has to drift gradually to stabilize at the new 
conditions. The effects may be tiny, but so are the differences you're 
looking for. Also, moving the frequency far away from "ideal" changes 
the tempco, since it's no longer at the ideal center of the turnover 
point. In reality, this may not matter much, since after all these 
years, things may have drifted and aged way out of ideal-ness anyway.


The EFC bias (varactor leakage) current changes too, which interacts 
with the external driving voltage source impedance. For lowest noise and 
loading effects, keep the EFC driving resistance as low as possible.


Ed

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