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.



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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  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" 
> To: ewkeh...@aol.com, "Discussion of precise time and frequency measurement" 
> 
> 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  
> > 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:  

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  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" 
>> To: ewkeh...@aol.com, "Discussion of precise time and frequency measurement" 
>> 
>> 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  
>>> 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 

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" 
> To: ewkeh...@aol.com, "Discussion of precise time and frequency measurement" 
> 
> 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  
> > 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

Re: [time-nuts] Building a mains frequency monitor

[Ben Hall]

On 4/8/2016 7:19 PM, Nick Sayer via time-nuts wrote:

The instructable I wrote about it is at
http://www.instructables.com/id/Science-fair-How-accurate-is-the-AC-line-frequency/

 There’s code for the Arduino and the Linux side as well as
schematics.


Hi Nick,

Awesome, thanks mucho!!!

thanks again,
ben, kd5byb

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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.
>>> ___
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>>> 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.
>>> ___
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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.
> 
>> ___
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>> 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.
> >  ___
> > time-nuts mailing  list -- time-nuts@febo.com
> > To unsubscribe, go to
>  https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > 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
> >
> >
> >> ___
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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
>> 
>> 
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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


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>>> and follow the instructions there.
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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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