Hi David:

I've got a number of the WWVB clocks and can see a few of them at the
same time.  It's common that they disagree by a few seconds.

Have Fun,

Brooke Clarke
http://www.PRC68.com

Dr. David Kirkby wrote:

WWVB clocks look at the Time Code treansmitted by WWVB, not at the carrier
which is used for precision timing.

-John

==============

On 25/06/11 20:19, Dr. David Kirkby wrote:

Typically better than 1s. If there is interference or the radio is disabled,
it won't be able to receive the time signal. Switch mode PSUs and CRT TVs
or computer monitors can interfere with the 60kHz time signal.

The clocks with an LCD display usually have an indicator which shows
signal strength if the clock successfully updated in the last hour.
If you have reception problems, try moving the clock. The built-in
ferrite rod is very directional.

Were you receiving Radio 4 on LW or via a digital service. You could
easily see a 3s delay on digital radio or TV.

--
Linux 2.6.32

I have two r-c clocks in the house and they both keep accurate time. One
clock is made by KLIK, the other by STAIGER - both from ARGOS.

The second-hand moves at the very moment I hear the pip, or as exactly as
the eye can tell. But I do not use Radio 4. Instead I check my times using
the pip sequence from RWM's time service broadcasts on either 4.996 or 9.996
MHz (good signal strengths in UK).

There is a danger with broadcasters these days that their studio source goes
through digital buffering and will be subject to delays. The time difference
between identical broadcasts via analogue circuits and digital circuits is
in the order of two seconds.
BBC time pip accuracy can be checked by listening to them at the same time
as listening to RWM.

Ron
G3SVW

----- Original Message -----
From: "Dr. David Kirkby" david.kirkby@onetel.net
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Saturday, June 25, 2011 8:19 PM
Subject: [time-nuts] How accurate are cheap radio controlled clocks?

On Sat, Jun 25, 2011 at 12:19 PM, Dr. David Kirkby
david.kirkby@onetel.net wrote:

I have a Casio watch that syncs to WWVB when I leave it near a window
overnight.  There's an indicator on the display that shows if it
synced sometime since midnight today (local time), as well as a mode
that will tell you the last time it did successfully sync.  So far,
whenever it has synced today, the difference between it and a
NTP-synced computer time display has always been a fraction of a
second.  Not zero, but well below a half second.  (And when comparing
to a computer, remember that graphics cards and LCD monitors may add
multiple frames of delay).

If the watch doesn't sync for a few days, its timekeeping slowly
drifts but it still takes days to accumulate one second of error.
When I first purchased it, it was 25 seconds fast but the status
display said that the last successful sync was about 8 months ago, so
the internal crystal is likely good to about 3 seconds per month.

On the other hand, I have often heard over-the-air time beeps from
radio stations that are off by 5 seconds or more, usually late.  I
don't know if they are generated by the studio's own clock that is
hand-set and not very accurate, or if the beep is accurately generated
at the mixing board but then fed through something that causes a
significant delay.  (For example, live radio programs have a
multi-second delay between studio and transmitter so they can bleep
out "bad words" that a caller might say before they are broadcast).
So I wouldn't trust a radio time beep for anything without first
comparing it to another source.

 Dave

John wrote:

The ones I have do not monitor WWVB constantly -- they do it once a
day in the middle of the night (signal permitting), at which time
they synch up and update an oscillator correction factor based on how
far they were off since the previous update.  Mine seem to stay
within 500 mS over 24 hours compared to 1PPS "ticks" from a
Thunderbolt (subject to the resolution limits of using my eyes and
ears as the two measurement inputs and the comparator between my
ears), which is as close as the Lady Heather display clock on my system.

Perhaps some newer WWVB clocks monitor more often than that, or even
constantly, but I have not seen any that synch more often than once
every 24 hours.  On one of mine, you can turn the WWVB Rx off.  The
instructions indicate that the expected battery life goes up 12-fold
if you do, which may explain why they don't recalibrate more often.

Best regards,

Charles

Hey Ed,

How are things in the land of mold, mildew and Jamesions?

Best 73,

Had
K7MLR

A fine is a tax for doing wrong.  A tax is a fine for doing well.

Peter Cooper, of Fermi Lab, says, "Every experimentalist knows
that the apparatus, or at least your understanding of it, is
always at fault until demonstrated otherwise." He also says,
"Nature is really unmoved by what I, or anyone else, believes."

On 06/25/11 08:45 PM, Eamon Skelton wrote:

I don't think there's an SMPS nearby, but there was a 100 W amateur transceiver.

Thanks.

198 kHz longwave - using a Kenwood HF transceiver which has general coverage
receive.

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