[time-nuts] GPS DO Alternatives

Bob Camp lists at rtty.us
Sun Dec 9 00:47:30 UTC 2012


A little math:

You can get an OCXO that will do 1x10^-10 per day and has a sub 5x10^-10 temp performance. It's likely that the temperature impact will be minimal in a normal environment. 

If you are after 1x10^-8, you need to correct roughly every 100 days. That's not anything you need a cpu to handle. Even if you are after 1x10^-9, the aging is likely predictable. A bump every 10 days and a measurement once a month likely does the trick. Still not much of a need for a CPU.

For a much easier / cheaper / less work solution - grab a cheap rubidium. Manually set it to ~ 1x10^-11. It will hold your 9 digits for at least a year. With some luck I'll hold 10 digits.


On Dec 8, 2012, at 1:59 PM, Chris Albertson <albertson.chris at gmail.com> wrote:

> On Sat, Dec 8, 2012 at 9:30 AM, <johncroos at aol.com> wrote:
>> Hello all -
>> "People talk about good deals on Thunderbolts but I have
>> yet to see one.  It seems peak Thunderbolt passed before I was
>> seriously looking."
>> *The box you put it in - suspending it above the bench on inspirational
>> thought probably
>> will not work. A nice box is easily $ 50.00 so who cares about adding
>> another flip flop or
>> counter at 25 cents each.
> The goal, well my goal is to build a GPSDO to this set of requirements
> 1) well under 1/2 the cost of the t-bolt.
> 2) can be made with common parts and skills most people have
> 3) is completely modifiable (open source software)
> So #1 above means you use a low cost box, perhaps the case and old CDROM
> was once housed in or maybe you gut and old PC chassis
> #2 pretty much means you have to keep theparts cound way down.  Yes a chip
> might cost only $1 but as soon as you get more then about three of those 25
> cent cips you need a PCB.   PCB making is not a common everyday skill so #2
> means a way-low parts count
> #3 means the uP is gong to have to come with a very easy to use and free
> open source toolchain.  Adruino is like that, there are others, but a bare
> uP chip is not going to work
> You are right that one way to engineer a product is to first set
> performance numbers.   But another more common way is to first identify a
> target customer and then set a target price.   In this case the target
> customer is a hobbyist with only basic skills who wants a low cost easy to
> build GPSDO that has can understand and modify himself.
> Next with those very hard to meet requirements (low cost, low parts count,
> simple to build) we can ask if the exected perfomance is "good enough"
> What is good enough.  I'd say if you could use the GPSDO a a local
> frequency standard for a counter that has 8 digits you are doing "well
> enough".  If you can get to 10 digital it is pretty good
> -- 
> Chris Albertson
> Redondo Beach, California
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

More information about the time-nuts mailing list