On 10/26/2016 02:54 AM, Hal Murray wrote:
tsho...@gmail.com said:
I'm all for a diversity of systems - putting all our eggs in the GPS basket
seems unwise (and I maintain WWV receivers hooked to NTP at home!)
What is available in the way of WWV receivers? Anybody got a summary handy?
Yes, diversity is generally good, as it is in a sociological context.
Despite being such a ubiquitous and critical system in all domains,
military and civilian, US and foreign, and therefore being a recipient
of extensive funding and R&D, it is a high-profile target to adversaries
by means of anti-satellite weapons, cyberattacks, ground segment
attacks, and jamming; additionally, the constellation is subject to the
natural threats that all satellites face, and the system is controlled
by a homogeneous structure of human entities, which reserve the right to
deny coverage to a subset (typically hotspots in times of conflict). It
was a goal of my time metrology project, so I did do research in this
area, expecting to use CHU (which also adds political diversity, for
then it would be US [GPS] and Canada [CHU]) and maybe also WWV, but I
abandoned the idea in favor of allocating the bulk of the budget to
procurement of equipment and supporting equipment for my own house
standard by means of a rubidium ensemble.
Yes, standalone WWV receivers of course do exist; if one wishes to go
this route, the only practical means is by purchasing one of those
ancient (late 70s era probably) Systron Donner time code generator units
off eBay, which you'll notice has a BNC port on the back for an HF
antenna (or just the audio feed---who knows? Documentation is scarce).
However, unless you need WWV-derived PPS, this approach is *greatly*
suboptimal; the best approach would be to find your desired HF
receiver(s) and connect them via sound card(s) to the NTP server(s),
using the WWV module (and/or CHU). Besides the unknowns resulting from
documentation scarcity, this approach brings flexibility and the
benefits of the ``less is more'' philosophy, for you gain: the freedom
to decide what models of equipment to incorporate; flexibility in
channels (you can also do CHU, and even within WWV you can do 2.5, 5,
10, 15, and/or 20 MHz); and avoidance of obsolescence---remember, you're
relying on some human entity's signal, who in this case of a
seemingly-unpopular (at least nowadays) signal is under little
obligation to preserve the characteristics and even presence of such a
signal---look at what happened with the WWVB signal change, which
effectively rendered what were once nice standard frequency WWVB
receivers into paperweights.
For the radio, the best overall approach might be using $32 or so
RTL-SDRs which feature a case. However, the reception quality of these
units is not so great, the DSP might overwhelm low-power and embedded
servers, and there might be latency issues; I'm not familiar enough with
SDRs to state for sure. Another cheap approach is to simply use $12 or
so, incl. shipping, handheld HF receivers, though from past experience
the reception quality of them is absolutely awful and they are portable,
consumer-grade devices, meaning that there's no antenna BNC port, there
might be no power input apart from the terminals in the battery
compartment, and there are no means of elegantly rack-mounting them. A
more costly approach is to use a general-purpose HF receiver (like
typical Icom or Yaesu units that typical amateur radio operators use) or
a professional HF receiver; unfortunately one is very limited in the
latter, which consists of, in ascending order of price: HP 3586C (a
measuring receiver actually), Ten-Tec (from the research I have done, is
generally similar to Watkins Johnson [WJ], but lacks high-reliability
specifications), and WJ.
For the sound card, it has been reported that those cheap Chinese USB
sound cards, costing <$2 each incl. shipping, are adequate; I actually
ordered a quantity-discounted lot of 5 or so of the popular variant
which contains status LEDs before changing plans, so that's the best
approach if you wish to use multiple sources or servers.
Note that for high-reliability setups, one must factor in potential
service degradation caused by civil unrest or remote equipment failure,
such as reduced station power output due to electricity shortages, loss
of some channels, or jamming by adversaries.
-Ruslan
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
