[time-nuts] GPSDO Alternatives

Chris Albertson albertson.chris at gmail.com
Thu Dec 6 09:17:52 UTC 2012


Don't need anything so complex.   A GPSDO depend on an OCXO that is VERY
stable.  It can be controlled with a very low bandwidth analog signal.

The output from a OCXO is divided down and then the phase of the divided
down 10MHz RF is compared to the PPS and you don't need to even know the
how far apart they are.  All you need to know is "led or lag"  just a one
bit answer.   An XOR gate or a flip flop can tell you that.

If you want to get more fancy you can connect a few temperature sensors to
the Arduino's ADC lines and push those over the USB port along with other
statistics.   Youcan also do things like control the time constants the
software uses via USB also.  But you don't need this.   It can be added
later or not.


On Wed, Dec 5, 2012 at 9:31 AM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> If the intent is to come up with something in the same league as the TBolt
> there are a few other things you will need:
>
> 1) Something to compare the two pps signals to within 0.1 ns.
> 2) A large amount of code on the control processor (there are a multitude
> of
> special cases ...)
> 3) A large amount of code on a PC to monitor it and control it (like Lady
> Heather)
> 4) A set of standards to compare it to while you train and debug it
> 5) The test gear to collect and analyze the comparison and debug data with
> (you will have many months of data)
> 6) Some sort of control over the feature list. The complexity of 2-5 will
> go
> up significantly each time a nice to have thing is added.
>
> Once you get past step one, the rest of that list dwarf's anything like
> which D/A to use. I'm not at all saying it can't be done. Only that the
> bulk
> of the effort starts after you have the hardware.
>
> Bob
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Jim Lux
> Sent: Wednesday, December 05, 2012 7:58 AM
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] GPSDO Alternatives
>
> On 12/5/12 12:06 AM, Bruce Griffiths wrote:
> > Hal Murray wrote:
> >> albertson.chris at gmail.com said:
> >>> What is the simplest phase detecter that could work?  I think only
> >>> that, and
> >>> then a duouble oven crystal from eBay, a GPS and and Arduido.
> >> You also need a good D2A to drive the EFC on the osc.
> >>
> >>
> > A synchronous filter of a suitably level translated (CMOS analog switch
> > plus low noise reference) PWM output should work well.
>
> True.. but I think the OP was wanting something that doesn't require
> designing a circuit and building it.
>
> So what you really want is a high performance DAC on a Arduino shield,
> or, alternately, a high performance DAC on a cheap eval board that you
> can easily hook up to an Ardino type processor.
>
> This is a bit trickier..
> Lots of ADC stuff out there, not so much DAC stuff.
>
> http://embeddednewbie.blogspot.com/2011/02/review-of-arduino-dac-solutions.h
> tml
>
> seems to have a number of approaches.  Adafruit has a shield with a
> Microchip MCP4921 12 bit serial dac
>
> here's a 16 bit solution http://www.shaduzlabs.com/article-12.html but
> it's a "build it yourself" solution.
>
> If you're not size/mass/power constrained, you might be able to find an
> inexpensive used programmable power supply.  I do this using a Prologix
> controller driving Agilent E3646 power supplies.. Big, Expensive, etc.
> but it does work.
>
> >>> Yes the Aruino is expensive compared to a bare uP chip but using one,
> >>> I thin
> >>> you could build a GPSDO without a PCB and the Arduino's USB
> >>> connection could
> >>> be usful for power and logging/control.
> >> I wouldn't want to power a GPSDO from USB.  It will get power cycled
> >> every
> >> time I need to work on the logging PC.  Besides, you only get 2.5
> >> watts.  The
> >> oven will probably take more than that during warm-up.
> >>
> >>
> > Bruce
> >
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-- 

Chris Albertson
Redondo Beach, California


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