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] Holdover recovery

[Azelio Boriani]

Yes, very interesting, good to have. I see differences: the most
notable is the plot of page 12 on the original italian version that is
missing on the ITU paper, that goes with the figure 4 on page 7 (of
the ITU one).

On Tue, Apr 5, 2016 at 12:57 AM, Magnus Danielson
 wrote:
> Hi,
>
> I had not seen the ITU-R version, nice.
> I have their paper and shared it with Hal on the side.
>
> This ITU-R version seems about the same, but I've got their names on it. I
> got a copy of their paper in english without their names on it, which might
> have been their input contribution to ITU-R. I then demanded a version with
> their names on it, so that I could share it, within a day I had that. When
> someone covered this aspect, why not spread it and they get the credit for
> it?
>
> I've visited them and seen this setup.
>
> Cheers,
> Magnus - who just got back to lodging/dorm-room after discussing things with
> Attila
>
>
> On 04/05/2016 12:01 AM, Logan Cummings wrote:
>>
>> My Italian is not very good, but I think this is the English translation
>> via ITU:
>>
>> https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2253-2012-PDF-E.pdf
>>
>> -Logan
>>
>> On Mon, Apr 4, 2016 at 1:10 PM,  wrote:
>>
>>> Here the italian version:
>>>
>>> http://www.crit.rai.it/eletel/2012-1/121-2.pdf
>>>
>>> Luciano
>>> www.timeok.it
>>>
>>>
>>> On Mon 04/04/16 21:28 , Magnus Danielson 
>>> wrote:
>>>
 Hi Hal,

 On 04/04/2016 05:39 AM, Hal Murray wrote:
>
>
> Has anybody studied what happens when a GPSDO comes out of holdover?
>>>
>>> Has
>
> anybody seen any specs? I don't think I have.
>
> I think you have a choice of quick recovery for time or frequency, but

 you
>
> can't get both.
>
> Suppose your setup has been in holdover for a while. The frequency is
> slightly off. The time offset of the PPS pulse will be the integral of

 the
>
> frequency offset.
>
> What happens when you come out of holdover? If you fix the frequency,

 the
>
> PPS will stay off.
>
> Suppose the PPS has drifted by 1 ns. If you correct that in 1 second,

 the
>
> frequency will need to be off by 1E9 during that second.


 The RAI laboratory in Torino have made such tests and published
 measurements and recommendations. For a long time it was only available
 in italian, but there is now an english version available.

 Cheers,
 Magnus
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 Links:
 --
 [1]

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>>> http://webmail.timeok.it/parse.php?redirect=https://www.febo.com/cgi-bin/ma

 ilman/listinfo/time-nuts

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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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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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Re: [time-nuts] Holdover recovery

[Magnus Danielson]

Hi,

I had not seen the ITU-R version, nice.
I have their paper and shared it with Hal on the side.

This ITU-R version seems about the same, but I've got their names on it. 
I got a copy of their paper in english without their names on it, which 
might have been their input contribution to ITU-R. I then demanded a 
version with their names on it, so that I could share it, within a day I 
had that. When someone covered this aspect, why not spread it and they 
get the credit for it?


I've visited them and seen this setup.

Cheers,
Magnus - who just got back to lodging/dorm-room after discussing things 
with Attila


On 04/05/2016 12:01 AM, Logan Cummings wrote:

My Italian is not very good, but I think this is the English translation
via ITU:

https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2253-2012-PDF-E.pdf

-Logan

On Mon, Apr 4, 2016 at 1:10 PM,  wrote:


Here the italian version:

http://www.crit.rai.it/eletel/2012-1/121-2.pdf

Luciano
www.timeok.it


On Mon 04/04/16 21:28 , Magnus Danielson 
wrote:


Hi Hal,

On 04/04/2016 05:39 AM, Hal Murray wrote:


Has anybody studied what happens when a GPSDO comes out of holdover?

Has

anybody seen any specs? I don't think I have.

I think you have a choice of quick recovery for time or frequency, but

you

can't get both.

Suppose your setup has been in holdover for a while. The frequency is
slightly off. The time offset of the PPS pulse will be the integral of

the

frequency offset.

What happens when you come out of holdover? If you fix the frequency,

the

PPS will stay off.

Suppose the PPS has drifted by 1 ns. If you correct that in 1 second,

the

frequency will need to be off by 1E9 during that second.


The RAI laboratory in Torino have made such tests and published
measurements and recommendations. For a long time it was only available
in italian, but there is now an english version available.

Cheers,
Magnus
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Re: [time-nuts] Holdover recovery

[Bob Camp]

Hi

On a surplus cell phone GPSDO it’s going to be:

1) System has been down for a while (= something failed) 
2) System is now working ( = something was fixed)
3) The primary system spec must now be met (+/- 100 ns time alignment).
4) The secondary system spec should be met (+/- 5x10^-8 frequency) 
5) Get it done now.

Both the time alignment and frequency specs are highly system dependent. The 
time
offset is likely to be aligned in a modulo 100 ns step. It then is fine tuned 
over some 
time period to take out the rest of the error. If it’s done over a 50 second 
period, they
can do it at a 1x10^-9 frequency offset (but probably don’t …. more likely it’s 
a higher 
offset at the start of the period).

Bob


> On Apr 3, 2016, at 11:39 PM, Hal Murray  wrote:
> 
> 
> Has anybody studied what happens when a GPSDO comes out of holdover?  Has 
> anybody seen any specs?  I don't think I have.
> 
> I think you have a choice of quick recovery for time or frequency, but you 
> can't get both.
> 
> Suppose your setup has been in holdover for a while.  The frequency is 
> slightly off.  The time offset of the PPS pulse will be the integral of the 
> frequency offset.
> 
> What happens when you come out of holdover?  If you fix the frequency, the 
> PPS will stay off.
> 
> Suppose the PPS has drifted by 1 ns.  If you correct that in 1 second, the 
> frequency will need to be off by 1E9 during that second.
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] Holdover recovery

[Logan Cummings]

My Italian is not very good, but I think this is the English translation
via ITU:

https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2253-2012-PDF-E.pdf

-Logan

On Mon, Apr 4, 2016 at 1:10 PM,  wrote:

> Here the italian version:
>
> http://www.crit.rai.it/eletel/2012-1/121-2.pdf
>
> Luciano
> www.timeok.it
>
>
> On Mon 04/04/16 21:28 , Magnus Danielson 
> wrote:
>
> > Hi Hal,
> >
> > On 04/04/2016 05:39 AM, Hal Murray wrote:
> > >
> > > Has anybody studied what happens when a GPSDO comes out of holdover?
> Has
> > > anybody seen any specs? I don't think I have.
> > >
> > > I think you have a choice of quick recovery for time or frequency, but
> > you
> > > can't get both.
> > >
> > > Suppose your setup has been in holdover for a while. The frequency is
> > > slightly off. The time offset of the PPS pulse will be the integral of
> > the
> > > frequency offset.
> > >
> > > What happens when you come out of holdover? If you fix the frequency,
> > the
> > > PPS will stay off.
> > >
> > > Suppose the PPS has drifted by 1 ns. If you correct that in 1 second,
> > the
> > > frequency will need to be off by 1E9 during that second.
> >
> > The RAI laboratory in Torino have made such tests and published
> > measurements and recommendations. For a long time it was only available
> > in italian, but there is now an english version available.
> >
> > Cheers,
> > Magnus
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
> > To unsubscribe, go to
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts [1]
> > and follow the instructions there.
> >
> >
> >
> > Links:
> > --
> > [1]
> >
> http://webmail.timeok.it/parse.php?redirect=https://www.febo.com/cgi-bin/ma
> > ilman/listinfo/time-nuts
> >
> Message sent via Atmail Open - http://atmail.org/
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Re: [time-nuts] Holdover recovery

[Azelio Boriani]

The only english text I'm able to find is:

Analysis of the GPS frequency reference stability

Laboratory analysis of the dynamic
behaviour of some GPS receivers has
allowed to identify a criticality in their
use as ‘clocks’ to synchronize DVB-T
SFN networks. To fix this criticality, the
Research Centre has defined a new criterion
for the design of GPS equipment
for use in broadcasting applications.
This criterion is proposed as an Italian
contribution to the ITU


On Mon, Apr 4, 2016 at 10:10 PM,   wrote:
> Here the italian version:
>
> http://www.crit.rai.it/eletel/2012-1/121-2.pdf
>
> Luciano
> www.timeok.it
>
>
> On Mon 04/04/16 21:28 , Magnus Danielson  wrote:
>
>> Hi Hal,
>>
>> On 04/04/2016 05:39 AM, Hal Murray wrote:
>> >
>> > Has anybody studied what happens when a GPSDO comes out of holdover? Has
>> > anybody seen any specs? I don't think I have.
>> >
>> > I think you have a choice of quick recovery for time or frequency, but
>> you
>> > can't get both.
>> >
>> > Suppose your setup has been in holdover for a while. The frequency is
>> > slightly off. The time offset of the PPS pulse will be the integral of
>> the
>> > frequency offset.
>> >
>> > What happens when you come out of holdover? If you fix the frequency,
>> the
>> > PPS will stay off.
>> >
>> > Suppose the PPS has drifted by 1 ns. If you correct that in 1 second,
>> the
>> > frequency will need to be off by 1E9 during that second.
>>
>> The RAI laboratory in Torino have made such tests and published
>> measurements and recommendations. For a long time it was only available
>> in italian, but there is now an english version available.
>>
>> Cheers,
>> Magnus
>> ___
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>>
>>
>>
>> Links:
>> --
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Re: [time-nuts] Holdover recovery

[timeok]

Here the italian version:

http://www.crit.rai.it/eletel/2012-1/121-2.pdf

Luciano
www.timeok.it


On Mon 04/04/16 21:28 , Magnus Danielson  wrote:

> Hi Hal,
> 
> On 04/04/2016 05:39 AM, Hal Murray wrote:
> >
> > Has anybody studied what happens when a GPSDO comes out of holdover? Has
> > anybody seen any specs? I don't think I have.
> >
> > I think you have a choice of quick recovery for time or frequency, but
> you
> > can't get both.
> >
> > Suppose your setup has been in holdover for a while. The frequency is
> > slightly off. The time offset of the PPS pulse will be the integral of
> the
> > frequency offset.
> >
> > What happens when you come out of holdover? If you fix the frequency,
> the
> > PPS will stay off.
> >
> > Suppose the PPS has drifted by 1 ns. If you correct that in 1 second,
> the
> > frequency will need to be off by 1E9 during that second.
> 
> The RAI laboratory in Torino have made such tests and published 
> measurements and recommendations. For a long time it was only available 
> in italian, but there is now an english version available.
> 
> Cheers,
> Magnus
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> 
> 
> Links:
> --
> [1]
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Re: [time-nuts] Holdover recovery

[Azelio Boriani]

In italian:

Can't find it in english...

On Mon, Apr 4, 2016 at 9:28 PM, Magnus Danielson
 wrote:
> Hi Hal,
>
> On 04/04/2016 05:39 AM, Hal Murray wrote:
>>
>>
>> Has anybody studied what happens when a GPSDO comes out of holdover?  Has
>> anybody seen any specs?  I don't think I have.
>>
>> I think you have a choice of quick recovery for time or frequency, but you
>> can't get both.
>>
>> Suppose your setup has been in holdover for a while.  The frequency is
>> slightly off.  The time offset of the PPS pulse will be the integral of
>> the
>> frequency offset.
>>
>> What happens when you come out of holdover?  If you fix the frequency, the
>> PPS will stay off.
>>
>> Suppose the PPS has drifted by 1 ns.  If you correct that in 1 second, the
>> frequency will need to be off by 1E9 during that second.
>
>
> The RAI laboratory in Torino have made such tests and published measurements
> and recommendations. For a long time it was only available in italian, but
> there is now an english version available.
>
> Cheers,
> Magnus
> ___
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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  wrote:

 Subject: Re: [time-nuts] Advise on building a DIY GPSDO?
 To: "'Discussion of precise time and frequency measurement'" 

 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] Holdover recovery

[Magnus Danielson]

Hi Hal,

On 04/04/2016 05:39 AM, Hal Murray wrote:


Has anybody studied what happens when a GPSDO comes out of holdover?  Has
anybody seen any specs?  I don't think I have.

I think you have a choice of quick recovery for time or frequency, but you
can't get both.

Suppose your setup has been in holdover for a while.  The frequency is
slightly off.  The time offset of the PPS pulse will be the integral of the
frequency offset.

What happens when you come out of holdover?  If you fix the frequency, the
PPS will stay off.

Suppose the PPS has drifted by 1 ns.  If you correct that in 1 second, the
frequency will need to be off by 1E9 during that second.


The RAI laboratory in Torino have made such tests and published 
measurements and recommendations. For a long time it was only available 
in italian, but there is now an english version available.


Cheers,
Magnus
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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 
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  
> 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 

[time-nuts] Replacement Oncore Modules - all gone for now

[Pete Lancashire]

The demand has been much more then I expected, and didn't expect almost
everyone one to want two.

I had no idea there were so many old HP units out there.

I do not know if I can fulfil all the requests. Packages will be sent FIFS
"First In First Shipped".

Again if I do not have an address that the Post Office will ship to, I
can't ship it.
If you are not in the US or Canada, I'll contact you on what the cost will
be.


For those that maybe just looking for a receiver, by today's standards
these things are not all that great. Don't be disappointed. I suggest
getting something newer.

I'll start boxing the ones I have pulled this week, and then next week
start pulling apart more of the devices the modules are in.

Regards,

-pete
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Re: [time-nuts] Holdover recovery

[jimlux]

On 4/3/16 8:39 PM, Hal Murray wrote:


Has anybody studied what happens when a GPSDO comes out of holdover?  Has
anybody seen any specs?  I don't think I have.

I think you have a choice of quick recovery for time or frequency, but you
can't get both.

Suppose your setup has been in holdover for a while.  The frequency is
slightly off.  The time offset of the PPS pulse will be the integral of the
frequency offset.

What happens when you come out of holdover?  If you fix the frequency, the
PPS will stay off.

Suppose the PPS has drifted by 1 ns.  If you correct that in 1 second, the
frequency will need to be off by 1E9 during that second.



This is something we've been developing some algorithms for. (and I 
think NTP does this already).. depending on whether you were high or low 
in frequency, you need to smoothly bring the frequency back, with some 
overshoot (to "catch up").


I think it really boils down so some simple requirements:

Time (aka phase) must always be monotonically increasing
Time and frequency (which is the derivative of time) and some number of 
higher order derivatives must be continuous.

The maximum error is bounded to some number.



As you've noted, going for the minimum error in time might lead to a 
discontinuity in frequency.


We have an interesting problem in that we want to discipline a clock 
which is inherently of high accuracy to a reference that is poorer in 
accuracy, but which is defined as the "master" so we need to follow it. 
 The usual NTP and similar time discipline algorithms are really 
predicated on a "flow down" from more accurate to less accurate.



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Re: [time-nuts] Holdover recovery

[Mike Cook]

> Le 4 avr. 2016 à 05:39, Hal Murray  a écrit :
> 
> 
> Has anybody studied what happens when a GPSDO comes out of holdover?  Has 
> anybody seen any specs?  I don't think I have.
> 
> I think you have a choice of quick recovery for time or frequency, but you 
> can't get both.
> 
> Suppose your setup has been in holdover for a while.  The frequency is 
> slightly off.  The time offset of the PPS pulse will be the integral of the 
> frequency offset.
> 
> What happens when you come out of holdover?  If you fix the frequency, the 
> PPS will stay off.
> 
> Suppose the PPS has drifted by 1 ns.  If you correct that in 1 second, the 
> frequency will need to be off by 1E9 during that second.
> 

I guess it is implementation dependent. I have observed this on Tbolt and PRS10 
a while back but the graphs have transformed into unfindium.
Something else on the redo list. I think what really happens is that the PPS 
lock is made on the nearest cycle when the GPS signal is recovered and then the 
frequency is adjusted using subsequent GPS data according to whatever the 
PLL/FLL constants were in effect at the time. So getting back to correct 
frequency could take a long time.

> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] Holdover recovery

[Tim Shoppa]

The chinese GPSDO's famous on E-bay are not really phase locked to begin
with, they are only frequency locked and often with a small frequency
offset. I don't think any of your questions apply to this kind of unit. See
e.g. http://www.ke5fx.com/gpscomp.htm

Units that have been spec'ed for holdover in terms of time delta, make
phase the number one priority and will gladly "oversteer" frequency to get
the phase to match back up after holdover and then settling down again,.
e.g. http://leapsecond.com/pages/z3801a-efc/

In recovery from a holdover where something went clearly wrong - the
holdover specs of the unit were greatly exceeded - they declare themselves
unlocked, and will do a phase jump and enter a "frequency lock" mode until
oscillator parameters are relearned and they again declare themselves
locked.

Tim N3QE

On Sun, Apr 3, 2016 at 11:39 PM, Hal Murray  wrote:

>
> Has anybody studied what happens when a GPSDO comes out of holdover?  Has
> anybody seen any specs?  I don't think I have.
>
> I think you have a choice of quick recovery for time or frequency, but you
> can't get both.
>
> Suppose your setup has been in holdover for a while.  The frequency is
> slightly off.  The time offset of the PPS pulse will be the integral of the
> frequency offset.
>
> What happens when you come out of holdover?  If you fix the frequency, the
> PPS will stay off.
>
> Suppose the PPS has drifted by 1 ns.  If you correct that in 1 second, the
> frequency will need to be off by 1E9 during that second.
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
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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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[time-nuts] Holdover recovery

[Hal Murray]

Has anybody studied what happens when a GPSDO comes out of holdover?  Has 
anybody seen any specs?  I don't think I have.

I think you have a choice of quick recovery for time or frequency, but you 
can't get both.

Suppose your setup has been in holdover for a while.  The frequency is 
slightly off.  The time offset of the PPS pulse will be the integral of the 
frequency offset.

What happens when you come out of holdover?  If you fix the frequency, the 
PPS will stay off.

Suppose the PPS has drifted by 1 ns.  If you correct that in 1 second, the 
frequency will need to be off by 1E9 during that second.


-- 
These are my opinions.  I hate spam.



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