[time-nuts] WWVB format change in 2012

[Majdi S. Abbas]

On Sun, Feb 28, 2016 at 03:09:32PM +0800, Sanjeev Gupta wrote:
> I am reviewing and expanding and for the NTPSec project <
> http://www.ntpsec.org >, a fork of NTP.
> 
> Among NTPSec's goals are a smaller, auditable, code-base; hence support for
> receivers last available in the early-1990s is being removed.

	I'm not sure I would make that assumption.  Given recent attacks
on NTP (that will ultimately require a new protocol to fix), the ability 
of more upstream references is better than fewer.

	Stripping things out that would provide more sources of trusted
time appears to be at odds with making NTP "more secure."

> I have been on this list for some years (thank you), but as I am in
> Singapore, I did not pay attention to the WWVB format change.  I understand
> that as a result of the change, precision equipment may not be able to
> recover a usable signal from the new modulation scheme, rendering it
> useless for the sub-100 microsec disciplining.

	So the common, cheaper receivers that just looked at the AM 
envelope are unaffected.  Higher grade, phase tracking receivers were
affected, but can be modified to restore the carrier, and thus are
still operable.

> However, I am not clear if WWV and WWVH are still usable by commercially
> available equipment, or of such equipment is also obsolete now.

	WWV and WWVH have worked pretty much the same way they do now
for decades; I have running WWV and WWVH refclocks, even the TrueTime
TL_3 (in REFCLOCK_TRUE.)

	Where this gets sticky is there is support for older receivers
(say, OMEGA and the like), in the same refclocks (continuing to use
TRUE as an example here.)

	So, you could safely remove the bits pertaining to OMEGA, but
I'd retain the WWV, WWVB, TCU, and XL-DC support.)  Since the XL-DC
is a GPS, I suppose you could implement support for it in gpsd.

	Other, older refclocks are in a similar state, where one
vendor used more or less the same serial protocol regardless of 
what the actual reference was.

	What are you trying to do?  Kill the refclocks entirely, or
just pare them down to essentials?

	Cheers,

	--msa