[time-nuts] WWV receivers?
kb8tq at n1k.org
Sat Oct 29 09:03:47 EDT 2016
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.
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.
> On Oct 29, 2016, at 1:36 AM, Nick Sayer via time-nuts <time-nuts at febo.com> wrote:
> That single-chip version is going to have a *LOT* less (and less variable) latency than an SDR.
>> On Oct 27, 2016, at 12:20 AM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
>> In message <5A002554-8D90-4C75-95DA-21DB45D61E95 at kfu.com>, Nick Sayer via time-
>> nuts writes:
>>> 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.
>> 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.
>> 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.
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