Re: [time-nuts] Looking for GPSDO for home use

[Tom Van Baak]

> Having done extensive testing on the ublox 6M that you can buy with antenna 
> for less than $ 23 new from DX.com I can say with certainty that the 1 Hz 
> pulse  is better than 1 E-9 accurate, closer to E-10. Depending on the 

Hi Bert,

There are lots of cheap GPS/1PPS receivers out there these days. Having tested 
many GPS receivers myself, let me help you out. I understand the number $23. 
But the number "1 E-9" by itself means nothing. Like, are you talking time or 
frequency? There's a big difference.

Tell us if your number is timing accuracy or units of frequency accuracy or 
stability. Also either way, the measurement interval (or tau) is critical:

a) If it's timing, then the units are usually seconds; e.g., 1 ns, 
peak-to-peak, or rms or even something like TDEV(tau) -- and tau is important.

b) If it's frequency, then the units of absolute frequency accuracy or relative 
frequency stability; e.g., 0.01 Hz out of 10 MHz over some tau, or 
MDEV/ADEV(tau) -- and tau is critical.

I say this because:

a) If the 1e-9 or 1e-10 number you quote is rms time accuracy, then you have a 
GPS receiver better than what NIST or USNO has!

b) If the 1e-9 or 1e-10 number you quote is frequency stability over a day, 
then you have the worst GPS receiver we've ever seen!

So please clarify your units, or share raw data, or plots, or something. It's 
rather important.

/tvb

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Re: [time-nuts] Looking for GPSDO for home use

[EWKehren]

Having done extensive testing on the ublox 6M that you can buy with antenna 
 for less than $ 23 new from DX.com I can say with certainty that the 1 Hz 
pulse  is better than 1 E-9 accurate, closer to E-10. Depending on the 
counter it could  be used to adjust a frequency counter to that accuracy. I am 
not talking time,  it does have a saw tooth element but the period is 
constant. Before some one  says for an extra $ 20 you can get the T version I 
have 
one with M12 imulator  and M12+'s, but the challenge is in making low cost do 
great things.
We do not have the time but some one may want to explore using a PlL with a 
 VCXO using the ! KHz that the 6M can be programmed to. Depending how the 1 
KHz  is generated and the proper filter 1 E-10 may be a possibility.
Bert Kehren
 
 
In a message dated 4/16/2014 11:07:21 A.M. Eastern Daylight Time,  
albertson.ch...@gmail.com writes:

On Tue, Apr 15,  2014 at 10:09 PM, David J Taylor <
david-tay...@blueyonder.co.uk>  wrote:
>
> []
> Even 1 PPS output seems like a workable  starting point, but at the
expense of a different and/or more difficult  path to get to a 10 MHz
reference signal I seek.
>
> Any  advance or pointer to source (reasonable cost, whatever that means!)
would  be appreciated.


Any GPS receiver with 1PPS is OK.All  PPS signals are interchangeable.
It is just a 5 volt 1Hz square wave.   The raising edge of the wave is
right at the "tick" of a new  second.

The GPSDO is simple too.  It counts the cycles of the  10MHz oscillator from
one PPS raising edge to the next and it should get  exactly 10,000,000
cycles.   If more or less are counted the  software moves the voltage on
OXCO's control pin up or  down.

Controllers can be more complex, but this much will get you  started.  The
simplest next step is to count for 10 seconds and get to  0.1 Hz then add an
interpolator and get to milli Hz

If you are going  to buy and set up a GPS receiver. The hardest part is the
antenna.  It  is best if it can see the entire sky, horizon to horizon and
if it is not  near any reflecting surfaces.  It is best if the antenna is
mounted on  a mast on the tallest building but a modern GPS will work if the
antenna is  playing on the desk near a window.  You can connect a computer
and get  software to plot data from inside the GPS but really all you need
to go is  apply power and get the PPS.

The old Motorola "Oncore" series of GPS is  reliable and low cost.   The
"UT" has a PPS one sigma error of  about 50 nanoseconds which is "good
enough"  they sell for under  $20.   The current new state of the art
version is about $60 or  $35 used.
Here is an  example
Motorola-UT-Plus-Oncore-Timing-GPS-Module
Be  SURE to buy the "timing" version.  There are non-timing or  navigation
versions.  Make sure it says "timing" in the  description.

GPS receivers spew out tons of data but you can ignore it  all.  All you
need is the PPS signal.

-- 

Chris  Albertson
Redondo Beach,  California
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Re: [time-nuts] Looking for GPSDO for home use

[David J Taylor]

From: Chris Albertson

If you are going to buy and set up a GPS receiver. The hardest part is the
antenna.  It is best if it can see the entire sky, horizon to horizon and
if it is not near any reflecting surfaces.  It is best if the antenna is
mounted on a mast on the tallest building but a modern GPS will work if the
antenna is playing on the desk near a window.  You can connect a computer
and get software to plot data from inside the GPS but really all you need
to go is apply power and get the PPS.

The old Motorola "Oncore" series of GPS is reliable and low cost.   The
"UT" has a PPS one sigma error of about 50 nanoseconds which is "good
enough"  they sell for under $20.   The current new state of the art
version is about $60 or $35 used.
Here is an example
Motorola-UT-Plus-Oncore-Timing-GPS-Module
Be SURE to buy the "timing" version.  There are non-timing or navigation
versions.  Make sure it says "timing" in the description.

GPS receivers spew out tons of data but you can ignore it all.  All you
need is the PPS signal.

Chris Albertson
===

Chris,

Thanks for your comments and advice - I agree based on my years of 
experience with using GPS modules for NTP!  The comments on antennas is 
particularly relevant as I have just placed an antenna outdoors for use with 
my Rapco GPSDO, and it has made a stunning difference to this unit from the 
last century.  All the units purchased this century (except the GPS 18 LVC, 
not the 18x) are much more sensitive and work well enough indoors - at least 
at this location on the second floor of a two-storey building.


The Arduino version piqued my interest, so the information on that is 
appreciated as well.


Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk 


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Re: [time-nuts] Looking for GPSDO for home use

[Mike George]

Tom:

I saw you post to David on the Time Nuts list offering availability of a 
Thunderbolt.
If you have additional units available  I would be interested in one as 
well.

Let me know if you have any available and the cost.

Thanks,
Mike George
N3MUY

On 4/15/2014 14:03, Tom Van Baak wrote:

Dave,

If you're just calibrating a frequency counter you may not need a GPSDO. A 
simple GPS 1PPS is all you need; just measure the time from the 1PPS to the 10 
MHz, wait a minute or an hour or a day and do it again. This will show you the 
time drift, from which you can calculate the frequency error.

Still, having a 10 MHz GPSDO available is usually more convenient, so I would 
not talk you out of it.

If you don't want to spend time to design your own GPSDO, or to build one of 
the dozen homebrew projects on the web, I would recommend you get a Trimble 
Thunderbolt. They are as turn-key as you can get, but also allow great hacking 
if you so choose.

I have some left over from the group buy. If you're interested contact me 
off-list.

Thanks,
/tvb

- Original Message -
From: "David Feldman" 
To: 
Sent: Tuesday, April 15, 2014 8:27 AM
Subject: [time-nuts] Looking for GPSDO for home use



I found this reflector after searching for GPSDO that would be suitable for 
individual purchase/use. Each time I found an article about GPSDO projects, 
that lead me to a surplus GPS module that is either no longer available, not 
current production, undocumented, or otherwise difficult to source. I don't 
mind doing my own building/integration, and am not adverse to starting with a 
used or suplus component, I'm not sure where to start in terms of sourcing the 
GPS module/antenna/etc. My main need is for something to serve as a primary 
frequency standard (i.e., 10 MHz output) I can use to set a voltage controlled 
OCXO I just installed in my (otherwise cheap chinese) frequency counter. It 
seems there are some modules that have/had 10 kHz output; that would work too. 
Even 1 PPS output seems like a workable starting point, but at the expense of a 
different and/or more difficult path to get to a 10 MHz reference signal I seek.

Any advance or pointer to source (reasonable cost, whatever that means!) would 
be appreciated.

Thanks!

Dave
wb0...@yahoo.com



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Re: [time-nuts] Looking for GPSDO for home use

[David J Taylor]

From: Chris Albertson

I'm using (most of) the circuit posted a few weeks ago to this list by Lars
Walenius.  I posted the code here a week or so ago.   I was impressed by
how simple his GPSDO was and have sense simplified his design even more.
The goal was not state of the art performance but an ultra simple design
and low cost.   Cost is about $8 another is about two dozen lines of code.
[]

Ah, Thanks, Chris.  I haven't been following too closely, so I thought the 
whole things was $8, with just the Arduino alone.  Perhaps if you do put in 
all on a Web page quite a few would be interested.


If no-one else can, I could host the Web page.

Thanks,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk 


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Re: [time-nuts] Looking for GPSDO for home use

[Chris Albertson]

On Tue, Apr 15, 2014 at 10:06 PM, David J Taylor <
david-tay...@blueyonder.co.uk> wrote:

>
> Looking forward to seeing the circuit diagram and downloading the code,
> Chris!


I'm using (most of) the circuit posted a few weeks ago to this list by Lars
Walenius.  I posted the code here a week or so ago.   I was impressed by
how simple his GPSDO was and have sense simplified his design even more.
 The goal was not state of the art performance but an ultra simple design
and low cost.   Cost is about $8 another is about two dozen lines of code.

I plan to make it even less complex but I want a few days of test data
before I change anything.

Here is how to build one:

1) get a GPS receiver that has a "PPS" or pulse per second output.Any
receiver will do but you really want a "timing mode" receiver.  You will
need an antenna that can see most of the sky and a power supply.  Get this
running reliably.

2) get a decent "OCXO" that is a crystal oscillator that is inside a
temperature controlled can and that has a pin where you apply a voltage to
fine tune the frequency.   I'm using a Bliley 10MHz square wave OCXO I
bought on eBay for $11.  There are better ones for $25.  Any of them will
work.  You will need to get a power supply to run it.  Get this working and
verify the output at least reasonable.

3) Next step is to connect the above two with a controller.   The
controller hardware is simply an Arduino development board.   You can buy a
"real" one that is made in Italy for about $30 or a much smaller version on
eBay for about $3.  They are functional the same.  I used one iof these:
pro-mini
but
yu need a "FIDDI" USB to serial adaptor to program it.  The self contained
version is easier to use like this one:
nano
this kind has the usb/erialon board.   The made in Ital version is a bit
larger see this:  http://www.adafruit.com/products/50

The schematic is easy (1) use 74HC390 to divide 10MHz by 2 and send 5MHz to
Arduino pin-5, (2) connect PPS from GPS to Aruino pin-2, (3) 10M resister
to pin-1, 3.9k to pin7.  connect bothresiters together then to "RC filter"
then the OCXO's control pin.  That's it.

One thing.  It is looking like you can skip the 74HC390 chip.  connect the
10MHz directly to the Arduino.  The arduino has a fast analog comparer that
can handle small amplitude sine waves.

This is the simplest GPSDO  later we can improve performance with software
anymore parts.   I'd build this on a solderless breadboard and then change
to perfboard.
-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Looking for GPSDO for home use

[Chris Albertson]

On Tue, Apr 15, 2014 at 10:09 PM, David J Taylor <
david-tay...@blueyonder.co.uk> wrote:
>
> []
> Even 1 PPS output seems like a workable starting point, but at the
expense of a different and/or more difficult path to get to a 10 MHz
reference signal I seek.
>
> Any advance or pointer to source (reasonable cost, whatever that means!)
would be appreciated.


Any GPS receiver with 1PPS is OK.All PPS signals are interchangeable.
 It is just a 5 volt 1Hz square wave.  The raising edge of the wave is
right at the "tick" of a new second.

The GPSDO is simple too.  It counts the cycles of the 10MHz oscillator from
one PPS raising edge to the next and it should get exactly 10,000,000
cycles.   If more or less are counted the software moves the voltage on
OXCO's control pin up or down.

Controllers can be more complex, but this much will get you started.  The
simplest next step is to count for 10 seconds and get to 0.1 Hz then add an
interpolator and get to milli Hz

If you are going to buy and set up a GPS receiver. The hardest part is the
antenna.  It is best if it can see the entire sky, horizon to horizon and
if it is not near any reflecting surfaces.  It is best if the antenna is
mounted on a mast on the tallest building but a modern GPS will work if the
antenna is playing on the desk near a window.  You can connect a computer
and get software to plot data from inside the GPS but really all you need
to go is apply power and get the PPS.

The old Motorola "Oncore" series of GPS is reliable and low cost.   The
"UT" has a PPS one sigma error of about 50 nanoseconds which is "good
enough"  they sell for under $20.   The current new state of the art
version is about $60 or $35 used.
Here is an example
Motorola-UT-Plus-Oncore-Timing-GPS-Module
Be SURE to buy the "timing" version.  There are non-timing or navigation
versions.  Make sure it says "timing" in the description.

GPS receivers spew out tons of data but you can ignore it all.  All you
need is the PPS signal.

-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Looking for GPSDO for home use

[David J Taylor]

[]
Even 1 PPS output seems like a workable starting point, but at the expense 
of a different and/or more difficult path to get to a 10 MHz reference 
signal I seek.


Any advance or pointer to source (reasonable cost, whatever that means!) 
would be appreciated.


Thanks!

Dave
wb0...@yahoo.com
===

David, for just the 1 PPS part:

 http://www.adafruit.com/products/746

or for a unit fitting directly onto a Raspberry Pi with no soldering:

 
http://ava.upuaut.net/store/index.php?route=product/product&path=59_60&product_id=95

73,
David GM8ARV
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk 


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Re: [time-nuts] Looking for GPSDO for home use

[David J Taylor]

If you are looking to build your first GPSDO.  I'd go with the simplest one
first.  I had a goal to build and document one that did not require a
custom PCB or programmed chip or any special test equipment other then a
DMM and a scope with price well under $50.  I've beat the price by a lot
but not documentation yet.
[]
=

Looking forward to seeing the circuit diagram and downloading the code, 
Chris!


From previous experience there will be folk wanting a "no soldering" option, 
so if you can persuade someone to provide a ready-made board, so much the 
better


David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk 


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Re: [time-nuts] Looking for GPSDO for home use

[Chris Albertson]

If you are looking to build your first GPSDO.  I'd go with the simplest one
first.  I had a goal to build and document one that did not require a
custom PCB or programmed chip or any special test equipment other then a
DMM and a scope with price well under $50.  I've beat the price by a lot
but not documentation yet.

My Arduino based GPSDO is back in operation.  It is literally the simplest
one that can still work.It's about $8 in parts but I've disconnected
one of the external chips and will try removing the remaining one.  The
total BOM then will be just a bare Arudion Pro Mini, three resisters and
two capacitors for about $4.

It is back up and running now for about 12 hours.  I have the output of the
simple GPSDO and the 10MHz signal from a Trimble Thunderbolt both up on my
dual trace scope.   The two 10MHz signals do move slowly relative tone
another.  It will move to the right for 20 or 30 minutes then moves back
left.   But it is already better than you'd need to calibrate a frequency
counter.

The little AVR chip inside the Adruino has all the hardware you need, a
fast counter that can be captured with a raising edge of a pulse and
several DACs and ADCs.  That is all I'm using right now.   In the past
people used to have to build this using small scale ICs. (maybe 74xxx type)
There are at least a half dozen ways to make this better.   The goal of
this project is to see which makes the most difference and order them by
"bang per buck"


On Tue, Apr 15, 2014 at 11:03 AM, Tom Van Baak  wrote:

> Dave,
>
> If you're just calibrating a frequency counter you may not need a GPSDO. A
> simple GPS 1PPS is all you need; just measure the time from the 1PPS to the
> 10 MHz, wait a minute or an hour or a day and do it again. This will show
> you the time drift, from which you can calculate the frequency error.
>
> Still, having a 10 MHz GPSDO available is usually more convenient, so I
> would not talk you out of it.
>
> If you don't want to spend time to design your own GPSDO, or to build one
> of the dozen homebrew projects on the web, I would recommend you get a
> Trimble Thunderbolt. They are as turn-key as you can get, but also allow
> great hacking if you so choose.
>
> I have some left over from the group buy. If you're interested contact me
> off-list.
>
> Thanks,
> /tvb
>
> ----- Original Message -----
> From: "David Feldman" 
> To: 
> Sent: Tuesday, April 15, 2014 8:27 AM
> Subject: [time-nuts] Looking for GPSDO for home use
>
>
> >
> > I found this reflector after searching for GPSDO that would be suitable
> for individual purchase/use. Each time I found an article about GPSDO
> projects, that lead me to a surplus GPS module that is either no longer
> available, not current production, undocumented, or otherwise difficult to
> source. I don't mind doing my own building/integration, and am not adverse
> to starting with a used or suplus component, I'm not sure where to start in
> terms of sourcing the GPS module/antenna/etc. My main need is for something
> to serve as a primary frequency standard (i.e., 10 MHz output) I can use to
> set a voltage controlled OCXO I just installed in my (otherwise cheap
> chinese) frequency counter. It seems there are some modules that have/had
> 10 kHz output; that would work too. Even 1 PPS output seems like a workable
> starting point, but at the expense of a different and/or more difficult
> path to get to a 10 MHz reference signal I seek.
> >
> > Any advance or pointer to source (reasonable cost, whatever that means!)
> would be appreciated.
> >
> > Thanks!
> >
> > Dave
> > wb0...@yahoo.com
> >
>
>
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>



-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Looking for GPSDO for home use

[Tom Van Baak]

Dave,

If you're just calibrating a frequency counter you may not need a GPSDO. A 
simple GPS 1PPS is all you need; just measure the time from the 1PPS to the 10 
MHz, wait a minute or an hour or a day and do it again. This will show you the 
time drift, from which you can calculate the frequency error.

Still, having a 10 MHz GPSDO available is usually more convenient, so I would 
not talk you out of it.

If you don't want to spend time to design your own GPSDO, or to build one of 
the dozen homebrew projects on the web, I would recommend you get a Trimble 
Thunderbolt. They are as turn-key as you can get, but also allow great hacking 
if you so choose.

I have some left over from the group buy. If you're interested contact me 
off-list.

Thanks,
/tvb

- Original Message - 
From: "David Feldman" 
To: 
Sent: Tuesday, April 15, 2014 8:27 AM
Subject: [time-nuts] Looking for GPSDO for home use


> 
> I found this reflector after searching for GPSDO that would be suitable for 
> individual purchase/use. Each time I found an article about GPSDO projects, 
> that lead me to a surplus GPS module that is either no longer available, not 
> current production, undocumented, or otherwise difficult to source. I don't 
> mind doing my own building/integration, and am not adverse to starting with a 
> used or suplus component, I'm not sure where to start in terms of sourcing 
> the GPS module/antenna/etc. My main need is for something to serve as a 
> primary frequency standard (i.e., 10 MHz output) I can use to set a voltage 
> controlled OCXO I just installed in my (otherwise cheap chinese) frequency 
> counter. It seems there are some modules that have/had 10 kHz output; that 
> would work too. Even 1 PPS output seems like a workable starting point, but 
> at the expense of a different and/or more difficult path to get to a 10 MHz 
> reference signal I seek.
> 
> Any advance or pointer to source (reasonable cost, whatever that means!) 
> would be appreciated.
> 
> Thanks!
> 
> Dave
> wb0...@yahoo.com
> 


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[time-nuts] Looking for GPSDO for home use

[David Feldman]

I found this reflector after searching for GPSDO that would be suitable for 
individual purchase/use. Each time I found an article about GPSDO projects, 
that lead me to a surplus GPS module that is either no longer available, not 
current production, undocumented, or otherwise difficult to source. I don't 
mind doing my own building/integration, and am not adverse to starting with a 
used or suplus component, I'm not sure where to start in terms of sourcing the 
GPS module/antenna/etc. My main need is for something to serve as a primary 
frequency standard (i.e., 10 MHz output) I can use to set a voltage controlled 
OCXO I just installed in my (otherwise cheap chinese) frequency counter. It 
seems there are some modules that have/had 10 kHz output; that would work too. 
Even 1 PPS output seems like a workable starting point, but at the expense of a 
different and/or more difficult path to get to a 10 MHz reference signal I seek.

Any advance or pointer to source (reasonable cost, whatever that means!) would 
be appreciated.

Thanks!

Dave
wb0...@yahoo.com

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