[time-nuts] WWVB Measurements

[Lenny Story]

Chris,

The beginning of the second, and the starting of the 10ms samples is
detected with a tight asm loop. (Soon to be replaced with a high
priority interrupt line)  Once detected the sample portion of the
state machine runs at 10ms. And terminates at the 990ms (99th sample),
I process the received bit and  go back to the wait_for_start state.

My thoughts are that the second starts are where the accuracy needs to be.

I'm starting to get an idea of its pps accuracy (or do I really mean
"stability" ?). I ran a quick test having the mcu measure what it
thinks the length of a second is using the internal timers (auto
reloading). I need to do more research on how to properly characterize
it.

-lenny

On 3/27/11, Chris Albertson <albertson.chris at gmail.com> wrote:
> On Sat, Mar 26, 2011 at 4:31 PM, Lenny Story <lenny at codematic.com> wrote:
>> Chris,
>> My design isn't really that sophisticated hardware wise. Its an 8051
>> variant, and the CMMR-60P which can be obtained from Sparkfun.com.  I do
>> wind my own antenna, which is just a quad, made from PVC and a metal
>> electrical box.  The circuit sits in the center.  It's done with a 2.5
>> inch
>> square, 4 layer board from pcbexpress.com.
>> The software samples the bit signal coming from the CMMR, every 10 ms
>> (essentially), and uses a 100 bit array to qualify it using a weighting
>> algorithm. The start of the bit train, and with it the sequence of 10ms
>> samples, is essentially polled very fast to catch the beginning of the
>> second as soon as possible.
>
> So you are looking at the output bit of the CMMR-60 once every 10 ms?
>   Then I'm guessing you will not get uS level precision.
> The software I'm writing runs under Linux and reads the bit every 1
> msBut I was wondering if I should do better and try for uS level
> timing
>
> I think your success with receivig WWVB must be the antenna.   Could
> you say more about it.
> =====
> Chris Albertson
> Redondo Beach, California
>

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