[time-nuts] wtd: WWVB info

[Brian Inglis]

On 2015-08-04 21:36, Hal Murray wrote:
>
> kb8tq at n1k.org said:
>> So far there have not been any home brew design radios show up that will
>> demodulate and lock to the new data format. There is plenty of info on the
>> transmit format. The demodulation approach is not crazy hard. That said,
>> there’s still a lot of work to get a receiver running.
>
> Has anybody looked into a software approach?  What sort of front end would
> you want?

WWVB is a 1 baud trinary (0/1/marker) AM signal which goes low at the start of the
second and goes high after 200ms, 500ms, or 800ms, and a 1 baud binary PM signal
with possible phase inversion on the carrier 100ms after the start of each second.

Given a $10 60kHz receiver, the AM data should be readable by any UART running at
10bps, with 1 start bit, 8 data bits including Mark parity, 1 stop bit.
Each "character" could then be decoded into one of the three symbols transmitted.

If all you want is the PPS and AM time code, it can also be done with an 8kHz
audio codec. The NTP CHU ref clock driver will decode CHU Bell 103 300bps
signals in software.

For the PM signal, you need an LF receiver and a detector for the possible phase
change before and after 100ms after PPS to extract the binary data.

-- 
Take care. Thanks, Brian Inglis