LED alarm clocks all lose accuracy over time

[Michael A. Terrell]

"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.

 

[Michael A. Terrell]

"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.


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

 

[Jeff Liebermann]

On Tue, 22 May 2012 15:49:04 +0000 (UTC), "Geoffrey S. Mendelson"
<gsm@mendelson.com> 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+Disappointing/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 jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[josephkk]

On Tue, 22 May 2012 15:49:04 +0000 (UTC), "Geoffrey S. Mendelson"
<gsm@mendelson.com> 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.

 

On Sat, 19 May 2012 16:17:37 +0000 (UTC), gregz <zekor@comcast.net>
wrote:

"N_Cook" <diverse@tcp.co.uk> wrote:
Bill Proms <none@anywhere.us> wrote in message
news:jp850p$fk2$1@dont-email.me...
I have 3 Intelli-Time LED alarm clocks around the house, just like the one
here:


http://www.acurite.com/clock/alarm-clock/intelli-time-digital-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

 

[Carolee]

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 fucking peckerhead.