[time-nuts] WWVB Measurements

Brooke Clarke brooke at pacific.net
Sun Mar 27 21:15:16 UTC 2011

Hi Lenny:

The CMMR-60P is an analog circuit designed for very low power 
consumption.  That translates to very high impedance circuitry.
I've been playing with them for years.  When I first tried them the 
reception was not 24/7, but rather mainly centered around local 
midnight, but the current batch gets good reception inside 24/7 with the 
stock small loop-stick antenna.  Therefore I have stopped working on a 
larger ferrite loop antenna.  Note they have app notes describing the 
ideal impedance for an antenna to optimize the performance with the 
CMMR-60P.  One of the limits on the antenna is it's temperature 
stability.  That was one of the areas I started to look into for the 
larger loop.

John Mills (THE NTP guru) has written a number of papers on and built 
examples of a matched filter type receiver for the HF station WWV, but 
the ideas would also be applicable to a WWVB receiver.  The performance 
he gets from WWV would knock your socks off so I expect a WWVB version 
would be even better.  In addition there are some things that could be 
done to improve it.

Have Fun,

Brooke Clarke

Lenny Story wrote:
> Chris,
> Regarding the decoding method.
> As i stated earlier, i'm using a CMMR-60p, which seems to just be a small
> DSP.  If i am remotely successful at my current version, my thoughts are
> that i would replace the CMMR with a similar DSP, and just FFT the crap out
> of the signal at 60khz... but i have no serious experience at this... so i
> could be just talking air here...
> -Lenny
> On Sat, Mar 26, 2011 at 6:54 PM, Chris Albertson
> <albertson.chris at gmail.com>wrote:
>> Lenny,
>> You are ahead of me by many months.  I'm building a WWVB receiver
>> also.  Actually I expect I will need to build several before I get
>> 24x7 coverage.  My breadboard works only at night in the So.
>> California area.   My plan is to place the entire receiver, antenna
>> and all on a mast far from the house and use an RS422 serial line to
>> send the data back to a computer indoors.
>> Do you intend to publish your work?   I'd be most interested in how
>> you decode the signal.   I'm conflicted between two approaches (1) To
>> declare the signal "invalid" if there is any error at all or (2) to
>> try and extract as much signal out of the noise as I can.  I may do
>> the latter and then have some kind of quality indicator.    The WWV
>> audio decoder built into the NTP reference implementation can extract
>> time code from what sounds like white noise and static to the human
>> ear using sophisticated DSP.  My first receiver will use #1.
>> About measuring the PPS.If you had a nice HP Universal counter with a
>> computer interface that would be best.  You put the PPS from a good
>> GPS on one channel and the PPS from WWVB on the other.   Lacking that
>> and if you only need to get down to uS level you can use two serial
>> orts in a Linux box and use PPS line disciplin on each oert the kernal
>> will time stamp the PPS when they happen and software can read and log
>> the time stamps. Use the command  "ldattach pps<device>" for each
>> serial port.  Good to about 1 uSwhich for WWVB might be enough
>> On Sat, Mar 26, 2011 at 1:26 PM, Lenny Story<lenny at codematic.com>  wrote:
>>> Greetings All,
>>> This is my first post to this board.
>>> I've completed the first run of a WWVB receiver board and Antenna (custom
>>> wound quad). Its an 8051 microcontroller, with a serial port really, but
>> it
>>> can decode the signal accurately pretty much all day long. (I'm just
>> north
>>> of boston, MA).
>>> I'm wanting to evaluate its performance, my guess is i'll have to produce
>> a
>>> plot of its PPS. In reading the LeapSecond.com site (awesome btw), the
>>> "Allen Deviation" is used.  As this is my first technical, experience in
>>> this area, is there a resource or method that is preferred by those who
>> know
>>> this technology ?
>>> The code reports the time delta between each detected second. If i log
>> the
>>> PPS deltas for an entire day (or week) of detected signal, is that enough
>>> data to start figuring out how to do the "Allen Deviation" calculations ?
>>> Any resources can you recommend to figuring out the graphs i need to
>> produce
>>> ?
>>> Thanks in advance for your help !
>>> -Lenny Story
>>> _______________________________________________
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>> --
>> =====
>> Chris Albertson
>> Redondo Beach, California
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