[time-nuts] Looking for GPSDO for home use

EWKehren at aol.com EWKehren at aol.com
Thu Apr 17 10:06:28 EDT 2014

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.chris at gmail.com writes:

On Tue, Apr 15,  2014 at 10:09 PM, David J Taylor <
david-taylor at 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
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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