Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default LED alarm clocks all lose accuracy over time

Jim Yanik wrote in message
4...
"Ian Field" wrote in
:


"gregz" wrote in message
-september
.org...
"N_Cook" wrote:
Bill Proms wrote in message
...
I have 3 Intelli-Time LED alarm clocks around the house, just like
the one
he




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jyanik
at
localnet
dot com


OT:
Have you seen the recent thread on rec.antiques.radio+phono ?


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Default LED alarm clocks all lose accuracy over time

Heath had an FM tuner with direct frequency entry.
I never saw another for home use, but there may
have been another for commercial use.


Not quite correct.

AFAIK, Heath made the world's first digitally tuned stereo FM tuner. The kit
was appallingly expensive -- around $550 35+ years ago. It used little cards
you notched for a particular station. I saw it at a hi-fi show, with the
Heath rep explaining how you could use it to monitor the station's broadcast
frequency. (In my best Menckenesque manner, I set him straight.)

Tuners with direct frequency entry were and are uncommon, because it
requires a keypad, plus a decoder to output the digital value needed to set
the local oscillator. As the tuner would have a station memory anyway, which
most people would use to store their favorite stations, direct entry has
little advantage (except during initial setup).

GE made at least two clock radios with direct entry. (Yes, I have one.)
Because there's no overlap between AM and FM frequencies (in kHz and MHz),
you didn't need to specify the band.

Component tuners with direct entry are virtually unheard-of. Toshiba had
one, I believe, and my Parasound T3 permits direct entry from the remote
control.

Does anyone know of any others?


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Default LED alarm clocks all lose accuracy over time

On Sun, 20 May 2012 00:41:44 -0700, isw wrote:

The 1pps output can be used to run a digital clock, but I would hate
to see the final cost.


Why use the 1 pps? Any cheap GPS you get on eBay will output NMEA
"sentences" in ASCII that tell you the precise time. Just use those.


The NEMA sentences are not synchronized to GPS time and add delays in
the decoding process. The time might be off a fraction of a secod.
However, using the NEMA sentence is probably adequate for a consumer
alarm clock. $GPZDA give the time as:
$--ZDA,hhmmss.ss,xx,xx,xxxx,xx,xx
hhmmss.ss = UTC
xx = Day, 01 to 31
xx = Month, 01 to 12
xxxx = Year
xx = Local zone description, 00 to +/- 13 hours
xx = Local zone minutes description (same sign as hours)

The 1pps output has the advantage of simplicity and easy of
integration with existing digital clock designs.

Say, $15 for the GPS, another $15 for an Arduino, $5 for an LCD, and
whatever crystal you have on hand, stuck in a home-made oven. Maybe
another $20 for all the "glue", and the rest, as they say, is just
software.


The cheapest GPS board or module that I could find is about $40.
http://www.sparkfun.com/categories/4?sort_by=price_asc&per_page=50
Chips seem to run about $8/1000. Using your prices, a commercial
digital alarm clock product would retail about $175-$200. Meanwhile,
WWVB controlled "atomic" alarm clocks are selling for $15.

This one decodes NEMA sentences, and has some compromises due to
running on battery power:
http://www.siliconchip.com.au/cms/A_111192/article.html
To conserve the battery, the GPS module is only used
to synchronise the clock every 44 hours and following
synchronisation, the clock will either skip seconds
or double-step to reach the correct time. After
synchronisation the microcontroller is also able to
calculate the inherent inaccuracy of its crystal oscillator
and will compensate by occasionally skipping or
double-stepping a second. This process can also compensate
for aging of the crystal and will keep the clock accurate
between synchronisations.
http://geoffg.net/GPS_Synchronised_Clock.html
http://www.siliconchip.com.au/cms/gallery/article.html?a=111709


--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Default LED alarm clocks all lose accuracy over time

On Sun, 20 May 2012 00:32:56 -0700, isw wrote:

Incidentally, I'm building my own 10MHz GPSDO for running my test
eqipment and ham junk. It's NOT a trivial or inexpensive exercise:
http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm


You can get short-term performance equal to a good crystal and long-term
accuracy pert' near equal to the cesium beam clocks on the satellites
for a whole lot less than that.

Start with a 10 MHz rock in a home-brew oven, and divide it down to make
a "regular clock". Compare the time given by that clock to GPS time, and
twiddle the crystal oscillator to make it track, using a very long time
constant filter in the loop. The longer it runs, the more accurate it
gets.


Good idea. However, if I'm going to go through the trouble of
dividing down to 1pps (1Hz), I might as well add a FLL (frequency lock
loop) and sync the oscillator a 1pps GPS reference.

The regular clock idea also has a potential problem. One missed pulse
and the clock is off by 1 full second. Since there's no way to detect
a missing pulse, or recover gracefully from such a clock slip, it has
the potential for going awry.

After it's run for a while, you can do without GPS updates for fairly
long periods (depending on how good your oscillator/oven is) with very
little loss in accuracy.


Maybe true, but I would have no easy way to determine if it needed to
be resynced with the GPS clock. If it drifted off frequency for some
reason, all my measurements would be off. Setting the frequency to
1*10^-11 takes days to set, and the same time to reset. Might as well
leave it on all the time.

In order to produce usable synchronization of simulcast data
transmitters, the frequency accuracy and stability has to be 0.05ppm
or (5*10^-8) for wide area coverage. That's not going to require a
GPSDO but it would be nice.

I've considered building that sort of rig where the oscillator's
frequency is controlled by altering the temperature of the oven.


Groan. Low noise oscillators use SC cut quartz crystals. That
produces a rather steep frequency/temp curve at room temperature, but
flattens out at about 80-100C. Vary the temperature around this flat
part of the curve, and you'll see almost no change in frequency.
Worse, it might go the wrong direction if it shows a peak or dip in
the curve.
http://www.conwin.com/pdfs/at_or_sc_for_ocxo.pdf
Nice idea, but it will only work if you use an AT cut crystal and then
only if you can deal with the dip in the curve.

The big
advantage of doing things that way is that there are no extra paths for
noise to get into the oscillator, as there would be if you used some
sort of variable capacitor.


Good idea, but glass piston trimmers and varactor electronic tuning
are usually good enough. Microphonics are the major danger of using
trimmers. If the trimmer is solidly built, and the components are
buried in RTV for shock proofing, it should be adequate.

The 1/f phase noise of an oscillator is directly related to the power
density of the device. That means using a moderately high current
device at about 10% of its rated current. That's also why nobody uses
low noise RF front end transistor for low noise oscillators. That
leaves flicker noise, which reduced with lots of negative feedback.

This should give you an idea of what commercial GPSDO oscillators are
doing:
http://www.leapsecond.com/pages/fury/phase.htm

Check the Flexradio forum for what the SDR users are running. A GPSDO
is preferred, but there are plenty of less accurate devices being
used. The stock radio has a TCXO. The GPSDO upgrade costs $700.
Little wonder users are looking at alternatives.
http://cart.flexradio.com/FLEX-6000-GPSDO-Upgrade_p_899.html

Incidentally, some data on the accuracy of the 60Hz power line
frequency:
http://www.leapsecond.com/pages/mains/




--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Default LED alarm clocks all lose accuracy over time

On Sun, 20 May 2012 00:13:49 -0700, isw wrote:

ALmost certainly a crystal; ceramic resonators have way too much drift
with temperature. 32 KHz crystals are very difficult to trim because
they don't like to have any extraneous capacitance hung on them.


32.768KHz crystals are somewhat of a special case when it comes to
trimming. The problem is that the crystals are tuning forks, not bulk
quartz devices like higher frequency devices. What's inside:
http://en.wikipedia.org/wiki/File:Inside_QuartzCrystal-Tuningfork.jpg
Typical specs are something like 7-12pF shunt capacitance. It is
possible to trim the frequency with a variable capacitor that is
centered around this capacitance. It's done all the time in
electronic wrist watches.


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


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Default LED alarm clocks all lose accuracy over time

gregz wrote:
"William Sommerwerck" wrote:
Many years ago I reviewed Heath's "Most-Accurate Clock" for one of Ed Dell's
magazines. It used the Bureau of Standards' shortwave time signals. Sync was
a bit touchy (I eventually replaced the carbon calibration pots with
ceramic), but it otherwise worked very well. It even had an interface that
allowed your computer to reset its clock each time the machine restarted.

When I needed money a few years back, I sold it on eBay for something like
$400, without anyone questioning the price.

If Heath wants to come back as a kit company, it needs to design products
that have no commercial equivalents.


Heath had an fm tuner with direct frequency entry push button. I never saw
another for home use, but there may have been another or commercial use.


I think it was GE that had an alarm clock like that in the late 70s. It
was actually pretty cool. It had a little keypad on it.

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Default LED alarm clocks all lose accuracy over time

Jeff Liebermann wrote:
dark if the US pulls the plug on WWVH and WWVB. That's not going to
happen. Quite the contrary, there are plans to add a US east coast
transmitter. See:
http://en.wikipedia.org/wiki/WWVB
under "Service Improvement Plans".


That's dead. What's left as of March 2012 is a plan to move from AM to BPSK,
which is supposed to make it possible to receive the signal farther away
and in areas with more noise and multipath distortion.

There was a trial in early March, any see any results yet?

How will this affect any old devices that use the AM signal method?

Will someone be selling, as I proposed (and shouldda patented) devices that
get the correct time via NTP and broadcast microwatt signals for local area
time sync?

Geoff.


--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379
In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(


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Default LED alarm clocks all lose accuracy over time


"Cydrome Leader" wrote in message
...
gregz wrote:
"William Sommerwerck" wrote:
Many years ago I reviewed Heath's "Most-Accurate Clock" for one of Ed
Dell's
magazines. It used the Bureau of Standards' shortwave time signals. Sync
was
a bit touchy (I eventually replaced the carbon calibration pots with
ceramic), but it otherwise worked very well. It even had an interface
that
allowed your computer to reset its clock each time the machine
restarted.

When I needed money a few years back, I sold it on eBay for something
like
$400, without anyone questioning the price.

If Heath wants to come back as a kit company, it needs to design
products
that have no commercial equivalents.


Heath had an fm tuner with direct frequency entry push button. I never
saw
another for home use, but there may have been another or commercial use.


I think it was GE that had an alarm clock like that in the late 70s. It
was actually pretty cool. It had a little keypad on it.



About that era, Henry's radio had a batch of project pages in their
catalogue - one of which was a digital clock.

I started building it but never got around to finishing it. Usual excuses;
can't afford the next lot of parts, by the time I got around to it the parts
had become obsolete etc.

The project was ongoing for many years and the parts added to it depended
where I was working at the time!

Pretty sure I still have the board in a tea chest at the back of the garage
somewhere.


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Default LED alarm clocks all lose accuracy over time

I think it was GE that had an alarm clock like that
in the late 70s. It was actually pretty cool. It had a
little keypad on it.


I mentioned that in a preceding post. It was the 7-4760, I believe. I still
have it. The keypad needed cleaning every couple of years.


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Default LED alarm clocks all lose accuracy over time

On Sun, 20 May 2012 18:34:03 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

Jeff Liebermann wrote:
dark if the US pulls the plug on WWVH and WWVB. That's not going to
happen. Quite the contrary, there are plans to add a US east coast
transmitter. See:
http://en.wikipedia.org/wiki/WWVB
under "Service Improvement Plans".


That's dead. What's left as of March 2012 is a plan to move from AM to BPSK,
which is supposed to make it possible to receive the signal farther away
and in areas with more noise and multipath distortion.

There was a trial in early March, any see any results yet?

How will this affect any old devices that use the AM signal method?


No. AM transmissions were to continue, alternating with phase shift
modulation.
http://www.jks.com/wwvb.pdf
In an attempt to cost-effectively address the reception
challenges, NIST is introducing a new protocol for
the WWVB broadcast, which will preserve its amplitude modulation
properties, in order to maintain backwards compatibility and not
impact existing devices, while adding phase-modulation that would
allow for the greatly improved performance.

Some details on the test. I couldn't find any conclusions or official
results:
http://www.jks.com/wwvb/wwvb.html

Will someone be selling, as I proposed (and shouldda patented) devices that
get the correct time via NTP and broadcast microwatt signals for local area
time sync?


Good idea. I haven't seen any such device. Instead of broadcasting,
this might be a good use for power line communications (HomePlug, X10,
etc.) or RF (Z-wave).

Incidentally, while broadcasters seem to be killing off their OTA time
signals (used to set VCR clocks), the cable providers are using OOB
(out of band) signaling to set the clock in their cable set top boxes.
You could probably retransmit that data to a wall clock.

If all else fails, you can call the NIST at 303-499-7111 for WWV and
just play the time over a speaker. Yep, it works.

Web clock:
http://nist.time.gov
It says accurate to 0.3 seconds.

More on such clocks:
http://www.precisionclock.com


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


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Default LED alarm clocks all lose accuracy over time

On 5/20/2012 9:45 AM, William Sommerwerck wrote:
Heath had an FM tuner with direct frequency entry.
I never saw another for home use, but there may
have been another for commercial use.

Not quite correct.

AFAIK, Heath made the world's first digitally tuned stereo FM tuner. The kit
was appallingly expensive -- around $550 35+ years ago. It used little cards
you notched for a particular station. I saw it at a hi-fi show, with the
Heath rep explaining how you could use it to monitor the station's broadcast
frequency. (In my best Menckenesque manner, I set him straight.)

Tuners with direct frequency entry were and are uncommon, because it
requires a keypad, plus a decoder to output the digital value needed to set
the local oscillator. As the tuner would have a station memory anyway, which
most people would use to store their favorite stations, direct entry has
little advantage (except during initial setup).

GE made at least two clock radios with direct entry. (Yes, I have one.)
Because there's no overlap between AM and FM frequencies (in kHz and MHz),
you didn't need to specify the band.

Component tuners with direct entry are virtually unheard-of. Toshiba had
one, I believe, and my Parasound T3 permits direct entry from the remote
control.

Does anyone know of any others?

Dick Sequerra made one as I recall, and the RACAL, Rhode and Schwartz,
and other surveillance receiver makers also had direct synthesis /
tuning as well.




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Default LED alarm clocks all lose accuracy over time

William Sommerwerck wrote:
I think it was GE that had an alarm clock like that
in the late 70s. It was actually pretty cool. It had a
little keypad on it.


I mentioned that in a preceding post. It was the 7-4760, I believe. I still
have it. The keypad needed cleaning every couple of years.


I once had the older vacuum flourescent version. They changed to LEDs at
one some point. I forgot how/why mine broke.
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Default LED alarm clocks all lose accuracy over time

In article ,
Jeff Liebermann wrote:

On Sun, 20 May 2012 00:41:44 -0700, isw wrote:

The 1pps output can be used to run a digital clock, but I would hate
to see the final cost.


Why use the 1 pps? Any cheap GPS you get on eBay will output NMEA
"sentences" in ASCII that tell you the precise time. Just use those.


The NEMA sentences are not synchronized to GPS time and add delays in
the decoding process. The time might be off a fraction of a secod.
However, using the NEMA sentence is probably adequate for a consumer
alarm clock.


Much better, in the long run -- the time they report has a bit of
sample-to-sample jitter, true, but the long-term drift is close enough
to zero to not matter.

You don't correct your local oscillator on the basis of its time
difference compared to a particular sample -- you correct it to force
the long-term drift to zero. The longer it runs, the more accurate it
becomes.

The notion of using irregular or not-continuous data samples to create
accurate clocks even over jittery channels has been around for a while.
Both MPEG 2 and Cable Modems use versions of it.

Isaac
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In article ,
Jeff Liebermann wrote:

On Sun, 20 May 2012 00:32:56 -0700, isw wrote:

Incidentally, I'm building my own 10MHz GPSDO for running my test
eqipment and ham junk. It's NOT a trivial or inexpensive exercise:
http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm


You can get short-term performance equal to a good crystal and long-term
accuracy pert' near equal to the cesium beam clocks on the satellites
for a whole lot less than that.

Start with a 10 MHz rock in a home-brew oven, and divide it down to make
a "regular clock". Compare the time given by that clock to GPS time, and
twiddle the crystal oscillator to make it track, using a very long time
constant filter in the loop. The longer it runs, the more accurate it
gets.


Good idea. However, if I'm going to go through the trouble of
dividing down to 1pps (1Hz), I might as well add a FLL (frequency lock
loop) and sync the oscillator a 1pps GPS reference.

The regular clock idea also has a potential problem. One missed pulse
and the clock is off by 1 full second. Since there's no way to detect
a missing pulse, or recover gracefully from such a clock slip, it has
the potential for going awry.


By "regular clock" I meant anything you like that reads out in "time of
day"; not necessarily something you bought.

I don't understand why there would ever be a missed once-per-second
pulse (assuming you know how to design digital stuff), but even so, the
next time a NMEA sentence comes along (or whenever you decide to read
the next one), you'd know you were off, and which way.

After it's run for a while, you can do without GPS updates for fairly
long periods (depending on how good your oscillator/oven is) with very
little loss in accuracy.


Maybe true, but I would have no easy way to determine if it needed to
be resynced with the GPS clock. If it drifted off frequency for some
reason, all my measurements would be off.


But if it ran at the same rate as the GPS clock, then it wouldn't be
drifting ...

Setting the frequency to
1*10^-11 takes days to set, and the same time to reset. Might as well
leave it on all the time.


Well, of course it's on all the time; there's no other way to keep the
oscillator stable. But if your local notion of time (what the NTP folks
call "epoch") tracks the data coming from the GPS, then it will
eventually be within that error band. And if it stays on longer, it'll
become ever more accurate (long-term).

In order to produce usable synchronization of simulcast data
transmitters, the frequency accuracy and stability has to be 0.05ppm
or (5*10^-8) for wide area coverage. That's not going to require a
GPSDO but it would be nice.

I've considered building that sort of rig where the oscillator's
frequency is controlled by altering the temperature of the oven.


Groan. Low noise oscillators use SC cut quartz crystals. That
produces a rather steep frequency/temp curve at room temperature, but
flattens out at about 80-100C. Vary the temperature around this flat
part of the curve, and you'll see almost no change in frequency.
Worse, it might go the wrong direction if it shows a peak or dip in
the curve.
http://www.conwin.com/pdfs/at_or_sc_for_ocxo.pdf
Nice idea, but it will only work if you use an AT cut crystal and then
only if you can deal with the dip in the curve.


Use whatever crystal you want/need to get the temperature/frequency
curve you need. Pick an oven temperature range that gives the slope you
need. I don't see what's so hard about it. It's not even clear to me why
you even need a low-noise oscillator for a clock, assuming it's being
disciplined by a more accurate "master" (the GPS time system).

The big
advantage of doing things that way is that there are no extra paths for
noise to get into the oscillator, as there would be if you used some
sort of variable capacitor.


Good idea, but glass piston trimmers and varactor electronic tuning
are usually good enough. Microphonics are the major danger of using
trimmers. If the trimmer is solidly built, and the components are
buried in RTV for shock proofing, it should be adequate.


Yes, but if they're not even there to begin with, then they're pretty
noiseless even without special measures ...

The 1/f phase noise of an oscillator is directly related to the power
density of the device. That means using a moderately high current
device at about 10% of its rated current. That's also why nobody uses
low noise RF front end transistor for low noise oscillators. That
leaves flicker noise, which reduced with lots of negative feedback.


The short-term noise and the long-term stability are different. That's
why super-precision sources use rubidium oscillators (low noise, poor
drift), stabilized by cesium devices (higher noise, essentially zero
long-term drift).

If you're building a clock, the noise and jitter aren't very important;
long-term drift is.

Isaac
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Default LED alarm clocks all lose accuracy over time

In article , "N_Cook"
wrote:

Klaatu wrote in message
...
"Bill Proms" wrote in message
...
I have 3 Intelli-Time LED alarm clocks around the house, just like the

one
he


http://www.acurite.com/clock/alarm-c...alarm-clock-13
027a2.html

I initially bought these due to them keeping time when the power goes

off
and auto resetting for DST. There is a problem, however. Each of the
clocks becomes inaccurate over time. If I set them all manually to the
same time, within a few months, each one will be off by 3-5 minutes.

So I ask, what is the problem and is there any way to repair it?

Thanks in advance,
Bill




http://www.ebay.com/itm/Westclox-700...rm-Clock-/2610
19821915?pt=LH_DefaultDomain_0&hash=item3cc5fe675b

or, if you want to see the display at night


http://www.ebay.com/itm/Atomic-Proje...61330?pt=US_Cl
ocks&hash=item484513a7b2

I've used one of the projection alarm clocks for 4 years now, with the
projector light on 24/7.
No problems. Its has battery back-up, but no projection if the power

fails.
All the alarm and wall clocks in the house are now atomic. So is my
wris****ch.
IMHO, If a clock doesn't show the correct time, its not a clock...its a
timer.



Confucius , he say, but even a stopped clock tells the right time twice a
day


And his smarter cousin says "Quite true, but can you tell me when I
should look at it to set my watch?"

Isaac


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Default LED alarm clocks all lose accuracy over time

On May 19, 7:13*pm, Jim Yanik wrote:
"Ian Field" wrote :











"gregz" wrote in message
-september
.org...
"N_Cook" wrote:
Bill Proms wrote in message
...
I have 3 Intelli-Time LED alarm clocks around the house, just like
the one
he


http://www.acurite.com/clock/alarm-c...igital-alarm-c
lock-13 027a2.html


I initially bought these due to them keeping time when the power
goes off
and auto resetting for DST. *There is a problem, however. *Each of
the clocks becomes inaccurate over time. *If I set them all
manually to the
same
time, within a few months, each one will be off by 3-5 minutes.


So I ask, what is the problem and is there any way to repair it?


Thanks in advance,
Bill


I've always put this down to hash on the mains being interpreted as
extra cycles by the clock monitoring input. The supply companies
contractually have to correct the mains frequency so an exact number
of cycles per day (50/60)x60x60x24, but at any instant can be above
or below the nominal frequency.


I doubt if any use power line for sync. Most have battery backup.
Crystals jump frequency from time to time.


Even one I bought recently uses mains sync, but it has a battery &
crystal divider backup to cover outages.


The mains frequency varies depending on peak demand/off peak, but long
term its average has less drift than the cheap crystal oscillator
they're going to put in a radio alarm clock.


radio alarm clock probably won't even use an xtal;like Jeff L. says,they
may use a cheap RC osc.

I note my MW oven clock that derives it's clock from line freq. has better
stability than other "digital" clocks.(like my PC clock....)

(of course,I use an internet program to keep the PC clock fairly close. I
used to use a program(Atomic Clock) that direct-dialed the Naval
Observatory,but the long distance calls cost too much.)

--
Jim Yanik
jyanik
at
localnet
dot com


Try PC Atomic Sync. You select your time server and the PC can sync
every hour or day or manual. I turn machines off at night and have the
sync program run once at boot AND set the PC 15 seconds fast. When
they start recording TV they never clip the head.

The OP referenced a clock that sets itself. How can it be wrong? WWVB
clocks usually have problems receiving the data during the day - too
much noise but work well at night. This implies you need a decent time
base between successful data reads. My 'goofy clock' uses the power
line as the time base but switches to the uProc clock during power
failures. The uProc clock can be 'calibrated' for reasonable accuracy.
What happens is the crystal frequency is divided down to make a fake
60Hz reference pulse when the power line is absent and the divisor is
'tweaked'. I have the WWVB receivers and the code is mostly written
for goofy.

G
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isw wrote:
If you're building a clock, the noise and jitter aren't very important;
long-term drift is.


It's also part of the modern perception that precision is much greater than
it is. A clock that reads hours and minutes is accurate to around 30 seconds.
A clock that reads hours minutes and seconds is accurate to 1/2 second.

Neither are accurate to a millisecond.

I it started with airlines who would write 12:30 for "sometime before 1
o'clock" for departure and 2:00 for "around 1:30" for arrival. People
expect exact numbers where they are approximate, and it is easy to
arrive on time if you allow enough "slop" to commenpensate for anything.

Mousillini (pardon the spelling) "made the trains run on time" by adjusting
the schedules to reality.

I've also seen it in ham radio where the frequency really is around 14.200,
but someone logs it as 14.203154 because that's what their (inacurate)
receiver reads it as and in computers where someone thinks floating
point numbers are integers. :-(

For most people a clock that reads in minutes is ok, and for almost everyone
who needs more accuracy seconds is ok. Just about every clock made stays
within a second for a few minutes, and auto correcting via GPS, NTP or WWV
would do well enough.

I would expect that an HF receiver clock where you set the minutes and it
autocorrects to the minute pips on WWV or CHU would do fairly well, and
in most of the US and Canada do it without the interference problems
the VLF radios have.

Note that I don't have access to any of those sources, or the EU equivalents.
The best that I can do is to run real NTP clients on all my computers,
which sync to a main NTP server on my network.

The main NTP server syncs to a variety of sources, which confuses it because
they are all within a millisecond of each other except for two Apple EU ones
which are 5 seconds off. I put them in a long time ago and probably should
remove them.

The irony of all of this is the only thing that needs accurate timing is
catching a bus, which never comes at any exact time anyway and recording
programs off of the DBS system I susbscibe to.

Since we have their PVR, it gets its time and programing information
from the feed, but is set to start recording early and end late.
They don't even trust themselves. :-)

Geoff

--
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In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(


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"Cydrome Leader" wrote in message
...
William Sommerwerck wrote:


I think it was GE that had an alarm clock like that
in the late 70s. It was actually pretty cool. It had a
little keypad on it.


I mentioned that in a preceding post. It was the 7-4760,
I believe. I still have it. The keypad needed cleaning
every couple of years.


I once had the older vacuum flourescent version. They
changed to LEDs at one some point. I forgot how/why
mine broke.


The vacuum-fluorescent version did 'not have a digital tuner. (I have that
one, too. It works, but it could stand a bit of fixing-up.)


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It's also part of the modern perception that precision
is much greater than it is. A clock that reads hours
and minutes is accurate to around 30 seconds. A
clock that reads hours minutes and seconds is
accurate to 1/2 second.


You're confusing accuracy and resolution. You're also ignoring the fact that
the user can //see// when the minutes change. If you make sure the minutes
change at the same time your reference clock changes, the clock's accuracy
can be less than one second.


I've also seen it in ham radio where the frequency really
is around 14.200, but someone logs it as 14.203154
because that's what their (inacurate) receiver reads it as
and in computers where someone thinks floating
point numbers are integers. :-(


I don't think most digital communications receivers display the frequency
with a precision the LO is capable of.


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I've also seen it in ham radio where the frequency
really is around 14.200, but someone logs it as
14.203154 because that's what their (inaccurate)
receiver reads it as, and in computers, where
someone thinks floating point numbers are integers.


I don't think most digital communications receivers
display the frequency with a precision the LO is
capable of.


WHOOPS! That should have been "incapable of".




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William Sommerwerck wrote:

WHOOPS! That should have been "incapable of".


Well, my 1980's Kenwood TS-430 is capable of tuning in 10Hz steps, and
the modern high priced rigs in 1Hz steps.

Geof.


--
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In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(


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My 1980's Kenwood TS-430 is capable of tuning in 10Hz
steps, and the modern high-priced rigs in 1Hz steps.


I'd like to make a joke about "high-priced [band]spread", but I will
refrain.

The former resolution would require the synthesizer's crystal to be accurate
to about 1 part in 100,000, which is not out of the question.

My Yaesu FTD-1000 is in storage. I don't remember its resolution, or the
tolerance of its crystals.


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On Mon, 21 May 2012 00:00:49 -0700, isw wrote:

I don't understand why there would ever be a missed once-per-second
pulse (assuming you know how to design digital stuff), but even so, the
next time a NMEA sentence comes along (or whenever you decide to read
the next one), you'd know you were off, and which way.


The missing pulse problem is with the 1pps clock implementation, not
the NEMA sentence reader. Clock slip with 1pps is very real. I can
do it with my weather station if I transmit on my VHF HT within about
2ft.

Maybe true, but I would have no easy way to determine if it needed to
be resynced with the GPS clock. If it drifted off frequency for some
reason, all my measurements would be off.


But if it ran at the same rate as the GPS clock, then it wouldn't be
drifting ...


Only if the clock didn't miss a pulse.

I think we have a problem here. You're mixing a NEMA sentence driven
clock, with a 1pps conventional counting clock. The NEMA sentence
device does NOT have a clock slip problem and does not need
recalibration. The 1pps counting clock can easily lose count and
offers no easy way to determine that the clock has slipped and that it
requires recalibration.

Setting the frequency to
1*10^-11 takes days to set, and the same time to reset. Might as well
leave it on all the time.


Well, of course it's on all the time; there's no other way to keep the
oscillator stable.


OK. Then forget about battery operation.

But if your local notion of time (what the NTP folks
call "epoch") tracks the data coming from the GPS, then it will
eventually be within that error band. And if it stays on longer, it'll
become ever more accurate (long-term).


Overkill (except for leap seconds). I don't think anyone cares about
sub-second accuracy in a home alarm clock. However, the last digit
(seconds) should be accurate.

Use whatever crystal you want/need to get the temperature/frequency
curve you need.


If I do that, the design becomes more difficult. For example, a
higher freq/temp slope for the crystal will require more insulation.
Crystals with such a slope tend to have large frequency drift during
aging characteristics. Reverse slopes in the operating area will
create some rather bizarre tuning characteristics.

Pick an oven temperature range that gives the slope you
need.


Well, if I use an AT cut crystal at 80C, the slope is about 2ppm/C. At
10MHz, that's 5Hz/C. You could probably adjust the temperature over a
20C range (to avoid the dip in the AT curve at 75C) yielding a 100Hz
range. Yep, that might work, but you'll need to reduce the oscillator
thermal mass, and greatly increase the insulation.

I don't see what's so hard about it.


Pretend you're on a large boat, which has about a 3 minute delay
between when you turn the rudder and when the vessel changes
direction. Newton's 2nd law and hysteresis delay at its best. To
speed up the turn, one tends to over shoot the rudder direction, and
then bring it back to the correct orientation. To anyone lacking
experience in piloting such an over-damped system, the path traveled
will be rather erratic. See control system damping calculations. your
manual oven corrections might be similarly erratic.

It's not even clear to me why
you even need a low-noise oscillator for a clock, assuming it's being
disciplined by a more accurate "master" (the GPS time system).


I don't need a low noise oscillator for an alarm clock. I mentioned
the low noise in reference to by building a GPSDO, which will be used
for everything from running my test equipment clock, to synchronizing
transmitters. I don't see any reason to build multiple versions when
one device will do it all.

The 1/f phase noise of an oscillator is directly related to the power
density of the device. That means using a moderately high current
device at about 10% of its rated current. That's also why nobody uses
low noise RF front end transistor for low noise oscillators. That
leaves flicker noise, which reduced with lots of negative feedback.


The short-term noise and the long-term stability are different. That's
why super-precision sources use rubidium oscillators (low noise, poor
drift), stabilized by cesium devices (higher noise, essentially zero
long-term drift).


True and thanks for recognizing that a rubidium source is not a
primary frequency standard. The issue with noise is that it has an
effect on accuracy in that one cannot measure the frequency to a
resolution less than the noise. For example, if there is 1Hz of FM
noise on the oscillator, the frequency cannot be measured to less than
1Hz. Of course, one could average the measurements, which only works
if the noise spectra is symmetrical. Also, 1Hz of FM noise at the
10MHz clock reference, multiplied up to a 10GHz transmitter, is
1000Hz, which is audible and quite fatal to data.

If you're building a clock, the noise and jitter aren't very important;
long-term drift is.


True. However, I'm building GPSDO, while you're building a GPS alarm
clock. I agree that the requirements are quite different.

Isaac


--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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On Mon, 21 May 2012 05:31:07 -0400, JW wrote:

Incidentally, I'm building my own 10MHz GPSDO for running my test
eqipment and ham junk. It's NOT a trivial or inexpensive exercise:
http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm


Too expensive.
Get this while it lasts for $135:
http://www.ebay.com/itm/TRIMBLE-GPS-...em27c728 a56b

I almost went for one of those, but instead decided on this:
http://www.ebay.com/itm/280655233263...3%26_rdc%3 D1


Try to find out which lamp they're using. Rubidium depletion is a
major cause of failure. I had an old TFT reference osc crap out on
me. The stupid lamp cost as much as the entire (used) unit. Some of
the cheap lamps have as little as 0.1mg inside, while the one's that
last almost forever have about 1mg.

Not quite as accurate as the thunderbolt, but good enough for my bench.


Yet another temptation to spend money...

I would have no problem with using either of these as a reference.
However, I have a unique problem. I have approximately 200ea Novatel
Allstar 12 boards which are looking for a home. The grand plan is to
build various projects (APRS tracker, GPSDO, GPS logger, test board,
etc) around these boards and possibly sell the kits.

Thanks.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Jim Yanik wrote:
"Ian Field" wrote in
:


"gregz" wrote in message
-september
.org...

"N_Cook" wrote:

Bill Proms wrote in message
...

I have 3 Intelli-Time LED alarm clocks around the house, just like
the one
he



http://www.acurite.com/clock/alarm-c...igital-alarm-c
lock-13 027a2.html

I initially bought these due to them keeping time when the power
goes off
and auto resetting for DST. There is a problem, however. Each of
the clocks becomes inaccurate over time. If I set them all
manually to the

same

time, within a few months, each one will be off by 3-5 minutes.

So I ask, what is the problem and is there any way to repair it?

Thanks in advance,
Bill



I've always put this down to hash on the mains being interpreted as
extra cycles by the clock monitoring input. The supply companies
contractually have to correct the mains frequency so an exact number
of cycles per day (50/60)x60x60x24, but at any instant can be above
or below the nominal frequency.

I doubt if any use power line for sync. Most have battery backup.
Crystals jump frequency from time to time.



Even one I bought recently uses mains sync, but it has a battery &
crystal divider backup to cover outages.

The mains frequency varies depending on peak demand/off peak, but long
term its average has less drift than the cheap crystal oscillator
they're going to put in a radio alarm clock.





radio alarm clock probably won't even use an xtal;like Jeff L. says,they
may use a cheap RC osc.

I note my MW oven clock that derives it's clock from line freq. has better
stability than other "digital" clocks.(like my PC clock....)


I wish the most recent MW oven I bought for our office worked like that.
Its clock gains about one minute a day and I doubt that there's any
syncing to the line frequency built in. It keeps far worse time than the
$10 battery powered wall clocks we use around the office.

Could be the problem is that the temperature of the electronics in that
MW oven moves around quite a bit more than those in the clock on the
wall next to it due to the high power loads when the oven is heating
stuff. That could screw up a simple RC or even xtal oscillator, eh?

OTOH the MW oven in our home's kitchen is always dead nuts on time,
barring power failures, after which it needs resetting.

Jeff

Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.

(of course,I use an internet program to keep the PC clock fairly close. I
used to use a program(Atomic Clock) that direct-dialed the Naval
Observatory,but the long distance calls cost too much.)



--


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jeff_wisnia wrote:
I wish the most recent MW oven I bought for our office worked like that.
Its clock gains about one minute a day and I doubt that there's any
syncing to the line frequency built in. It keeps far worse time than the
$10 battery powered wall clocks we use around the office.


More likely it has one of those chips that detects if there is power line
signal or battery backup and uses a built in crystal to keep time if the
power line goes off.

Unfortunately, at least one of the cheap Chinese versions is broken and uses
the crystal all of the time. I have a clock like that.

The crystals are spec'ed to run a microprocessor in the chip and not keep
time. :-(

Geoff.

--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379
In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(


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On Sun, 20 May 2012 17:25:54 +0000 (UTC), the renowned Cydrome Leader
wrote:

gregz wrote:
"William Sommerwerck" wrote:
Many years ago I reviewed Heath's "Most-Accurate Clock" for one of Ed Dell's
magazines. It used the Bureau of Standards' shortwave time signals. Sync was
a bit touchy (I eventually replaced the carbon calibration pots with
ceramic), but it otherwise worked very well. It even had an interface that
allowed your computer to reset its clock each time the machine restarted.

When I needed money a few years back, I sold it on eBay for something like
$400, without anyone questioning the price.

If Heath wants to come back as a kit company, it needs to design products
that have no commercial equivalents.


Heath had an fm tuner with direct frequency entry push button. I never saw
another for home use, but there may have been another or commercial use.


I think it was GE that had an alarm clock like that in the late 70s. It
was actually pretty cool. It had a little keypad on it.


I had one of those- nice. IIRC, the keys failed over time though.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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"Geoffrey S. Mendelson" wrote:

Bill Proms wrote:

As a possible replacement, I have considered an atomic LED clock, but these
appear to be next to impossible to come by for some reason. I see LCD
atomic clocks everywhere, but most or all have to have the backlight pressed
to see the time in dim conditions.


It's because the US is trying to get rid of those broadcasts. With GPS they
are obsolete.



Then why did they replace the WWVB towers & transmitters a couple
years ago? They built a better antenna array, and raised the
transmitter power so that it can be received in Florida on a $20 'Atomic
clock'.

Not only are they not looking to discontinue the service, but they
are looking at a new modulation method to improve noise immunity. This
web page from NIST says that there are about 50,000,000 radio controlled
clocks using WWVB in the United States:

http://www.nist.gov/pml/newsletter/radio.cfm

--
You can't have a sense of humor, if you have no sense.
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Jeff Liebermann wrote:

On Sun, 20 May 2012 00:41:44 -0700, isw wrote:

The 1pps output can be used to run a digital clock, but I would hate
to see the final cost.


Why use the 1 pps? Any cheap GPS you get on eBay will output NMEA
"sentences" in ASCII that tell you the precise time. Just use those.


The NEMA sentences are not synchronized to GPS time and add delays in
the decoding process. The time might be off a fraction of a secod.
However, using the NEMA sentence is probably adequate for a consumer
alarm clock. $GPZDA give the time as:
$--ZDA,hhmmss.ss,xx,xx,xxxx,xx,xx
hhmmss.ss = UTC
xx = Day, 01 to 31
xx = Month, 01 to 12
xxxx = Year
xx = Local zone description, 00 to +/- 13 hours
xx = Local zone minutes description (same sign as hours)

The 1pps output has the advantage of simplicity and easy of
integration with existing digital clock designs.

Say, $15 for the GPS, another $15 for an Arduino, $5 for an LCD, and
whatever crystal you have on hand, stuck in a home-made oven. Maybe
another $20 for all the "glue", and the rest, as they say, is just
software.


The cheapest GPS board or module that I could find is about $40.
http://www.sparkfun.com/categories/4?sort_by=price_asc&per_page=50
Chips seem to run about $8/1000. Using your prices, a commercial
digital alarm clock product would retail about $175-$200. Meanwhile,
WWVB controlled "atomic" alarm clocks are selling for $15.

This one decodes NEMA sentences, and has some compromises due to
running on battery power:
http://www.siliconchip.com.au/cms/A_111192/article.html
To conserve the battery, the GPS module is only used
to synchronise the clock every 44 hours and following
synchronisation, the clock will either skip seconds
or double-step to reach the correct time. After
synchronisation the microcontroller is also able to
calculate the inherent inaccuracy of its crystal oscillator
and will compensate by occasionally skipping or
double-stepping a second. This process can also compensate
for aging of the crystal and will keep the clock accurate
between synchronisations.
http://geoffg.net/GPS_Synchronised_Clock.html
http://www.siliconchip.com.au/cms/gallery/article.html?a=111709



$7.79 Trimble GPS module:

http://www.ebay.com/itm/190626494449

$5.99 GPS antenna with MMCX connector:

http://www.ebay.com/itm/170496886891

$32.00 for a GPS receiver & antenna module:

http://www.ebay.com/itm/180815989220


Be VERY careful if you buy any Rockwell GPS receiver boards on Ebay.
At least one seller is advertising a board with 10 KHz out then ship a
different board, even though they have been sent the information by
people who have tried to use them.

--
You can't have a sense of humor, if you have no sense.
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N_Cook wrote:

Confucius, he say, but even a stopped clock tells the right time twice a
day



Confucius was confused.


--
You can't have a sense of humor, if you have no sense.


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In article ,
Jeff Liebermann wrote:

On Mon, 21 May 2012 00:00:49 -0700, isw wrote:

I don't understand why there would ever be a missed once-per-second
pulse (assuming you know how to design digital stuff), but even so, the
next time a NMEA sentence comes along (or whenever you decide to read
the next one), you'd know you were off, and which way.


The missing pulse problem is with the 1pps clock implementation, not
the NEMA sentence reader. Clock slip with 1pps is very real. I can
do it with my weather station if I transmit on my VHF HT within about
2ft.

Maybe true, but I would have no easy way to determine if it needed to
be resynced with the GPS clock. If it drifted off frequency for some
reason, all my measurements would be off.


But if it ran at the same rate as the GPS clock, then it wouldn't be
drifting ...


Only if the clock didn't miss a pulse.

I think we have a problem here. You're mixing a NEMA sentence driven
clock, with a 1pps conventional counting clock. The NEMA sentence
device does NOT have a clock slip problem and does not need
recalibration. The 1pps counting clock can easily lose count and
offers no easy way to determine that the clock has slipped and that it
requires recalibration.


I'm proposing to build a time-of-the-year clock that uses a (say) 10 MHz
oscillator for a timebase, with dividers (hardware or software) to
provide all the various outputs. The time-of-year output is available to
the frequency-controlling loop, which compares its value with what it
gets from the NMEA sentences -- if the local clock is ahead, slow down
the 10 MHz, and vice-versa.

After a while, that oscillator is going to be dead on.

Setting the frequency to
1*10^-11 takes days to set, and the same time to reset. Might as well
leave it on all the time.


Well, of course it's on all the time; there's no other way to keep the
oscillator stable.


OK. Then forget about battery operation.


Using temperature to control frequency, probably; using other means, not
much of a problem. A decent GPS chip set, a little CMOS computer, and an
LCD for readout will come in at a small fraction of a watt. If you
picked a better-than-average crystal, stability-wise, you could turn off
everything but the oscillator for most of the time and still get
exceptional long-term accuracy. I expect that some clever design could
produce an "oven" that could be heated by a quarter-watt resistor glued
to the crystal case, so even using the temperature-control-of-frequency
method could still give you something that could operate all day on a
battery.

But if your local notion of time (what the NTP folks
call "epoch") tracks the data coming from the GPS, then it will
eventually be within that error band. And if it stays on longer, it'll
become ever more accurate (long-term).


Overkill (except for leap seconds). I don't think anyone cares about
sub-second accuracy in a home alarm clock. However, the last digit
(seconds) should be accurate.


Right. But what they might care about is that the clock never drifts
away from "real" time, no matter what the power line does. That, of
course, is the appeal of all "radio clocks".

Use whatever crystal you want/need to get the temperature/frequency
curve you need.


If I do that, the design becomes more difficult. For example, a
higher freq/temp slope for the crystal will require more insulation.


Not really. Remember, it's in a temperature-controlled oven. The
temperature control loop will keep the crystal at whatever temperature
is called for to keep the frequency at precisely 10.000... MHz.

Crystals with such a slope tend to have large frequency drift during
aging characteristics.


Which will be compensated for continuously by the loop.

Reverse slopes in the operating area will
create some rather bizarre tuning characteristics.


Well, don't operate it in that regime ...

Pick an oven temperature range that gives the slope you
need.


Well, if I use an AT cut crystal at 80C, the slope is about 2ppm/C. At
10MHz, that's 5Hz/C. You could probably adjust the temperature over a
20C range (to avoid the dip in the AT curve at 75C) yielding a 100Hz
range. Yep, that might work, but you'll need to reduce the oscillator
thermal mass, and greatly increase the insulation.


Nope. Very slow response times are no problem. The loop will eventually
arrange things so that precisely ten million cycles will elapse per one
second elapsed, over the long term. Still, small thermal mass is easy --
just pick a small crystal package, and heat that package directly with a
small resistor or two. Insulation is cheap and a lot of it is not a
problem. I'd use fairly long, very thin, stainless steel wires to
connect the crystal (and those resistors) to the rest of the circuit,
too. One major source of problems on high-stability oscillators is
thermal or acoustical shock running right up the connecting wires
directly to the quartz itself. I've seen ovenized oscillators that were
disrupted every time the thermostat clicked, and not because of
electrical transients.

I don't see what's so hard about it.


Pretend you're on a large boat, which has about a 3 minute delay
between when you turn the rudder and when the vessel changes
direction. Newton's 2nd law and hysteresis delay at its best. To
speed up the turn, one tends to over shoot the rudder direction, and
then bring it back to the correct orientation. To anyone lacking
experience in piloting such an over-damped system, the path traveled
will be rather erratic. See control system damping calculations. your
manual oven corrections might be similarly erratic.


I've done a few control loops, some of them a bit "peculiar". If you
insist on having the fastest possible transition to the new heading to
within some specified error band, then you're correct. It you're willing
to do things a lot more slowly while still (eventually) arriving at the
new heading, then the loop gets very simple. For the above problem, just
put a really slow motor on the power steering for the rudder.

It's not even clear to me why
you even need a low-noise oscillator for a clock, assuming it's being
disciplined by a more accurate "master" (the GPS time system).


I don't need a low noise oscillator for an alarm clock. I mentioned
the low noise in reference to by building a GPSDO, which will be used
for everything from running my test equipment clock, to synchronizing
transmitters. I don't see any reason to build multiple versions when
one device will do it all.


Consider the 10 MHz output from this sort of clock as the frequency
reference for whatever sort of synthesizer you want. If the clock runs
at the proper rate, the oscillator is at the specified frequency. After
it's run for a while, the frequency will always be very, very close to
exactly ten megahertz.

The 1/f phase noise of an oscillator is directly related to the power
density of the device. That means using a moderately high current
device at about 10% of its rated current. That's also why nobody uses
low noise RF front end transistor for low noise oscillators. That
leaves flicker noise, which reduced with lots of negative feedback.


The short-term noise and the long-term stability are different. That's
why super-precision sources use rubidium oscillators (low noise, poor
drift), stabilized by cesium devices (higher noise, essentially zero
long-term drift).


True and thanks for recognizing that a rubidium source is not a
primary frequency standard. The issue with noise is that it has an
effect on accuracy in that one cannot measure the frequency to a
resolution less than the noise. For example, if there is 1Hz of FM
noise on the oscillator, the frequency cannot be measured to less than
1Hz. Of course, one could average the measurements, which only works
if the noise spectra is symmetrical. Also, 1Hz of FM noise at the
10MHz clock reference, multiplied up to a 10GHz transmitter, is
1000Hz, which is audible and quite fatal to data.


One of the advantages of this sort of loop (thermally controlled) is
that there is literally nothing in the circuit that prevents the noise
from being as low as it can possibly be for whatever sort of oscillator
you choose, while still constraining it to being very close to the
design frequency.

Isaac
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Michael A. Terrell wrote:

"Geoffrey S. Mendelson" wrote:
It's because the US is trying to get rid of those broadcasts. With GPS they
are obsolete.



Then why did they replace the WWVB towers & transmitters a couple
years ago? They built a better antenna array, and raised the
transmitter power so that it can be received in Florida on a $20 'Atomic
clock'.


They are playing "cheap catch up". The original plans were to build an
east coast station, but they were unable to get any government installation
to "host" it, (NIMBY) and lost the funding.

Not only are they not looking to discontinue the service, but they
are looking at a new modulation method to improve noise immunity. This
web page from NIST says that there are about 50,000,000 radio controlled
clocks using WWVB in the United States:


The are using the improved modulation to keep relevant. In most large cities,
the noise from computer and home electronic equipment, BPL (still very much
in use but not for internet to customers), aDSL, etc has made it next
to impossible to receive a signal.

They exist today because people are willing to accept the poor service they
get as it is the only game in town at that price tag. Most users never
pay attention to how often they get sync, if ever.

If they have to pay $100-$150 for a BPSK decoding clock, GPS or Wifi NTP clocks
will seem a lot better deal.

I'd love to know how they came up with the number of clocks in use. Anyone
have an idea?

Geoff.



--
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In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(


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On Tue, 22 May 2012 11:49:04 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

The are using the improved modulation to keep relevant. In most large cities,
the noise from computer and home electronic equipment, BPL (still very much
in use but not for internet to customers), aDSL, etc has made it next
to impossible to receive a signal.


Many switching power supplies run at about 60KHz. I have one
somewhere around my computer/TV pile, which kills WWVB reception if I
get anywhere near it.

They exist today because people are willing to accept the poor service they
get as it is the only game in town at that price tag. Most users never
pay attention to how often they get sync, if ever.


Most WWVB devices have an indicator on the LCD display to show that
the clock was recently synced with WWVB time. My weather stations and
assorted digital clocks all have this feature.

If they have to pay $100-$150 for a BPSK decoding clock, GPS or Wifi NTP clocks
will seem a lot better deal.


It's my understanding that only the modulation scheme will change, not
the encoded data. A universal chip that works using both system
should be possible without a major price jump.

I'm a bit mystified with the "new type of PM receiving antenna"
mentioned in:
http://www.nist.gov/pml/newsletter/radio.cfm
I didn't know that antennas were modulation specific.

I'd love to know how they came up with the number of clocks in use. Anyone
have an idea?


Same as how they get wi-fi device numbers. Marketing research firms,
that specialize in selling industry statistics and predictions, survey
the chip manufacturers for how many chips they've sold. In this case,
the leading manufactory is C-Max:
http://www.c-max-time.com
I suspect the largest numbers are in "atomic time" wris****ches.

The accuracy of sales statistics are always questionable, but are
usually accurate within an order of magnitude. The problem is while
sales statistics are fairly simple to generate, devices in use are
not. One could add up all the sales from the last 10 years, assume
that few of the devices were trashed, and produce a very large number
in use. Whether it has any value is very doubtful. Besides, sales
statistics is what companies are willing to pay for, and that's what
the marketing research firms tend to produce.


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

Many switching power supplies run at about 60KHz. I have one
somewhere around my computer/TV pile, which kills WWVB reception if I
get anywhere near it.


Exactly, how many people have one?



Most WWVB devices have an indicator on the LCD display to show that
the clock was recently synced with WWVB time. My weather stations and
assorted digital clocks all have this feature.


What's recent? 1 minute? 1 Hour? 1 Day? a Week?


It's my understanding that only the modulation scheme will change, not
the encoded data. A universal chip that works using both system
should be possible without a major price jump.


Well no. The data is the same, but a new receiver needs to be used.
The old one just did on/off for an AM pulse, the new one uses BPSK,
which is two tone modulation. So not only does it have to decode
the carrier being there at all, it has to decode two different tones.

Then you have to decode the BPSK stream to get the data. This not a big
deal, you could do it with a sound card and a microprocessor, but it's
a different receiver design, and reprograming the microprocessor.

The kind of thing that if you really were going to sell 50 million of them
you could do it for a few dollars a chipset/board, which is probably what the
current ones cost, but if you want to break even with 10,000 you have to
sell them for at least $100, maybe more.

It's like I saw an article about an Israeli startup that had sold 200,000 of
their product. The article was entitled "sales of xxx disappointing".
I guess they planned on selling a million of them. :-(


I'm a bit mystified with the "new type of PM receiving antenna"
mentioned in:
http://www.nist.gov/pml/newsletter/radio.cfm
I didn't know that antennas were modulation specific.


Where have you been the last five years? I surprised that you have not
been swamped with HDTV antennas. :-)

I expect it's another gimick to say you need to buy a higher gain antenna,
or that's why your device can't sync. I expect that everyone will need
to buy 1/2 wavelength end fed wires.

(for the humor impared, that's a joke, a wavelength is 5 kilometers).


Geoff.
--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379
In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(


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"Geoffrey S. Mendelson" wrote:

Michael A. Terrell wrote:
?
? "Geoffrey S. Mendelson" wrote:
?? It's because the US is trying to get rid of those broadcasts. With GPS they
?? are obsolete.
?
?
? Then why did they replace the WWVB towers ? transmitters a couple
? years ago? They built a better antenna array, and raised the
? transmitter power so that it can be received in Florida on a $20 'Atomic
? clock'.

They are playing "cheap catch up". The original plans were to build an
east coast station, but they were unable to get any government installation
to "host" it, (NIMBY) and lost the funding.



So, they gave up and started the upgrade in the late '90s?


? Not only are they not looking to discontinue the service, but they
? are looking at a new modulation method to improve noise immunity. This
? web page from NIST says that there are about 50,000,000 radio controlled
? clocks using WWVB in the United States:

The are using the improved modulation to keep relevant. In most large cities,
the noise from computer and home electronic equipment, BPL (still very much
in use but not for internet to customers), aDSL, etc has made it next
to impossible to receive a signal.



BPL isn't used around here. Progress Energy drives down the street
and pings the transponders in their meters. The SW bands are fairly
dead, these days. The SMPS in traffic lihts cause more noise than
anything else, and appear to operate on the low end of the AM BCB,


They exist today because people are willing to accept the poor service they
get as it is the only game in town at that price tag. Most users never
pay attention to how often they get sync, if ever.



I am near Orlando, Florida and have no problem with my WWVB clocks.
The one in this room is about ten feet from several computers &
monitors, yet it matches the internet time on the screen.


If they have to pay $100-$150 for a BPSK decoding clock, GPS or Wifi NTP clocks
will seem a lot better deal.



Who says they will cost that much? Custom ICs will make it into a
single or two chip design. FQPSK would require a lot more processing,
and the only place I used it was in the Microdyne DR2000 & RCB2000
telemetry recievers. Some people don't want to screw with wi-fi crap.
There are times when every availible channel is full of noise



I'd love to know how they came up with the number of clocks in use. Anyone
have an idea?

Geoff.

--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379
In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(



--
You can't have a sense of humor, if you have no sense.


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"Geoffrey S. Mendelson" wrote:

Well no. The data is the same, but a new receiver needs to be used.
The old one just did on/off for an AM pulse, the new one uses BPSK,
which is two tone modulation. So not only does it have to decode
the carrier being there at all, it has to decode two different tones.



The carrier was amplitude modulated by reducing the carrier level,
not CW.

The same carrier can be phase modulated and provide both data
streams.


--
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On Tue, 22 May 2012 15:49:04 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

Jeff Liebermann wrote:

Many switching power supplies run at about 60KHz. I have one
somewhere around my computer/TV pile, which kills WWVB reception if I
get anywhere near it.


Exactly, how many people have one?


My guess(tm) is that it's the power supply in my DirecTV DVR. There
are plenty of those out there.

Most WWVB devices have an indicator on the LCD display to show that
the clock was recently synced with WWVB time. My weather stations and
assorted digital clocks all have this feature.


What's recent? 1 minute? 1 Hour? 1 Day? a Week?


The manual for the wx station says within 24 hrs. That makes sense as
60KHz skywave doesn't work too well until after about midnight. I
suspect it's lucky to get one update per day. That should be
sufficient to deal with any clock drift. When I was stupidly running
it next to my computer/TV pile, it would never update. I vaguely
recall that it drifted fast at about 5 minutes per month. Now that it
gets updates, it's dead on. See:
http://tf.nist.gov/general/pdf/1976.pdf
Section 4, for recommended synchronization practices.

It's my understanding that only the modulation scheme will change, not
the encoded data. A universal chip that works using both system
should be possible without a major price jump.


Well no. The data is the same, but a new receiver needs to be used.
The old one just did on/off for an AM pulse, the new one uses BPSK,
which is two tone modulation. So not only does it have to decode
the carrier being there at all, it has to decode two different tones.


Nope. It's not two tone. It's a phase shift of the AM carrier,
switching from 0 degrees to 180 degrees for 0/1. See video at:
http://www.youtube.com/watch?v=mOjwxq5flTg
I had thought that they were going to broadcast each separately, but
apparently it's simply adding PSK to the existing AM carrier. Clever,
methinks.

Then you have to decode the BPSK stream to get the data.


Yes, you have to modify the chip. However, it's really easy to build
a BPSK to OOK (on off keying) converter, so an adapter is possible.

This not a big
deal, you could do it with a sound card and a microprocessor, but it's
a different receiver design, and reprograming the microprocessor.


While it's possible to demodulate a 60KHz carrier with a sound card,
it would require a high end 192KHz card, and not a generic card that
maxes out at 44KHz.

The kind of thing that if you really were going to sell 50 million of them
you could do it for a few dollars a chipset/board, which is probably what the
current ones cost, but if you want to break even with 10,000 you have to
sell them for at least $100, maybe more.


Well, keep your eye on C-Max. When they produce a suitable BPSK chip,
that should set the price point. It's this type of potentially high
volume market that really attracts the chip vendors.

It's like I saw an article about an Israeli startup that had sold 200,000 of
their product. The article was entitled "sales of xxx disappointing".
I guess they planned on selling a million of them. :-(


Kinda like the Windoze Phone 7?
http://www.dailytech.com/Ballmer+Admits+Windows+Phone+7+Sales+Are+Disappoin ting/article22747.htm
It was really clever of MS to prematurely announce the WP8, and then
leak that there's no upgrade path from the WP7 to the WP8.

I'm a bit mystified with the "new type of PM receiving antenna"
mentioned in:
http://www.nist.gov/pml/newsletter/radio.cfm
I didn't know that antennas were modulation specific.


Where have you been the last five years? I surprised that you have not
been swamped with HDTV antennas. :-)


Sigh. I assumed that it was too early for the marketing hype in the
"atomic clock" market. My apologies for being so naive.

Incidentally, I designed stick-on metallic label, that you attach to
your ordinary TV antenna, that turns it into an HDTV antenna.

I expect it's another gimick to say you need to buy a higher gain antenna,
or that's why your device can't sync. I expect that everyone will need
to buy 1/2 wavelength end fed wires.

(for the humor impared, that's a joke, a wavelength is 5 kilometers).


Sorry, but zoning ordinances do not allow covering the neighborhood
with giant antennas. The authorities claim that it attracts
lightning, cosmic rays, and aliens from outer space.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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On Tue, 22 May 2012 15:49:04 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:


Well no. The data is the same, but a new receiver needs to be used.
The old one just did on/off for an AM pulse, the new one uses BPSK,
which is two tone modulation. So not only does it have to decode
the carrier being there at all, it has to decode two different tones.


Ummm. No. BPSK is a variant of Manchester encoding.

Binary Phase Shift Keying. Single frequency.

Then you have to decode the BPSK stream to get the data. This not a big
deal, you could do it with a sound card and a microprocessor, but it's
a different receiver design, and reprograming the microprocessor.

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On Sat, 19 May 2012 16:17:37 +0000 (UTC), gregz
wrote:

"N_Cook" wrote:
Bill Proms wrote in message
...
I have 3 Intelli-Time LED alarm clocks around the house, just like the one
he


http://www.acurite.com/clock/alarm-c...alarm-clock-13
027a2.html

I initially bought these due to them keeping time when the power goes off
and auto resetting for DST. There is a problem, however. Each of the
clocks becomes inaccurate over time. If I set them all manually to the

same
time, within a few months, each one will be off by 3-5 minutes.

So I ask, what is the problem and is there any way to repair it?

Thanks in advance,
Bill



I've always put this down to hash on the mains being interpreted as extra
cycles by the clock monitoring input. The supply companies contractually
have to correct the mains frequency so an exact number of cycles per day
(50/60)x60x60x24, but at any instant can be above or below the nominal
frequency.


I doubt if any use power line for sync. Most have battery backup. Crystals
jump frequency from time to time.

Greg

I have an LED alarm clock that definitely uses the powerline frequency
to keep time. I know this because I have a rotary phase converter to
supply three phase power to my shop. When ever I use certain CNC
machines with DC spindle drives the clock runs much faster. When I use
machines with VFD spindle drives the clock gains only a little time
and when powering only induction motors the clock is not affected at
all. Looking at the power in the house with an oscilloscope a friend
of mine who designs inverter power supplies showed me the noise on the
powerline when the machines were running. It is a cheap clock though
and is the only one that has this behavior.
Eric
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On 05/19/12 12:51, Bill Proms wrote:


So I ask, what is the problem and is there any way to repair it?

Thanks in advance,
Bill


Maybe you should switch to sundials, you ****ing peckerhead.
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