[time-nuts] The USFS Frequency Standard...
phk at phk.freebsd.dk
Sat Feb 11 11:20:19 EST 2017
In message <2126B261-3E4E-46D4-9181-1FB368244304 at n1k.org>, Bob Camp writes:
>One *could* make a WWVB “new modulation” receiver with some sort
>of MCU demo board and a handful of parts. It would be fine for a basement
>lab / learning sort of project.
With reasonable OCXO as timebase, it would do much more than that.
SRS sold the SR700 Loran receiver as a "Cesium replacement".
>the longer you wait to start that project, the better a board you will have
>as the base of the project.
Current boards are more than capable of this, a 12 ADC at 1MSPS is plenty.
>How many people want to spend more than a year on that sort of thing
Unless you're a total programming beginner, you will have carrier lock in
* Configure ADC for 1MSPS
* Interrupt routine: exponentially average the samples into a 50
bucket circular buffer
* Control-Loop (not time-critical):
* Multiply 50 buckets with synthetic sine/cos function,
* Average the 2x50 results to get I/Q phase signal.
* Feed phase into PLL to steer OCXO.
* Bonus: Decode timegram.
I did that with Loran-C, which is a *much* harder signal, I did it
8 years ago, and I did it in two weeks.
 If you use a platform with enough memory, for instance a BBB,
use a one million (=full second) buffer instead, you will be
able to pull any and all VLF signals out of it. For instance
the US navy runs a couple of stations with frequency stability
comparable to WWV. On a BBB you could even add a FRI length
buffer also, to receive the Wildwood Loran-C.
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
More information about the time-nuts