[time-nuts] Looking for GPSDO for home use
EWKehren at aol.com
EWKehren at aol.com
Thu Apr 17 14:06:28 UTC 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
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.
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.
Redondo Beach, California
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