Re: [time-nuts] True Position GPSDP + Rb X72

[Stephan Flor via time-nuts]

The True Position GPSDO is working, locked to 8 satellites. It's 10MHz output 
is extremely close to the X72's output. Using an oscilloscope to compare the 
signals  with a lissajous pattern, there is only a very small, slow movement, 
barely perceivable. I don't  need to do any calibration to the X72. Steve
 

On Sunday, October 1, 2017 10:45 AM, Stephan Flor via time-nuts 
 wrote:
 

 I figured it out. It was the ASCII settings, it's working now.  
  
  - ASCII Sending,  "Echo typed characters locally"
  - ASCII Receiving,  "Append line feeds to incoming line ends"
Thanks,Steve 

    On Sunday, October 1, 2017 8:30 AM, Stephan Flor  wrote:
 

 
 
I received my True Position GPSDO. I'm testing it.I am connected to it via a 
rs232 port, and using HyperTerminal on a XP laptop to communicate. I'm getting 
the boot message "GETVER 12.0.1 BOOT".
This may be a stupid question, but how do I get the boot message to stop so I 
can send the "$PROCEED" command?  If I type while the message is scrolling, I 
have no courser, and no text appears on the screen. 
Thanks,Steve    On Friday, September 29, 2017 5:32 PM, Attila Kinali 
 wrote:
 

 On Sun, 24 Sep 2017 01:06:36 -0400
ewkehren via time-nuts  wrote:

> Starting with a 10 second clean up loop for a FEI 5680/GPSDO to now 600 
> Seconds using Wenzel's j circuit for the Tbolt we have a variety of boards.

Which one is Wenzel's j circuit? Google does not seem to be able to find it.
And going through relevant circuits on wenzel.com didnt reveal any j circuit.
-- 
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] True Position GPSDP + Rb X72

[Stephan Flor via time-nuts]

I figured it out. It was the ASCII settings, it's working now.   
   
   - ASCII Sending,  "Echo typed characters locally"
   - ASCII Receiving,  "Append line feeds to incoming line ends"
Thanks,Steve 

On Sunday, October 1, 2017 8:30 AM, Stephan Flor  wrote:
 

 
 
I received my True Position GPSDO. I'm testing it.I am connected to it via a 
rs232 port, and using HyperTerminal on a XP laptop to communicate. I'm getting 
the boot message "GETVER 12.0.1 BOOT".
This may be a stupid question, but how do I get the boot message to stop so I 
can send the "$PROCEED" command?  If I type while the message is scrolling, I 
have no courser, and no text appears on the screen. 
Thanks,SteveOn Friday, September 29, 2017 5:32 PM, Attila Kinali 
 wrote:
 

 On Sun, 24 Sep 2017 01:06:36 -0400
ewkehren via time-nuts  wrote:

> Starting with a 10 second clean up loop for a FEI 5680/GPSDO to now 600 
> Seconds using Wenzel's j circuit for the Tbolt we have a variety of boards.

Which one is Wenzel's j circuit? Google does not seem to be able to find it.
And going through relevant circuits on wenzel.com didnt reveal any j circuit.
-- 
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] True Position GPSDP + Rb X72

[Stephan Flor via time-nuts]

 
I received my True Position GPSDO. I'm testing it.I am connected to it via a 
rs232 port, and using HyperTerminal on a XP laptop to communicate. I'm getting 
the boot message "GETVER 12.0.1 BOOT".
This may be a stupid question, but how do I get the boot message to stop so I 
can send the "$PROCEED" command?  If I type while the message is scrolling, I 
have no courser, and no text appears on the screen. 
Thanks,SteveOn Friday, September 29, 2017 5:32 PM, Attila Kinali 
 wrote:
 

 On Sun, 24 Sep 2017 01:06:36 -0400
ewkehren via time-nuts  wrote:

> Starting with a 10 second clean up loop for a FEI 5680/GPSDO to now 600 
> Seconds using Wenzel's j circuit for the Tbolt we have a variety of boards.

Which one is Wenzel's j circuit? Google does not seem to be able to find it.
And going through relevant circuits on wenzel.com didnt reveal any j circuit.
-- 
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] True Position GPSDP + Rb X72

[Attila Kinali]

On Sun, 24 Sep 2017 01:06:36 -0400
ewkehren via time-nuts  wrote:

> Starting with a 10 second clean up loop for a FEI 5680/GPSDO to now 600 
> Seconds using Wenzel's j circuit for the Tbolt we have a variety of boards.

Which one is Wenzel's j circuit? Google does not seem to be able to find it.
And going through relevant circuits on wenzel.com didnt reveal any j circuit.
-- 
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] True Position GPSDP + Rb X72

[KA2WEU--- via time-nuts]

Meaning home=home ?  just kidding. ,long staying constant 
 
73 de Ulrich 
 
 
In a message dated 9/24/2017 8:45:35 A.M. Eastern Daylight Time,  
mag...@rubidium.dyndns.org writes:

Hi,

On 09/24/2017 02:30 PM, Bob kb8tq wrote:
>  Hi
> 
> 
>> On Sep 23, 2017, at 9:39 PM, Hal Murray   wrote:
>>
>>
>>  kb...@n1k.org said:
>>> If the main use is feeding test gear (and  not direct synthesis) an Rb 
may do
>>> pretty well. Most  instruments assume a dirty reference signal and 
clean it
>>> up  internally.
>>
>> What's the bandwidth on the typical  cleanup PLL?  How well does that 
match
>> the noise from a  Rb?
> 
> It’s like any other PLL with noise involved. You look at  the noise of 
the Rb, the
> noise of the particular cleanup oscillator,  and your system 
requirements. In some
> cases that comes out to a few  seconds. For Time Nut grade with a really 
good
> OCXO you are at some  pretty long numbers.
> 
> If the Rb starts at 2x10^-11 at 1 second  and goes down by square root 
tau: At
> 100 seconds you are at 2x10^12.  Still not as good as a really good OCXO. 
At
> 10,000 seconds you might  get to 2x10^-13 (but probably will not). Your 
OCXO
> likely will climb  out of the “parts in 10^-13” range before 10,000 
seconds.
> 
>  Lots of fun.

Once up on a time, you could order the OSA cesiums width  different 
oscillators, essentially to buy into different balances between  
oscillator cost and performance. The time constant is adapter with  
regards to oscillator type, as the trade off shifts.

I can't recall  any other cesium or rubidium that did this, but HP 
upgraded oscillators at  one point for this reason  too.

Cheers,
Magnus
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Re: [time-nuts] True Position GPSDP + Rb X72

[Magnus Danielson]

Hi,

On 09/24/2017 02:30 PM, Bob kb8tq wrote:

Hi



On Sep 23, 2017, at 9:39 PM, Hal Murray  wrote:


kb...@n1k.org said:

If the main use is feeding test gear (and not direct synthesis) an Rb may do
pretty well. Most instruments assume a dirty reference signal and clean it
up internally.


What's the bandwidth on the typical cleanup PLL?  How well does that match
the noise from a Rb?


It’s like any other PLL with noise involved. You look at the noise of the Rb, 
the
noise of the particular cleanup oscillator, and your system requirements. In 
some
cases that comes out to a few seconds. For Time Nut grade with a really good
OCXO you are at some pretty long numbers.

If the Rb starts at 2x10^-11 at 1 second and goes down by square root tau: At
100 seconds you are at 2x10^12. Still not as good as a really good OCXO. At
10,000 seconds you might get to 2x10^-13 (but probably will not). Your OCXO
likely will climb out of the “parts in 10^-13” range before 10,000 seconds.

Lots of fun.


Once up on a time, you could order the OSA cesiums width different 
oscillators, essentially to buy into different balances between 
oscillator cost and performance. The time constant is adapter with 
regards to oscillator type, as the trade off shifts.


I can't recall any other cesium or rubidium that did this, but HP 
upgraded oscillators at one point for this reason too.


Cheers,
Magnus
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Re: [time-nuts] True Position GPSDP + Rb X72

[Bob kb8tq]

Hi


> On Sep 23, 2017, at 9:39 PM, Hal Murray  wrote:
> 
> 
> kb...@n1k.org said:
>> If the main use is feeding test gear (and not direct synthesis) an Rb may do
>> pretty well. Most instruments assume a dirty reference signal and clean it
>> up internally.  
> 
> What's the bandwidth on the typical cleanup PLL?  How well does that match 
> the noise from a Rb?

It’s like any other PLL with noise involved. You look at the noise of the Rb, 
the 
noise of the particular cleanup oscillator, and your system requirements. In 
some
cases that comes out to a few seconds. For Time Nut grade with a really good 
OCXO you are at some pretty long numbers. 

If the Rb starts at 2x10^-11 at 1 second and goes down by square root tau: At
100 seconds you are at 2x10^12. Still not as good as a really good OCXO. At 
10,000 seconds you might get to 2x10^-13 (but probably will not). Your OCXO
likely will climb out of the “parts in 10^-13” range before 10,000 seconds. 

Lots of fun.

Bob


> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] True Position GPSDP + Rb X72

[ewkehren via time-nuts]

Starting with a 10 second clean up loop for a FEI 5680/GPSDO to now 600 Seconds 
using Wenzel's j circuit for the Tbolt we have a variety of boards. I am 
presently out of country but when back will gladly attach some board designs, 
material cost is minimal  if there is interest.Bert Kehren


Sent from my Galaxy Tab® A
 Original message From: Hal Murray <hmur...@megapathdsl.net> 
Date: 9/23/17  9:39 PM  (GMT-05:00) To: Discussion of precise time and 
frequency measurement <time-nuts@febo.com> Cc: hmur...@megapathdsl.net Subject: 
Re: [time-nuts] True Position GPSDP + Rb X72 

kb...@n1k.org said:
> If the main use is feeding test gear (and not direct synthesis) an Rb may do
> pretty well. Most instruments assume a dirty reference signal and clean it
> up internally.  

What's the bandwidth on the typical cleanup PLL?  How well does that match 
the noise from a Rb?


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] True Position GPSDP + Rb X72

[Hal Murray]

kb...@n1k.org said:
> If the main use is feeding test gear (and not direct synthesis) an Rb may do
> pretty well. Most instruments assume a dirty reference signal and clean it
> up internally.  

What's the bandwidth on the typical cleanup PLL?  How well does that match 
the noise from a Rb?


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] True Position GPSDP + Rb X72

[Bob kb8tq]

Hi

If the main use is feeding test gear (and not direct synthesis) an Rb may do 
pretty well. Most
instruments assume a dirty reference signal and clean it up internally. 

1 Hz at 20 GHz is 5x10^-11 most sources you measure up there will not be stable 
to 1Hz 
at a 1 second gate. The Rb will be in this vicinity (frequency wise) second to 
second. Long
term drift will not be an issue with monthly calibration. It should be ok for 
temperature in
a constant environment.

Backing off to 1 Hz at 2 GHz takes you down to 5x10^-10. At that point the Rb 
is “plenty good
enough”. Keep it in a reasonably constant environment, calibrate it once a year 
and you’re fine. 

Bob

> On Sep 22, 2017, at 9:32 PM, Stephan Flor via time-nuts  
> wrote:
> 
> The highest frequency I can generate is 2.5 GHz. My counter can measure 20 
> GHz, to 1 HZ. At the moment I'm have a frequency locking problem with the 
> extension module in my HP 8660C, so I can't even get to 2.5 GHz, only 110 MHz 
> at the moment. I gust got some extender boards, so I hope to have it fixed 
> soon. The X72 gives me a solid 10.00 MHz, I would like to see what I get 
> when I use the Rb as a clock for the signal generator, at 2.5 GHz. I guess I 
> only need to verify the calibration with the GPSDO, when I get it, and get it 
> working. Then I can calibrate everything else.
>  So, to make a long answer short, I don't think I need the level of accuracy 
> that these devices are capable of. I just have a neurotic need to try and 
> make things as exact as I possibly can. Also, this is just a hobby, and 
> learning experience for me, so I can take my time to work things out.Thank 
> you,Steve 
> 
>On Thursday, September 21, 2017 12:09 PM, Chris Caudle 
>  wrote:
> 
> 
> On Wed, September 20, 2017 3:44 pm, Stephan Flo via time-nuts wrote:
>> I just wanted a 10 MHz sync for my test equipment that was calibrated.
>> May be the GPSDO is all I need.
> 
> Even an undisciplined rubidium oscillator is going to be very close to
> nominal 10MHz.  You have never stated your desired precision that I have
> seen. The X72 manual says that the output should be within 1E-9 in under
> 10 minutes, and within 5E-11 after 30 minutes.  Does any of the equipment
> you use have finer precision than that?
> 
> -- 
> Chris Caudle
> 
> 
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Re: [time-nuts] True Position GPSDP + Rb X72

[Stephan Flor via time-nuts]

The highest frequency I can generate is 2.5 GHz. My counter can measure 20 GHz, 
to 1 HZ. At the moment I'm have a frequency locking problem with the extension 
module in my HP 8660C, so I can't even get to 2.5 GHz, only 110 MHz at the 
moment. I gust got some extender boards, so I hope to have it fixed soon. The 
X72 gives me a solid 10.00 MHz, I would like to see what I get when I use 
the Rb as a clock for the signal generator, at 2.5 GHz. I guess I only need to 
verify the calibration with the GPSDO, when I get it, and get it working. Then 
I can calibrate everything else.
 So, to make a long answer short, I don't think I need the level of accuracy 
that these devices are capable of. I just have a neurotic need to try and make 
things as exact as I possibly can. Also, this is just a hobby, and learning 
experience for me, so I can take my time to work things out.Thank you,Steve 

On Thursday, September 21, 2017 12:09 PM, Chris Caudle 
 wrote:
 

 On Wed, September 20, 2017 3:44 pm, Stephan Flo via time-nuts wrote:
> I just wanted a 10 MHz sync for my test equipment that was calibrated.
> May be the GPSDO is all I need.

Even an undisciplined rubidium oscillator is going to be very close to
nominal 10MHz.  You have never stated your desired precision that I have
seen. The X72 manual says that the output should be within 1E-9 in under
10 minutes, and within 5E-11 after 30 minutes.  Does any of the equipment
you use have finer precision than that?

-- 
Chris Caudle


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Re: [time-nuts] True Position GPSDP + Rb X72

[Bob kb8tq]

Hi

Given the noise levels of typical Rb’s - use XOR gates as the mixers. 

Do a either a simple LPF on the output or ignore the HF component 
(each approach is a bit of a tradeoff). 

Once you have the beat notes, feed them into timer inputs on your uC
chip of choice. 

If you do the filters as R/C’s they are cheap. If you just re-clock, you
maybe add a flip flop or two to each channel. Total BOM for the DMTD
part of it would be < $1 not counting the OCXO. 

All of the previous comments about “why would you want to do this?” 
still apply. Most of the small Rb’s we can get our hands on have really 
awful phase noise and spurs. That’s not true of all small Rb’s, but buying
them new in small volume at $2K each is not something most of us 
are interested in doing ….

Lots of fun

Bob


> On Sep 22, 2017, at 9:37 AM, Attila Kinali  wrote:
> 
> On Wed, 20 Sep 2017 10:21:51 -0400
> Bob kb8tq  wrote:
> 
>> An alternative is to add an offset oscillator to the mix and look at beat 
>> notes. It does not have to be ultra close. An 11 MHz offset signal would 
>> take the 
>> 12 ns down to an effective 1.2 ns. Odd frequency OCXO’s sell cheap on
> 
> I considered the DMTD approach as well, but couldn't come up with a
> good idea how to make it easy and reliable to implement.
> How would you approach this?
> 
> 
>   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] True Position GPSDP + Rb X72

[Attila Kinali]

On Wed, 20 Sep 2017 10:21:51 -0400
Bob kb8tq  wrote:

> An alternative is to add an offset oscillator to the mix and look at beat 
> notes. It does not have to be ultra close. An 11 MHz offset signal would take 
> the 
> 12 ns down to an effective 1.2 ns. Odd frequency OCXO’s sell cheap on

I considered the DMTD approach as well, but couldn't come up with a
good idea how to make it easy and reliable to implement.
How would you approach this?


Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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[time-nuts] True Position GPSDP + Rb X72

[Mark Sims]

X72 support in Lady Heather is a new feature not in the current v5.0 release.   
If you are running under Linux or can build the v5.0 Windows code, I can send 
you the latest version tp compile.

The X72 has a DDS synthesizer on it that lets you vary the output freq in steps 
of 2.03E-12 parts.  My X72's are off around 6E-10 from nominal (DDS word set to 
0).   

Besides the disciplining code Heather also has a calibration routine that can 
adjust the DDS to on frequency.  It works by connecting a 1PPS  input to the 
X72, setting the DDS word to 0, collecting data for a specified time interval 
(like one hour).  It then calculates how far the 1PPS in and 1PPS out are apart 
using the X72's built in 16.67 ns res TIC.  From that it determines the DDS 
word needed to cancel the 1PPS drift.   

The X72 has a command for saving something in EEPROM (they never say what it 
actually saves).  I don't know if the DDS word is part of what it saves...  I 
think different firmware versions save different things.
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Re: [time-nuts] True Position GPSDP + Rb X72

[Chris Caudle]

On Wed, September 20, 2017 3:44 pm, Stephan Flo via time-nuts wrote:
> I just wanted a 10 MHz sync for my test equipment that was calibrated.
> May be the GPSDO is all I need.

Even an undisciplined rubidium oscillator is going to be very close to
nominal 10MHz.  You have never stated your desired precision that I have
seen. The X72 manual says that the output should be within 1E-9 in under
10 minutes, and within 5E-11 after 30 minutes.  Does any of the equipment
you use have finer precision than that?

-- 
Chris Caudle


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Re: [time-nuts] True Position GPSDP + Rb X72

[Stephan Flor via time-nuts]

Thank you for the great  feedback.  You guys make me realize that I need to 
learn more, I have some studying to do.  I will study while I wait for the True 
position to arrive. Then I have to get it working. I just wanted a 10 MHz sync 
for my test equipment that was calibrated. May be the GPSDO is all I need. 
Steve 

On Wednesday, September 20, 2017 7:28 AM, Bob kb8tq  wrote:
 

 Hi


> On Sep 20, 2017, at 8:39 AM, Attila Kinali  wrote:
> 
> On Tue, 19 Sep 2017 18:09:16 + (UTC)
> Stephan Flor via time-nuts  wrote:
> 
>> Hi everyone,I'm new to this list, and I wanted to get the opinion of some 
>> mere experienced people on my project idea.I just got a Symmetricom X72 Rb 
>> oscillator, and I have a True position GPSDO on the way.  I wan't to have a 
>> self calibrating 10 MHz signal to synchronize my hobby rf lab equipment.
>> My idea is to make a GPS disciplined Rubidium oscillator, by removing the 
>> crystal oscillator ans substituting the X72 in the GPSDO circuit.I would 
>> just 
>> have to make a op amp circuit to change the 0 to 4v correction signal from 
>> the True Position, to a 0 to 5v signal for the X72.
> 
> Unfortunately, this doesn't work as easily as you thing.
> The control loop inside the GPSDO is designed for an OCXO. This means
> that its loop constant is in the 10s to 100s of seconds, while for
> an GPSDRb you would need 10'000s to 100'000s of seconds. The other,
> more criticial issue is the sensitivity of the tuning input. Most
> OCXOs have something like 1-10ppm of tuning range. The tuning range
> of an Rb is usually 2 to 3 orders of magnitude smaller. In a normal
> PI loop, this shouldn't be an issue. But you don't know what the
> internal logic does. So at least be careful with that.
> 
> The more common way to build such a system is to do a phase comparison
> between the 10MHz output of the GPSDO and the Rb, then steer the Rb
> using a seperate control loop electronics. One easy way to do this
> would be using a uC with a capture compare unit, at least one with 16bit,
> better with 24bits and more (e.g. STM32F4xx). Divide both 10MHz outputs
> down to roughly 1kHz-10kHz using 74LVC161. With this you can measure
> the phase differnce between the two with about 12ns precision (limited
> by the uC, not the dividers). Average over 2-3 days and you are good.

An alternative is to add an offset oscillator to the mix and look at beat 
notes. It does not have to be ultra close. An 11 MHz offset signal would take 
the 
12 ns down to an effective 1.2 ns. Odd frequency OCXO’s sell cheap on
eBay.

Bob


> 
> For additional precision, you can use an TDC7200 to measure the time
> difference with around 50-100ps precision, at which point the GPSDO
> noise and the stability of the Rb will be the limiting elements.
> 
> 
>             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] True Position GPSDP + Rb X72

[Stephan Flor via time-nuts]

Thank you Mark. I'm just starting to learn about Rb oscillators and GPSDO.  I 
started on this while repairing my old HP 8660c signal generator, and I wanted 
to get all of my equipment on a common sync clock. I bought the X72, because it 
was small, thinking I may be able to replace the ocxo in the 8660c with it.   
Now I regret wasting $100 on the X72. I will download Lady Heather and see what 
I can do with it, while I wait for my True Position to arrive. Thank you,Steve 

On Wednesday, September 20, 2017 11:18 AM, Mark Sims  
wrote:
 

 GPS disciplined rubidium oscillators are generally not a good idea.  Rubidiums 
tend to be quite a bit more noisy than OCXOs.  Their advantage is their long 
term frequency stability.  The GPS system in a GPSDO compensates for the OCXO 
drift,  so the only advantage of a GPS disciplined Rb is if you lose the GPS 
signal for a long time.

Also, remember Mark's Law of Rubidium Oscillators...  the small the oscillator, 
the crappier it is.  The X72 is a very small Rb oscillator and , guess what,  
it's rather crappy.  Noisy,  temperature sensitive,  not all that good 
frequency stability.  A decent OCXO can out-perform it.

Lady Heather now supports the X72 (and SA22.c).  It has a disciplining routine 
that can lock it to a 1PPS input.  It uses the X72's built in time interval 
counter that has a 16.667 ns resolution (due to noise and synchronizing issues 
more like 33 ns).

Later firmware versions of the X72 and SA22.c have a built in 1PPS disciplining 
routine,  but I am not too impressed with it.  It seems rather temperamental 
(or just plain mental) and I have seen it go off into la-la land and refuse to 
lock.
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[time-nuts] True Position GPSDP + Rb X72

[Mark Sims]

GPS disciplined rubidium oscillators are generally not a good idea.  Rubidiums 
tend to be quite a bit more noisy than OCXOs.  Their advantage is their long 
term frequency stability.  The GPS system in a GPSDO compensates for the OCXO 
drift,  so the only advantage of a GPS disciplined Rb is if you lose the GPS 
signal for a long time.

Also, remember Mark's Law of Rubidium Oscillators...  the small the oscillator, 
the crappier it is.  The X72 is a very small Rb oscillator and , guess what,  
it's rather crappy.   Noisy,  temperature sensitive,  not all that good 
frequency stability.   A decent OCXO can out-perform it.

Lady Heather now supports the X72 (and SA22.c).  It has a disciplining routine 
that can lock it to a 1PPS input.  It uses the X72's built in time interval 
counter that has a 16.667 ns resolution (due to noise and synchronizing issues 
more like 33 ns).

Later firmware versions of the X72 and SA22.c have a built in 1PPS disciplining 
routine,  but I am not too impressed with it.  It seems rather temperamental 
(or just plain mental) and I have seen it go off into la-la land and refuse to 
lock.
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Re: [time-nuts] True Position GPSDP + Rb X72

[Bob kb8tq]

Hi


> On Sep 20, 2017, at 8:39 AM, Attila Kinali  wrote:
> 
> On Tue, 19 Sep 2017 18:09:16 + (UTC)
> Stephan Flor via time-nuts  wrote:
> 
>> Hi everyone,I'm new to this list, and I wanted to get the opinion of some 
>> mere experienced people on my project idea.I just got a Symmetricom X72 Rb 
>> oscillator, and I have a True position GPSDO on the way.  I wan't to have a 
>> self calibrating 10 MHz signal to synchronize my hobby rf lab equipment.
>> My idea is to make a GPS disciplined Rubidium oscillator, by removing the 
>> crystal oscillator ans substituting the X72 in the GPSDO circuit.I would 
>> just 
>> have to make a op amp circuit to change the 0 to 4v correction signal from 
>> the True Position, to a 0 to 5v signal for the X72.
> 
> Unfortunately, this doesn't work as easily as you thing.
> The control loop inside the GPSDO is designed for an OCXO. This means
> that its loop constant is in the 10s to 100s of seconds, while for
> an GPSDRb you would need 10'000s to 100'000s of seconds. The other,
> more criticial issue is the sensitivity of the tuning input. Most
> OCXOs have something like 1-10ppm of tuning range. The tuning range
> of an Rb is usually 2 to 3 orders of magnitude smaller. In a normal
> PI loop, this shouldn't be an issue. But you don't know what the
> internal logic does. So at least be careful with that.
> 
> The more common way to build such a system is to do a phase comparison
> between the 10MHz output of the GPSDO and the Rb, then steer the Rb
> using a seperate control loop electronics. One easy way to do this
> would be using a uC with a capture compare unit, at least one with 16bit,
> better with 24bits and more (e.g. STM32F4xx). Divide both 10MHz outputs
> down to roughly 1kHz-10kHz using 74LVC161. With this you can measure
> the phase differnce between the two with about 12ns precision (limited
> by the uC, not the dividers). Average over 2-3 days and you are good.

An alternative is to add an offset oscillator to the mix and look at beat 
notes. It does not have to be ultra close. An 11 MHz offset signal would take 
the 
12 ns down to an effective 1.2 ns. Odd frequency OCXO’s sell cheap on
eBay.

Bob


> 
> For additional precision, you can use an TDC7200 to measure the time
> difference with around 50-100ps precision, at which point the GPSDO
> noise and the stability of the Rb will be the limiting elements.
> 
> 
>   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] True Position GPSDP + Rb X72

[Attila Kinali]

On Tue, 19 Sep 2017 18:09:16 + (UTC)
Stephan Flor via time-nuts  wrote:

> Hi everyone,I'm new to this list, and I wanted to get the opinion of some 
> mere experienced people on my project idea.I just got a Symmetricom X72 Rb 
> oscillator, and I have a True position GPSDO on the way.  I wan't to have a 
> self calibrating 10 MHz signal to synchronize my hobby rf lab equipment.
> My idea is to make a GPS disciplined Rubidium oscillator, by removing the 
> crystal oscillator ans substituting the X72 in the GPSDO circuit.I would just 
> have to make a op amp circuit to change the 0 to 4v correction signal from 
> the True Position, to a 0 to 5v signal for the X72.

Unfortunately, this doesn't work as easily as you thing.
The control loop inside the GPSDO is designed for an OCXO. This means
that its loop constant is in the 10s to 100s of seconds, while for
an GPSDRb you would need 10'000s to 100'000s of seconds. The other,
more criticial issue is the sensitivity of the tuning input. Most
OCXOs have something like 1-10ppm of tuning range. The tuning range
of an Rb is usually 2 to 3 orders of magnitude smaller. In a normal
PI loop, this shouldn't be an issue. But you don't know what the
internal logic does. So at least be careful with that.

The more common way to build such a system is to do a phase comparison
between the 10MHz output of the GPSDO and the Rb, then steer the Rb
using a seperate control loop electronics. One easy way to do this
would be using a uC with a capture compare unit, at least one with 16bit,
better with 24bits and more (e.g. STM32F4xx). Divide both 10MHz outputs
down to roughly 1kHz-10kHz using 74LVC161. With this you can measure
the phase differnce between the two with about 12ns precision (limited
by the uC, not the dividers). Average over 2-3 days and you are good.

For additional precision, you can use an TDC7200 to measure the time
difference with around 50-100ps precision, at which point the GPSDO
noise and the stability of the Rb will be the limiting elements.


Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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[time-nuts] True Position GPSDP + Rb X72

[Stephan Flor via time-nuts]

Hi everyone,I'm new to this list, and I wanted to get the opinion of some mere 
experienced people on my project idea.I just got a Symmetricom X72 Rb 
oscillator, and I have a True position GPSDO on the way.  I wan't to have a 
self calibrating 10 MHz signal to synchronize my hobby rf lab equipment.
My idea is to make a GPS disciplined Rubidium oscillator, by removing the 
crystal oscillator ans substituting the X72 in the GPSDO circuit.I would just 
have to make a op amp circuit to change the 0 to 4v correction signal from the 
True Position, to a 0 to 5v signal for the X72.
The X72 seems to work well, 10.00 MHz on my HP 5350B, last calibrated by 
the US Navy in 1994. I just ordered the True position, from China, so I won't 
see that for a while, then I need to get it working.
What do you think? Good idea or waste of time?  Will the True Position software 
be able to cope with the change? I haven't done any programming is at least 20 
years, so, I hope I can do this with hard ware.
Also, does anyone have ideas for a low cost 10 MHz 50 ohm distribution amp? 
Thanks,Steve



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