[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 <tvb at leapsecond.com> 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" <wb0gaz at yahoo.com>
> To: <time-nuts at febo.com>
> 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
> > wb0gaz at yahoo.com
> >
>
>
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-- 

Chris Albertson
Redondo Beach, California