Anyone any insight into this error? Yesterday , coincidently? the
longest day. Set the alarm function for 06:30. Luckily woke just after
06:00 and decided to get up . Synchronous mains clock read 06:08 but
radio-code clock read 04:08, minute and seconds agreeing with another
radio-code clock but it had decided to go east 2 time zones. Still like
that about 07:00 but on returning in the evening the erroneous clock had
reset itself. How to predict when this error will reoccur? any
amelioration, plenty of LCD contrast so presumably the batteries are ok?

On Mon, 22 Jun 2015 07:40:09 +0100, N_Cook wrote:

Anyone any insight into this error? Yesterday , coincidently? the
longest day. Set the alarm function for 06:30. Luckily woke just after
06:00 and decided to get up . Synchronous mains clock read 06:08 but
radio-code clock read 04:08, minute and seconds agreeing with another
radio-code clock but it had decided to go east 2 time zones. Still like
that about 07:00 but on returning in the evening the erroneous clock had
reset itself. How to predict when this error will reoccur? any
amelioration, plenty of LCD contrast so presumably the batteries are ok?

Nope. My clocks are just fine. Sometimes my WWVB based clocks go
nuts from RF noise in the shop. They then reset themselves after
midnight, when 60 KHz propagation is best. In the UK, you're probably
using MSF.
http://www.npl.co.uk/science-technology/time-frequency/products-and-services/time/msf-radio-time-signal
They do have some scheduled outages, but that's not the problem this
time:
http://www.npl.co.uk/science-technology/time-frequency/products-and-services/time/msf-outages
Offhand, I would guess(tm) that your unspecified model radio clock has
a dying battery. My various clocks do some rather strange things when
the battery is low.

You might want to fasten your seat belt on June 30th.
http://www.dailymail.co.uk/sciencetech/article-3131840/The-longest-day-Leap-second-make-61-second-minute-end-June-experts-warn-break-internet.html
http://www.wired.com/2015/01/leap-second-rattle-internet-theres-plot-kill/
http://money.cnn.com/2015/01/13/technology/leap-second/
The good news is that you'll get an extra second of sleep during the
night of June 30th.

Mo
http://www.leapsecond.com/java/nixie.htm
http://802.11junk.com/jeffl/crud/GPS-vs-UTC.jpg

At the tone, the time will be:
http://www.leapsecond.com/java/gpsclock.htm
Ummm... never mind.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 22/06/2015 08:16, Jeff Liebermann wrote:
On Mon, 22 Jun 2015 07:40:09 +0100, N_Cook wrote:

Anyone any insight into this error? Yesterday , coincidently? the
longest day. Set the alarm function for 06:30. Luckily woke just after
06:00 and decided to get up . Synchronous mains clock read 06:08 but
radio-code clock read 04:08, minute and seconds agreeing with another
radio-code clock but it had decided to go east 2 time zones. Still like
that about 07:00 but on returning in the evening the erroneous clock had
reset itself. How to predict when this error will reoccur? any
amelioration, plenty of LCD contrast so presumably the batteries are ok?

Nope. My clocks are just fine. Sometimes my WWVB based clocks go
nuts from RF noise in the shop. They then reset themselves after
midnight, when 60 KHz propagation is best. In the UK, you're probably
using MSF.
http://www.npl.co.uk/science-technology/time-frequency/products-and-services/time/msf-radio-time-signal
They do have some scheduled outages, but that's not the problem this
time:
http://www.npl.co.uk/science-technology/time-frequency/products-and-services/time/msf-outages
Offhand, I would guess(tm) that your unspecified model radio clock has
a dying battery. My various clocks do some rather strange things when
the battery is low.

You might want to fasten your seat belt on June 30th.
http://www.dailymail.co.uk/sciencetech/article-3131840/The-longest-day-Leap-second-make-61-second-minute-end-June-experts-warn-break-internet.html
http://www.wired.com/2015/01/leap-second-rattle-internet-theres-plot-kill/
http://money.cnn.com/2015/01/13/technology/leap-second/
The good news is that you'll get an extra second of sleep during the
night of June 30th.

Mo
http://www.leapsecond.com/java/nixie.htm
http://802.11junk.com/jeffl/crud/GPS-vs-UTC.jpg

At the tone, the time will be:
http://www.leapsecond.com/java/gpsclock.htm
Ummm... never mind.


Not specified as litterally no name/model on it. Casio watch, I
compared it to , was fine . At least I now know not to rely on
"no-name" and use it in alarm mode with another alarm clock. If it went
erroneous "to the west" it would not be so problematic

"N_Cook" wrote in message
...
Anyone any insight into this error? Yesterday , coincidently? the longest
day. Set the alarm function for 06:30. Luckily woke just after 06:00 and
decided to get up . Synchronous mains clock read 06:08 but radio-code
clock read 04:08, minute and seconds agreeing with another radio-code
clock but it had decided to go east 2 time zones. Still like that about
07:00 but on returning in the evening the erroneous clock had reset
itself. How to predict when this error will reoccur? any amelioration,
plenty of LCD contrast so presumably the batteries are ok?

As the minuits agree, but the hours are off, I would look for a setting as
to which time zone the clock is set for.

On 22/06/2015 14:59, Ralph Mowery wrote:
"N_Cook" wrote in message
...
Anyone any insight into this error? Yesterday , coincidently? the longest
day. Set the alarm function for 06:30. Luckily woke just after 06:00 and
decided to get up . Synchronous mains clock read 06:08 but radio-code
clock read 04:08, minute and seconds agreeing with another radio-code
clock but it had decided to go east 2 time zones. Still like that about
07:00 but on returning in the evening the erroneous clock had reset
itself. How to predict when this error will reoccur? any amelioration,
plenty of LCD contrast so presumably the batteries are ok?

As the minuits agree, but the hours are off, I would look for a setting as
to which time zone the clock is set for.



I've never seen an option to change country of use, or any legend like
LON for London as in the Casio. Automatically seems to selct UK , the
strongest signal? along with automatic daylight saving changes.
Just pressed reset to remind me that no country option comes up and
within 10 minutes had sync'd with the Casio , in effect.
Tried Google Images but this one not seen in the first 3 pages of pics
of silver desktop "radio controlled" LCD clocks

So perhaps that was the failure mechanism. Rugby went down for
maintainence or its signal got locally shadowed/echoed/interferred with
and if Darmstadt was a stronger/clearer? signal , perhaps reset itself
to CET time for a while. The Casio having a preset station option , it
may loose updating but it would not try to find another code source.

On 22/06/2015 16:25, N_Cook wrote:
So perhaps that was the failure mechanism. Rugby went down for
maintainence or its signal got locally shadowed/echoed/interferred with
and if Darmstadt was a stronger/clearer? signal , perhaps reset itself
to CET time for a while. The Casio having a preset station option , it
may loose updating but it would not try to find another code source.

Ah, CET is in advance of GMT (BST - 1 ) not behind, and I doubt there is
a transmitter for the Cape Verde Islands.

I have an Oregon Scientific alarm clock that has five prominent buttons on its face: Clock, UP, DOWN, ALARM, ZONE.

I have hit the zone button by mistake before.
It steps through the 4 US time zones.

N_Cook wrote:
Anyone any insight into this error? Yesterday , coincidently? the
longest day. Set the alarm function for 06:30. Luckily woke just after
06:00 and decided to get up . Synchronous mains clock read 06:08 but
radio-code clock read 04:08, minute and seconds agreeing with another
radio-code clock but it had decided to go east 2 time zones. Still
like that about 07:00 but on returning in the evening the erroneous
clock had reset itself. How to predict when this error will reoccur?
any amelioration, plenty of LCD contrast so presumably the batteries
are ok?

I have a clock that has been off by 1 or 2 hours a couple of times. I just
figured that it made a mistake interpreting the received signal, perhaps due to
interference. It has corrected by the next day each time.

On 23/06/2015 02:09, Bob F wrote:
N_Cook wrote:
Anyone any insight into this error? Yesterday , coincidently? the
longest day. Set the alarm function for 06:30. Luckily woke just after
06:00 and decided to get up . Synchronous mains clock read 06:08 but
radio-code clock read 04:08, minute and seconds agreeing with another
radio-code clock but it had decided to go east 2 time zones. Still
like that about 07:00 but on returning in the evening the erroneous
clock had reset itself. How to predict when this error will reoccur?
any amelioration, plenty of LCD contrast so presumably the batteries
are ok?

I have a clock that has been off by 1 or 2 hours a couple of times. I just
figured that it made a mistake interpreting the received signal, perhaps due to
interference. It has corrected by the next day each time.




Did the errors occur overnight or during the day when you could more
likely get local interference?
Looked inside and only identifying features are these overlay numbers on
the 2 boards
ykf14547 ad085220 ad085211
otherwise little more than 2 crystals and 2 black epoxy humps over RF
end and LCD handling SM chips

My "radio time code" system never fails: I have a shortwave
radio, tune in time signals at 5, 10, 15, or 20mHz, and set
all my clocks and watches at the beep.

Works like a charm!

On 23/06/2015 09:21, wrote:
My "radio time code" system never fails: I have a shortwave
radio, tune in time signals at 5, 10, 15, or 20mHz, and set
all my clocks and watches at the beep.

Works like a charm!


How do you know if there is a digital relay link somewhere in the
transmission train?
I used to rely on the teletext time that came with the VITS of analogue
TV, but all gone belly-up with digital MUX. In the UK we have the
ridiculous business of the genuine radio pips relayed onto the "radio"
sections of MUX TV, can be up to 10 seconds out via the codec delays.

"N_Cook" wrote in message
...
On 23/06/2015 09:21, wrote:
My "radio time code" system never fails: I have a shortwave
radio, tune in time signals at 5, 10, 15, or 20mHz, and set
all my clocks and watches at the beep.

Works like a charm!


How do you know if there is a digital relay link somewhere in the
transmission train?
I used to rely on the teletext time that came with the VITS of analogue
TV, but all gone belly-up with digital MUX. In the UK we have the
ridiculous business of the genuine radio pips relayed onto the "radio"
sections of MUX TV, can be up to 10 seconds out via the codec delays.

If using a short wave receiver the signal is being picked up direct from a
station in the US. The only delay is the time it takes for the signal to
get to you by radio which is around the earth about 7 times in one second
and the delay of the sound from the speaker to you rear.
Both are much faster than you cn hit a button on the clock to set the time.

N_Cook wrote:
Anyone any insight into this error? Yesterday , coincidently? the
longest day. Set the alarm function for 06:30. Luckily woke just after
06:00 and decided to get up . Synchronous mains clock read 06:08 but
radio-code clock read 04:08, minute and seconds agreeing with another
radio-code clock but it had decided to go east 2 time zones. Still like
that about 07:00 but on returning in the evening the erroneous clock had
reset itself. How to predict when this error will reoccur? any
amelioration, plenty of LCD contrast so presumably the batteries are ok?

I live in a fringe reception area for the german time signal at 77.5kHz and have many clocks that use this signal but because a marginal reception they do not always sync. The curious thing about this is every night I have a different set of clocks sync, they seem to decide at random when the signal was good enough.

The oldest one is 13 years old and is an alarm clock I check daily, in these years I have had it three times take an incorrect time/date probably from interference. It either takes the right time or does not sync, three times in 13 years seems not bad for the simple parity bit protection the protocol uses.

I think, however, it is somewhat dangerous to have the clocks sync at night *after* you have checked they are set correctly, so if bad reception sets wrong data they will fail to wake you up at the right time.

Jeroni Paul wrote: "The oldest one is 13 years old and is an alarm clock I check daily,
in these years I have had it three times take an incorrect time/date probably from
interference. It either takes the right time or does not sync, three times in 13 years seems
not bad for the simple parity bit protection the protocol uses.

I think, however, it is somewhat dangerous to have the clocks sync at night *after* you have
checked they are set correctly, so if bad reception sets wrong data they will fail to wake you
up at the right time. "


Enough reasons for me not to use the freakin' things...

I've got the best time sync source of all, courtesy
the NIST and WWVB!

On Sat, 27 Jun 2015 14:38:33 -0700 (PDT), Jeroni Paul
wrote:

I live in a fringe reception area for the german time
signal at 77.5kHz

Spain? According the coverage map at:
http://www.ptb.de/cms/en/ptb/fachabteilungen/abt4/fb-44/ag-442/dissemination-of-legal-time/dcf77/reach-of-dcf77.html
Yes, the signal is probably not very strong and you're in the skywave
only region.

and have many clocks that use this signal but because
a marginal reception they do not always sync.

That sounds like the older amplitude modulated system. DCF77 also
transmits a phase modulated signal,
https://en.wikipedia.org/wiki/DCF77#Phase_modulation
which works better for weak signal due to better processing gain. I'm
in the USA and have not tried it with over-the-air DCF77, but have
played with simulators and with WWVB, which also has a phase modulated
BPSK signal. The problem is that the technology seems to be patented
and chips are not forthcoming. Also, the addition of BPSK modulation
caused some old WWVB receiver chips to fail. No clue what the
situation was with DCF77 but it might be worth checking.

The curious thing about this is every night I have a different set
of clocks sync, they seem to decide at random when the signal was
good enough.

Kinda sounds like you're getting some local interference. It doesn't
take much computah or switcher noise to trash the signal, especially
when it's weak in the first place. If your devices have a loopstick
for an antenna, they are directional, with the strongest signal
perpendicular to the loopstick. I was having random updates until I
moved my WWVB clock away from several switching power supplies.

The oldest one is 13 years old and is an alarm clock I check daily,
in these years I have had it three times take an incorrect time/date
probably from interference. It either takes the right time or does
not sync, three times in 13 years seems not bad for the simple parity
bit protection the protocol uses.

It's a bit more than just the parity bit. Some chips require that the
correct time be received successfully more than once before it will
sync. This is a function of the chip design.

I think, however, it is somewhat dangerous to have the clocks sync
at night *after* you have checked they are set correctly, so if
bad reception sets wrong data they will fail to wake you up at
the right time.

Sorry, but you don't have a choice as to what time to sync.
Propagation at VLF frequencies works best after midnight in the USA. I
think it's the same for a north-south path, but I'm not sure. Note
the increases in coverage area after midnight for WWVB:
http://tf.nist.gov/stations/wwvbcoverage.htm
http://www.febo.com/time-freq/wwvb/sig-strength/
I couldn't find something similar for DCF77.





--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 27 Jun 2015, Jeff Liebermann wrote:

On Sat, 27 Jun 2015 14:38:33 -0700 (PDT), Jeroni Paul
wrote:

I live in a fringe reception area for the german time
signal at 77.5kHz

Spain? According the coverage map at:
http://www.ptb.de/cms/en/ptb/fachabteilungen/abt4/fb-44/ag-442/dissemination-of-legal-time/dcf77/reach-of-dcf77.html
Yes, the signal is probably not very strong and you're in the skywave
only region.

and have many clocks that use this signal but because
a marginal reception they do not always sync.

That sounds like the older amplitude modulated system. DCF77 also
transmits a phase modulated signal,
https://en.wikipedia.org/wiki/DCF77#Phase_modulation
which works better for weak signal due to better processing gain. I'm
in the USA and have not tried it with over-the-air DCF77, but have
played with simulators and with WWVB, which also has a phase modulated
BPSK signal. The problem is that the technology seems to be patented
and chips are not forthcoming. Also, the addition of BPSK modulation
caused some old WWVB receiver chips to fail. No clue what the
situation was with DCF77 but it might be worth checking.

The curious thing about this is every night I have a different set
of clocks sync, they seem to decide at random when the signal was
good enough.

Kinda sounds like you're getting some local interference. It doesn't
take much computah or switcher noise to trash the signal, especially
when it's weak in the first place. If your devices have a loopstick
for an antenna, they are directional, with the strongest signal
perpendicular to the loopstick. I was having random updates until I
moved my WWVB clock away from several switching power supplies.

The oldest one is 13 years old and is an alarm clock I check daily,
in these years I have had it three times take an incorrect time/date
probably from interference. It either takes the right time or does
not sync, three times in 13 years seems not bad for the simple parity
bit protection the protocol uses.

It's a bit more than just the parity bit. Some chips require that the
correct time be received successfully more than once before it will
sync. This is a function of the chip design.

I think, however, it is somewhat dangerous to have the clocks sync
at night *after* you have checked they are set correctly, so if
bad reception sets wrong data they will fail to wake you up at
the right time.

Sorry, but you don't have a choice as to what time to sync.
Propagation at VLF frequencies works best after midnight in the USA. I
think it's the same for a north-south path, but I'm not sure. Note
the increases in coverage area after midnight for WWVB:
http://tf.nist.gov/stations/wwvbcoverage.htm
http://www.febo.com/time-freq/wwvb/sig-strength/
I couldn't find something similar for DCF77.

I thought low frequencies were used by WWVB (and WWVL before it) because
it was all ground-wave, and well penetrating.

If it was on shortwave, you would be stuck with a given frequency for a
givne time, which of course is why WWV transmits on a bunch of
frequencies.

The reason I've seen for late night sync'ing (and which makes sense) is
that in the wee hours of the morning, fewer people are up, thus much less
manmade interference. So the CFLs are turned off, the tv sets are turned
off (probably a bigger issue when they were actually CRTs, all that
horizontal sync frequencies into the deflection coil), lots of other
things that might be on in the daytime are off so they aren't making as
much noise.

I've noticed this. My Casio Waveceptor watch starts looking at midnight
local time, and if I have the CFL on at the time, it likely doesn't sync
up, but will at a later hour (the watch is better than most of the clocks,
since it tries multiple times). COnversely, if I have the CFL off, it
generally will sync at midnight.

And I'm probably at the far edge of the reliable reception area.

Of course, with at least some of the clocks, one does have the option of
pressing button (or putting the batteries back in) so the clock tries to
sync up, no matter what time it is.

Michael

On 27/06/2015 22:38, Jeroni Paul wrote:
N_Cook wrote:
Anyone any insight into this error? Yesterday , coincidently? the
longest day. Set the alarm function for 06:30. Luckily woke just after
06:00 and decided to get up . Synchronous mains clock read 06:08 but
radio-code clock read 04:08, minute and seconds agreeing with another
radio-code clock but it had decided to go east 2 time zones. Still like
that about 07:00 but on returning in the evening the erroneous clock had
reset itself. How to predict when this error will reoccur? any
amelioration, plenty of LCD contrast so presumably the batteries are ok?

I live in a fringe reception area for the german time signal at 77.5kHz and have many clocks that use this signal but because a marginal reception they do not always sync. The curious thing about this is every night I have a different set of clocks sync, they seem to decide at random when the signal was good enough.

The oldest one is 13 years old and is an alarm clock I check daily, in these years I have had it three times take an incorrect time/date probably from interference. It either takes the right time or does not sync, three times in 13 years seems not bad for the simple parity bit protection the protocol uses.

I think, however, it is somewhat dangerous to have the clocks sync at night *after* you have checked they are set correctly, so if bad reception sets wrong data they will fail to wake you up at the right time.


Have you had the situation of the displayed time jumping by an hour or two?
As an alarm clock, losing synch and drifting a second or two , to a
background quartz crystal clock, is no great problem

On Sat, 27 Jun 2015 23:37:42 -0400, Michael Black
wrote:

I thought low frequencies were used by WWVB (and WWVL before it) because
it was all ground-wave, and well penetrating.

The skywave doesn't magically go away at lower frequencies. For
example, here's a study on hearing both WWVB and JJY (Japan) in
Germany, which certainly would require skywave propagation.
http://df6nm.bplaced.net/LF/MSFgaps/MSFgaps.htm
See 3rd graph from the top. Unfortunately, I've never bothered to do
any DXing on VLF, but have been told that it's possible to hear Europe
and Japan in California if the conditions are right. VLF DX list:
http://www.dxinfocentre.com/time-vlf.htm

Unlike HF (high freq) propagation, which is "bent" by the ionosphere
back towards the ground, VLF frequencies are reflected off the D
layer.
http://vlf.stanford.edu/research/introduction-vlf

If it was on shortwave, you would be stuck with a given frequency for a
givne time, which of course is why WWV transmits on a bunch of
frequencies.

Actually, VLF has the same problem. Beyond some distance (which
varies with antenna size and power level), the various time sync
stations become very sensitive to ionospheric layer conditions, which
is mostly controlled by the sun. During the day, skywave propagation
sucks, while ground wave is unaffected. However, when there's dark
over most of the distance between the transmitter and the receiver,
the skywave returns. More on how it works:
http://solar-center.stanford.edu/SID/activities/ionosphere.html

The reason I've seen for late night sync'ing (and which makes sense) is
that in the wee hours of the morning, fewer people are up, thus much less
manmade interference.

That would be so nice if it were true, but it's not. It's not man
made interference that causes most reception problems, it's lightning
and atmospheric RF noise that are extremely high at VLF frequencies.
See the graph at:
https://en.wikipedia.org/wiki/Atmospheric_noise
https://en.wikipedia.org/wiki/Atmospheric_noise#/media/File:Atmosphericnoise.PNG
At 60 KHz, the noise level is about 80dB above the normal thermal
noise. When designing a receiver for 60 KHz, the problem is not the
usual NF (noise figure) and gain, but rather being able to remain
linear and handle the overload produced by the noise. That's why you
often see VLF receiver front ends with heat sinks on the RF
transistors.

Incidentally, the high noise levels is also why you can get away with
using tiny antennas with loss instead of gain. A bigger antenna will
amplify the noise and the signal equally which doesn't improve things.
A bigger antenna also produces more voltage at the receiver input,
which has to handled by an increasingly higher voltage and power input
stage. However, what a bigger antenna might do is increase the Q of
the antenna (i.e. decrease the antenna bandwidth) which would pickup
less off frequency noise, which will help increase the SNR (signal to
noise ratio).

So the CFLs are turned off, the tv sets are turned
off (probably a bigger issue when they were actually CRTs, all that
horizontal sync frequencies into the deflection coil), lots of other
things that might be on in the daytime are off so they aren't making as
much noise.

Look again at the noise graph, and notice the red line added showing
man made noises. At 60 KHz, the man made noise is about equal to the
atmospheric noise.

If you want to pursue such a noise source survey, I suggest you build
a loop resonant at 60 KHz and plug into an oscilloscope looking for
noise. I suggest a very high Q magnetic loop so that it only picks up
noise very close to 60 KHz. Just about anything with a switching
power supply should show up as a noise source. I have some opinions
on CFL lamps, LED lamps, and plasma TVs which I'm not quite sure are
correct, so I'll not comment on those. Let's just say I have some
very quiet LED lamps and some VERY noisy LED lamps.

I've noticed this. My Casio Waveceptor watch starts looking at midnight
local time, and if I have the CFL on at the time, it likely doesn't sync
up, but will at a later hour (the watch is better than most of the clocks,
since it tries multiple times). COnversely, if I have the CFL off, it
generally will sync at midnight.

That sounds about right. The chip, usually made by C-Max uses an
algorithm to determine when to listen. The problem is battery life.
It makes no sense to listen during daylight hours, so it doesn't. If
it sync at midnight, it doesn't try again later. If it fails, it
retries according to some pattern. I used to have the link to the
details, but can't find it right now. This is close but not the one I
was looking for:
http://www.c-max-time.com/tech/software6005.php

And I'm probably at the far edge of the reliable reception area.

Probably true with a wris****ch receiver or consumer device. Not true
with a proper loop antenna, which gets much better range. In the
early 1980's, I setup a WWVB receiver in an area infested with high
electrical noise. None of the commodity WWVB clocks would work. A
shielded loop antenna and overkill coax shielding did the trick.
Something like this, except my loop was circular and about 1 meter
wide:
http://www.ka7oei.com/wwvb_antenna.html

Of course, with at least some of the clocks, one does have the option of
pressing button (or putting the batteries back in) so the clock tries to
sync up, no matter what time it is.

I hacked one of clocks to do that so I could make measurements:
http://802.11junk.com/jeffl/WWVB%20test/
The receiver inside the antenna has an "enable" line to turn it on and
off. In this device, it's labeled PON. The clock/display/control
chip enables it according to the previously mentioned algorithm. I
tied the line high (after disconnecting it from the clock) so that it
would run continuously. It takes about 3 weeks to kill the two AAA
batteries when running continuously.

Clean signal that will decode correctly:
http://802.11junk.com/jeffl/WWVB%20test/loopstick-perpendicular-to-WWVB.jpg
Noisy signal that won't work:
http://802.11junk.com/jeffl/WWVB%20test/end-pointed-at-WWVB.jpg
http://802.11junk.com/jeffl/WWVB%20test/loopstick-vertical.jpg


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 6/27/2015 10:26 PM, wrote:
Jeroni Paul wrote: "The oldest one is 13 years old and is an alarm clock I check daily,
in these years I have had it three times take an incorrect time/date probably from
interference. It either takes the right time or does not sync, three times in 13 years seems
not bad for the simple parity bit protection the protocol uses.

I think, however, it is somewhat dangerous to have the clocks sync at night *after* you have
checked they are set correctly, so if bad reception sets wrong data they will fail to wake you
up at the right time. "


Enough reasons for me not to use the freakin' things...

I've got the best time sync source of all, courtesy
the NIST and WWVB!


Second best. They adjust those ones to match that yellow thing up in
the sky.

Cheers

Phil Hobbs

(We just had a leap second.)

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Jeff Liebermann wrote:
I live in a fringe reception area for the german time
signal at 77.5kHz

Spain? According the coverage map at:
http://www.ptb.de/cms/en/ptb/fachabteilungen/abt4/fb-44/ag-442/dissemination-of-legal-time/dcf77/reach-of-dcf77.html
Yes, the signal is probably not very strong and you're in the skywave
only region.

Good observer, yes, Spain. Also the Pyrenees are in the way blocking most ground signal.

and have many clocks that use this signal but because
a marginal reception they do not always sync.

That sounds like the older amplitude modulated system. DCF77 also
transmits a phase modulated signal,
https://en.wikipedia.org/wiki/DCF77#Phase_modulation

I knew about the phase modulated encoding on the signal but I am not sure if any of my clocks use that. The older ones sure do not, time ago I dissassembled the oldest alarm clock and scoped the signal output from its radio board and I could see the 0.1/0.2 sec signal drop.

There is a long wave radio transmitter in France at 162 kHz that carries time information by phase modulation of its carrier:
https://en.wikipedia.org/wiki/Alloui...ve_transmitter
I find it an efficient way to use existing resources, also you can check for reception by listening with a LW radio.

The curious thing about this is every night I have a different set
of clocks sync, they seem to decide at random when the signal was
good enough.

Kinda sounds like you're getting some local interference. It doesn't
take much computah or switcher noise to trash the signal, especially
when it's weak in the first place. If your devices have a loopstick
for an antenna, they are directional, with the strongest signal
perpendicular to the loopstick. I was having random updates until I
moved my WWVB clock away from several switching power supplies.

Yet, if I had one clock next to a noise source I would expect it to sync less times than the rest. But no, there appears to be a random distribution.

The oldest one is 13 years old and is an alarm clock I check daily,
in these years I have had it three times take an incorrect time/date
probably from interference. It either takes the right time or does
not sync, three times in 13 years seems not bad for the simple parity
bit protection the protocol uses.

It's a bit more than just the parity bit. Some chips require that the
correct time be received successfully more than once before it will
sync. This is a function of the chip design.

That's what I belived, but then how did it receive incorrect data? Did it actually receive the same wrong data twice in a row? The algorithm could also check for a reasonable deviation against the current setting.

I think, however, it is somewhat dangerous to have the clocks sync
at night *after* you have checked they are set correctly

Sorry, but you don't have a choice as to what time to sync.

Maybe a setting to enable sync only during weekends or only when the alarm function is disabled.

N_Cook wrote:
Have you had the situation of the displayed time jumping by an hour or two?
As an alarm clock, losing synch and drifting a second or two , to a
background quartz crystal clock, is no great problem

I think on one occasion it was several hours off. You could tell it was a wrong bit value as the data would be wrong by a multiple of two.

On Mon, 6 Jul 2015 12:03:13 -0700 (PDT), Jeroni Paul
wrote:

Jeff Liebermann wrote:
That sounds like the older amplitude modulated system. DCF77 also
transmits a phase modulated signal,
https://en.wikipedia.org/wiki/DCF77#Phase_modulation

I knew about the phase modulated encoding on the signal but I
am not sure if any of my clocks use that. The older ones sure
do not, time ago I dissassembled the oldest alarm clock and
scoped the signal output from its radio board and I could see
the 0.1/0.2 sec signal drop.

I haven't looked into the situation for about a year. I also don't
know the situation in Europe. To the best of my limited knowledge,
there are no commodity clocks and no commodity chips being made that
use phase modulation, in the USA. The technology appears to be owned
by Everset, which has done absolutely nothing for several years. I
could find no distributor that carries their chips. My previous
requests for samples, pricing, and delivery were ignored:
http://eversetclocks.com
If you find a consumer grade WWVB chip or receiver that do BPSK, I
would be interested.

There is a long wave radio transmitter in France at 162 kHz that carries time information by phase modulation of its carrier:
https://en.wikipedia.org/wiki/Alloui...ve_transmitter
I find it an efficient way to use existing resources, also you can check for reception by listening with a LW radio.

https://en.wikipedia.org/wiki/TDF_time_signal
I'm not sure, but might be able to take the demodulated output of a
162 KHz receiver, and feed it to a decoder made for DCF77, and get
accurate time updates. I searched with Google and found nothing in
the way of a consumer grade DCF time clock.

You can probably get better info from the Time-Nuts mailing list:
https://www.febo.com/pipermail/time-nuts/

Yet, if I had one clock next to a noise source I would expect it to
sync less times than the rest. But no, there appears to be a random
distribution.

Nope. WWVB sends the time code at the rate of 1 bit/second (1 baud).
One frame is 60 seconds. Hopefully, the European systems are similar.
http://www.nist.gov/pml/div688/grp40/wwvbtimecode.cfm
All it takes is one noise hit every 60 seconds, and you'll receive
nothing. If your local noise source is intermittent or random, then
it's more a matter of timing and bad luck that will determine if the
clock decodes anything useful.

It's a bit more than just the parity bit. Some chips require that the
correct time be received successfully more than once before it will
sync. This is a function of the chip design.

That's what I belived, but then how did it receive incorrect data?

Good question. I don't know. The only time I've seen an incorrect
display was when I was building a WWVB emulator and spraying garbage
data everywhe
http://www.instructables.com/id/WWVB-radio-time-signal-generator-for-ATTINY45-or-A/?ALLSTEPS
However, I've never seen a random erroneous date or time.

Did it actually receive the same wrong data twice in a row?

Very unlikely that it might receive the same garbage successfully
twice in a row but possible. However, note that the redundancy
requirement is totally in the chip uses, which might vary in
programming and capabilities.

The algorithm could also check for a reasonable deviation against
the current setting.

I don't think so. Once it gets a valid time to display, it turns off
the receiver to save battery power. No need to decode more than one
or maybe two frames.

Maybe a setting to enable sync only during weekends or only
when the alarm function is disabled.

Personally, I want a graph of signal strength and SNR over a few days
period. Whether anyone is willing to pay for such a feature is
debatable.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 04 Jul 2015 13:10:22 -0400, Phil Hobbs
wrote:

On 6/27/2015 10:26 PM, wrote:
I've got the best time sync source of all, courtesy
the NIST and WWVB!

Second best. They adjust those ones to match that yellow thing up in
the sky.
Cheers
Phil Hobbs

Does the NIST use a sundial for a primary time standard? I realize
that budget cuts have necessitated economy measures, this seems a bit
extreme.

(We just had a leap second.)

Yep. That felt good. I got one second of extra sleep.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 07/07/2015 02:37 PM, Jeff Liebermann wrote:
On Sat, 04 Jul 2015 13:10:22 -0400, Phil Hobbs
wrote:

On 6/27/2015 10:26 PM, wrote:
I've got the best time sync source of all, courtesy the NIST and
WWVB!

Second best. They adjust those ones to match that yellow thing up
in the sky. Cheers Phil Hobbs

Does the NIST use a sundial for a primary time standard?

In a way, they do. Civil time is adjusted to match mean solar time.

I realize that budget cuts have necessitated economy measures, this
seems a bit extreme.

(We just had a leap second.)

Yep. That felt good. I got one second of extra sleep.

I was awake, advancing science.

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

On 07/07/2015 19:37, Jeff Liebermann wrote:
On Sat, 04 Jul 2015 13:10:22 -0400, Phil Hobbs
wrote:

On 6/27/2015 10:26 PM, wrote:
I've got the best time sync source of all, courtesy
the NIST and WWVB!

Second best. They adjust those ones to match that yellow thing up in
the sky.
Cheers
Phil Hobbs

Does the NIST use a sundial for a primary time standard? I realize
that budget cuts have necessitated economy measures, this seems a bit
extreme.

(We just had a leap second.)

Yep. That felt good. I got one second of extra sleep.



The new generation of atomic clocks, accurate to 1 second in 15 billion
years,supposedly - how do they know , without a more accurate clock than
that to check it against?

On Wed, 08 Jul 2015 09:22:02 +0100, N_Cook wrote:

The new generation of atomic clocks, accurate to 1 second in 15 billion
years,supposedly - how do they know , without a more accurate clock than
that to check it against?

Possibly by consensus. Just make reference measurements on as many
inaccurate sources as possible, average them together, and by the
magic of statistics, the average will be more accurate than any
individual measurement. That's because given a sufficiently large
supply of erroneous data, the errors tend to be in opposite directions
and cancel each other. For example, you could average the noon sight
reading from a huge number of sundials or sextants, and the average
will give you NIST grade accuracy.

If this is a problem for you, just buy one of these:
https://www.kickstarter.com/projects/846511652/the-worlds-first-true-atomic-wris****ch-the-cesium/description
and you won't have to worry about the sundials and sextants that the
NIST probably secretly uses for calibration. You'll have a personal
time standard that you can trust. Or, just build your own:
http://www.leapsecond.com/pages/atomic-bill/
Once you have an accurate clock, all you need to do is decide which
time standard you want to use (LT, GPS, UTC, GMT, GMAT, GAST, SAT,
TAI, Loran, MST, UT, TDT, TBT, TGC/TBC, etc. This might help you
decide how to set your cesium wrist watch:
http://www.ucolick.org/~sla/leapsecs/timescales.html
Note that some of these are NOT astronomically based, do not include
leap seconds, were established for political reasons, and don't agree
with other standards. For example, the current differences between
UTC, GPS, and TAI at:
http://www.leapsecond.com/java/gpsclock.htm
Also, please note that all of these standards were created and are
managed by various committees, and we all know how ineffective a
committee can be at getting things right.

Perhaps you should just get a wrist sundial:
https://www.google.com/search?q=wrist+sundial&tbm=isch
One can't trust the time gods to get it right:
http://802.11junk.com/jeffl/crud/GPS-vs-UTC.jpg



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 08/07/15 18:22, N_Cook wrote:
On 07/07/2015 19:37, Jeff Liebermann wrote:
On Sat, 04 Jul 2015 13:10:22 -0400, Phil Hobbs
wrote:
(We just had a leap second.)
Yep. That felt good. I got one second of extra sleep.
The new generation of atomic clocks, accurate to 1 second in 15 billion
years,supposedly - how do they know , without a more accurate clock than
that to check it against?

They don't call it "Coordinated Universal Time" (UTC) for nothing.

My wife is a manager at Australia's National Measurement Institute,
and works directly with the local "Time Lord" who's ultimately
responsible for one of the six atomic clocks that are used to determine
UTC. He's a nice bloke, too.

Of course, nothing in this would allow us to detect a systematic
slow-down in time itself, but if the effect was undetectable, how would
it matter? As long as everything slowed down at the same rate, it would
cause no effect that we could measure. So we compare the six clocks as
they wander around each other, and we try to pick a mean line between
them and call that line "coordinated time". And of course we do research
to try to find a way to build a clock which tracks that mean line better
than current ones do, which is how we got to where we are.

Clifford Heath.

On 7/8/2015 4:22 AM, N_Cook wrote:
On 07/07/2015 19:37, Jeff Liebermann wrote:
On Sat, 04 Jul 2015 13:10:22 -0400, Phil Hobbs
wrote:

On 6/27/2015 10:26 PM, wrote:
I've got the best time sync source of all, courtesy
the NIST and WWVB!

Second best. They adjust those ones to match that yellow thing up in
the sky.
Cheers
Phil Hobbs

Does the NIST use a sundial for a primary time standard? I realize
that budget cuts have necessitated economy measures, this seems a bit
extreme.

(We just had a leap second.)

Yep. That felt good. I got one second of extra sleep.



The new generation of atomic clocks, accurate to 1 second in 15 billion
years,supposedly - how do they know , without a more accurate clock than
that to check it against?

It's a specific case of a very general problem, namely how to estimate
and control systematic errors in a measurement. Generally speaking, if
your hydrogen maser and your neighbour's caesium clock and your Russian
brother-in-law's Bose-Einstein condensation agree, you can be pretty
confident. Otherwise it's a real headache.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Clifford Heath: The biggest variant here is the planet
itself. Earth is slowing down, overall, at a more rapid
rate than any of the world's atomic clocks are speeding
up or slowing down. It's why an "ephemeris" second is
inserted every so many years.

On 09/07/15 20:54, wrote:
Clifford Heath: The biggest variant here is the planet
itself.

No, the planet is not changing the rate at which time passes, and it's
not affecting our ability to measure time.

Earth is slowing down, overall, at a more rapid
rate than any of the world's atomic clocks are speeding
up or slowing down. It's why an "ephemeris" second is
inserted every so many years.

Yes, but that has nothing to do with how we improve our ability to
measure time. Remember I was responding to N_Cook's comment:

"The new generation of atomic clocks, accurate to 1 second in 15 billion
years,supposedly - how do they know , without a more accurate clock than
that to check it against?"

The earth's slowing is also somewhat chaotic, inasmuch as equatorial
weather affects the sea-level heights, which introduces noise into the
earth's angular moment of inertia, and hence its rate of rotation. That
has nothing however to do with how we know we're measuring time accurately.

On 10/07/15 11:14, Jeff Liebermann wrote:
On Fri, 10 Jul 2015 01:37:30 +1000, Clifford Heath
wrote:
The fun starts when tracking spacecraft in otter space.

Awesome. Are there any Youtube videos of spacecraft in otter space?
I do love otters, they're my favourite creatures.

On 10/07/15 12:07, Phil Hobbs wrote:
On 7/9/2015 9:14 PM, Jeff Liebermann wrote:
It would be a major disaster if a leap second were
thrown into the timing if you're tracking a spacecraft such as Voyager
1 moving at 17 km/sec (38,000 mph).
You'd be off by 17 km. Is Voyager 1's position known to that accuracy?
Didn't think so.

And yet if you were aiming at Pluto via a slingshot around Venus, you
don't want to be 17km off on approach to Venus. I can't do the math, but
I suspect it's rather closer to 17cm.

On 10/07/15 13:33, Jeff Liebermann wrote:
On Fri, 10 Jul 2015 02:58:26 +1000, Clifford Heath
wrote:
On 10/07/15 11:14, Jeff Liebermann wrote:
The fun starts when tracking spacecraft in otter space.
Awesome. Are there any Youtube videos of spacecraft in otter space?
I do love otters, they're my favourite creatures.
Photos of some otter space otters:
https://www.google.com/search?q=space+otter&tbm=isch
I don't really like otters.

I've only seen sea otters once, on a visit to Monterey.
I guess you also are more fond of animals you don't have locally.

The common otter is super cute. One day, I want to learn how to ot.
it looks like fun.

On Fri, 10 Jul 2015 01:37:30 +1000, Clifford Heath
wrote:

The earth's slowing is also somewhat chaotic, inasmuch as equatorial
weather affects the sea-level heights, which introduces noise into the
earth's angular moment of inertia, and hence its rate of rotation. That
has nothing however to do with how we know we're measuring time accurately.

It might help to mention that we have two types of time accuracy. One
is sidereal time, where 12AM on Jan 1 is astronomically correct and is
used to aim telescopes on earth. This is where we says "at the tone,
the time will be... (beep). The other is the length of 1 second,
minute, hour, day... year which is a numerical count of how many
wavelengths of light or cycles of atomic gigahertz
vibrations pass during these intervals also known as atomic time.

The problem is that the two systems don't quite coincide. The current
difference between UTC and International Atomic Time (UTC-TAI) is now
36 sec and growing. The recent leap second just made things worse.

The fun starts when tracking spacecraft in otter space. Not only does
one have to deal with relativistic effects, but one also has to use a
time system that is independent of how the earth spins, wobbles, and
thrashes around. It would be a major disaster if a leap second were
thrown into the timing if you're tracking a spacecraft such as Voyager
1 moving at 17 km/sec (38,000 mph).

There's quite a bit of detail summarized here including what would
happen if GPS (atomic) time were "harmonized" with local time.
http://www.ucolick.org/~sla/leapsecs/
Only the top part is up to date but the old stuff is interesting.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 7/9/2015 9:14 PM, Jeff Liebermann wrote:
On Fri, 10 Jul 2015 01:37:30 +1000, Clifford Heath
wrote:

The earth's slowing is also somewhat chaotic, inasmuch as equatorial
weather affects the sea-level heights, which introduces noise into the
earth's angular moment of inertia, and hence its rate of rotation. That
has nothing however to do with how we know we're measuring time accurately.

It might help to mention that we have two types of time accuracy. One
is sidereal time, where 12AM on Jan 1 is astronomically correct and is
used to aim telescopes on earth.

Nope. Sidereal time is different from civil (solar) time. The Earth
rotates 365 and change times per year with respect to the Sun, but 366
and (the same) change with respect to the fixed stars. So the two get
out of phase pretty fast.

This is where we says "at the tone,
the time will be... (beep). The other is the length of 1 second,
minute, hour, day... year which is a numerical count of how many
wavelengths of light or cycles of atomic gigahertz
vibrations pass during these intervals also known as atomic time.



The problem is that the two systems don't quite coincide. The current
difference between UTC and International Atomic Time (UTC-TAI) is now
36 sec and growing. The recent leap second just made things worse.

Well, worse if you don't think that the Gregorian reform was an advance.
Pretty soon the vernal equinox would have been in February.
Personally I think that civil time is more important than atomic time.
Folks who need to know the difference, do.

If we knuckle under to atomic time in civil life, our version of the
Julian problem is that midnight by the clock will soon start occurring
at sundown. The leap second inconvenience principally affects software
developers (and those who trust them).


The fun starts when tracking spacecraft in otter space. Not only does
one have to deal with relativistic effects, but one also has to use a
time system that is independent of how the earth spins, wobbles, and
thrashes around. It would be a major disaster if a leap second were
thrown into the timing if you're tracking a spacecraft such as Voyager
1 moving at 17 km/sec (38,000 mph).

You'd be off by 17 km. Is Voyager 1's position known to that accuracy?
Didn't think so.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

On 10/07/15 19:59, wrote:
Clifford Heath wrote: "No, the planet is not changing
the rate at which time passes, and it's not affecting our
ability to measure time. "

HOW can you make such a statement???
If the planet is gradually slowing down,
over millions of years as reported, the
period of time from noon to noon(or
midnight to midnight), is getting LONGER.

Whoosh! You completely missed the point.

The reason we know it's getting longer is because
we have clocks that *aren't* slowing down. I was
talking entirely about *how we know* they aren't
slowing down.

Our hyper-accurate master clocks have
to account for that somehow.

No,they don't. They just count the time passing,
and we decide what numbers to assign to the days,
hours, minutes, seconds. The *numbers* are not
the *time*.

"The earth's slowing is also somewhat chaotic, inasmuch as equatorial
weather affects the sea-level heights, which introduces noise into the
earth's angular moment of inertia, and hence its rate of rotation. That
has nothing however to do with how we know we're measuring time accurately. "

OF COURSE IT DOES!! If our super-accurate
clocks don't account for an inconsistent Earth,
then sunrises, sunsets, and everything else
will start happening later & later by those clocks.

And that is *exactly* what is happening.
That is why we need leap seconds etc, to
adjust the *numbering* to match the planet's
motion. But adjusting the numbering doesn't
make time pass slower or faster.

On Thu, 09 Jul 2015 22:07:57 -0400, Phil Hobbs
wrote:

On 7/9/2015 9:14 PM, Jeff Liebermann wrote:
On Fri, 10 Jul 2015 01:37:30 +1000, Clifford Heath
wrote:

The earth's slowing is also somewhat chaotic, inasmuch as equatorial
weather affects the sea-level heights, which introduces noise into the
earth's angular moment of inertia, and hence its rate of rotation. That
has nothing however to do with how we know we're measuring time accurately.

It might help to mention that we have two types of time accuracy. One
is sidereal time, where 12AM on Jan 1 is astronomically correct and is
used to aim telescopes on earth.

Nope. Sidereal time is different from civil (solar) time. The Earth
rotates 365 and change times per year with respect to the Sun, but 366
and (the same) change with respect to the fixed stars. So the two get
out of phase pretty fast.

Sorry, my mistake.

The problem is that the two systems don't quite coincide. The current
difference between UTC and International Atomic Time (UTC-TAI) is now
36 sec and growing. The recent leap second just made things worse.

Well, worse if you don't think that the Gregorian reform was an advance.
Pretty soon the vernal equinox would have been in February.

The Julian calendar was working just fine for 1500 years as everyone
know how to tweak the date so that it matches the solar calendar. That
was fine for farmers and bankers, but didn't do much for the church,
which had the bad taste to celebrate their holidays by the calendar
month and date. Most everyone else used the signs of the zodiac to
set the beginning of the month. That worked well for the GUM (great
unwashed masses) except that the church equated the zodiac with pagan
religions, alchemy and witchcraft, so that wasn't going to work. A
pope previous to Gregory XIII tried to switch the holidays to the
zodiac months (can't find the name) but gave up before going public.
I suspect that Gregory XIII must have had second throughts when he
allowed the astronomers to fix the calendar. At least they named it
after him, so I guess he was happy.

Incidentally, if you want a really screwed up calendar, try the Hebrew
calendar, which adds an extra month every 2 or 3 years, every 7 of 11
years.
https://en.wikipedia.org/wiki/Hebrew_calendar
There's nothing like a duplicated month (adar) to create confusion.

Personally I think that civil time is more important than atomic time.
Folks who need to know the difference, do.

If we knuckle under to atomic time in civil life, our version of the
Julian problem is that midnight by the clock will soon start occurring
at sundown. The leap second inconvenience principally affects software
developers (and those who trust them).

I don't see a problem. If every political time standards organization
can have it's own time standard, I see no reason why they can't expand
theirs to a calendar standard. You just pick the calendar that is
appropriate for whatever you're doing. It's not much different than
the US before the railroads, where every town had it's own time and
DST standard.

Yeah, there were some hiccups in 2012.
http://www.wired.com/2012/07/leap-second-bug-wreaks-havoc-with-java-linux/
http://www.wired.com/2012/07/leap-second-glitch-explained/
I missed the fire drill, but still managed to get wakened by a
customer wanting to know why their backup failed. Stupid me had set
cron to start the backup exactly at midnight. That worked, but one
second later, it started a 2nd backup during the leap second. Why, I
don't know, but that's what the log files showed. I killed both
processes and started over.

The fun starts when tracking spacecraft in otter space. Not only does
one have to deal with relativistic effects, but one also has to use a
time system that is independent of how the earth spins, wobbles, and
thrashes around. It would be a major disaster if a leap second were
thrown into the timing if you're tracking a spacecraft such as Voyager
1 moving at 17 km/sec (38,000 mph).

You'd be off by 17 km. Is Voyager 1's position known to that accuracy?
Didn't think so.

I was thinking of it in terms of the change in angular error for the
rotation of the earth.
degrees = 17km/40,075km * 360 degrees = 0.15 degrees
Let's see if that works. Voyager 1 and 2 uses the DSN (deep space
network) with 34 or 70 meter dishes at about 8 GHz. That's about 67dB
gain and a -3db beamwidth of about 0.07 degrees for the 34 meter dish,
and 73 db gain and 0.04 degree beamwidth for the 70 meter dish. Since
the DSN tracks the rotation of the earth, a change of 0.15 degrees
would move the main lobe sufficiently to miss the spacecraft.
http://www.satsig.net/pointing/antenna-beamwidth-calculator.htm
http://www.uhf-satcom.com/misc/datasheet/dh2va.pdf

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Fri, 10 Jul 2015 02:58:26 +1000, Clifford Heath
wrote:

On 10/07/15 11:14, Jeff Liebermann wrote:
On Fri, 10 Jul 2015 01:37:30 +1000, Clifford Heath
wrote:
The fun starts when tracking spacecraft in otter space.

Awesome. Are there any Youtube videos of spacecraft in otter space?
I do love otters, they're my favourite creatures.

Yep:
https://www.youtube.com/results?search_query=otter+in+space

Photos of some otter space otters:
https://www.google.com/search?q=space+otter&tbm=isch

I don't really like otters. Years ago, I was diving off Monastary
Beach in Carmel, CA. There was an otter floating on the surface
sleeping. My dive partner decided to poke the otter with a pole. It
looked down at us, and went back to sleep. However, my partner kept
poking the otter until it became irritated. It dived down under us,
came up, and bit me in the buttocks though my wet suit. It wasn't
much of a bite, but did manage to ruin my day.

These days, I look at them with otter contempt.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 10/07/2015 03:07, Phil Hobbs wrote:
On 7/9/2015 9:14 PM, Jeff Liebermann wrote:
On Fri, 10 Jul 2015 01:37:30 +1000, Clifford Heath
wrote:

The earth's slowing is also somewhat chaotic, inasmuch as equatorial
weather affects the sea-level heights, which introduces noise into the
earth's angular moment of inertia, and hence its rate of rotation. That
has nothing however to do with how we know we're measuring time
accurately.

It might help to mention that we have two types of time accuracy. One
is sidereal time, where 12AM on Jan 1 is astronomically correct and is
used to aim telescopes on earth.

Nope. Sidereal time is different from civil (solar) time. The Earth
rotates 365 and change times per year with respect to the Sun, but 366
and (the same) change with respect to the fixed stars. So the two get
out of phase pretty fast.

This is where we says "at the tone,
the time will be... (beep). The other is the length of 1 second,
minute, hour, day... year which is a numerical count of how many
wavelengths of light or cycles of atomic gigahertz
vibrations pass during these intervals also known as atomic time.



The problem is that the two systems don't quite coincide. The current
difference between UTC and International Atomic Time (UTC-TAI) is now
36 sec and growing. The recent leap second just made things worse.

Well, worse if you don't think that the Gregorian reform was an advance.
Pretty soon the vernal equinox would have been in February. Personally
I think that civil time is more important than atomic time. Folks who
need to know the difference, do.

If we knuckle under to atomic time in civil life, our version of the
Julian problem is that midnight by the clock will soon start occurring
at sundown. The leap second inconvenience principally affects software
developers (and those who trust them).


The fun starts when tracking spacecraft in otter space. Not only does
one have to deal with relativistic effects, but one also has to use a
time system that is independent of how the earth spins, wobbles, and
thrashes around. It would be a major disaster if a leap second were
thrown into the timing if you're tracking a spacecraft such as Voyager
1 moving at 17 km/sec (38,000 mph).

You'd be off by 17 km. Is Voyager 1's position known to that accuracy?
Didn't think so.

Cheers

Phil Hobbs

IIRC the Etruscan day started at midday, the Jewish day at 6am, the
midnight start is just a hangover from the Romans, so sundown start is
no great problem