Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi

I would very much second the recommendation of Gardner’s book. It has been
the best way to get into PLL’s for a *long* time. It is unique in that the 
current edition
 is still as relevant today as the book was when it first came out.

Bob

> On Apr 28, 2016, at 2:00 AM, Charles Steinmetz  wrote:
> 
> I wrote:
> 
>> And here are links to the best PLL design texts I'm aware of:
>> 
>> Gardner:  
>> Best:  
>> Egan 1:  
>> Egan 2:  
>> Stephens:  
>> Wolaver:  
> 
> I should have added that the Gardner book is absolutely essential for anyone 
> designing PLLs, IMO.
> 
> Best is excellent.  Chapter 9 is specifically devoted to higher-order loops 
> (through 5th order).
> 
> Stephens covers DPLLs from a different angle than Gardner.
> 
> Egan marches to his own drum, so the way the subject is divided, the topics 
> covered, and some of the notation does not necessarily match other texts.  
> These can be the hardest to follow, but Egan is very thorough.
> 
> Wolaver's book covers PLL basics comprehensively and is both a great 
> introductory text as well as an excellent review text to jog the memory of an 
> experienced PLL designer.
> 
> Different people learn differently, so a book that is ideal for one person is 
> not necessarily the best for another person.  Some graduate-level students 
> find Best, Stephens, and both Egan books hard to follow, while others find 
> them very helpful.  I've never heard anyone complain about Gardner or 
> Wolaver, except to the extent that they don't cover a topic of interest to 
> the student.
> 
> Best regards,
> 
> Charles
> 
> 
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Magnus Danielson]

Lars and Charles,

On 04/28/2016 05:27 AM, Charles Steinmetz wrote:

Lars wrote:


Could you please explain a little more about this:
 * * *
What is the systematic ripple?
Is the comparison frequency normally 1Hz (1PPS)?
What is the algorithms used?
If I sample the difference between the PPS and the divided 10MHz
output every second and have a third order loop driving a DAC will I
get systematic errors?


Um -- please do not take this the wrong way, but you seem to be
asking for short-cuts and cookbook solutions to very complex design
issues in advanced PLL design, apparently without having a good
understanding of the basics of PLL design (as indicated by your
questions: what is the comparison frequency, what is systematic ripple,
etc.).

That is just not the way it works.  System designs are organic --
everything affects everything else.  One needs a comprehensive
understanding of the whole subject to deal with all of the consequences
of each contemplated design choice.  There are just too many degrees of
freedom in a design at that level of complexity and performance to make
short-cuts and cookbook solutions possible.

Most anyone can throw together a first-order PLL using cookbook
solutions and make it basically work (i.e., the loop doesn't oscillate
and it converges to lock).  But this doesn't even begin to make a decent
GPSDO design.  Not only must the loop converge and not oscillate, the
loop tuning must match the OCXO being used, it must hold errors down to
PPT levels and below, and it must address errors at the second, third,
and higher levels of analysis.  There is just no easy, or formulaic way
to incorporate results of the required, interdependent analyses without
actually performing those analyses.  There are no short-cuts.

Here is a post from October on the same subject:

  

And here are links to the best PLL design texts I'm aware of:

  Gardner:  
  Best:  
  Egan 1:  
  Egan 2:  
  Stephens:  
  Wolaver:  

I suggest that you get all of these books (or, at minimum, three of
them, after reviewing the tables of content and some relevant pages
using Google Books or "look inside" on Amazon) and study them -- really
study them.  (I'm betting that if you study any three of them, you will
end up getting the other three and probably other books as well.)  In
time, you will be able to answer the questions you are asking, and to
pose the next several hundred questions you will need to answer to
design a well-optimized GPSDO.


I have found that I use Gardner, Best and Wolaver together. They 
complement each other in a nice fashion.


Gardner is the authoritative text, and reading it carefully gives a 
qualitative understanding.


Best is maybe somewhat more easier to get to, but also have some 
approaches that sometimes complements the Gardner.


The Wolaver book is really a very nice complement to the Gardner, it 
provides a very smooth reading but also more variations of circuits and 
some analysis which isn't in the other books that can be really helpful.


If you want to learn and extend in the field, I would not go without the 
Gardner and Wolaver. There might be other books covering what Best covers.


I have additional books, but these is what I find that I use for PLLs.
There is also the "Jitter in Digital Transmission Systems" which can 
provide additional insights that the others lack.


Cheers,
Magnus
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Charles Steinmetz]

I wrote:


And here are links to the best PLL design texts I'm aware of:

 Gardner:  
 Best:  
 Egan 1:  
 Egan 2:  
 Stephens:  
 Wolaver:  


I should have added that the Gardner book is absolutely essential for 
anyone designing PLLs, IMO.


Best is excellent.  Chapter 9 is specifically devoted to higher-order 
loops (through 5th order).


Stephens covers DPLLs from a different angle than Gardner.

Egan marches to his own drum, so the way the subject is divided, the 
topics covered, and some of the notation does not necessarily match 
other texts.  These can be the hardest to follow, but Egan is very thorough.


Wolaver's book covers PLL basics comprehensively and is both a great 
introductory text as well as an excellent review text to jog the 
memory of an experienced PLL designer.


Different people learn differently, so a book that is ideal for one 
person is not necessarily the best for another person.  Some 
graduate-level students find Best, Stephens, and both Egan books hard 
to follow, while others find them very helpful.  I've never heard 
anyone complain about Gardner or Wolaver, except to the extent that 
they don't cover a topic of interest to the student.


Best regards,

Charles


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Re: [time-nuts] Advise on building a DIY GPSDO?

[Charles Steinmetz]

Lars wrote:


Could you please explain a little more about this:
 * * *
What is the systematic ripple?
Is the comparison frequency normally 1Hz (1PPS)?
What is the algorithms used?
If I sample the difference between the PPS and the divided 10MHz 
output every second and have a third order loop driving a DAC will I 
get systematic errors?


Um -- please do not take this the wrong way, but you seem to be 
asking for short-cuts and cookbook solutions to very complex design 
issues in advanced PLL design, apparently without having a good 
understanding of the basics of PLL design (as indicated by your 
questions: what is the comparison frequency, what is systematic 
ripple, etc.).


That is just not the way it works.  System designs are organic -- 
everything affects everything else.  One needs a comprehensive 
understanding of the whole subject to deal with all of the 
consequences of each contemplated design choice.  There are just too 
many degrees of freedom in a design at that level of complexity and 
performance to make short-cuts and cookbook solutions possible.


Most anyone can throw together a first-order PLL using cookbook 
solutions and make it basically work (i.e., the loop doesn't 
oscillate and it converges to lock).  But this doesn't even begin to 
make a decent GPSDO design.  Not only must the loop converge and not 
oscillate, the loop tuning must match the OCXO being used, it must 
hold errors down to PPT levels and below, and it must address errors 
at the second, third, and higher levels of analysis.  There is just 
no easy, or formulaic way to incorporate results of the required, 
interdependent analyses without actually performing those 
analyses.  There are no short-cuts.


Here is a post from October on the same subject:

 

And here are links to the best PLL design texts I'm aware of:

 Gardner:  
 Best:  
 Egan 1:  
 Egan 2:  
 Stephens:  
 Wolaver:  

I suggest that you get all of these books (or, at minimum, three of 
them, after reviewing the tables of content and some relevant pages 
using Google Books or "look inside" on Amazon) and study them -- 
really study them.  (I'm betting that if you study any three of them, 
you will end up getting the other three and probably other books as 
well.)  In time, you will be able to answer the questions you are 
asking, and to pose the next several hundred questions you will need 
to answer to design a well-optimized GPSDO.


Best regards,

Charles


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Re: [time-nuts] Advise on building a DIY GPSDO?

[Magnus Danielson]

Lars,

On 04/27/2016 02:14 PM, Lars Walenius wrote:

Thanks Magnus and Charles,

Could you please explain a little more about this:

Charles wrote:

  Loop filters in commercial GPSDOs use algorithms that suppress
systematic ripple on the VCO control related to the comparison frequency.

Magnus wrote:

It will be there, so you need to manage it one way or another.


What is the systematic ripple?


On the comparison frequency, whatever it is, there will be measurements 
and adjustments. The overtones of the sample rate it represents will be 
a systematic "tone".



Is the comparison frequency normally 1Hz (1PPS)?


Yes.


What is the algorithms used?


There can be many. Oversampling and smoothing that way helps for 
instance. Resolution in adjustment is an indirect way.



If I sample the difference between the PPS and the divided 10MHz output every 
second and have a third order loop driving a DAC will I get systematic errors?


Yes. Depending on how picky you are you can live with it or you find 
ways to manage it.


Cheers,
Magnus


Lars

Från: Magnus Danielson<mailto:mag...@rubidium.dyndns.org>
Skickat: den 27 april 2016 10:02
Till: time-nuts@febo.com<mailto:time-nuts@febo.com>
Kopia: mag...@rubidium.se<mailto:mag...@rubidium.se>
Ämne: Re: [time-nuts] Advise on building a DIY GPSDO?



On 04/27/2016 01:12 AM, Charles Steinmetz wrote:

Lars wrote:


I have wondered what is meant by a proper digital filter below?

Is a proper digital filter something more than the LP-filter + PI-loop
I use in the DIY Arduino GPSDO?
What is used in commercial GPSDOs?


The loops are substantially more sophisticated than a simple LP filter
-- typically 3rd order or higher.


The lowpass-filter + PI-loop is third order.


  Well-designed commercial GPSDOs also
have several time constants so they can achieve basic lock using a wider
loop, then narrow the loop in steps until it is fully narrow (unless S/N
is low, in which case they may not reach full narrow and should set an
alarm).


Some care needs to be taken in articulating the filter such that you do
not have to scale the state as you change the parameters. This is
however fairly simple for both the low-pass filter and integrator (which
hold state).

With some care you can articulate the P and I in the forms of equations
relating to the loop parameters you want and compensating for the
DAC/EFC control gain (exact value not important, but getting bandwidth
and damping in the right neightborhood is).

The heuristics about when changing parameters takes some learning. One
of the design criteria is to be able to always capture, but you also
want it to go as quick as possible. Finding a good balance can be
problematic. There is tricks to track-in quicker.


  Loop filters in commercial GPSDOs use algorithms that suppress
systematic ripple on the VCO control related to the comparison frequency.


It will be there, so you need to manage it one way or another.


It is extremely unlikely that someone would stumble upon workable
parameters for this sort of loop by trial and error.  One needs to
measure and characterize the open-loop behavior, then carefully design
the loop filter to achieve the desired result.


If you know what you are doing, you can get a good start using analysis,
knowing the damping and bandwidth you want. It always becomes a measure
and trim exercise.

Cheers,
Magnus
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Lars Walenius]

Thanks Magnus and Charles,

Could you please explain a little more about this:

Charles wrote:
>>  Loop filters in commercial GPSDOs use algorithms that suppress
>> systematic ripple on the VCO control related to the comparison frequency.
Magnus wrote:
>It will be there, so you need to manage it one way or another.

What is the systematic ripple?
Is the comparison frequency normally 1Hz (1PPS)?
What is the algorithms used?
If I sample the difference between the PPS and the divided 10MHz output every 
second and have a third order loop driving a DAC will I get systematic errors?

Lars

Från: Magnus Danielson<mailto:mag...@rubidium.dyndns.org>
Skickat: den 27 april 2016 10:02
Till: time-nuts@febo.com<mailto:time-nuts@febo.com>
Kopia: mag...@rubidium.se<mailto:mag...@rubidium.se>
Ämne: Re: [time-nuts] Advise on building a DIY GPSDO?



On 04/27/2016 01:12 AM, Charles Steinmetz wrote:
> Lars wrote:
>
>> I have wondered what is meant by a proper digital filter below?
>>
>> Is a proper digital filter something more than the LP-filter + PI-loop
>> I use in the DIY Arduino GPSDO?
>> What is used in commercial GPSDOs?
>
> The loops are substantially more sophisticated than a simple LP filter
> -- typically 3rd order or higher.

The lowpass-filter + PI-loop is third order.

>  Well-designed commercial GPSDOs also
> have several time constants so they can achieve basic lock using a wider
> loop, then narrow the loop in steps until it is fully narrow (unless S/N
> is low, in which case they may not reach full narrow and should set an
> alarm).

Some care needs to be taken in articulating the filter such that you do
not have to scale the state as you change the parameters. This is
however fairly simple for both the low-pass filter and integrator (which
hold state).

With some care you can articulate the P and I in the forms of equations
relating to the loop parameters you want and compensating for the
DAC/EFC control gain (exact value not important, but getting bandwidth
and damping in the right neightborhood is).

The heuristics about when changing parameters takes some learning. One
of the design criteria is to be able to always capture, but you also
want it to go as quick as possible. Finding a good balance can be
problematic. There is tricks to track-in quicker.

>  Loop filters in commercial GPSDOs use algorithms that suppress
> systematic ripple on the VCO control related to the comparison frequency.

It will be there, so you need to manage it one way or another.

> It is extremely unlikely that someone would stumble upon workable
> parameters for this sort of loop by trial and error.  One needs to
> measure and characterize the open-loop behavior, then carefully design
> the loop filter to achieve the desired result.

If you know what you are doing, you can get a good start using analysis,
knowing the damping and bandwidth you want. It always becomes a measure
and trim exercise.

Cheers,
Magnus
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Magnus Danielson]

On 04/27/2016 01:12 AM, Charles Steinmetz wrote:

Lars wrote:


I have wondered what is meant by a proper digital filter below?

Is a proper digital filter something more than the LP-filter + PI-loop
I use in the DIY Arduino GPSDO?
What is used in commercial GPSDOs?


The loops are substantially more sophisticated than a simple LP filter
-- typically 3rd order or higher.


The lowpass-filter + PI-loop is third order.


 Well-designed commercial GPSDOs also
have several time constants so they can achieve basic lock using a wider
loop, then narrow the loop in steps until it is fully narrow (unless S/N
is low, in which case they may not reach full narrow and should set an
alarm).


Some care needs to be taken in articulating the filter such that you do 
not have to scale the state as you change the parameters. This is 
however fairly simple for both the low-pass filter and integrator (which 
hold state).


With some care you can articulate the P and I in the forms of equations 
relating to the loop parameters you want and compensating for the 
DAC/EFC control gain (exact value not important, but getting bandwidth 
and damping in the right neightborhood is).


The heuristics about when changing parameters takes some learning. One 
of the design criteria is to be able to always capture, but you also 
want it to go as quick as possible. Finding a good balance can be 
problematic. There is tricks to track-in quicker.



 Loop filters in commercial GPSDOs use algorithms that suppress
systematic ripple on the VCO control related to the comparison frequency.


It will be there, so you need to manage it one way or another.


It is extremely unlikely that someone would stumble upon workable
parameters for this sort of loop by trial and error.  One needs to
measure and characterize the open-loop behavior, then carefully design
the loop filter to achieve the desired result.


If you know what you are doing, you can get a good start using analysis, 
knowing the damping and bandwidth you want. It always becomes a measure 
and trim exercise.


Cheers,
Magnus
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Charles Steinmetz]

Lars wrote:


I have wondered what is meant by a proper digital filter below?

Is a proper digital filter something more than the LP-filter + 
PI-loop I use in the DIY Arduino GPSDO?

What is used in commercial GPSDOs?


The loops are substantially more sophisticated than a simple LP 
filter -- typically 3rd order or higher.  Well-designed commercial 
GPSDOs also have several time constants so they can achieve basic 
lock using a wider loop, then narrow the loop in steps until it is 
fully narrow (unless S/N is low, in which case they may not reach 
full narrow and should set an alarm).  Loop filters in commercial 
GPSDOs use algorithms that suppress systematic ripple on the VCO 
control related to the comparison frequency.


It is extremely unlikely that someone would stumble upon workable 
parameters for this sort of loop by trial and error.  One needs to 
measure and characterize the open-loop behavior, then carefully 
design the loop filter to achieve the desired result.


Best regards,

Charles


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Re: [time-nuts] Advise on building a DIY GPSDO?

[Lars Walenius]

Hello Charles and others

I have wondered what is meant by a proper digital filter below? Now I was 
reminded by the KS-24361 holdover graphs from Hal.

Is a proper digital filter something more than the LP-filter + PI-loop I use in 
the DIY Arduino GPSDO?
What is used in commercial GPSDO´s?

I am also quite sure that a home-built GPSDO will not "rival all comers," but 
you will learn a lot!

I also enclose an screen shoot from a two day run with my Arduino GPSDO in hold 
mode. This combination works well with about 1000-1500 secs of time constant 
and is an example that you need long time constants with good oscillators. It 
is also an example that you can learn a lot without expensive equipment. The 
TIC was linearized with a third order polynomial and data for linearization was 
gathered with the use of a PICDIV PD26 and processed in Excel. With the PD26 it 
is possible to have data with very accurate 200ns spacing together with the 1ns 
TIC.

BTW I saw that Nick Sayer now is using the ”Arduino” 1ns TIC in his open source 
GPSDO. His latest program also used a LP-filter+PI-loop what I could see.

Lars


Från: Charles Steinmetz<mailto:csteinm...@yandex.com>
Skickat: den 5 april 2016 07:08
Till: Discussion of precise time and frequency 
measurement<mailto:time-nuts@febo.com>
Ämne: Re: [time-nuts] Advise on building a DIY GPSDO?

Don wrote:

>5.  Design a voltage tracking / filter to match the OCXO
>control requirements.
>6.  And, ...ta-dah;
>7.  You have a 10MHz, bench frequency standard that will
>rival all others

Not very likely.  The whole point of a GPSDO is for the frequency to
be controlled by the more stable source (OCXO or GPS) at all
integration times (tau).  But the OCXO will typically be more stable
than the GPS for tau less than several hundred seconds (see graph
below -- black line is GPS, brown line is a typical OCXO).  So, the
PLL needs to have a time constant of hundreds of seconds.  Such a PLL
filter cannot practicably be designed in the analog domain, so one
needs to design a digital filter with appropriate time constant and
damping.  Because of the very long time constant, it is almost
necessary for the filter to have more than one, switchable time
constants to avoid extremely long lock times.

Very few home builders are capable of designing a proper digital
filter suitable for this application (the counter-based loops of most
published DIY GPSDO designs are not proper digital filters).

So, no -- it is very unlikely that a home-built GPSDO will "rival all
comers," whether the builder designs his or her own circuit or uses
one of the many published circuits.

Best regards,

Charles


Graph below.  Note that a properly designed GPSDO would show
stability that follows the OCXO (brown line) at low tau, and the GPS
(black line) above the point where they intersect -- here, about 350
seconds.  Note that a loop filter with proper damping will NOT
exhibit a "hump" near the crossover (many GPSDOs do exhibit a
pronounced hump, betraying that their loop filters are not properly designed).
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Andrew Rodland]

On Sun, Apr 3, 2016 at 6:04 PM, Nicolas Braud-Santoni
 wrote:
> Hi,
>
> I've been slowly becoming a fellow timenut over the last few years,
>   though said nuttery had yet to go beyond adding some wiring to
>   get the PPS signal out of my GPS and into my NTPd.
>
>
> Lately, I have been looking into designing & building a home-brew
>   GPSDO (and my copy of TAoE 3rd ed. came in quite handy), but quite
>   a few questions came up:
>
> - Does it indeed make sense to build a GPSDO using an “ordinary”
>   high-quality oscillator? (as opposed to using a Ru standard)
>
>   It seems that decomissioned rubidium standards are large, rather
>   expensive (hundreds of €), consume lots of power and have
>   uncertain lifetime.

Depending on your definition of large and expensive, I'd say it's not
so bad. I've been able to get X72s and more recently SA.22cs off of
fleabay for between $100 and $150 (about 90 - 130 EUR at present
rates). They're pretty small, steady-state power draw is about 5
watts, and although the lifetime is a question, a good seller should
show you the diagnostic output including power-on hours and various
temperatures and voltages -- the one I trust does!

> - Are there recommendations people can make for not-too-expensive
>   VCOs to use in a GPSDO?
>
> - Are there GPS modules that people here can recommend?
>
>   I have been looking at the uBlox NEO-7 and the GNS TC6000GN-P1
>   GPS modules.  Both retail around 40€, and promise <100ns PPS jitter.
>   I would probably prefer the NEO-7, because uBlox makes more precise
>   PPS jitter claims for GPS, with 30ns RMS and 60ns for 99 percentile.

The uBlox ones are nice. I have one sitting around but I haven't
gotten around to writing a protocol decoder for it yet, so I'm using
an older Trimble Resolution T. If your goal is purely hobby and you
want to save some money, that might be a perfectly good option -- you
can find them for very cheap, and if your main aim is to build an NTP
server then anything better than the Trimble will be lost in the noise
anyway. Like the uBlox ones, the Trimble supports doing
survey-in/stationary mode for the best time stability.

> - While trying to design this on my own is fun and educational, are
>   there existing designs for DIY GPSDOs that I should look at?

I'm not making any great promises of educational value, but I've spent
a bunch of time building GPS-disciplined NTP servers on the Arduino
platform as a purely hobby thing and I do have a bit to share. I've
failed repeatedly to do a decent write-up of my work in blog form, but
I do have code and I'd be happy to answer questions about it.

First: https://github.com/arodland/Due-GPS-NTP-Server . This one is
newer, and it runs on the ARM-based Arduino Due (actually a clone
board called the Taijiuino that allows using the SAM3X's onboard
Ethernet MAC). It works with a Symmetricom rubidium oscillator and
either Trimble or SiRF GPS. It has a timing granularity of 32ns and
the NTP stdev as measured from my desktop is about 5 microseconds. It
also sends out statistics packets every second over UDP that I use to
make graphs, and has a serial CLI for tweaking the settings :)

Second: https://github.com/arodland/Arduino-GPS-NTP-Server . This is
the older version. I don't keep up with it anymore, it only supports
the SiRF GPS driver, it uses an FLL algorithm that I no longer think
is right, and it doesn't discipline an external oscillator, it just
does digital frequency synthesis on the Arduino's own 16MHz clock.
However there's some potentially interesting stuff in there in terms
of managing the timer interrupts, keeping time, and doing all of the
requisite math on an 8-bit chip without burning more cycles than we
have available, as well as hacking the Arduino Ethernet Shield to
support an interrupt-driven mode to allow better timestamping of
incoming packets. It has a timing granularity of 500ns and due to the
iffy performance of the WizNet ethernet adapter the NTP stdev is in
the 10-20 microsecond range (it was worse than that before I figured
out the interrupt trick).

> For reference, my use-case (beyond simply building it) is two-fold:
> - I want an accurate ref. clock for my local NTP setup.
> - I need a frequency reference for QRSS (low-power RF transmissions),
>   and getting a 8MHz reference out of the GPSDO would help a lot  :)

In that case you may want to forget the rubidiums that I mentioned and
go for a VCXO after all; my rubidiums use digital frequency synthesis,
and I understand that makes them unusable for radio work -- unless
you're just using them as a reference to lock some other, cleaner,
oscillator.
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bruce Griffiths]

Just drive the mixer LO at 8MHz and replace the 14MHZ bandpass filter with a 
2MHz bandpass filter.
Bruce 

On Sunday, 10 April 2016 7:23 PM, Bruce Griffiths 
<bruce.griffi...@xtra..co.nz> wrote:
 

 No, you can just drive the mixer LO with 8MHz and use a 2MHz bandpass filte=
r (plus the 10MHz bandpass filter) on the mixer RF output rather than 14MHz 
 bandpass filter.
Bruce

  From: Herbert Poetzl <herb...@13thfloor.at>
 To: Bruce Griffiths <bruce.griffi...@xtra.co.nz>; Discussion of precise time 
and frequency measurement <time-nuts@febo.com> 
 Sent: Sunday, 10 April 2016 5:24 PM
 Subject: Re: [time-nuts] Advise on building a DIY GPSDO?
  
On Sun, Apr 10, 2016 at 01:16:11AM +, Bruce Griffiths wrote:
> It can easily be done using a variant of the dual conjugate
> regenerative divider.

> Feed the 24 MHz signal into the LO port of a mixer.Use a dual
> bandpass filters centred on 14MHz and 10MHz to filter the IF
> port amplify the outputs of the bandpass filters and drive the
> mixer RF port with  the combined 10MHz and 14MHz signals. 

> The 10MHz signal can be extracted from the amplified 10MHz
> output via a splitter. 

> When  the loop gain and phasing is correct for both the 10MHz
> and 14MHz signals the circuit will produce the required output.
> Excess gain is eliminated by the mixers compression of the IF
> signal.

> The circuitry is all analog with no digital components whatsoever.

Thanks Bruce!

That is something I do understand, although the original
idea was to go from 8MHz to 10MHz, but I presume the 24MHz
can be filtered out from the overtones after running the
8MHz signal through a comparator.

Cheers,
Herbert

> Bruce

>    On Sunday, 10 April 2016 12:10 PM, Will <zl1...@gmx.com> wrote:


>  Hi all,

> I'm fairly new here and might not fully understand things.

> Earlier in this thread it was suggested that one lock an 8Mhz
> signal to a 10 Mhz signal by analogue methods.

> To quote A Plummer:

> "and it is relative easy to make 10MHz from 8MHz with analog
> frequency manipulation, which generates less jitter
> 73"

> and H Poetzl asked the same thing as I am:

> "On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
>> and it is relative easy to make 10MHz from 8MHz with analog
>> frequency manipulation, which generates less jitter

> Could you elaborate on this a little if time permits?
> I'm more a 'digital person' but it sounds interesting.

> Thanks in advance,
> Herbert"

> I have not seen how that is done as suddenly the signals are 24Mhz and 10 Mhz 
> and digital dividers and multipliers are used.


> One other point. Attila mentioned using "LEA-M8T". I assume the T suffix 
> relates to Time rather than the plain GPS. What is the difference? Apart from 
> 50% higher cost.


> Cheers
> Will
> ZL1TAO


>> Sent: Sunday, April 10, 2016 at 7:00 AM
>> From: "Bob Camp" <kb...@n1k.org>
>> To: ewkeh...@aol.com, "Discussion of precise time and frequency measurement" 
>> <time-nuts@febo.com>
>> Subject: Re: [time-nuts] Advise on building a DIY GPSDO?

>> Hi

>> Averaged over a long enough time (and without any hanging bridges) the 
>> frequency accuracy 
>> will be fine. The frequency accuracy of a 1 pps output on a GPS is “fine” on 
>> the same basis. Since
>> 200 KHz is a “round division” off of any of the likely TCXO’s you will not 
>> have any jitter or spurs in the “static” 
>> case.

>> Bob


>>> On Apr 9, 2016, at 10:07 AM, Bert Kehren via time-nuts <time-nuts@febo.com> 
>>> wrote:

>>> I do not know what U blox does but I know when we use 200 KHz out of the 1  
>>> pps output on a $ 10 ublox 6 we consistently get better than 1 E-10 closer 
>>> to 1  E-11 out of the Morion have the data
>>> Bert Kehren


>>> In a message dated 4/9/2016 10:01:05 A.M. Eastern Daylight Time,  
>>> kb...@n1k.org writes:

>>> Hi

>>>> On Apr 8, 2016, at 9:39 PM, time...@metachaos.net  wrote:


>>>> Hello Bob,

>>>> Friday, April 8, 2016,  6:13:07 PM, you wrote:

>>>>> Hi

>>>>> If you  start from a 24 MHz TCXO (different modules use different TCXO’
>>> s):

>>>>> On an 8 MHz output, most of the time you divide by three.  

>>>>> On a 10 MHz output, you need to divide by 2.4. The net  result is that 
>>> you 
>>>>> divide by 2 sometimes and 3 other times.  

>>>>> In the 10 MHz case, there is a *lot* of energy at 12 MHz  and 8 MHz, 
>>> along with
>>>>> the 10 MHz output. 

>>>>> In  the 8 MHz case, most of the RF energy is

Re: [time-nuts] Advise on building a DIY GPSDO?

[Herbert Poetzl]

On Sun, Apr 10, 2016 at 01:16:11AM +, Bruce Griffiths wrote:
> It can easily be done using a variant of the dual conjugate
> regenerative divider.

> Feed the 24 MHz signal into the LO port of a mixer.Use a dual
> bandpass filters centred on 14MHz and 10MHz to filter the IF
> port amplify the outputs of the bandpass filters and drive the
> mixer RF port with  the combined 10MHz and 14MHz signals. 

> The 10MHz signal can be extracted from the amplified 10MHz
> output via a splitter. 

> When  the loop gain and phasing is correct for both the 10MHz
> and 14MHz signals the circuit will produce the required output.
> Excess gain is eliminated by the mixers compression of the IF
> signal.

> The circuitry is all analog with no digital components whatsoever.

Thanks Bruce!

That is something I do understand, although the original
idea was to go from 8MHz to 10MHz, but I presume the 24MHz
can be filtered out from the overtones after running the
8MHz signal through a comparator.

Cheers,
Herbert

> Bruce

> On Sunday, 10 April 2016 12:10 PM, Will <zl1...@gmx.com> wrote:


>  Hi all,

> I'm fairly new here and might not fully understand things.

> Earlier in this thread it was suggested that one lock an 8Mhz
> signal to a 10 Mhz signal by analogue methods.

> To quote A Plummer:

> "and it is relative easy to make 10MHz from 8MHz with analog
> frequency manipulation, which generates less jitter
> 73"

> and H Poetzl asked the same thing as I am:

> "On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
>> and it is relative easy to make 10MHz from 8MHz with analog
>> frequency manipulation, which generates less jitter

> Could you elaborate on this a little if time permits?
> I'm more a 'digital person' but it sounds interesting.

> Thanks in advance,
> Herbert"

> I have not seen how that is done as suddenly the signals are 24Mhz and 10 Mhz 
> and digital dividers and multipliers are used.


> One other point. Attila mentioned using "LEA-M8T". I assume the T suffix 
> relates to Time rather than the plain GPS. What is the difference? Apart from 
> 50% higher cost.


> Cheers
> Will
> ZL1TAO


>> Sent: Sunday, April 10, 2016 at 7:00 AM
>> From: "Bob Camp" <kb...@n1k.org>
>> To: ewkeh...@aol.com, "Discussion of precise time and frequency measurement" 
>> <time-nuts@febo.com>
>> Subject: Re: [time-nuts] Advise on building a DIY GPSDO?

>> Hi

>> Averaged over a long enough time (and without any hanging bridges) the 
>> frequency accuracy 
>> will be fine. The frequency accuracy of a 1 pps output on a GPS is “fine” on 
>> the same basis. Since
>> 200 KHz is a “round division” off of any of the likely TCXO’s you will not 
>> have any jitter or spurs in the “static” 
>> case.

>> Bob


>>> On Apr 9, 2016, at 10:07 AM, Bert Kehren via time-nuts <time-nuts@febo.com> 
>>> wrote:

>>> I do not know what U blox does but I know when we use 200 KHz out of the 1  
>>> pps output on a $ 10 ublox 6 we consistently get better than 1 E-10 closer 
>>> to 1  E-11 out of the Morion have the data
>>> Bert Kehren


>>> In a message dated 4/9/2016 10:01:05 A.M. Eastern Daylight Time,  
>>> kb...@n1k.org writes:

>>> Hi

>>>> On Apr 8, 2016, at 9:39 PM, time...@metachaos.net  wrote:


>>>> Hello Bob,

>>>> Friday, April 8, 2016,  6:13:07 PM, you wrote:

>>>>> Hi

>>>>> If you  start from a 24 MHz TCXO (different modules use different TCXO’
>>> s):

>>>>> On an 8 MHz output, most of the time you divide by three.  

>>>>> On a 10 MHz output, you need to divide by 2.4. The net  result is that 
>>> you 
>>>>> divide by 2 sometimes and 3 other times.  

>>>>> In the 10 MHz case, there is a *lot* of energy at 12 MHz  and 8 MHz, 
>>> along with
>>>>> the 10 MHz output. 

>>>>> In  the 8 MHz case, most of the RF energy is at 8 MHz.

>>>>> 

>>>>> To correct the output by 1 ppm on the 8 MHz output,  you need to either 
>>> drop or
>>>>> add one pulse out of every million  pulses. Effectively you divide the 
>>> 24 MHz by
>>>>> 2 or by 4 when you do  that. You get a bit of 12 MHz or a bit of 6 MHz 
>>> as a result.
>>>> If you  know you are doing a 24Mhz and a 10Mhz, why not divide the first 
>>> by 12
>>>> and the second by 5 and then phase lock the resulting 2Mhz? Or divide by 
>>> 24
>>>> and 10, respectively and lock the 1Mhz? That way, everyth

Re: [time-nuts] Advise on building a DIY GPSDO?

[Hal Murray]

zl1...@gmx.com said:
> One other point. Attila mentioned using "LEA-M8T". I assume the T suffix
> relates to Time rather than the plain GPS. What is the difference? Apart
> from 50% higher cost. 

If you use GPS for navigation, you need 4 satellites to get 4 equations that 
you can solve for X, Y, Z, and T (or the polar equivalents).

If you know X, Y, and Z, you can get T from only 1 satellite.  You can also 
do a better job of sorting out the errors if you can hear multiple 
satellites.  That takes special firmware.


-- 
These are my opinions.  I hate spam.



___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Advise on building a DIY GPSDO?

[Bruce Griffiths]

It can easily be done using a variant of the dual conjugate regenerative 
divider.Feed the 24 MHz signal into the LO port of a mixer.Use a dual bandpass 
filters centred on 14MHz and 10MHz to filter the IF port amplify the outputs of 
the bandpass filters and drive the mixer RF port with  the combined 10MHz and 
14MHz signals. The 10MHz signal can be extracted from the amplified 10MHz 
output via a splitter. When  the loop gain and phasing is correct for both the 
10MHz and 14MHz signals the circuit will produce the required output. Excess 
gain is eliminated by the mixers compression of the IF signal.
The circuitry is all analog with no digital components whatsoever.

Bruce
 

On Sunday, 10 April 2016 12:10 PM, Will <zl1...@gmx.com> wrote:
 

 Hi all,

I'm fairly new here and might not fully understand things.

Earlier in this thread it was suggested that one lock an 8Mhz signal to a 10 
Mhz signal by analogue methods.

To quote A Plummer:

"and it is relative easy to make 10MHz from 8MHz with analog frequency
manipulation, which generates less jitter
73"

and H Poetzi asked the same thing as I am:

"On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
> and it is relative easy to make 10MHz from 8MHz with analog
> frequency manipulation, which generates less jitter

Could you elaborate on this a little if time permits?
I'm more a 'digital person' but it sounds interesting.

Thanks in advance,
Herbert"

I have not seen how that is done as suddenly the signals are 24Mhz and 10 Mhz 
and digital dividers and multipliers are used.


One other point. Attila mentioned using "LEA-M8T". I assume the T suffix 
relates to Time rather than the plain GPS. What is the difference? Apart from 
50% higher cost.


Cheers
Will
ZL1TAO


> Sent: Sunday, April 10, 2016 at 7:00 AM
> From: "Bob Camp" <kb...@n1k.org>
> To: ewkeh...@aol.com, "Discussion of precise time and frequency measurement" 
> <time-nuts@febo.com>
> Subject: Re: [time-nuts] Advise on building a DIY GPSDO?
>
> Hi
> 
> Averaged over a long enough time (and without any hanging bridges) the 
> frequency accuracy 
> will be fine. The frequency accuracy of a 1 pps output on a GPS is “fine” on 
> the same basis. Since
> 200 KHz is a “round division” off of any of the likely TCXO’s you will not 
> have any jitter or spurs in the “static” 
> case.
> 
> Bob
> 
> 
> > On Apr 9, 2016, at 10:07 AM, Bert Kehren via time-nuts <time-nuts@febo.com> 
> > wrote:
> > 
> > I do not know what U blox does but I know when we use 200 KHz out of the 1  
> > pps output on a $ 10 ublox 6 we consistently get better than 1 E-10 closer 
> > to 1  E-11 out of the Morion have the data
> > Bert Kehren
> > 
> > 
> > In a message dated 4/9/2016 10:01:05 A.M. Eastern Daylight Time,  
> > kb...@n1k.org writes:
> > 
> > Hi
> > 
> >> On Apr 8, 2016, at 9:39 PM, time...@metachaos.net  wrote:
> > 
> >> 
> >> Hello Bob,
> >> 
> >> Friday, April 8, 2016,  6:13:07 PM, you wrote:
> >> 
> >>> Hi
> >> 
> >>> If you  start from a 24 MHz TCXO (different modules use different TCXO’
> > s):
> >> 
> >>> On an 8 MHz output, most of the time you divide by three.  
> >> 
> >>> On a 10 MHz output, you need to divide by 2.4. The net  result is that 
> > you 
> >>> divide by 2 sometimes and 3 other times.  
> >> 
> >>> In the 10 MHz case, there is a *lot* of energy at 12 MHz  and 8 MHz, 
> > along with
> >>> the 10 MHz output. 
> >> 
> >>> In  the 8 MHz case, most of the RF energy is at 8 MHz.
> >> 
> >>> 
> >> 
> >>> To correct the output by 1 ppm on the 8 MHz output,  you need to either 
> > drop or
> >>> add one pulse out of every million  pulses. Effectively you divide the 
> > 24 MHz by
> >>> 2 or by 4 when you do  that. You get a bit of 12 MHz or a bit of 6 MHz 
> > as a result.
> >> If you  know you are doing a 24Mhz and a 10Mhz, why not divide the first 
> > by 12
> >> and the second by 5 and then phase lock the resulting 2Mhz? Or divide by 
> > 24
> >> and 10, respectively and lock the 1Mhz? That way, everything is  exact.
> > 
> > The bigger problem is that the 24 MHz is *not* exact. It is  simply a free 
> > running TCXO
> > that happens to be in a GPS module. It has a  basic accuracy of +/- 1 ppm 
> > or something 
> > similar. It is no better or worse  than any other TCXO you could buy. 
> > 
> > To make it accurate they have two  choices:
> > 
> > 1) Put a vo

Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi


To filter out the close in noise on the output of the GPS module (regardless of
output frequency) you need a very narrow bandwidth loop. Cross over points in 
the 
0.01 Hz to < 0.001 Hz range are not at all unusual for these loops. Starting 
off at a high(er)
frequency does not help in this case. 
 
The module puts out information on the serial port that “corrects” the PPS 
output by 
more than an order of magnitude over the correction on the other outputs. That 
makes 
it more attractive than a higher frequency output (it’s more accurate). The 
only reason 
not to use it would be if the PLL is easier. With the very narrow bandwidth 
involved, there 
is no significant advantage in the PLL. 

Bob

> On Apr 9, 2016, at 6:20 PM, Will <zl1...@gmx.com> wrote:
> 
> Hi all,
> 
> I'm fairly new here and might not fully understand things.
> 
> Earlier in this thread it was suggested that one lock an 8Mhz signal to a 10 
> Mhz signal by analogue methods.
> 
> To quote A Plummer:
> 
> "and it is relative easy to make 10MHz from 8MHz with analog frequency
> manipulation, which generates less jitter
> 73"
> 
> and H Poetzi asked the same thing as I am:
> 
> "On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
>> and it is relative easy to make 10MHz from 8MHz with analog
>> frequency manipulation, which generates less jitter
> 
> Could you elaborate on this a little if time permits?
> I'm more a 'digital person' but it sounds interesting.
> 
> Thanks in advance,
> Herbert"
> 
> I have not seen how that is done as suddenly the signals are 24Mhz and 10 Mhz 
> and digital dividers and multipliers are used.
> 
> 
> One other point. Attila mentioned using "LEA-M8T". I assume the T suffix 
> relates to Time rather than the plain GPS. What is the difference? Apart from 
> 50% higher cost.
> 
> 
> Cheers
> Will
> ZL1TAO
> 
> 
>> Sent: Sunday, April 10, 2016 at 7:00 AM
>> From: "Bob Camp" <kb...@n1k.org>
>> To: ewkeh...@aol.com, "Discussion of precise time and frequency measurement" 
>> <time-nuts@febo.com>
>> Subject: Re: [time-nuts] Advise on building a DIY GPSDO?
>> 
>> Hi
>> 
>> Averaged over a long enough time (and without any hanging bridges) the 
>> frequency accuracy 
>> will be fine. The frequency accuracy of a 1 pps output on a GPS is “fine” on 
>> the same basis. Since
>> 200 KHz is a “round division” off of any of the likely TCXO’s you will not 
>> have any jitter or spurs in the “static” 
>> case.
>> 
>> Bob
>> 
>> 
>>> On Apr 9, 2016, at 10:07 AM, Bert Kehren via time-nuts <time-nuts@febo.com> 
>>> wrote:
>>> 
>>> I do not know what U blox does but I know when we use 200 KHz out of the 1  
>>> pps output on a $ 10 ublox 6 we consistently get better than 1 E-10 closer 
>>> to 1  E-11 out of the Morion have the data
>>> Bert Kehren
>>> 
>>> 
>>> In a message dated 4/9/2016 10:01:05 A.M. Eastern Daylight Time,  
>>> kb...@n1k.org writes:
>>> 
>>> Hi
>>> 
>>>> On Apr 8, 2016, at 9:39 PM, time...@metachaos.net  wrote:
>>> 
>>>> 
>>>> Hello Bob,
>>>> 
>>>> Friday, April 8, 2016,  6:13:07 PM, you wrote:
>>>> 
>>>>> Hi
>>>> 
>>>>> If you  start from a 24 MHz TCXO (different modules use different TCXO’
>>> s):
>>>> 
>>>>> On an 8 MHz output, most of the time you divide by three.  
>>>> 
>>>>> On a 10 MHz output, you need to divide by 2.4. The net  result is that 
>>> you 
>>>>> divide by 2 sometimes and 3 other times.  
>>>> 
>>>>> In the 10 MHz case, there is a *lot* of energy at 12 MHz  and 8 MHz, 
>>> along with
>>>>> the 10 MHz output. 
>>>> 
>>>>> In  the 8 MHz case, most of the RF energy is at 8 MHz.
>>>> 
>>>>> 
>>>> 
>>>>> To correct the output by 1 ppm on the 8 MHz output,  you need to either 
>>> drop or
>>>>> add one pulse out of every million  pulses. Effectively you divide the 
>>> 24 MHz by
>>>>> 2 or by 4 when you do  that. You get a bit of 12 MHz or a bit of 6 MHz 
>>> as a result.
>>>> If you  know you are doing a 24Mhz and a 10Mhz, why not divide the first 
>>> by 12
>>>> and the second by 5 and then phase lock the resulting 2Mhz? Or divide by 
>>> 24
>>>> and 10, respectively and lock the 1M

Re: [time-nuts] Advise on building a DIY GPSDO?

[Will]

Hi all,

I'm fairly new here and might not fully understand things.

Earlier in this thread it was suggested that one lock an 8Mhz signal to a 10 
Mhz signal by analogue methods.

To quote A Plummer:

"and it is relative easy to make 10MHz from 8MHz with analog frequency
manipulation, which generates less jitter
73"

and H Poetzi asked the same thing as I am:

"On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
> and it is relative easy to make 10MHz from 8MHz with analog
> frequency manipulation, which generates less jitter

Could you elaborate on this a little if time permits?
I'm more a 'digital person' but it sounds interesting.

Thanks in advance,
Herbert"

I have not seen how that is done as suddenly the signals are 24Mhz and 10 Mhz 
and digital dividers and multipliers are used.


One other point. Attila mentioned using "LEA-M8T". I assume the T suffix 
relates to Time rather than the plain GPS. What is the difference? Apart from 
50% higher cost.


Cheers
Will
ZL1TAO


> Sent: Sunday, April 10, 2016 at 7:00 AM
> From: "Bob Camp" <kb...@n1k.org>
> To: ewkeh...@aol.com, "Discussion of precise time and frequency measurement" 
> <time-nuts@febo.com>
> Subject: Re: [time-nuts] Advise on building a DIY GPSDO?
>
> Hi
> 
> Averaged over a long enough time (and without any hanging bridges) the 
> frequency accuracy 
> will be fine. The frequency accuracy of a 1 pps output on a GPS is “fine” on 
> the same basis. Since
> 200 KHz is a “round division” off of any of the likely TCXO’s you will not 
> have any jitter or spurs in the “static” 
> case.
> 
> Bob
> 
> 
> > On Apr 9, 2016, at 10:07 AM, Bert Kehren via time-nuts <time-nuts@febo.com> 
> > wrote:
> > 
> > I do not know what U blox does but I know when we use 200 KHz out of the 1  
> > pps output on a $ 10 ublox 6 we consistently get better than 1 E-10 closer 
> > to 1  E-11 out of the Morion have the data
> > Bert Kehren
> > 
> > 
> > In a message dated 4/9/2016 10:01:05 A.M. Eastern Daylight Time,  
> > kb...@n1k.org writes:
> > 
> > Hi
> > 
> >> On Apr 8, 2016, at 9:39 PM, time...@metachaos.net  wrote:
> > 
> >> 
> >> Hello Bob,
> >> 
> >> Friday, April 8, 2016,  6:13:07 PM, you wrote:
> >> 
> >>> Hi
> >> 
> >>> If you  start from a 24 MHz TCXO (different modules use different TCXO’
> > s):
> >> 
> >>> On an 8 MHz output, most of the time you divide by three.  
> >> 
> >>> On a 10 MHz output, you need to divide by 2.4. The net  result is that 
> > you 
> >>> divide by 2 sometimes and 3 other times.  
> >> 
> >>> In the 10 MHz case, there is a *lot* of energy at 12 MHz  and 8 MHz, 
> > along with
> >>> the 10 MHz output. 
> >> 
> >>> In  the 8 MHz case, most of the RF energy is at 8 MHz.
> >> 
> >>> 
> >> 
> >>> To correct the output by 1 ppm on the 8 MHz output,  you need to either 
> > drop or
> >>> add one pulse out of every million  pulses. Effectively you divide the 
> > 24 MHz by
> >>> 2 or by 4 when you do  that. You get a bit of 12 MHz or a bit of 6 MHz 
> > as a result.
> >> If you  know you are doing a 24Mhz and a 10Mhz, why not divide the first 
> > by 12
> >> and the second by 5 and then phase lock the resulting 2Mhz? Or divide by 
> > 24
> >> and 10, respectively and lock the 1Mhz? That way, everything is  exact.
> > 
> > The bigger problem is that the 24 MHz is *not* exact. It is  simply a free 
> > running TCXO
> > that happens to be in a GPS module. It has a  basic accuracy of +/- 1 ppm 
> > or something 
> > similar. It is no better or worse  than any other TCXO you could buy. 
> > 
> > To make it accurate they have two  choices:
> > 
> > 1) Put a voltage control input on the TCXO and turn it into a  TCVCXO, then 
> > lock it up 
> > with a loop.
> > 
> > 2) Let the oscillator free run  and “fix up” the output.
> > 
> > For a variety of reasons, none of the small  GPS modules go with option 
> > number 1. They 
> > all go with option number 2. The  24 Hz error on the (maybe)  24 MHz gets 
> > taken out by dropping
> > 24 edges  every second. That’s not a lot of edges, it’s not going to turn 
> > the output  into absolute 
> > garbage you can see on a scope. It is plenty of nonsense to  mess up a 
> > radio or a piece of test gear. 
> > 
> > One easy way to look at it:  You have ~1 ppm jitter on the output (in the 
> &g

Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi

Averaged over a long enough time (and without any hanging bridges) the 
frequency accuracy 
will be fine. The frequency accuracy of a 1 pps output on a GPS is “fine” on 
the same basis. Since
200 KHz is a “round division” off of any of the likely TCXO’s you will not have 
any jitter or spurs in the “static” 
case.

Bob


> On Apr 9, 2016, at 10:07 AM, Bert Kehren via time-nuts  
> wrote:
> 
> I do not know what U blox does but I know when we use 200 KHz out of the 1  
> pps output on a $ 10 ublox 6 we consistently get better than 1 E-10 closer 
> to 1  E-11 out of the Morion have the data
> Bert Kehren
> 
> 
> In a message dated 4/9/2016 10:01:05 A.M. Eastern Daylight Time,  
> kb...@n1k.org writes:
> 
> Hi
> 
>> On Apr 8, 2016, at 9:39 PM, time...@metachaos.net  wrote:
> 
>> 
>> Hello Bob,
>> 
>> Friday, April 8, 2016,  6:13:07 PM, you wrote:
>> 
>>> Hi
>> 
>>> If you  start from a 24 MHz TCXO (different modules use different TCXO’
> s):
>> 
>>> On an 8 MHz output, most of the time you divide by three.  
>> 
>>> On a 10 MHz output, you need to divide by 2.4. The net  result is that 
> you 
>>> divide by 2 sometimes and 3 other times.  
>> 
>>> In the 10 MHz case, there is a *lot* of energy at 12 MHz  and 8 MHz, 
> along with
>>> the 10 MHz output. 
>> 
>>> In  the 8 MHz case, most of the RF energy is at 8 MHz.
>> 
>>> 
>> 
>>> To correct the output by 1 ppm on the 8 MHz output,  you need to either 
> drop or
>>> add one pulse out of every million  pulses. Effectively you divide the 
> 24 MHz by
>>> 2 or by 4 when you do  that. You get a bit of 12 MHz or a bit of 6 MHz 
> as a result.
>> If you  know you are doing a 24Mhz and a 10Mhz, why not divide the first 
> by 12
>> and the second by 5 and then phase lock the resulting 2Mhz? Or divide by 
> 24
>> and 10, respectively and lock the 1Mhz? That way, everything is  exact.
> 
> The bigger problem is that the 24 MHz is *not* exact. It is  simply a free 
> running TCXO
> that happens to be in a GPS module. It has a  basic accuracy of +/- 1 ppm 
> or something 
> similar. It is no better or worse  than any other TCXO you could buy. 
> 
> To make it accurate they have two  choices:
> 
> 1) Put a voltage control input on the TCXO and turn it into a  TCVCXO, then 
> lock it up 
> with a loop.
> 
> 2) Let the oscillator free run  and “fix up” the output.
> 
> For a variety of reasons, none of the small  GPS modules go with option 
> number 1. They 
> all go with option number 2. The  24 Hz error on the (maybe)  24 MHz gets 
> taken out by dropping
> 24 edges  every second. That’s not a lot of edges, it’s not going to turn 
> the output  into absolute 
> garbage you can see on a scope. It is plenty of nonsense to  mess up a 
> radio or a piece of test gear. 
> 
> One easy way to look at it:  You have ~1 ppm jitter on the output (in the 
> example of 1 ppm of error). A  
> phase locked GPSDO with only simple filtering of a 1 pps would get you  
> down to 0.01 ppm of jitter. 
> A sawtooth corrected 1 pps would get you to  0.01 ppm. A good filter would 
> get you to <0.1 ppm.
> Yes, I’m using a  very hand waving definition of jitter here, but it does 
> illustrate the point.  You could 
> look at the jitter on the pulse drop as 0.04 ppm.  
> 
> Bob
> 
>> 
>> 
>> Mike
>> 
>>> That can  be filtered out with a RF filter. The same is true with a 
> (somewhat  more
>>> complex) filter on the 10 MHz output.
>> 
>>> In  addition to the “big” RF spurs, you get a low frequency component 
> to the  output
>>> modulation. You are “phase hitting” the output eight times  a second. 
> That gives you
>>> an 8 Hz sideband along with the further  removed stuff. Since it’s not 
> simple / clean
>>> phase modulation,  there are more sidebands than just the few mentioned 
> above. 
>> 
>>> What messes things up even more is that you never are quite doing  one 
> ppm. You are doing
>>> corrections like 0.12356 ppm this second  and 0.120201 ppm the next 
> second. 
>>> The pattern of pulse drop and  add is not as simple as you might hope. 
> The low 
>>> frequency part of  the jitter (and it will be there) is no different 
> than the noise  on
>>> a 1 pps output. You still need to do very long time constant  (or very 
> narrow band)
>>> filtering to take it out. 
>> 
>>> Bob
>> 
 On Apr 8, 2016, at 7:06 AM, Herbert  Poetzl  
> wrote:
 
 On  Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer  wrote:
> and it is relative easy to make 10MHz from 8MHz  with analog
> frequency manipulation, which generates less  jitter
 
 Could you elaborate on this a little  if time permits? 
 I'm more a 'digital person' but it sounds  interesting.
 
 Thanks in  advance,
 Herbert
 
> 73
 
> On 4/4/2016 4:27 PM, Attila Kinali  wrote:
>> On Mon, 4 Apr 2016 17:56:29  -0400
>> Bob Camp   wrote:
 
>>> The variable frequency  output on the uBlox (and other) GPS

Re: [time-nuts] Advise on building a DIY GPSDO?

[Bert Kehren via time-nuts]

I do not know what U blox does but I know when we use 200 KHz out of the 1  
pps output on a $ 10 ublox 6 we consistently get better than 1 E-10 closer 
to 1  E-11 out of the Morion have the data
Bert Kehren
 
 
In a message dated 4/9/2016 10:01:05 A.M. Eastern Daylight Time,  
kb...@n1k.org writes:

Hi

> On Apr 8, 2016, at 9:39 PM, time...@metachaos.net  wrote:

> 
> Hello Bob,
> 
> Friday, April 8, 2016,  6:13:07 PM, you wrote:
> 
>> Hi
> 
>> If you  start from a 24 MHz TCXO (different modules use different TCXO’
s):
>  
>> On an 8 MHz output, most of the time you divide by three.  
> 
>> On a 10 MHz output, you need to divide by 2.4. The net  result is that 
you 
>> divide by 2 sometimes and 3 other times.  
> 
>> In the 10 MHz case, there is a *lot* of energy at 12 MHz  and 8 MHz, 
along with
>> the 10 MHz output. 
> 
>> In  the 8 MHz case, most of the RF energy is at 8 MHz.
> 
>>  
> 
>> To correct the output by 1 ppm on the 8 MHz output,  you need to either 
drop or
>> add one pulse out of every million  pulses. Effectively you divide the 
24 MHz by
>> 2 or by 4 when you do  that. You get a bit of 12 MHz or a bit of 6 MHz 
as a result.
> If you  know you are doing a 24Mhz and a 10Mhz, why not divide the first 
by 12
>  and the second by 5 and then phase lock the resulting 2Mhz? Or divide by 
 24
> and 10, respectively and lock the 1Mhz? That way, everything is  exact.

The bigger problem is that the 24 MHz is *not* exact. It is  simply a free 
running TCXO
that happens to be in a GPS module. It has a  basic accuracy of +/- 1 ppm 
or something 
similar. It is no better or worse  than any other TCXO you could buy. 

To make it accurate they have two  choices:

1) Put a voltage control input on the TCXO and turn it into a  TCVCXO, then 
lock it up 
with a loop.

2) Let the oscillator free run  and “fix up” the output.

For a variety of reasons, none of the small  GPS modules go with option 
number 1. They 
all go with option number 2. The  24 Hz error on the (maybe)  24 MHz gets 
taken out by dropping
24 edges  every second. That’s not a lot of edges, it’s not going to turn 
the output  into absolute 
garbage you can see on a scope. It is plenty of nonsense to  mess up a 
radio or a piece of test gear. 

One easy way to look at it:  You have ~1 ppm jitter on the output (in the 
example of 1 ppm of error). A  
phase locked GPSDO with only simple filtering of a 1 pps would get you  
down to 0.01 ppm of jitter. 
A sawtooth corrected 1 pps would get you to  0.01 ppm. A good filter would 
get you to <0.1 ppm.
Yes, I’m using a  very hand waving definition of jitter here, but it does 
illustrate the point.  You could 
look at the jitter on the pulse drop as 0.04 ppm.  

Bob

> 
> 
> Mike
> 
>> That can  be filtered out with a RF filter. The same is true with a 
(somewhat  more
>> complex) filter on the 10 MHz output.
> 
>> In  addition to the “big” RF spurs, you get a low frequency component 
to the  output
>> modulation. You are “phase hitting” the output eight times  a second. 
That gives you
>> an 8 Hz sideband along with the further  removed stuff. Since it’s not 
simple / clean
>> phase modulation,  there are more sidebands than just the few mentioned 
above. 
>  
>> What messes things up even more is that you never are quite doing  one 
ppm. You are doing
>> corrections like 0.12356 ppm this second  and 0.120201 ppm the next 
second. 
>> The pattern of pulse drop and  add is not as simple as you might hope. 
The low 
>> frequency part of  the jitter (and it will be there) is no different 
than the noise  on
>> a 1 pps output. You still need to do very long time constant  (or very 
narrow band)
>> filtering to take it out. 
>  
>> Bob
> 
>>> On Apr 8, 2016, at 7:06 AM, Herbert  Poetzl  
wrote:
>>> 
>>> On  Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer  wrote:
 and it is relative easy to make 10MHz from 8MHz  with analog
 frequency manipulation, which generates less  jitter
>>> 
>>> Could you elaborate on this a little  if time permits? 
>>> I'm more a 'digital person' but it sounds  interesting.
>>> 
>>> Thanks in  advance,
>>> Herbert
>>> 
  73
>>> 
 On 4/4/2016 4:27 PM, Attila Kinali  wrote:
> On Mon, 4 Apr 2016 17:56:29  -0400
> Bob Camp   wrote:
>>> 
>> The variable frequency  output on the uBlox (and other) GPS
>> receivers has  come up many times in the past.
>>> 
>>  If you dig into the archives you can find quite a bit  of
>> data on the (lack of) performance of the  high(er) frequency
>> outputs from the various GPS  modules. They all depend on
>> cycle add / drop at  the frequency of their free running TCXO.
>>  Regardless of the output frequency, that will put a *lot*  of
>> jitter into the output.
>  That's why you should put the output frequency of the ublox  modules
> to an integer divisor of 24MHz. Ie 8MHz works  but not 10MHz.
>>> 
>   Attila Kinali
>>>  
>>> 

Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi



> On Apr 8, 2016, at 10:31 PM, Graham / KE9H  wrote:
> 
> The lowest jitter way to do this kind of conversion is to multiply the
> signal up to some common multiple frequency, then divide it back down to
> where you want to be.  For instance, with 8 or 24 MHz, multiply up to 240
> MHz, then divide by 24 to get 10 MHz.
> 
> Modern clock generator chips have this capability built in.  As an example,
> the TI LMK04100 series clock chip.  It actually has an on-board 1200 MHz
> VCO, and all the phase-lock loop hardware to multiply up, and, and five
> different divider chains, so you can get up to five different output
> frequencies as long as the math works out.  Everything is constrained to
> integer multiples and integer division, so there is none of the dithering
> discussed above.  But you have a lot of integer options when the common
> multiple is up at 1200 MHz. Much lower sidebands and phase noise.  Also the
> ability to add a crystal VCO as a clean-up filter loop if your input
> reference is dirty to begin with.
> 
> In my application, I am looking at taking a 10 MHz Oven-VCXO input and
> putting out both a 24 MHz clock for the master clock of a BeagleBone Black,
> and 480 kHz for a Shera style control loop for GPS disciplining.
> 
> --- Graham
> 
> ==

In the context of the original question:

There is no setting on the GPS module to multiply the clock frequency 
internally 
and then divide it. The only settings on the module are for outputs at or below
the internal TCXO frequency. 

Bob


> 
> On Fri, Apr 8, 2016 at 5:13 PM, Bob Camp  wrote:
> 
>> Hi
>> 
>> If you start from a 24 MHz TCXO (different modules use different TCXO’s):
>> 
>> On an 8 MHz output, most of the time you divide by three.
>> 
>> On a 10 MHz output, you need to divide by 2.4. The net result is that you
>> divide by 2 sometimes and 3 other times.
>> 
>> In the 10 MHz case, there is a *lot* of energy at 12 MHz and 8 MHz, along
>> with
>> the 10 MHz output.
>> 
>> In the 8 MHz case, most of the RF energy is at 8 MHz.
>> 
>> 
>> 
>> To correct the output by 1 ppm on the 8 MHz output, you need to either
>> drop or
>> add one pulse out of every million pulses. Effectively you divide the 24
>> MHz by
>> 2 or by 4 when you do that. You get a bit of 12 MHz or a bit of 6 MHz as a
>> result.
>> That can be filtered out with a RF filter. The same is true with a
>> (somewhat more
>> complex) filter on the 10 MHz output.
>> 
>> In addition to the “big” RF spurs, you get a low frequency component to
>> the output
>> modulation. You are “phase hitting” the output eight times a second. That
>> gives you
>> an 8 Hz sideband along with the further removed stuff. Since it’s not
>> simple / clean
>> phase modulation, there are more sidebands than just the few mentioned
>> above.
>> 
>> What messes things up even more is that you never are quite doing one ppm.
>> You are doing
>> corrections like 0.12356 ppm this second and 0.120201 ppm the next second.
>> The pattern of pulse drop and add is not as simple as you might hope. The
>> low
>> frequency part of the jitter (and it will be there) is no different than
>> the noise on
>> a 1 pps output. You still need to do very long time constant (or very
>> narrow band)
>> filtering to take it out.
>> 
>> Bob
>> 
>>> On Apr 8, 2016, at 7:06 AM, Herbert Poetzl  wrote:
>>> 
>>> On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
 and it is relative easy to make 10MHz from 8MHz with analog
 frequency manipulation, which generates less jitter
>>> 
>>> Could you elaborate on this a little if time permits?
>>> I'm more a 'digital person' but it sounds interesting.
>>> 
>>> Thanks in advance,
>>> Herbert
>>> 
 73
>>> 
 On 4/4/2016 4:27 PM, Attila Kinali wrote:
> On Mon, 4 Apr 2016 17:56:29 -0400
> Bob Camp  wrote:
>>> 
>> The variable frequency output on the uBlox (and other) GPS
>> receivers has come up many times in the past.
>>> 
>> If you dig into the archives you can find quite a bit of
>> data on the (lack of) performance of the high(er) frequency
>> outputs from the various GPS modules. They all depend on
>> cycle add / drop at the frequency of their free running TCXO.
>> Regardless of the output frequency, that will put a *lot* of
>> jitter into the output.
> That's why you should put the output frequency of the ublox modules
> to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.
>>> 
>Attila Kinali
>>> 
>>> 
 ___
 time-nuts mailing list -- time-nuts@febo.com
 To unsubscribe, go to
 https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
 and follow the instructions there.
>>> ___
>>> time-nuts mailing list -- time-nuts@febo.com
>>> To unsubscribe, go to
>> 

Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi

> On Apr 8, 2016, at 9:39 PM, time...@metachaos.net wrote:
> 
> Hello Bob,
> 
> Friday, April 8, 2016, 6:13:07 PM, you wrote:
> 
>> Hi
> 
>> If you start from a 24 MHz TCXO (different modules use different TCXO’s):
> 
>> On an 8 MHz output, most of the time you divide by three. 
> 
>> On a 10 MHz output, you need to divide by 2.4. The net result is that you 
>> divide by 2 sometimes and 3 other times. 
> 
>> In the 10 MHz case, there is a *lot* of energy at 12 MHz and 8 MHz, along 
>> with
>> the 10 MHz output. 
> 
>> In the 8 MHz case, most of the RF energy is at 8 MHz.
> 
>> 
> 
>> To correct the output by 1 ppm on the 8 MHz output, you need to either drop 
>> or
>> add one pulse out of every million pulses. Effectively you divide the 24 MHz 
>> by
>> 2 or by 4 when you do that. You get a bit of 12 MHz or a bit of 6 MHz as a 
>> result.
> If you know you are doing a 24Mhz and a 10Mhz, why not divide the first by 12
> and the second by 5 and then phase lock the resulting 2Mhz? Or divide by 24
> and 10, respectively and lock the 1Mhz? That way, everything is exact.

The bigger problem is that the 24 MHz is *not* exact. It is simply a free 
running TCXO
that happens to be in a GPS module. It has a basic accuracy of +/- 1 ppm or 
something 
similar. It is no better or worse than any other TCXO you could buy. 

To make it accurate they have two choices:

1) Put a voltage control input on the TCXO and turn it into a TCVCXO, then lock 
it up 
with a loop.

2) Let the oscillator free run and “fix up” the output.

For a variety of reasons, none of the small GPS modules go with option number 
1. They 
all go with option number 2. The 24 Hz error on the (maybe)  24 MHz gets taken 
out by dropping
24 edges every second. That’s not a lot of edges, it’s not going to turn the 
output into absolute 
garbage you can see on a scope. It is plenty of nonsense to mess up a radio or 
a piece of test gear. 

One easy way to look at it: You have ~1 ppm jitter on the output (in the 
example of 1 ppm of error). A 
phase locked GPSDO with only simple filtering of a 1 pps would get you down to 
0.01 ppm of jitter. 
A sawtooth corrected 1 pps would get you to 0.01 ppm. A good filter would get 
you to <0.1 ppm.
Yes, I’m using a very hand waving definition of jitter here, but it does 
illustrate the point. You could 
look at the jitter on the pulse drop as 0.04 ppm. 

Bob

> 
> 
> Mike
> 
>> That can be filtered out with a RF filter. The same is true with a (somewhat 
>> more
>> complex) filter on the 10 MHz output.
> 
>> In addition to the “big” RF spurs, you get a low frequency component to the 
>> output
>> modulation. You are “phase hitting” the output eight times a second. That 
>> gives you
>> an 8 Hz sideband along with the further removed stuff. Since it’s not simple 
>> / clean
>> phase modulation, there are more sidebands than just the few mentioned 
>> above. 
> 
>> What messes things up even more is that you never are quite doing one ppm. 
>> You are doing
>> corrections like 0.12356 ppm this second and 0.120201 ppm the next second. 
>> The pattern of pulse drop and add is not as simple as you might hope. The 
>> low 
>> frequency part of the jitter (and it will be there) is no different than the 
>> noise on
>> a 1 pps output. You still need to do very long time constant (or very narrow 
>> band)
>> filtering to take it out. 
> 
>> Bob
> 
>>> On Apr 8, 2016, at 7:06 AM, Herbert Poetzl  wrote:
>>> 
>>> On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
 and it is relative easy to make 10MHz from 8MHz with analog
 frequency manipulation, which generates less jitter
>>> 
>>> Could you elaborate on this a little if time permits? 
>>> I'm more a 'digital person' but it sounds interesting.
>>> 
>>> Thanks in advance,
>>> Herbert
>>> 
 73
>>> 
 On 4/4/2016 4:27 PM, Attila Kinali wrote:
> On Mon, 4 Apr 2016 17:56:29 -0400
> Bob Camp  wrote:
>>> 
>> The variable frequency output on the uBlox (and other) GPS
>> receivers has come up many times in the past.
>>> 
>> If you dig into the archives you can find quite a bit of
>> data on the (lack of) performance of the high(er) frequency
>> outputs from the various GPS modules. They all depend on
>> cycle add / drop at the frequency of their free running TCXO.
>> Regardless of the output frequency, that will put a *lot* of
>> jitter into the output.
> That's why you should put the output frequency of the ublox modules
> to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.
>>> 
>Attila Kinali
>>> 
>>> 
 ___
 time-nuts mailing list -- time-nuts@febo.com
 To unsubscribe, go to 
 https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
 and follow the instructions there.
>>> ___
>>> time-nuts mailing list -- time-nuts@febo.com

Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi

> On Apr 8, 2016, at 10:35 PM, Herbert Poetzl  wrote:
> 
> On Fri, Apr 08, 2016 at 06:13:07PM -0400, Bob Camp wrote:
>> Hi
> 
>> If you start from a 24 MHz TCXO (different modules use
>> different TCXO’s):
> 
>> On an 8 MHz output, most of the time you divide by three. 
> 
>> On a 10 MHz output, you need to divide by 2.4. 
>> The net result is that you divide by 2 sometimes and 3 
>> other times.   
> 
>> In the 10 MHz case, there is a *lot* of energy at 12 MHz 
>> and 8 MHz, along with the 10 MHz output. 
> 
>> In the 8 MHz case, most of the RF energy is at 8 MHz.
> 
> Thanks for the input, but alternating between dividing
> by two and three doesn't really sound like "analog 
> frequency manipulation" to me.
> 
> Maybe I'm completely wrong here, maybe I just need to
> see an analog circuit which does this.

This is exactly what the GPS module is doing when it creates the output from 
the 24 MHz clock. 
Unless there is another clock in the system, all the output transitions take 
place on a 24 MHz edge.
The net result is a drop / add of pulses.The alternatives are:

1) Use a higher clock rate (24 MHz was given earlier)

2) Phase lock an oscillator (the modules do not do this)

3) Do the phasing / DSB / SSB stuff that NIST likes (again, not done in these 
modules). 

4) Do a full DDS and put out an analog waveform.

5) Run a DDS through a very narrow filter

That’s pretty much a complete list. Number 2, 3 and 5 are narrowband, so that 
makes them unattractive 
for a general purpose output. The pulse drop and add stuff is cheap and easy.  
Number 4 does not
produce a logic output and at a ratio like 24 to 10 has many of the same spur 
issues. 

Bob


> 
> Best,
> Herbert
> 
>> 
> 
>> To correct the output by 1 ppm on the 8 MHz output, you 
>> need to either drop or add one pulse out of every million
>> pulses. Effectively you divide the 24 MHz by 2 or by 4 
>> when you do that. 
> 
>> You get a bit of 12 MHz or a bit of 6 MHz as a result.
>> That can be filtered out with a RF filter. 
> 
>> The same is true with a (somewhat more complex) filter 
>> on the 10 MHz output.
> 
>> In addition to the “big” RF spurs, you get a low frequency 
>> component to the output modulation. 
> 
>> You are “phase hitting” the output eight times a second. 
> 
>> That gives you an 8 Hz sideband along with the further 
>> removed stuff. Since it’s not simple / clean phase 
>> modulation, there are more sidebands than just the few 
>> mentioned above.
> 
>> What messes things up even more is that you never are quite
>> doing one ppm. You are doing corrections like 0.12356 ppm  
>> this second and 0.120201 ppm the next second. The pattern 
>> of pulse drop and add is not as simple as you might hope. 
> 
>> The low frequency part of the jitter (and it will be there) is
>> no different than the noise on a 1 pps output. You still need
>> to do very long time constant (or very narrow band) filtering
>> to take it out.
> 
>> Bob
> 
>>> On Apr 8, 2016, at 7:06 AM, Herbert Poetzl  wrote:
> 
>>> On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
 and it is relative easy to make 10MHz from 8MHz with analog
 frequency manipulation, which generates less jitter
> 
>>> Could you elaborate on this a little if time permits? 
>>> I'm more a 'digital person' but it sounds interesting.
> 
>>> Thanks in advance,
>>> Herbert
> 
 73
> 
 On 4/4/2016 4:27 PM, Attila Kinali wrote:
> On Mon, 4 Apr 2016 17:56:29 -0400
> Bob Camp  wrote:
> 
>> The variable frequency output on the uBlox (and other) GPS
>> receivers has come up many times in the past.
> 
>> If you dig into the archives you can find quite a bit of
>> data on the (lack of) performance of the high(er) frequency
>> outputs from the various GPS modules. They all depend on
>> cycle add / drop at the frequency of their free running TCXO.
>> Regardless of the output frequency, that will put a *lot* of
>> jitter into the output.
> That's why you should put the output frequency of the ublox modules
> to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.
> 
>   Attila Kinali
> 
> 
 ___
 time-nuts mailing list -- time-nuts@febo.com
 To unsubscribe, go to 
 https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
 and follow the instructions there.
>>> ___
>>> time-nuts mailing list -- time-nuts@febo.com
>>> To unsubscribe, go to 
>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
> 
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
> ___
> time-nuts mailing 

Re: [time-nuts] Advise on building a DIY GPSDO?

[Attila Kinali]

On Fri, 8 Apr 2016 21:31:31 -0500
"Graham / KE9H"  wrote:

> The lowest jitter way to do this kind of conversion is to multiply the
> signal up to some common multiple frequency, then divide it back down to
> where you want to be.  For instance, with 8 or 24 MHz, multiply up to 240
> MHz, then divide by 24 to get 10 MHz.

In this case, I would rather recommend against multiplying up first.
The added complexity (which is quite a bit, compared to a simple digital
divider) is managable, but there is an issue with intermodulation products
that is not so easy to deal with:

The input signal, which comes out of a digital "synthesis" chain within
the GPS module, is anything but clean. There are lots of spurs close to
the carrier. Due to this, the multiplied signal will contain lots of
intermodulation products, which will degrade the signal considerably.
And these intermodulation products will not magically vanish once you
divide down again. It would be better to multiply the 10MHz signal up
to 60MHz and divide down to 12MHz instead.

Additionally to this, keep in mind that division will decrease the noise
floor with only 10*log(N) when done using digital division instead of
the 20*log(N) when done analog (using regenerative dividers, lamda dividers
and such). Ie, multiplying a signal by 10 and then dividing it down by 10 
using digital logic will increase the noise floor by 10dB. (see [1])

Given all this, the gain in performance using a multiply-divide chain
for the PLL instead of a divide-divide chain, is irelevant considering
how dirty the GPS module provided reference frequency is.

Attila Kinali


[1] "The sampling theorem in Pi and Lambda dividers", 
by Calosso, Rubiola, 2013, 
http://rubiola.org/pdf-articles/conference/2013-ifcs-Frequency-dividers.pdf
slides: http://rubiola.org/pdf-slides/2013C-IFCS--Dividers.pdf

-- 
Reading can seriously damage your ignorance.
-- unknown
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and follow the instructions there.

Re: [time-nuts] Advise on building a DIY GPSDO?

[Bert Kehren via time-nuts]

Am I missing something? KISS. If you start out with a 10 MHz OCXO use a tvb 
 PIC to divide down to a lower frequency a 74HC74 to get symmetrical output 
of a  $ 10 u-blox 6 and the PIC and 86 XOR. If no PIC capability ebay has 
LS90's for a  one off. 
Bert Kehren
 
 
In a message dated 4/9/2016 7:06:26 A.M. Eastern Daylight Time,  
ke9h.gra...@gmail.com writes:

The lowest  jitter way to do this kind of conversion is to multiply the
signal up to  some common multiple frequency, then divide it back down to
where you want  to be.  For instance, with 8 or 24 MHz, multiply up to 240
MHz, then  divide by 24 to get 10 MHz.

Modern clock generator chips have this  capability built in.  As an example,
the TI LMK04100 series clock  chip.  It actually has an on-board 1200 MHz
VCO, and all the  phase-lock loop hardware to multiply up, and, and five
different divider  chains, so you can get up to five different output
frequencies as long as  the math works out.  Everything is constrained to
integer multiples  and integer division, so there is none of the dithering
discussed  above.  But you have a lot of integer options when the common
multiple  is up at 1200 MHz. Much lower sidebands and phase noise.  Also  
the
ability to add a crystal VCO as a clean-up filter loop if your  input
reference is dirty to begin with.

In my application, I am  looking at taking a 10 MHz Oven-VCXO input and
putting out both a 24 MHz  clock for the master clock of a BeagleBone Black,
and 480 kHz for a Shera  style control loop for GPS disciplining.

--- Graham

==

On  Fri, Apr 8, 2016 at 5:13 PM, Bob Camp  wrote:

>  Hi
>
> If you start from a 24 MHz TCXO (different modules use  different TCXO’s):
>
> On an 8 MHz output, most of the time you  divide by three.
>
> On a 10 MHz output, you need to divide by  2.4. The net result is that you
> divide by 2 sometimes and 3 other  times.
>
> In the 10 MHz case, there is a *lot* of energy at 12  MHz and 8 MHz, along
> with
> the 10 MHz output.
>
>  In the 8 MHz case, most of the RF energy is at 8 MHz.
>
>  
>
> To correct the output by 1 ppm on the 8 MHz output, you  need to either
> drop or
> add one pulse out of every million  pulses. Effectively you divide the 24
> MHz by
> 2 or by 4 when  you do that. You get a bit of 12 MHz or a bit of 6 MHz as 
a
>  result.
> That can be filtered out with a RF filter. The same is true  with a
> (somewhat more
> complex) filter on the 10 MHz  output.
>
> In addition to the “big” RF spurs, you get a low  frequency component to
> the output
> modulation. You are “phase  hitting” the output eight times a second. 
That
> gives you
> an 8  Hz sideband along with the further removed stuff. Since it’s not
>  simple / clean
> phase modulation, there are more sidebands than just  the few mentioned
> above.
>
> What messes things up even  more is that you never are quite doing one 
ppm.
> You are doing
>  corrections like 0.12356 ppm this second and 0.120201 ppm the next  
second.
> The pattern of pulse drop and add is not as simple as you  might hope. The
> low
> frequency part of the jitter (and it will  be there) is no different than
> the noise on
> a 1 pps output.  You still need to do very long time constant (or very
> narrow  band)
> filtering to take it out.
>
> Bob
>
>  > On Apr 8, 2016, at 7:06 AM, Herbert Poetzl   
wrote:
> >
> > On Mon, Apr 04, 2016 at 06:07:54PM -0700,  Alexander Pummer wrote:
> >> and it is relative easy to make 10MHz  from 8MHz with analog
> >> frequency manipulation, which generates  less jitter
> >
> > Could you elaborate on this a little if  time permits?
> > I'm more a 'digital person' but it sounds  interesting.
> >
> > Thanks in advance,
> >  Herbert
> >
> >> 73
> >
> >> On  4/4/2016 4:27 PM, Attila Kinali wrote:
> >>> On Mon, 4 Apr 2016  17:56:29 -0400
> >>> Bob Camp   wrote:
> >
>  The variable frequency output on  the uBlox (and other) GPS
>  receivers has come up many  times in the past.
> >
>  If you dig into the  archives you can find quite a bit of
>  data on the  (lack of) performance of the high(er) frequency
>   outputs from the various GPS modules. They all depend on
>   cycle add / drop at the frequency of their free running  TCXO.
>  Regardless of the output frequency, that will  put a *lot* of
>  jitter into the output.
>  >>> That's why you should put the output frequency of the ublox  modules
> >>> to an integer divisor of 24MHz. Ie 8MHz works but  not 10MHz.
> >
> >>>   Attila Kinali
> >
>  >
> >> ___
>  >> time-nuts mailing list -- time-nuts@febo.com
> >> To  unsubscribe, go to
> >>  https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >> and  follow the instructions there.
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> > and  

Re: [time-nuts] Advise on building a DIY GPSDO?

[Graham / KE9H]

The lowest jitter way to do this kind of conversion is to multiply the
signal up to some common multiple frequency, then divide it back down to
where you want to be.  For instance, with 8 or 24 MHz, multiply up to 240
MHz, then divide by 24 to get 10 MHz.

Modern clock generator chips have this capability built in.  As an example,
the TI LMK04100 series clock chip.  It actually has an on-board 1200 MHz
VCO, and all the phase-lock loop hardware to multiply up, and, and five
different divider chains, so you can get up to five different output
frequencies as long as the math works out.  Everything is constrained to
integer multiples and integer division, so there is none of the dithering
discussed above.  But you have a lot of integer options when the common
multiple is up at 1200 MHz. Much lower sidebands and phase noise.  Also the
ability to add a crystal VCO as a clean-up filter loop if your input
reference is dirty to begin with.

In my application, I am looking at taking a 10 MHz Oven-VCXO input and
putting out both a 24 MHz clock for the master clock of a BeagleBone Black,
and 480 kHz for a Shera style control loop for GPS disciplining.

--- Graham

==

On Fri, Apr 8, 2016 at 5:13 PM, Bob Camp  wrote:

> Hi
>
> If you start from a 24 MHz TCXO (different modules use different TCXO’s):
>
> On an 8 MHz output, most of the time you divide by three.
>
> On a 10 MHz output, you need to divide by 2.4. The net result is that you
> divide by 2 sometimes and 3 other times.
>
> In the 10 MHz case, there is a *lot* of energy at 12 MHz and 8 MHz, along
> with
> the 10 MHz output.
>
> In the 8 MHz case, most of the RF energy is at 8 MHz.
>
> 
>
> To correct the output by 1 ppm on the 8 MHz output, you need to either
> drop or
> add one pulse out of every million pulses. Effectively you divide the 24
> MHz by
> 2 or by 4 when you do that. You get a bit of 12 MHz or a bit of 6 MHz as a
> result.
> That can be filtered out with a RF filter. The same is true with a
> (somewhat more
> complex) filter on the 10 MHz output.
>
> In addition to the “big” RF spurs, you get a low frequency component to
> the output
> modulation. You are “phase hitting” the output eight times a second. That
> gives you
> an 8 Hz sideband along with the further removed stuff. Since it’s not
> simple / clean
> phase modulation, there are more sidebands than just the few mentioned
> above.
>
> What messes things up even more is that you never are quite doing one ppm.
> You are doing
> corrections like 0.12356 ppm this second and 0.120201 ppm the next second.
> The pattern of pulse drop and add is not as simple as you might hope. The
> low
> frequency part of the jitter (and it will be there) is no different than
> the noise on
> a 1 pps output. You still need to do very long time constant (or very
> narrow band)
> filtering to take it out.
>
> Bob
>
> > On Apr 8, 2016, at 7:06 AM, Herbert Poetzl  wrote:
> >
> > On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
> >> and it is relative easy to make 10MHz from 8MHz with analog
> >> frequency manipulation, which generates less jitter
> >
> > Could you elaborate on this a little if time permits?
> > I'm more a 'digital person' but it sounds interesting.
> >
> > Thanks in advance,
> > Herbert
> >
> >> 73
> >
> >> On 4/4/2016 4:27 PM, Attila Kinali wrote:
> >>> On Mon, 4 Apr 2016 17:56:29 -0400
> >>> Bob Camp  wrote:
> >
>  The variable frequency output on the uBlox (and other) GPS
>  receivers has come up many times in the past.
> >
>  If you dig into the archives you can find quite a bit of
>  data on the (lack of) performance of the high(er) frequency
>  outputs from the various GPS modules. They all depend on
>  cycle add / drop at the frequency of their free running TCXO.
>  Regardless of the output frequency, that will put a *lot* of
>  jitter into the output.
> >>> That's why you should put the output frequency of the ublox modules
> >>> to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.
> >
> >>> Attila Kinali
> >
> >
> >> ___
> >> time-nuts mailing list -- time-nuts@febo.com
> >> To unsubscribe, go to
> >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >> and follow the instructions there.
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
> > To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
>
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Re: [time-nuts] Advise on building a DIY GPSDO?

[timenut]

Hello Bob,

Friday, April 8, 2016, 6:13:07 PM, you wrote:

> Hi

> If you start from a 24 MHz TCXO (different modules use different TCXO’s):

> On an 8 MHz output, most of the time you divide by three. 

> On a 10 MHz output, you need to divide by 2.4. The net result is that you 
> divide by 2 sometimes and 3 other times. 

> In the 10 MHz case, there is a *lot* of energy at 12 MHz and 8 MHz, along with
> the 10 MHz output. 

> In the 8 MHz case, most of the RF energy is at 8 MHz.

> 

> To correct the output by 1 ppm on the 8 MHz output, you need to either drop or
> add one pulse out of every million pulses. Effectively you divide the 24 MHz 
> by
> 2 or by 4 when you do that. You get a bit of 12 MHz or a bit of 6 MHz as a 
> result.
If you know you are doing a 24Mhz and a 10Mhz, why not divide the first by 12
and the second by 5 and then phase lock the resulting 2Mhz? Or divide by 24
and 10, respectively and lock the 1Mhz? That way, everything is exact.


Mike

> That can be filtered out with a RF filter. The same is true with a (somewhat 
> more
> complex) filter on the 10 MHz output.

> In addition to the “big” RF spurs, you get a low frequency component to the 
> output
> modulation. You are “phase hitting” the output eight times a second. That 
> gives you
> an 8 Hz sideband along with the further removed stuff. Since it’s not simple 
> / clean
> phase modulation, there are more sidebands than just the few mentioned above. 

> What messes things up even more is that you never are quite doing one ppm. 
> You are doing
> corrections like 0.12356 ppm this second and 0.120201 ppm the next second. 
> The pattern of pulse drop and add is not as simple as you might hope. The low 
> frequency part of the jitter (and it will be there) is no different than the 
> noise on
> a 1 pps output. You still need to do very long time constant (or very narrow 
> band)
> filtering to take it out. 

> Bob

>> On Apr 8, 2016, at 7:06 AM, Herbert Poetzl  wrote:
>> 
>> On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
>>> and it is relative easy to make 10MHz from 8MHz with analog
>>> frequency manipulation, which generates less jitter
>> 
>> Could you elaborate on this a little if time permits? 
>> I'm more a 'digital person' but it sounds interesting.
>> 
>> Thanks in advance,
>> Herbert
>> 
>>> 73
>> 
>>> On 4/4/2016 4:27 PM, Attila Kinali wrote:
 On Mon, 4 Apr 2016 17:56:29 -0400
 Bob Camp  wrote:
>> 
> The variable frequency output on the uBlox (and other) GPS
> receivers has come up many times in the past.
>> 
> If you dig into the archives you can find quite a bit of
> data on the (lack of) performance of the high(er) frequency
> outputs from the various GPS modules. They all depend on
> cycle add / drop at the frequency of their free running TCXO.
> Regardless of the output frequency, that will put a *lot* of
> jitter into the output.
 That's why you should put the output frequency of the ublox modules
 to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.
>> 
 Attila Kinali
>> 
>> 
>>> ___
>>> time-nuts mailing list -- time-nuts@febo.com
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>>> and follow the instructions there.
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-- 
Best regards,
 Timenutmailto:time...@metachaos.net

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Re: [time-nuts] Advise on building a DIY GPSDO?

[Herbert Poetzl]

On Fri, Apr 08, 2016 at 06:13:07PM -0400, Bob Camp wrote:
> Hi

> If you start from a 24 MHz TCXO (different modules use
> different TCXO’s):

> On an 8 MHz output, most of the time you divide by three. 

> On a 10 MHz output, you need to divide by 2.4. 
> The net result is that you divide by 2 sometimes and 3 
> other times.   

> In the 10 MHz case, there is a *lot* of energy at 12 MHz 
> and 8 MHz, along with the 10 MHz output. 

> In the 8 MHz case, most of the RF energy is at 8 MHz.

Thanks for the input, but alternating between dividing
by two and three doesn't really sound like "analog 
frequency manipulation" to me.

Maybe I'm completely wrong here, maybe I just need to
see an analog circuit which does this.

Best,
Herbert

> 

> To correct the output by 1 ppm on the 8 MHz output, you 
> need to either drop or add one pulse out of every million
> pulses. Effectively you divide the 24 MHz by 2 or by 4 
> when you do that. 

> You get a bit of 12 MHz or a bit of 6 MHz as a result.
> That can be filtered out with a RF filter. 

> The same is true with a (somewhat more complex) filter 
> on the 10 MHz output.

> In addition to the “big” RF spurs, you get a low frequency 
> component to the output modulation. 

> You are “phase hitting” the output eight times a second. 

> That gives you an 8 Hz sideband along with the further 
> removed stuff. Since it’s not simple / clean phase 
> modulation, there are more sidebands than just the few 
> mentioned above.

> What messes things up even more is that you never are quite
> doing one ppm. You are doing corrections like 0.12356 ppm  
> this second and 0.120201 ppm the next second. The pattern 
> of pulse drop and add is not as simple as you might hope. 

> The low frequency part of the jitter (and it will be there) is
> no different than the noise on a 1 pps output. You still need
> to do very long time constant (or very narrow band) filtering
> to take it out.

> Bob

>> On Apr 8, 2016, at 7:06 AM, Herbert Poetzl  wrote:

>> On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
>>> and it is relative easy to make 10MHz from 8MHz with analog
>>> frequency manipulation, which generates less jitter

>> Could you elaborate on this a little if time permits? 
>> I'm more a 'digital person' but it sounds interesting.

>> Thanks in advance,
>> Herbert

>>> 73

>>> On 4/4/2016 4:27 PM, Attila Kinali wrote:
 On Mon, 4 Apr 2016 17:56:29 -0400
 Bob Camp  wrote:

> The variable frequency output on the uBlox (and other) GPS
> receivers has come up many times in the past.

> If you dig into the archives you can find quite a bit of
> data on the (lack of) performance of the high(er) frequency
> outputs from the various GPS modules. They all depend on
> cycle add / drop at the frequency of their free running TCXO.
> Regardless of the output frequency, that will put a *lot* of
> jitter into the output.
 That's why you should put the output frequency of the ublox modules
 to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.

Attila Kinali


>>> ___
>>> time-nuts mailing list -- time-nuts@febo.com
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>>> and follow the instructions there.
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Alex Pummer]

"Could you elaborate on this a little if time permits? I'm more a 
'digital person' but it sounds interesting. Thanks in advance, Herbert "


Yes Herbert
here is;
first divide 24MHz by two you get a very good quality absolute 50% duty 
cycle 12MHz, than you feed that 12MHx into mixer [which could be a 
transitional gate like HC4066 ] the other --LO input of the mixer you 
need to drive with a 10MHz oscillator, the output of the mixer will be 
2MHz, which you filter amplify and using to drive a freq multiplier, you 
have to multiply by 5 to get 10MHz  that is your 10MHz input of the 
mixer's LO port,
That was a very old style but very reliable way to do and since you have 
the LC filters you will not have to much jitter issue.
Also you could go a more modern way; divide the 24MHz by 6, but make it, 
that you have 50% duty-cycle  [you could make it with a CMOS device,  by 
loading during the counting a hex counter ] use one 10MHz better quality 
crystal oscillator, of its output has to be divided by 5 also with 50% 
duty-cycle output! than use one EX-or style phase detector and close the 
loop with proper filter. Depend on the quality of your crystal 
oscillator you will have a very low phase noise 10MHz source.
And you could make a few other variant by mixing the idea of the two 
previous and others .
It is important to use the components at the frequency at which they 
well perform, but keep the phase comparation at as high frequency as you 
could [side bands are easier to filer out if they are fare away from the 
carrier ], also use proper shielding and power-supply filtering

73
KJ6UHN
Alex

On 4/8/2016 3:13 PM, Bob Camp wrote:

Hi

If you start from a 24 MHz TCXO (different modules use different TCXO’s):

On an 8 MHz output, most of the time you divide by three.

On a 10 MHz output, you need to divide by 2.4. The net result is that you
divide by 2 sometimes and 3 other times.

In the 10 MHz case, there is a *lot* of energy at 12 MHz and 8 MHz, along with
the 10 MHz output.

In the 8 MHz case, most of the RF energy is at 8 MHz.



To correct the output by 1 ppm on the 8 MHz output, you need to either drop or
add one pulse out of every million pulses. Effectively you divide the 24 MHz by
2 or by 4 when you do that. You get a bit of 12 MHz or a bit of 6 MHz as a 
result.
That can be filtered out with a RF filter. The same is true with a (somewhat 
more
complex) filter on the 10 MHz output.

In addition to the “big” RF spurs, you get a low frequency component to the 
output
modulation. You are “phase hitting” the output eight times a second. That gives 
you
an 8 Hz sideband along with the further removed stuff. Since it’s not simple / 
clean
phase modulation, there are more sidebands than just the few mentioned above.

What messes things up even more is that you never are quite doing one ppm. You 
are doing
corrections like 0.12356 ppm this second and 0.120201 ppm the next second.
The pattern of pulse drop and add is not as simple as you might hope. The low
frequency part of the jitter (and it will be there) is no different than the 
noise on
a 1 pps output. You still need to do very long time constant (or very narrow 
band)
filtering to take it out.

Bob


On Apr 8, 2016, at 7:06 AM, Herbert Poetzl  wrote:

On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:

and it is relative easy to make 10MHz from 8MHz with analog
frequency manipulation, which generates less jitter

Could you elaborate on this a little if time permits?
I'm more a 'digital person' but it sounds interesting.

Thanks in advance,
Herbert


73
On 4/4/2016 4:27 PM, Attila Kinali wrote:

On Mon, 4 Apr 2016 17:56:29 -0400
Bob Camp  wrote:

The variable frequency output on the uBlox (and other) GPS
receivers has come up many times in the past.
If you dig into the archives you can find quite a bit of
data on the (lack of) performance of the high(er) frequency
outputs from the various GPS modules. They all depend on
cycle add / drop at the frequency of their free running TCXO.
Regardless of the output frequency, that will put a *lot* of
jitter into the output.

That's why you should put the output frequency of the ublox modules
to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.
Attila Kinali



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Checked by AVG - 

Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi

If you start from a 24 MHz TCXO (different modules use different TCXO’s):

On an 8 MHz output, most of the time you divide by three. 

On a 10 MHz output, you need to divide by 2.4. The net result is that you 
divide by 2 sometimes and 3 other times. 

In the 10 MHz case, there is a *lot* of energy at 12 MHz and 8 MHz, along with 
the 10 MHz output. 

In the 8 MHz case, most of the RF energy is at 8 MHz.



To correct the output by 1 ppm on the 8 MHz output, you need to either drop or
add one pulse out of every million pulses. Effectively you divide the 24 MHz by
2 or by 4 when you do that. You get a bit of 12 MHz or a bit of 6 MHz as a 
result. 
That can be filtered out with a RF filter. The same is true with a (somewhat 
more 
complex) filter on the 10 MHz output.

In addition to the “big” RF spurs, you get a low frequency component to the 
output 
modulation. You are “phase hitting” the output eight times a second. That gives 
you
an 8 Hz sideband along with the further removed stuff. Since it’s not simple / 
clean
phase modulation, there are more sidebands than just the few mentioned above. 

What messes things up even more is that you never are quite doing one ppm. You 
are doing 
corrections like 0.12356 ppm this second and 0.120201 ppm the next second. 
The pattern of pulse drop and add is not as simple as you might hope. The low 
frequency part of the jitter (and it will be there) is no different than the 
noise on 
a 1 pps output. You still need to do very long time constant (or very narrow 
band)
filtering to take it out. 

Bob

> On Apr 8, 2016, at 7:06 AM, Herbert Poetzl  wrote:
> 
> On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
>> and it is relative easy to make 10MHz from 8MHz with analog
>> frequency manipulation, which generates less jitter
> 
> Could you elaborate on this a little if time permits? 
> I'm more a 'digital person' but it sounds interesting.
> 
> Thanks in advance,
> Herbert
> 
>> 73
> 
>> On 4/4/2016 4:27 PM, Attila Kinali wrote:
>>> On Mon, 4 Apr 2016 17:56:29 -0400
>>> Bob Camp  wrote:
> 
 The variable frequency output on the uBlox (and other) GPS
 receivers has come up many times in the past.
> 
 If you dig into the archives you can find quite a bit of
 data on the (lack of) performance of the high(er) frequency
 outputs from the various GPS modules. They all depend on
 cycle add / drop at the frequency of their free running TCXO.
 Regardless of the output frequency, that will put a *lot* of
 jitter into the output.
>>> That's why you should put the output frequency of the ublox modules
>>> to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.
> 
>>> Attila Kinali
> 
> 
>> ___
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Herbert Poetzl]

On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
> and it is relative easy to make 10MHz from 8MHz with analog
> frequency manipulation, which generates less jitter

Could you elaborate on this a little if time permits? 
I'm more a 'digital person' but it sounds interesting.

Thanks in advance,
Herbert

> 73

> On 4/4/2016 4:27 PM, Attila Kinali wrote:
>> On Mon, 4 Apr 2016 17:56:29 -0400
>> Bob Camp  wrote:

>>> The variable frequency output on the uBlox (and other) GPS
>>> receivers has come up many times in the past.

>>> If you dig into the archives you can find quite a bit of
>>> data on the (lack of) performance of the high(er) frequency
>>> outputs from the various GPS modules. They all depend on
>>> cycle add / drop at the frequency of their free running TCXO.
>>> Regardless of the output frequency, that will put a *lot* of
>>> jitter into the output.
>> That's why you should put the output frequency of the ublox modules
>> to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.

>>  Attila Kinali


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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bert Kehren via time-nuts]

Having been a time nut for almost 50 years knot knowing it I  like to add 
my thoughts. Starting in the late 60's I won second place at IEEE  student 
contest for my counter design using 7 segment lamp and Motorola RTL in  the 
70's I buried a Sulzer using bank coin bags filled with sand to close the  
hole and application notes at TI using TI LED and IC's, in the 80's bought an  
Efraton FRK and did my first DO using a Tracor Omega converted to 60 KHz  
and a Philbrick DAC. I was the u processor  using every 6 month using the  
Tracor to recalculate the time for pulses to the DAC counter. I had then and  
still do now have problems with computers and processors. When Brooks came 
out  with his GPSDO i bought 10 A boards and started dialog with Brooks. 
Thanks  to Corby I joined time nuts and continued work with Richard McCorkle. 
One of the  results is a GPSDO for FE 5680, 5650 and 405 that is readied for 
release by Cash  Olsen. It took extensive testing fine tuning and more 
testing. During that time  I also had the opportunity to communicate with pro's 
on that subject and came  away even for the pro's it is not a walk in the 
woods. Tom's 2008 comparison  mentioned in this thread 
http://leapsecond.com/pages/gpsdo is very informative it clearly shows the 
relationship between OCXO 
 and digital loop. Few HP units are as good as his and there is a wide  
distribution when it comes to 10811's. The tbolt shows clearly the impact of 
the  fact that it changes the frequency to correct the 1  pps.
Miller is very impressive and we have done one using u-lox-6 and a MV89  
with similar results mainly intended for Ham's. Working on a 100 MHz version 
for  Ham uwave work
Summary true GPSDO is complex and long time work, Miller is simple and  low 
cost and maximum bang for your buck. 
One more comment on u-blox. In my opinion unless you plan on doing saw  
tooth correction the T version is a waste of money. Also if you plan on using  
the Miller circuit buy a $ 10 version and use a PIC to program in the higher 
 output frequency a version that stores it in EEROM costs three times as 
much  relying on the battery unless it is always powered up may be a problem 
once you  are out in the field and have no PC to change from the 1pps  default
Bert Kehren
 
 
In a message dated 4/6/2016 4:20:14 A.M. Eastern Daylight Time,  
hmur...@megapathdsl.net writes:


albertson.ch...@gmail.com said:
>  I may never get  around tooth's as the Rb is very good all by itself to 
the
> limit of my  ability to measure it.

Wait longer.  :)

If your Rb doesn't  have a PPS, make one.  One of tvb's divider chips is 
probably the  simplest approach.  You can probably do it with an Arduino if 
you  have one handy and like writing that sort of code.


Compare the PPS  from the Rb with the one from your GPS.  It's probably 
simplest if  your Rb PPS is offset a bit from the GPS PPS.  The idea is to 
make  the difference always have the same sign.

Feed both PPS pulses to some  equipment that can measure the time 
difference.  
Collect  data.

If you have a typical low cost (non GPSDO) GPS device, you should  be able 
to 
make graphs like the ones that show a hanging bridge.   Look at a sawtooth 
region, not a bridge.  Pick the top or the bottom  or the middle or 
whatever 
you can remember.  Call that the  offset.  Wait an hour collect more data.  
Has your offset  shifted?  If not wait longer...

You are measuring the average  frequency of the Rb.  It might be 
temperature 
sensitive.  Can  you see the offset change over a day?  (That assumes you 
turn 
the  heat down at night...)  Or maybe you are seeing the GPS night/day  
shift.


-- 
These are my opinions.  I hate  spam.



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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi

One thing to keep in mind: 

If you are looking at stuff like sawtooth on most (but not all) GPS modules, the
counter you use to take the data does not have to be some sort of monster
machine. An old 5334 or 5335 will let you see the basic structure. If you spend 
time 
shopping, neither one is terribly expensive. If you need one “right now” you 
will
pay a lot for the availability (like > 3X the price). 

There are also things like the PicTIc that have way more resolution than you 
would
need. They are not in the same league as a 53132 either. They will give you 
quite
a bit more resolution than the 5334. 

Lots of choices, no big need to spend a boatload of money. 

Bob

> On Apr 6, 2016, at 3:00 AM, Hal Murray  wrote:
> 
> 
> albertson.ch...@gmail.com said:
>> I may never get around tooth's as the Rb is very good all by itself to the
>> limit of my ability to measure it.
> 
> Wait longer.  :)
> 
> If your Rb doesn't have a PPS, make one.  One of tvb's divider chips is 
> probably the simplest approach.  You can probably do it with an Arduino if 
> you have one handy and like writing that sort of code.
> 
> Compare the PPS from the Rb with the one from your GPS.  It's probably 
> simplest if your Rb PPS is offset a bit from the GPS PPS.  The idea is to 
> make the difference always have the same sign.
> 
> Feed both PPS pulses to some equipment that can measure the time difference.  
> Collect data.
> 
> If you have a typical low cost (non GPSDO) GPS device, you should be able to 
> make graphs like the ones that show a hanging bridge.  Look at a sawtooth 
> region, not a bridge.  Pick the top or the bottom or the middle or whatever 
> you can remember.  Call that the offset.  Wait an hour collect more data.  
> Has your offset shifted?  If not wait longer...
> 
> You are measuring the average frequency of the Rb.  It might be temperature 
> sensitive.  Can you see the offset change over a day?  (That assumes you turn 
> the heat down at night...)  Or maybe you are seeing the GPS night/day shift.
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Hal Murray]

albertson.ch...@gmail.com said:
>  I may never get around tooth's as the Rb is very good all by itself to the
> limit of my ability to measure it.

Wait longer.  :)

If your Rb doesn't have a PPS, make one.  One of tvb's divider chips is 
probably the simplest approach.  You can probably do it with an Arduino if 
you have one handy and like writing that sort of code.

Compare the PPS from the Rb with the one from your GPS.  It's probably 
simplest if your Rb PPS is offset a bit from the GPS PPS.  The idea is to 
make the difference always have the same sign.

Feed both PPS pulses to some equipment that can measure the time difference.  
Collect data.

If you have a typical low cost (non GPSDO) GPS device, you should be able to 
make graphs like the ones that show a hanging bridge.  Look at a sawtooth 
region, not a bridge.  Pick the top or the bottom or the middle or whatever 
you can remember.  Call that the offset.  Wait an hour collect more data.  
Has your offset shifted?  If not wait longer...

You are measuring the average frequency of the Rb.  It might be temperature 
sensitive.  Can you see the offset change over a day?  (That assumes you turn 
the heat down at night...)  Or maybe you are seeing the GPS night/day shift.


-- 
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi

Building a GPSDO *after* you have a lab full of gear is a very different 
proposition than
building one because cash is tight and nobody mentioned the $43 surplus units. 

There’s no right and wrong here, just a need to look at “why?” before you get 
going. 

Bob

> On Apr 5, 2016, at 5:40 PM, Chris Albertson  wrote:
> 
> Thank you, My goal was to build the simplest and lowest cost GPSDO that
> could still work.   The major cost item was the $20 crystal oscillator I
> bought on eBay and a $19 Motorola "Oncore" 8 channel GPS Receiver.  The
> rest of the stuff cost about $5.   I don't count the cost of the GPS
> because it was already driving NTP.   SO I'd calling it a $25 GPS.  It's
> performance is acceptable to driving the 10MHz input of a basic frequency
> counter.
> 
> I already owned a T-Bolt and an Rb oscillator and a few counters and dual
> trace scope.  So I compare the $25 unit to the t-bolt and see it drifts off
> a tiny bit then the software seethes and pushes it back.   If I know more
> about running PID controllers it would work better.
> 
> Lars W. actually did the design and posted it here.  I build most of his
> design, leaving some stuff out and rewrote all the software to be about
> 1/20th as many lines of code.  My goal was to be as simple and cheap as
> possible.
> 
> I think if the goal is to build something and the learn how it works, build
> a VERY simple device then in a series of tiny "baby steps" improve it.
> 
> If I ever get around to it.  I will add my $35 surplus Rb unit to the same
> cheap Arduino.  It should work will.  I can do hours/days integration
> times.  The Rb has a digital only freq. adjustment that has steps of about
> 10E-11 or so.  All I need is to keep it on the correct step.
> 
> Another reason to build rather than buy is because you want something that
> you can't buy.  That will be my next GPSDO.  I want a "good" crystal and an
> internal Rb standard that can be used when GPS is not available (for
> portable use) and I want it to run on common LiPo batteries used for power
> tools.  The idea is that when it is at home I plug in the 1PPS cable and
> the units "syncs" to GPS and the Rb is put in frequency.   I may never get
> around tooth's as the Rb is very good all by itself to the limit of my
> ability to measure it.
> 
> 
> 
> 
> On Mon, Apr 4, 2016 at 12:00 PM, Chris Caudle  wrote:
> 
>> 
>> 
>> want to build next, then go ahead and have fun.  Chris Albertson's arduino
>> based design is probably as good a place to start as any, it should be
>> cheap and I think the pieces are easier to find than that CPLD based
>> design that relies on having a GPS that can output 10kHz instead of just
>> PPS.
>> 
>> --
>> Chris Caudle
>> 
>> 
>> 
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>> 
> 
> 
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Chris Albertson]

Thank you, My goal was to build the simplest and lowest cost GPSDO that
could still work.   The major cost item was the $20 crystal oscillator I
bought on eBay and a $19 Motorola "Oncore" 8 channel GPS Receiver.  The
rest of the stuff cost about $5.   I don't count the cost of the GPS
because it was already driving NTP.   SO I'd calling it a $25 GPS.  It's
performance is acceptable to driving the 10MHz input of a basic frequency
counter.

I already owned a T-Bolt and an Rb oscillator and a few counters and dual
trace scope.  So I compare the $25 unit to the t-bolt and see it drifts off
a tiny bit then the software seethes and pushes it back.   If I know more
about running PID controllers it would work better.

Lars W. actually did the design and posted it here.  I build most of his
design, leaving some stuff out and rewrote all the software to be about
1/20th as many lines of code.  My goal was to be as simple and cheap as
possible.

I think if the goal is to build something and the learn how it works, build
a VERY simple device then in a series of tiny "baby steps" improve it.

If I ever get around to it.  I will add my $35 surplus Rb unit to the same
cheap Arduino.  It should work will.  I can do hours/days integration
times.  The Rb has a digital only freq. adjustment that has steps of about
10E-11 or so.  All I need is to keep it on the correct step.

Another reason to build rather than buy is because you want something that
you can't buy.  That will be my next GPSDO.  I want a "good" crystal and an
internal Rb standard that can be used when GPS is not available (for
portable use) and I want it to run on common LiPo batteries used for power
tools.  The idea is that when it is at home I plug in the 1PPS cable and
the units "syncs" to GPS and the Rb is put in frequency.   I may never get
around tooth's as the Rb is very good all by itself to the limit of my
ability to measure it.




On Mon, Apr 4, 2016 at 12:00 PM, Chris Caudle  wrote:

>
>
> want to build next, then go ahead and have fun.  Chris Albertson's arduino
> based design is probably as good a place to start as any, it should be
> cheap and I think the pieces are easier to find than that CPLD based
> design that relies on having a GPS that can output 10kHz instead of just
> PPS.
>
> --
> Chris Caudle
>
>
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
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> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Nick Sayer via time-nuts]

I’m coming at this thread a bit late, but I’m part-way down the DIY GPSDO 
design path and I’d like to share my looking-back perspective, for what it’s 
worth.

I think it’s good to start with some sort of goal in mind. The problem with 
that statement is that as a beginner, I didn’t fully comprehend the vocabulary 
as well as I (think) I do now.

If you share what you come up with, you can be confident that there will be 
criticism of your design. That criticism will seem to you more harsh than it 
will likely have been intended. Distill the criticism to as many testable 
design changes as you can and try them out - hopefully (as much as practicable) 
one at a time in isolation so you can see the impact on the stability.

That takes one to the next challenge… You must be able to measure your design’s 
performance. This means getting ahold of a TIA that’s at least an order of 
magnitude better than your performance target. If you can’t trust your 
measurements, you’ll never be able to tell if your design is doing better or 
worse as you make changes. But a TIA isn’t all… You need to also be able to 
measure power supply stability (noise and ripple) and things like that, so that 
means a good scope and proper short-lead scope probes for doing it (Dave Jones 
has a good video on this topic over at eevblog.com). You’re going to need to be 
able to get performance logs from your device while it’s running so you can see 
what your firmware is doing. You’re going to want to do this while your device 
is in its enclosure (an OCXO will perform much, much better in an enclosure 
than not in one).

As a beginner, I advise designing from new components. This, in principle, 
gives you some hopes of getting support from the component manufacturers. 
Connor Winfield has been very helpful in answering questions, as has Semtech 
(for their SC189 switching controller). Design with the datasheet in one hand 
and your pencil in the other. :) For OCXOs, pay particular attention to the 
manufacturer’s recommendations for board layout and chassis considerations. The 
manufacturers want your designs to work - they sell more of their stuff that 
way. Take heed of their advice. :) Designing from new will very likely take you 
into the world of surface mount. If you haven’t done it before, SMD is easier 
than you think. It didn’t take me long before I came to view SMD as actually 
easier and faster than through-hole.

Most of all, the people here are by far the most helpful resource I’ve found. 
Even those whose criticism seemed harsh at first have had an impact on the 
design I have today. And I believe I can say without fear of contradiction that 
every change has been an incremental improvement. And credit for a lot of that 
goes to people subscribed here.

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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi

This comes back (very much) to: 

What is your objective? 

If the full performance delivered by a surplus part is your objective, then the 
Miller is not what you 
are after. Since it sells for about 2X the current crop of surplus parts … that 
is a bit of an issue as
well. There are a *lot* of different aspects of these devices beyond what any 
one plot can show. That
is why the testing part of it is an issue. It is not a deal breaker. It is not 
something to stop you dead. It’s
something to plan and budget for.

Bob


> On Apr 5, 2016, at 2:16 AM, Dimitri.p  wrote:
> 
> Miller GPSDO vs HP Z3801A,  Jackson Labs Fury GPSDO,  vs Trimble Thunderbolt  
> compared Feb 2008
> 
> http://leapsecond.com/pages/gpsdo
> 
> It seems the Miller GPSDO, for an "unlikely" design, it can hold its own 
> pretty good.
> 
> 
> 
> At 06:56 PM 4/4/2016, you wrote:
>> Don wrote:
>> 
>>> 5.  Design a voltage tracking / filter to match the OCXO
>>> control requirements.
>>> 6.  And, ...ta-dah;
>>> 7.  You have a 10MHz, bench frequency standard that will
>>> rival all others
>> 
>> Not very likely.  The whole point of a GPSDO is for the frequency to be 
>> controlled by the more stable source (OCXO or GPS) at all integration times 
>> (tau).  But the OCXO will typically be more stable than the GPS for tau less 
>> than several hundred seconds (see graph below -- black line is GPS, brown 
>> line is a typical OCXO).  So, the PLL needs to have a time constant of 
>> hundreds of seconds.  Such a PLL filter cannot practicably be designed in 
>> the analog domain, so one needs to design a digital filter with appropriate 
>> time constant and damping.  Because of the very long time constant, it is 
>> almost necessary for the filter to have more than one, switchable time 
>> constants to avoid extremely long lock times.
>> 
>> Very few home builders are capable of designing a proper digital filter 
>> suitable for this application (the counter-based loops of most published DIY 
>> GPSDO designs are not proper digital filters).
>> 
>> So, no -- it is very unlikely that a home-built GPSDO will "rival all 
>> comers," whether the builder designs his or her own circuit or uses one of 
>> the many published circuits.
>> 
>> Best regards,
>> 
>> Charles
>> 
>> 
>> Graph below.  Note that a properly designed GPSDO would show stability that 
>> follows the OCXO (brown line) at low tau, and the GPS (black line) above the 
>> point where they intersect -- here, about 350 seconds.  Note that a loop 
>> filter with proper damping will NOT exhibit a "hump" near the crossover 
>> (many GPSDOs do exhibit a pronounced hump, betraying that their loop filters 
>> are not properly designed).
>> 
>> 
>> 
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Dimitri.p]

Miller GPSDO vs HP Z3801A,  Jackson Labs Fury GPSDO,  vs Trimble 
Thunderbolt  compared Feb 2008


http://leapsecond.com/pages/gpsdo

It seems the Miller GPSDO, for an "unlikely" design, it can hold its 
own pretty good.




At 06:56 PM 4/4/2016, you wrote:

Don wrote:


5.  Design a voltage tracking / filter to match the OCXO
control requirements.
6.  And, ...ta-dah;
7.  You have a 10MHz, bench frequency standard that will
rival all others


Not very likely.  The whole point of a GPSDO is for the frequency to 
be controlled by the more stable source (OCXO or GPS) at all 
integration times (tau).  But the OCXO will typically be more stable 
than the GPS for tau less than several hundred seconds (see graph 
below -- black line is GPS, brown line is a typical OCXO).  So, the 
PLL needs to have a time constant of hundreds of seconds.  Such a 
PLL filter cannot practicably be designed in the analog domain, so 
one needs to design a digital filter with appropriate time constant 
and damping.  Because of the very long time constant, it is almost 
necessary for the filter to have more than one, switchable time 
constants to avoid extremely long lock times.


Very few home builders are capable of designing a proper digital 
filter suitable for this application (the counter-based loops of 
most published DIY GPSDO designs are not proper digital filters).


So, no -- it is very unlikely that a home-built GPSDO will "rival 
all comers," whether the builder designs his or her own circuit or 
uses one of the many published circuits.


Best regards,

Charles


Graph below.  Note that a properly designed GPSDO would show 
stability that follows the OCXO (brown line) at low tau, and the GPS 
(black line) above the point where they intersect -- here, about 350 
seconds.  Note that a loop filter with proper damping will NOT 
exhibit a "hump" near the crossover (many GPSDOs do exhibit a 
pronounced hump, betraying that their loop filters are not properly designed).




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Re: [time-nuts] Advise on building a DIY GPSDO?

[Charles Steinmetz]

Don wrote:


5.  Design a voltage tracking / filter to match the OCXO
control requirements.
6.  And, ...ta-dah;
7.  You have a 10MHz, bench frequency standard that will
rival all others


Not very likely.  The whole point of a GPSDO is for the frequency to 
be controlled by the more stable source (OCXO or GPS) at all 
integration times (tau).  But the OCXO will typically be more stable 
than the GPS for tau less than several hundred seconds (see graph 
below -- black line is GPS, brown line is a typical OCXO).  So, the 
PLL needs to have a time constant of hundreds of seconds.  Such a PLL 
filter cannot practicably be designed in the analog domain, so one 
needs to design a digital filter with appropriate time constant and 
damping.  Because of the very long time constant, it is almost 
necessary for the filter to have more than one, switchable time 
constants to avoid extremely long lock times.


Very few home builders are capable of designing a proper digital 
filter suitable for this application (the counter-based loops of most 
published DIY GPSDO designs are not proper digital filters).


So, no -- it is very unlikely that a home-built GPSDO will "rival all 
comers," whether the builder designs his or her own circuit or uses 
one of the many published circuits.


Best regards,

Charles


Graph below.  Note that a properly designed GPSDO would show 
stability that follows the OCXO (brown line) at low tau, and the GPS 
(black line) above the point where they intersect -- here, about 350 
seconds.  Note that a loop filter with proper damping will NOT 
exhibit a "hump" near the crossover (many GPSDOs do exhibit a 
pronounced hump, betraying that their loop filters are not properly designed).
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bill Hawkins]

No disrespect intended, but it seems to me that human technology is
built on the published experience/mistakes of others.

A newbie would do well to read the experiences of others before
investing the first penny in hardware.

TVB, Magnus Danielson, Bob Camp, Jim Lux, Attila Kinali and others have
been there and done that. So have I but I wouldn't compare myself to
them. First I got the $300 HP Z3? GPSDO units, then I tried some equally
expensive Lucent units. I did get the $750 HP Rubidium and learned from
the construction and operation. Then I got the $1200 Caesium standard
and learned that I'd have trouble shipping it. That stuff is all gone
now, much of it to paid junk haulers.

I don't regret it, though. Education can be expensive. The high point
was talking to a Minnesota professor of physics about the FTL neutrinos.

Time and frequency can be measured to a precision/accuracy that is not
possible for volts, amps, and ohms. It's exciting stuff, and
correspondingly difficult.

FWIW

Bill Hawkins


-Original Message-
From: Alexander Pummer
Sent: Monday, April 04, 2016 4:49 PM

Building it cost you time and money, most likely much more than to buy,
but you gain experience and you learn the limits of the different
techniques, what you would not get to know other way
73
KJ6UHN
Alex


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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi

…. and this fulfills the requirement I mentioned:

“I just want to build one to say I’ve done it” 

There is *absolutely* nothing at all wrong with that. If this is your goal, you 
have
accomplished it. You likely have learned somethings along the way. 

If you have a performance goal that is anywhere close to what the $50 to $150
surplus devices will do, this sort of design will not do the job.

Figuring out what you want to do *does* matter a lot. 

Bob

> On Apr 4, 2016, at 8:48 PM, dlewis6767  wrote:
> 
> Lots' of help herein; ...but,  also lots' of nay-sayers, too.
> 
> Don't let the nay-sayers scare you.  
> 
> A VERY accurate, newbie-based, GPSDO can be built with minimal
> investment or cost.
> 
> It's not hard at all.  Just Do-It.  Mistakes allowed.
> 
> I have built two GPSDO's from scratch.  Both worked very well against
> each other measured with an HP 5370B; against my rubidium; as well as
> my cesium.
> 
> Just look at it at the 'building-block' level. (no real need for an
> embedded computer unless you like code more so than dips.  :-)
> 
> 
> 1.  Get a good, used, GPS receiver with a 10Khz output.
> 2.  Get a good, used, 10MHz OCXO with a voltage control.
> 3.  Design a simple divide-by-thousand divider.
> 4.  Exclusive-or these two using a 4046 PLL (comparator 1)
> 5.  Design a voltage tracking / filter to match the OCXO control
> requirements.
> 6.  And, ...ta-dah;  
> 7.  You have a 10MHz, bench frequency standard that will rival all
> others; and the best partyou designed and built it!
> 8.  NOTE:  Take the unused, SR flip-flop output of the 4046 PLL and
> connect a small, analog, milliampmeter.  It will swing back and forth
> trackin the XOR function until your GPSDO 'locks'; then become
> stationary.
> 
> Basic? Yes!  Over-simplified?  Probably.  
> 
> But it will work and you will feel like you accomplished your goal of
> 'doing-it-yourself'.
> 
> -Don
> ==
> 
> 
> 
> 
> 
>> 
> 
> -- 
> dlewis6767 
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Alexander Pummer]

and it is relative easy to make 10MHz from 8MHz with analog frequency 
manipulation, which generates less jitter

73

On 4/4/2016 4:27 PM, Attila Kinali wrote:

On Mon, 4 Apr 2016 17:56:29 -0400
Bob Camp  wrote:


The variable frequency output on the uBlox (and other) GPS receivers
has come up many times in the past.
If you dig into the archives you can find quite a bit of data on the
(lack of) performance of the high(er) frequency outputs from the various GPS
modules. They all depend on cycle add / drop at the frequency of their free
running TCXO. Regardless of the output frequency, that will put a *lot* of
jitter into the output.

That's why you should put the output frequency of the ublox modules
to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.

Attila Kinali



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Re: [time-nuts] Advise on building a DIY GPSDO?

[dlewis6767]

Lots' of help herein; ...but,  also lots' of nay-sayers, too.

Don't let the nay-sayers scare you.  

A VERY accurate, newbie-based, GPSDO can be built with minimal
investment or cost.

It's not hard at all.  Just Do-It.  Mistakes allowed.

I have built two GPSDO's from scratch.  Both worked very well against
each other measured with an HP 5370B; against my rubidium; as well as
my cesium.

Just look at it at the 'building-block' level. (no real need for an
embedded computer unless you like code more so than dips.  :-)


1.  Get a good, used, GPS receiver with a 10Khz output.
2.  Get a good, used, 10MHz OCXO with a voltage control.
3.  Design a simple divide-by-thousand divider.
4.  Exclusive-or these two using a 4046 PLL (comparator 1)
5.  Design a voltage tracking / filter to match the OCXO control
requirements.
6.  And, ...ta-dah;  
7.  You have a 10MHz, bench frequency standard that will rival all
others; and the best partyou designed and built it!
8.  NOTE:  Take the unused, SR flip-flop output of the 4046 PLL and
connect a small, analog, milliampmeter.  It will swing back and forth
trackin the XOR function until your GPSDO 'locks'; then become
stationary.

Basic? Yes!  Over-simplified?  Probably.  

But it will work and you will feel like you accomplished your goal of
'doing-it-yourself'.

-Don
==





> 

-- 
dlewis6767 
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi

Even with an integer divide, it’s still going to toss in a full cycle of the 
TCXO from time to time. It will 
be an integer, except when it is not ….

Bob

> On Apr 4, 2016, at 7:27 PM, Attila Kinali  wrote:
> 
> On Mon, 4 Apr 2016 17:56:29 -0400
> Bob Camp  wrote:
> 
>> The variable frequency output on the uBlox (and other) GPS receivers
>> has come up many times in the past. 
>> If you dig into the archives you can find quite a bit of data on the
>> (lack of) performance of the high(er) frequency outputs from the various GPS
>> modules. They all depend on cycle add / drop at the frequency of their free
>> running TCXO. Regardless of the output frequency, that will put a *lot* of
>> jitter into the output. 
> 
> That's why you should put the output frequency of the ublox modules
> to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.
> 
>   Attila Kinali
> 
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
> -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Attila Kinali]

On Mon, 4 Apr 2016 17:56:29 -0400
Bob Camp  wrote:

> The variable frequency output on the uBlox (and other) GPS receivers
> has come up many times in the past. 
> If you dig into the archives you can find quite a bit of data on the
> (lack of) performance of the high(er) frequency outputs from the various GPS
> modules. They all depend on cycle add / drop at the frequency of their free
> running TCXO. Regardless of the output frequency, that will put a *lot* of
> jitter into the output. 

That's why you should put the output frequency of the ublox modules
to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi

The variable frequency output on the uBlox (and other) GPS receivers has come 
up many times in the past. 
If you dig into the archives you can find quite a bit of data on the (lack of) 
performance of the high(er) frequency
outputs from the various GPS modules. They all depend on cycle add / drop at 
the frequency of their free running 
TCXO. Regardless of the output frequency, that will put a *lot* of jitter into 
the output. 

Bob


> On Apr 4, 2016, at 4:15 PM, Dimitri.p  wrote:
> 
> Regarding "as good a place to start as any",  ublox receivers will do 10KHz 
> all day long.
> I didn't realize ublox receivers have dual output until after I built a 
> couple of other GPSDOs, (well, maybe four)
> 
> As for a good  OCXO: other than the Morion MV89a, ($20-$50)  for anything 
> else, figure about one or two hundred bucks depending on new vs used and 
> "luck".
> 
> But as it's been said before it all depends on if you are building "to use" 
> or "to play/learn/experiment/get your hands dirty"
> 
> Building does not save money or time and buying doen't give you an excuse to 
> fire up the soldering iron.
> Decisions...decisions...
> 
> 
> Dimitri.p
> 
> 
> At 12:00 PM 4/4/2016, Chris Caudle wrote:
>> On Mon, April 4, 2016 11:18 am, Tom Holmes wrote:
>> > The preceding questions always come up when a newbie
>> > comes up on the list wanting to build their own GPSDO.
>> 
>> It is good to make sure the person actually wants to build a GPSDO.
>> A few years back I was in a similar position, and my answer was I actually
>> needed a high accuracy reference to check frequency accuracy of some
>> clocks, and the recommendation was just get a Thunderbolt.  I didn't know
>> about surplus GPSDO's available so that was good advice for me, I didn't
>> actually >want< to build a GPSDO myself.  It would have been fun, but the
>> end goal was more important to me.
>> 
>> So I think really the first question should be do you want to build a
>> GPSDO, or do you want a high accuracy time and frequency source for its
>> own use?  Because if you want to own a GPSDO to use, building one yourself
>> is probably not the way to go.  Get a surplus unit, or save up a little
>> more and get a new Jackson Labs.
>> If you just like to build stuff and a GPSDO is the particular stuff you
>> want to build next, then go ahead and have fun.  Chris Albertson's arduino
>> based design is probably as good a place to start as any, it should be
>> cheap and I think the pieces are easier to find than that CPLD based
>> design that relies on having a GPS that can output 10kHz instead of just
>> PPS.
>> 
>> --
>> Chris Caudle
>> 
>> 
>> 
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> 
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Alexander Pummer]

Building it cost you time and money, most likely much more than to buy,  
but you gain experience and you learn the limits of the different 
techniques, what you would not get to know other way

73
KJ6UHN
Alex

On 4/4/2016 1:15 PM, Dimitri.p wrote:
Regarding "as good a place to start as any",  ublox receivers will do 
10KHz all day long.
I didn't realize ublox receivers have dual output until after I built 
a couple of other GPSDOs, (well, maybe four)


As for a good  OCXO: other than the Morion MV89a, ($20-$50)  for 
anything else, figure about one or two hundred bucks depending on new 
vs used and "luck".


But as it's been said before it all depends on if you are building "to 
use" or "to play/learn/experiment/get your hands dirty"


Building does not save money or time and buying doen't give you an 
excuse to fire up the soldering iron.

Decisions...decisions...


Dimitri.p


At 12:00 PM 4/4/2016, Chris Caudle wrote:

On Mon, April 4, 2016 11:18 am, Tom Holmes wrote:
> The preceding questions always come up when a newbie
> comes up on the list wanting to build their own GPSDO.

It is good to make sure the person actually wants to build a GPSDO.
A few years back I was in a similar position, and my answer was I 
actually

needed a high accuracy reference to check frequency accuracy of some
clocks, and the recommendation was just get a Thunderbolt.  I didn't 
know

about surplus GPSDO's available so that was good advice for me, I didn't
actually >want< to build a GPSDO myself.  It would have been fun, but 
the

end goal was more important to me.

So I think really the first question should be do you want to build a
GPSDO, or do you want a high accuracy time and frequency source for its
own use?  Because if you want to own a GPSDO to use, building one 
yourself

is probably not the way to go.  Get a surplus unit, or save up a little
more and get a new Jackson Labs.
If you just like to build stuff and a GPSDO is the particular stuff you
want to build next, then go ahead and have fun.  Chris Albertson's 
arduino

based design is probably as good a place to start as any, it should be
cheap and I think the pieces are easier to find than that CPLD based
design that relies on having a GPS that can output 10kHz instead of just
PPS.

--
Chris Caudle



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-
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2016.0.7538 / Virus Database: 4545/11957 - Release Date: 
04/04/16


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Re: [time-nuts] Advise on building a DIY GPSDO?

[Dimitri.p]

Regarding "as good a place to start as any",  ublox receivers will do 
10KHz all day long.
I didn't realize ublox receivers have dual output until after I built 
a couple of other GPSDOs, (well, maybe four)


As for a good  OCXO: other than the Morion MV89a, ($20-$50)  for 
anything else, figure about one or two hundred bucks depending on new 
vs used and "luck".


But as it's been said before it all depends on if you are building 
"to use" or "to play/learn/experiment/get your hands dirty"


Building does not save money or time and buying doen't give you an 
excuse to fire up the soldering iron.

Decisions...decisions...


Dimitri.p


At 12:00 PM 4/4/2016, Chris Caudle wrote:

On Mon, April 4, 2016 11:18 am, Tom Holmes wrote:
> The preceding questions always come up when a newbie
> comes up on the list wanting to build their own GPSDO.

It is good to make sure the person actually wants to build a GPSDO.
A few years back I was in a similar position, and my answer was I actually
needed a high accuracy reference to check frequency accuracy of some
clocks, and the recommendation was just get a Thunderbolt.  I didn't know
about surplus GPSDO's available so that was good advice for me, I didn't
actually >want< to build a GPSDO myself.  It would have been fun, but the
end goal was more important to me.

So I think really the first question should be do you want to build a
GPSDO, or do you want a high accuracy time and frequency source for its
own use?  Because if you want to own a GPSDO to use, building one yourself
is probably not the way to go.  Get a surplus unit, or save up a little
more and get a new Jackson Labs.
If you just like to build stuff and a GPSDO is the particular stuff you
want to build next, then go ahead and have fun.  Chris Albertson's arduino
based design is probably as good a place to start as any, it should be
cheap and I think the pieces are easier to find than that CPLD based
design that relies on having a GPS that can output 10kHz instead of just
PPS.

--
Chris Caudle



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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Stewart]

As a victim of the "I'm gonna build a GPSDO" virus, I think the cautions are 
well worth mentioning.  Building a decent GPSDO sounds like such a simple 
thing, but it slowly turns into a rabbit hole as you discover you need ever 
better test equipment, and a microscope, and hot air rework station, and 
gaining the skills in designing the electronics and laying out boards.  And 
then there's the time.  I've got over 2 years invested in nothing but this 
GPSDO project.  I'm retired, so I'm not talking about an hour or two after 
work, either.

I wouldn't discourage anyone from doing it, if they have a good idea what it's 
going to cost going into it; both in terms of time and money.  Suddenly 
discovering that you really, really need a Cs standard else all the work you've 
done is wasted, is a big shock.

I'd have to agree with others that the best path to take is to find a proven 
design and build it.  Then decide whether you truly want to come up with 
something of your own.  Just remember the cost.

Bob


On Mon, 4/4/16, Tom Holmes <thol...@woh.rr.com> wrote:

 Subject: Re: [time-nuts] Advise on building a DIY GPSDO?
 To: "'Discussion of precise time and frequency measurement'" 
<time-nuts@febo.com>
 Date: Monday, April 4, 2016, 11:18 AM
 
 The preceding questions
 always come up when a newbie comes up on the list wanting to
 build their own GPSDO. They are all good questions from an
 engineering/management viewpoint, but this latest incident
 reminded me of conversations I had with my father some 50+
 years ago when I wanted to tackle some project and needed
 some resources. His most common question was why do you want
 to do this? My usual poorly thought out answer (hey, I was
 an adolescent at the time) was simply "because I want
 to". I would then get the obligatory lecture on needing
 a better reason and having a plan, but then he would often
 provide some subset of the resources I asked for ($$) so
 that I could proceed. Naturally, I resented these probing
 interrogations into my motives and poor project management
 skills, but learned to accept them as the cost of doing
 business with the old man. Being an engineer himself, he
 understood that whether or not the project was a success
 that I would learn something from the enterpr
  ise. 
 
 I'm
 not saying that the questions posed are not relevant and
 important, as well as useful; I just wonder if we are
 discouraging the learning process that most of us went
 through to get where we are.
 
 Tom Holmes, N8ZM
 
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Chris Caudle]

On Mon, April 4, 2016 11:18 am, Tom Holmes wrote:
> The preceding questions always come up when a newbie
> comes up on the list wanting to build their own GPSDO.

It is good to make sure the person actually wants to build a GPSDO.
A few years back I was in a similar position, and my answer was I actually
needed a high accuracy reference to check frequency accuracy of some
clocks, and the recommendation was just get a Thunderbolt.  I didn't know
about surplus GPSDO's available so that was good advice for me, I didn't
actually >want< to build a GPSDO myself.  It would have been fun, but the
end goal was more important to me.

So I think really the first question should be do you want to build a
GPSDO, or do you want a high accuracy time and frequency source for its
own use?  Because if you want to own a GPSDO to use, building one yourself
is probably not the way to go.  Get a surplus unit, or save up a little
more and get a new Jackson Labs.
If you just like to build stuff and a GPSDO is the particular stuff you
want to build next, then go ahead and have fun.  Chris Albertson's arduino
based design is probably as good a place to start as any, it should be
cheap and I think the pieces are easier to find than that CPLD based
design that relies on having a GPS that can output 10kHz instead of just
PPS.

-- 
Chris Caudle



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Re: [time-nuts] Advise on building a DIY GPSDO?

[Tom Holmes]

The preceding questions always come up when a newbie comes up on the list 
wanting to build their own GPSDO. They are all good questions from an 
engineering/management viewpoint, but this latest incident reminded me of 
conversations I had with my father some 50+ years ago when I wanted to tackle 
some project and needed some resources. His most common question was why do you 
want to do this? My usual poorly thought out answer (hey, I was an adolescent 
at the time) was simply "because I want to". I would then get the obligatory 
lecture on needing a better reason and having a plan, but then he would often 
provide some subset of the resources I asked for ($$) so that I could proceed. 
Naturally, I resented these probing interrogations into my motives and poor 
project management skills, but learned to accept them as the cost of doing 
business with the old man. Being an engineer himself, he understood that 
whether or not the project was a success that I would learn something from the 
enterpr
 ise. 

I'm not saying that the questions posed are not relevant and important, as well 
as useful; I just wonder if we are discouraging the learning process that most 
of us went through to get where we are.

Tom Holmes, N8ZM


-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp
Sent: Sunday, April 03, 2016 10:03 PM
To: Discussion of precise time and frequency measurement <time-nuts@febo.com>
Subject: Re: [time-nuts] Advise on building a DIY GPSDO?

HI

Ok, let’s back up a bit. The first question is: why? 

There are a few basic answers ( and many not so basic ones):

1) Because you want to save money over the $40 GPSDO’s that are on eBay.

2) Because you want to learn how a GPSDO works.

3) Because you want to make a GPSDO that performs better in a specific 
application 

If it’s 1, I’d suggest that you will have a hard time doing a useful  one up 
design for less than 
you can buy a surplus unit for. I’d extend that to include the wide range of of 
units in the < $200
delivered price range. 

If it’s 2 or 3, you will need a pretty well equipped bench to make much 
headway. The cost and time
associated with those bits and pieces is not at all trivial. You both need good 
measurement 
capability *and* a lab standard to compare to. 

The next question is: what for?

Again a few basic answers: 

1) Anything that works at all is fine, it’s just an experiment. 

2) It’s going to be a lab standard that drives the following gear …..

3) It will drive my 100 GHz narrowband data radio project 

Focusing on 2 and 3:

Phase noise is going to be pretty important for a microwave system. Short term 
stability will be 
important for things like frequent counters. A design that does both *is* 
possible. It also is fairly
complicated.

Each of these decisions loop back and drive the bench gear you will need under 
the first question. 

Lots of branches and that’s only two questions.

Bob



> On Apr 3, 2016, at 6:04 PM, Nicolas Braud-Santoni <nico...@braud-santoni.eu> 
> wrote:
> 
> Hi,
> 
> I've been slowly becoming a fellow timenut over the last few years,
>  though said nuttery had yet to go beyond adding some wiring to
>  get the PPS signal out of my GPS and into my NTPd.
> 
> 
> Lately, I have been looking into designing & building a home-brew
>  GPSDO (and my copy of TAoE 3rd ed. came in quite handy), but quite
>  a few questions came up:
> 
> - Does it indeed make sense to build a GPSDO using an “ordinary”
>  high-quality oscillator? (as opposed to using a Ru standard)
> 
>  It seems that decomissioned rubidium standards are large, rather
>  expensive (hundreds of €), consume lots of power and have
>  uncertain lifetime.
> 
> - Are there recommendations people can make for not-too-expensive
>  VCOs to use in a GPSDO?
> 
> - Are there GPS modules that people here can recommend?
> 
>  I have been looking at the uBlox NEO-7 and the GNS TC6000GN-P1
>  GPS modules.  Both retail around 40€, and promise <100ns PPS jitter.
>  I would probably prefer the NEO-7, because uBlox makes more precise
>  PPS jitter claims for GPS, with 30ns RMS and 60ns for 99 percentile.
> 
> 
> - Some GPS chips offer higher-frequency pulse signals: are those
>  generated with an on-chip PLL?  If not, does it make sense to feed
>  this to the PLL, instead of the 1Hz pulse, to get higher loop gain?
>  (On the other hand, the loop gain must not be too high, as the PLL
>  is meant to get rid of the phase noise in the reference signal)
> 
> - While trying to design this on my own is fun and educational, are
>  there existing designs for DIY GPSDOs that I should look at?
> 
>  I saw Jim Harman's message from last month[0], but this only
>  included the schematic, without the Arduino code that controls the
>  PLL.
> 
>  [0] https://www.febo

Re: [time-nuts] Advise on building a DIY GPSDO?

[Hal Murray]

> Lots of branches and that’s only two questions.

Another interesting question is how good is your antenna?

If your antenna is great and you can tolerate occasional off time, you don't 
need to pay much attention to holdover.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

HI

Ok, let’s back up a bit. The first question is: why? 

There are a few basic answers ( and many not so basic ones):

1) Because you want to save money over the $40 GPSDO’s that are on eBay.

2) Because you want to learn how a GPSDO works.

3) Because you want to make a GPSDO that performs better in a specific 
application 

If it’s 1, I’d suggest that you will have a hard time doing a useful  one up 
design for less than 
you can buy a surplus unit for. I’d extend that to include the wide range of of 
units in the < $200
delivered price range. 

If it’s 2 or 3, you will need a pretty well equipped bench to make much 
headway. The cost and time
associated with those bits and pieces is not at all trivial. You both need good 
measurement 
capability *and* a lab standard to compare to. 

The next question is: what for?

Again a few basic answers: 

1) Anything that works at all is fine, it’s just an experiment. 

2) It’s going to be a lab standard that drives the following gear …..

3) It will drive my 100 GHz narrowband data radio project 

Focusing on 2 and 3:

Phase noise is going to be pretty important for a microwave system. Short term 
stability will be 
important for things like frequent counters. A design that does both *is* 
possible. It also is fairly
complicated.

Each of these decisions loop back and drive the bench gear you will need under 
the first question. 

Lots of branches and that’s only two questions.

Bob



> On Apr 3, 2016, at 6:04 PM, Nicolas Braud-Santoni  
> wrote:
> 
> Hi,
> 
> I've been slowly becoming a fellow timenut over the last few years,
>  though said nuttery had yet to go beyond adding some wiring to
>  get the PPS signal out of my GPS and into my NTPd.
> 
> 
> Lately, I have been looking into designing & building a home-brew
>  GPSDO (and my copy of TAoE 3rd ed. came in quite handy), but quite
>  a few questions came up:
> 
> - Does it indeed make sense to build a GPSDO using an “ordinary”
>  high-quality oscillator? (as opposed to using a Ru standard)
> 
>  It seems that decomissioned rubidium standards are large, rather
>  expensive (hundreds of €), consume lots of power and have
>  uncertain lifetime.
> 
> - Are there recommendations people can make for not-too-expensive
>  VCOs to use in a GPSDO?
> 
> - Are there GPS modules that people here can recommend?
> 
>  I have been looking at the uBlox NEO-7 and the GNS TC6000GN-P1
>  GPS modules.  Both retail around 40€, and promise <100ns PPS jitter.
>  I would probably prefer the NEO-7, because uBlox makes more precise
>  PPS jitter claims for GPS, with 30ns RMS and 60ns for 99 percentile.
> 
> 
> - Some GPS chips offer higher-frequency pulse signals: are those
>  generated with an on-chip PLL?  If not, does it make sense to feed
>  this to the PLL, instead of the 1Hz pulse, to get higher loop gain?
>  (On the other hand, the loop gain must not be too high, as the PLL
>  is meant to get rid of the phase noise in the reference signal)
> 
> - While trying to design this on my own is fun and educational, are
>  there existing designs for DIY GPSDOs that I should look at?
> 
>  I saw Jim Harman's message from last month[0], but this only
>  included the schematic, without the Arduino code that controls the
>  PLL.
> 
>  [0] https://www.febo.com/pipermail/time-nuts/2016-February/096134.html
> 
> - Should I prefer using an IC implementation of the PLL (this seems
>  simpler) or should I consider having my own implementation?
> 
>  Option 2 is what Jim has gone with[0], and in principle that could
>  let me learn correction coefficients for ageing and temperature,
>  but this seem like a big overreach for a first attempt.
> 
> 
> For reference, my use-case (beyond simply building it) is two-fold:
> - I want an accurate ref. clock for my local NTP setup.
> - I need a frequency reference for QRSS (low-power RF transmissions),
>  and getting a 8MHz reference out of the GPSDO would help a lot  :)
> 
> 
> Best regards,
> 
>  Nicolas
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bill Hawkins]

Perhaps you should quantify your goals - unless you are simply looking
for the best you can do with the money you have.

Then discover Tom Van Baak's website www.leapsecond.com - There is very
little that he has not tried at one time or another.

The short answer is that you use crystal oscillators for the short time
constant accuracy that is not available from Rubidium.

Good fortune.

Bill Hawkins

-Original Message-
From: Nicolas Braud-Santoni
Sent: Sunday, April 03, 2016 5:04 PM
To: time-nuts@febo.com
Subject: [time-nuts] Advise on building a DIY GPSDO?

Hi,

I've been slowly becoming a fellow timenut over the last few years,
  though said nuttery had yet to go beyond adding some wiring to
  get the PPS signal out of my GPS and into my NTPd.


%<--- [snip]

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Re: [time-nuts] Advise on building a DIY GPSDO?

[Attila Kinali]

Salut Nicolas,

On Mon, 4 Apr 2016 00:04:29 +0200
Nicolas Braud-Santoni  wrote:

> Lately, I have been looking into designing & building a home-brew
>   GPSDO (and my copy of TAoE 3rd ed. came in quite handy), but quite
>   a few questions came up:

I have put together a short list of GPSDO designs and their 
advantages/disadvantages a few weeks ago, you might want to have
a look at this:
https://attila.kinali.ch/blog/2016/02/07/gps-disciplined-oscillator

> - Does it indeed make sense to build a GPSDO using an “ordinary”
>   high-quality oscillator? (as opposed to using a Ru standard)

It largely depends on what you want/need.
An Rb reference is more stable and you can integrate over several hours
or even days instead of minutes to hours.
 
>   It seems that decomissioned rubidium standards are large, rather
>   expensive (hundreds of €), consume lots of power and have
>   uncertain lifetime.

That's the big disadvantage of the Rb approach.


> - Are there recommendations people can make for not-too-expensive
>   VCOs to use in a GPSDO?

the Connor-Winfield DOT-050 seems to be quite decent, if you look at
Nick Sawyers measurements. Other than that, a 10811 is pretty decent
and quite stable, but also costs usually >100USD on ebay.

People have used Morion's MV-89, Isotemp 131, etc...
 
> - Are there GPS modules that people here can recommend?
> 
>   I have been looking at the uBlox NEO-7 and the GNS TC6000GN-P1
>   GPS modules.  Both retail around 40€, and promise <100ns PPS jitter.
>   I would probably prefer the NEO-7, because uBlox makes more precise
>   PPS jitter claims for GPS, with 30ns RMS and 60ns for 99 percentile.

Get a LEA-6T, NEO/LEA-M8T or LEA-M8F.
You really do want the "fixed position" feature.
Unless you want to go "low cost"


> - Some GPS chips offer higher-frequency pulse signals: are those
>   generated with an on-chip PLL?  If not, does it make sense to feed
>   this to the PLL, instead of the 1Hz pulse, to get higher loop gain?
>   (On the other hand, the loop gain must not be too high, as the PLL
>   is meant to get rid of the phase noise in the reference signal)

Depends on the chip.
Usually there is no "PLL" per se on the chip/module but rather they use
the on board TCXO/XO with an counter and use pulse skipping to get to
the right frequency and phase. Note, the LEA's have two modi, one where
they have "controlled" frequency and one where they have "controlled" phase.


> - While trying to design this on my own is fun and educational, are
>   there existing designs for DIY GPSDOs that I should look at?

See above blog post.

> - Should I prefer using an IC implementation of the PLL (this seems
>   simpler) or should I consider having my own implementation?

Depends. What loop bandwidth do you expect? Is it seconds? That can be
done with a PLL chip. Or is it minutes/hours/days? Then you have to
do it digitally.

> For reference, my use-case (beyond simply building it) is two-fold:
> - I want an accurate ref. clock for my local NTP setup.

For this you don't even need a GPSDO. Just use a normal GPS receiver
(which can be bought for less than 30USD on ebay), place it somewhere
with good skyview and you will get something in the order of 30-60ns
jitter, which is way beyond what your PC can measure anyways.

> - I need a frequency reference for QRSS (low-power RF transmissions),
>   and getting a 8MHz reference out of the GPSDO would help a lot  :)

How good has this reference to be? How much frequency deviation does it
tolerate? How much phase and frequency drift does it tolerate?

It might be, that a good OCXO is already stable enough for QRSS.
Or just an cheap OCXO locked to an FE-5680 with a low (<10Hz)
loop bandwidth.

Attila Kinali


-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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[time-nuts] Advise on building a DIY GPSDO?

[Nicolas Braud-Santoni]

Hi,

I've been slowly becoming a fellow timenut over the last few years,
  though said nuttery had yet to go beyond adding some wiring to
  get the PPS signal out of my GPS and into my NTPd.


Lately, I have been looking into designing & building a home-brew
  GPSDO (and my copy of TAoE 3rd ed. came in quite handy), but quite
  a few questions came up:

- Does it indeed make sense to build a GPSDO using an “ordinary”
  high-quality oscillator? (as opposed to using a Ru standard)

  It seems that decomissioned rubidium standards are large, rather
  expensive (hundreds of €), consume lots of power and have
  uncertain lifetime.

- Are there recommendations people can make for not-too-expensive
  VCOs to use in a GPSDO?

- Are there GPS modules that people here can recommend?

  I have been looking at the uBlox NEO-7 and the GNS TC6000GN-P1
  GPS modules.  Both retail around 40€, and promise <100ns PPS jitter.
  I would probably prefer the NEO-7, because uBlox makes more precise
  PPS jitter claims for GPS, with 30ns RMS and 60ns for 99 percentile.


- Some GPS chips offer higher-frequency pulse signals: are those
  generated with an on-chip PLL?  If not, does it make sense to feed
  this to the PLL, instead of the 1Hz pulse, to get higher loop gain?
  (On the other hand, the loop gain must not be too high, as the PLL
  is meant to get rid of the phase noise in the reference signal)

- While trying to design this on my own is fun and educational, are
  there existing designs for DIY GPSDOs that I should look at?

  I saw Jim Harman's message from last month[0], but this only
  included the schematic, without the Arduino code that controls the
  PLL.

  [0] https://www.febo.com/pipermail/time-nuts/2016-February/096134.html

- Should I prefer using an IC implementation of the PLL (this seems
  simpler) or should I consider having my own implementation?

  Option 2 is what Jim has gone with[0], and in principle that could
  let me learn correction coefficients for ageing and temperature,
  but this seem like a big overreach for a first attempt.


For reference, my use-case (beyond simply building it) is two-fold:
- I want an accurate ref. clock for my local NTP setup.
- I need a frequency reference for QRSS (low-power RF transmissions),
  and getting a 8MHz reference out of the GPSDO would help a lot  :)


Best regards,

  Nicolas


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