tshoppa@gmail.com said:

What is available in the way of WWV receivers?  Anybody got a summary handy?

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On 10/26/2016 02:54 AM, Hal Murray wrote:

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

If you’re in North America, a CHU receiver is a lot easier to make than WWV/WWVH. The CHU timecode is just BEL 103 AFSK at 300 baud - it was a one-chip solution 20 years ago when I made one in college. On the software side, you’ll want a serial line discipline kernel module of some sort that timestamps the incoming characters. The result is as good as HF radio will get you, which is to say probably 2 or 3 orders of magnitude minimum worse than GPS.

IMHO the diversity of which you speak is exactly what NTP delivers. I believe NIST and USNO run NTP servers that aren’t sourced from GPS. Folks with Cesium clocks could conceivably do the same to provide independent standards.

I started to set up a WWV based reference clock.  As for a receiver SDR is
the best way to go but I built a tunnel front end.  It is easy to do
because it needs to only work at ne specify frequency so you can use a
crystal filter with norrow bandwidth.  The SDR receiver did direct
conversion that sampled in quadrature using a stereo sound card type
interface.  I disagree that even the cheap sound cards are good enough.
Get one that does 24-bit sample because they have enough dynamic range so
they can still work without a human operator tuning a gain knob.

The part I did not do was to modify the NTP reference clock drivers to
accept audio feed from Jack Audio.  This would allow internal software to
route audio between applications and not have to use multiple sound cards
and analog cables which seems silly.

Other projects came up and I figure it the world ends and the Internet goes
dark and GPS fails I can still know what time it is by watching the sun set
over the ocean every day.

Actually I've disconnected the GPS from my NTP server and notice only a 5
millisecond error on average using just pool servers

On Wed, Oct 26, 2016 at 5:46 AM, Nick Sayer via time-nuts <
time-nuts@febo.com> wrote:

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Chris Albertson
Redondo Beach, California

In message 5A002554-8D90-4C75-95DA-21DB45D61E95@kfu.com, Nick Sayer via time-
nuts writes:

We have CPUs and sounds-cards these days...

Also: The KiwiSDR is nearly perfect hardware, no matter which VLF/HF
station you want:  You can track GPS and four (possibly 8) VLF/HF
stations at the same time.

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phk@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.

That single-chip version is going to have a LOT less (and less variable) latency than an SDR.

Hi

Let’s see…. WWV (not WWVB) gets here via a variety of propagation mechanisms
that vary over the day. According to NIST (who probably know :) that puts a random timing
variation of ~1 ms on the signal. Since some modes get me a signal and others don’t, there
is no real reason to assume it is random. It can easily be an offset that varies month to month.

Net result, forget about the chip delays. The signal already has a bunch of built in variability
that will swamp anything in the silicon.

https://www.nist.gov/pml/time-and-frequency-division/nist-radio-broadcasts-frequently-asked-questions-faq

Also in the same data is the fact that the “as transmitted” signal is good to 100 ns. That’s plenty good
enough for the system as described. It also is a pretty modest number for a GPS timing module. One
would guess that the number is a bit better than 100 ns (it is NIST after all). It also does not directly
compare to the GPS number since there are UTC offset numbers there as well. Bottom line is that
there inevitably are numbers like that buried in the system once you get past the 1 ms.

Bob

Good thread. Thanks for the clue on the kiwiSDR. I went to the sites and
lots of fun playing with the receivers. As an example hearing LORAN C in
the Asia region.
Certainly seems the receiver is pretty sensitive and capable. Went hunting
for various low frequency timing signals such as JJY and the submarine
crusher signals. All were heard.
I agree with Bobs comments that the signal at WWV range can be all over the
place and though seasonal effects can be a somewhat accounted for the
reality is, its still pretty random. The changes can occur slowly or
rapidly.
Regards
Paul
WB8TSL

On Sat, Oct 29, 2016 at 9:03 AM, Bob Camp kb8tq@n1k.org wrote:

Are you sure the single chip receiver is not itself an SDR?  Maybe using a
little 8-bit uP inside?  I don't know.

In any case the jitter on the SDR depends on the sample rate clock.  If you
use a decent audio interface the clocks are not bad.  A little 4-pin
crystal oscillator controls the sampling.  Compared to the propagation
delay the quality of that crystal is a not a big deal.

On Fri, Oct 28, 2016 at 10:36 PM, Nick Sayer via time-nuts <
time-nuts@febo.com> wrote:

--

Chris Albertson
Redondo Beach, California

No, no, no.

The single chip in this case is an AFSK decoder. You still have to have an ordinary HF AM radio.