that WWV has some problem, the propagation path is not very stabile,
therefore the arriving signal is phase modulated, if you look it for
short time the phase modulation looks like frequency modulation it means
the frequency is changing = not stabile, WWVB is a bit better since it
ha a more stabile propagation path due to it's much lower frequency,
60kHz but there are al our nice switching mode power supplies which
generating lots of concurrence for WWVB, so it is not so simple task to
receive it clean
73
KJ6UHN
Alex
On 3/1/2014 6:31 PM, Tom Van Baak wrote:
Hi Bob,
Everything about time & frequency is simply a matter of degree, of decimals
points. If all you require is 1 second accuracy then any old WWVB RC clock will
work.
If you want 0.1 second, or 10 ms, or 1 ms accuracy a PC running NTP should work.
As you push closer to the microsecond level you need a correspondingly better
internal stable frequency source (e.g., rubidium) or external accurate time
source (e.g., GPS). Most of us use GPS one way or another, achieving 100 ns
accuracy with no effort and 10 ns with extreme effort.
Listening to WWV makes a nice example. Where I am near Seattle, say 1000 miles
from NIST, the radio wave delay from Ft Collins (due to speed of light, 1
ns/foot, or 5 us/mile) is about 5 ms. The delay from the WWV radio speaker to
my ear (due to the speed of sound, 1 ms/foot, or 5 s/mile) is about 5 ms.
/tvb
----- Original Message -----
From: "Bob Albert" <bob91...@yahoo.com>
To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com>
Sent: Saturday, March 01, 2014 6:04 PM
Subject: Re: [time-nuts] Another "atomic" clock question
All this is very interesting. However, my interest is frequency. In other
words, I want to know that my standard oscillators are as close to desired
frequency as possible, and how close that turns out to be.
Yes, the Internet gives me time of day as close as I care to know. I have an
'atomic' clock from LaCrosse that resets itself nightly, although it's fussy
about where in the house I put it. If I put it where I'd like, it won't receive
WWVB, so I put it across the room. I called the company inquiring about
augmenting the internal antenna but they were of no help.
While watching the clock and listening to WWV, it seems the clock is a fraction
of a second behind. Even that doesn't matter, but calibrating the counter time
base is another kind of thing.
I am trying to understand how this is done. Should I ever get a rubidium
standard, I'd want to check its calibration, and that's not a trivial exercise.
Bob
On Saturday, March 1, 2014 4:56 PM, Paul Alfille <paul.alfi...@gmail.com> wrote:
There are WWVB clocks with serial output. Arcron made one that I added
linux ntp support for some years back.
http://www.atomictimeclock.com/radsynarcron.htm
http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver27.html
As I recall, it was under $100, quite nicely styled, and is sitting here on
my desk. (Reception on the East Coast can be spotty, so I've switched to
standard internet net time source).
On Mon, Feb 24, 2014 at 7:44 AM, Bob Camp <li...@rtty.us> wrote:
Hi
Ok, so 0.1 second at the sync point is indeed a reasonable estimate. If
that's all you need to deal with (you correct out the crystal offset one
way or the other) then:
At 1 day you have 11.5 ppm accuracy. Roughly a 100 Hz beat note with WWV
at 10 MHz.
At 10 days you have 1.15 ppm. Roughly a 1 Hz beat note at 10 MHz.
At 100 days you have 0.115 ppm. That would be about a 10 second period
beat note.
None of that is to say that a beat note is all there is to getting
accuracy off of WWV or that the two approaches deliver the same net
accuracy. Yes I've done the 10 second beat thing, it can be done with care
and a good stable WWV signal.
Bob
On Feb 23, 2014, at 5:21 PM, Tom Van Baak <t...@leapsecond.com> wrote:
Now that you have brought up this subject, do you know of any way to
use these LaCrosse clocks to calibrate frequency standards?
I suggest using a direct electric (1.5 VDC high-Z) or indirect magnetic
(high gain) pickup on the coil to get the +/- pulse per second. Compare
this time with your local frequency standard and over several days you
should get accuracy better than 10 ms per day (1e-7). Here's an example of
a raw phase plot:
http://leapsecond.com/pages/Junghans/
/tvb
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