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'[PIC]: How to obtain the official US time clock?'
2002\12\17@115641 by Tony Pan

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Hi,

I really need to design a product that knows the official U.S. time, aside
from other features. Can someone tell me what is required for the hardware
and software to acquire the official time? And what kind of connections are
required?

Thanks a lot!

Tony

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2002\12\17@122858 by Michael Reid

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How to obtain the official US time clock?

try this link to Atmel.  They bought Temic a few years ago, who was the
original manufacturer of these chips. They have 2 chips for decoding the
atomic time clock.  The clock broadcasts are at 60kHz for the US version and
are easy to receive.

http://www.atmel-wm.com/products/gab_prod_level2_2.php3?dom1=45&dom2=188&cas

This link has 2 pdf's for download.  The first one goes over the chip and
the various clock information for German, English, Japanese, and US signals.

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2002\12\17@123534 by Tim Webb

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I heard that you can get the official universal time from a GPS Satellite
Maybe you can communicate serially to a GPS receiver module.


{Original Message removed}

2002\12\17@123650 by Jim Rickenbacker

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www.boulder.nist.gov/timefreq/stations/wwv.html

{Quote hidden}

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2002\12\17@123651 by Olin Lathrop

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> I really need to design a product that knows the official U.S. time,
aside
> from other features. Can someone tell me what is required for the
hardware
> and software to acquire the official time? And what kind of connections
are
> required?

There are several ways to do this, but you need to first decide what
accuracy you require.  If the gizmo already has an internet connection,
then the contacting a NNTP server requires no additional hardware.  There
are other options:

1  -  Have the user set it occasionally and use a real time clock in
between.

2  -  Decode the WWVL long wave broadcasts.  These are designed for this
purpose, but your hardware is susceptable to antenna orientation and
distance from Boulder.  Here in MA we are 2000 miles from Boulder and
placement and orientation of automatic clocks makes a big difference.  I
have two automatic clocks, and they only seem to pick up the signal at
night, sometimes.

3  -  Decode WWV broadcast.  These are at several shortwave frequencies.
I know 10MHz is one of them, and I think there are also broadcasts at
2.5MHz, 5MHz, and 15MHz, but I'm not sure.  These may be more difficult to
decode, but the coverage should be wider.  I'm not totally sure they even
have encoded data on them.

4  -  Canada also broadcasts a time standard.  The radio station is called
CHU if I remember right.  I don't know whether it contains coded
information that a micro can use.


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Embed Inc, embedded system specialists in Littleton Massachusetts
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2002\12\17@124511 by Tim Webb

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Check our these URL's:

http://www.ntp-time-server.com/gps-time-server/gps-time-server.htm

http://www.trimble.com/lassensq.html

http://www.trimble.com/thunderbolt.html


{Original Message removed}

2002\12\17@125604 by Tim Webb

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You can get these modules cheap...

OEM GPS board on Ebay - Current bid $10.00


http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1945533330


{Original Message removed}

2002\12\17@132957 by Jim

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> Decode the WWVL long wave broadcasts.
               ^

Make that "WWVB"
             ^

http://www.boulder.nist.gov/timefreq/stations/wwvb.htm


> placement and orientation of automatic clocks makes a big difference.  I
> have two automatic clocks, and they only seem to pick up the signal at
> night, sometimes.

Signal propagation at these frequencies is primarily via
"ground wave" - with little propagation via 'sky wave' as
one is accustomed to experiencing at night on the AM broadcast
band ...

More likely your clock sets itself at this time (night) versus
continuously running the VLF receiver (and thereby draining
the battery) OR there is less interference from man-made
devices at this time (TV sets, standard video display monitors,
etc).

The over-earth path loss at 60 KHz is around 120 dB.

Given WWVB's approximate 50 KW transmit power (and assuming
through antenna efficiency values for simplicity at 50%) the
resultant received values are [1]:

Field strength at receiving site  1.56  micro-volts per metre
50-ohm matched receiver input     981.52  micro-volts
Receiver S-meter reading          S9 + 26  decibels

Real-world receive power-value figures will be much lower due
the ferrite rod antenna normally used to receive the 60 KHz
WWVB signal.

RF Jim

[1] Program name: GRNDWAV3.exe
   Author: R.J.Edwards G4FGQ
   (C) 4th July 2001


{Original Message removed}

2002\12\17@134657 by Robert Rolf

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CHU does have a computer readable output
http://inms-ienm.nrc-cnrc.gc.ca/time/chuhistory.html

"The warble tone at seconds 31 to 39 allow any computer with a
Bell 103 compatible 300 bps modem to receive and decode an
accurate source of time."

Germany also has a standard time broadcast as does Japan.

However the world has moved to using GPS to globally
distribute accurate time. It is just FARRRRR more reliable.

Olin Lathrop wrote:
{Quote hidden}

WWVB is the 60kHz station
WWVH is HF station in Hawaii
http://www.boulder.nist.gov/timefreq/stations/wwvb.html

> purpose, but your hardware is susceptable to antenna orientation and
> distance from Boulder.  Here in MA we are 2000 miles from Boulder and
> placement and orientation of automatic clocks makes a big difference.  I
> have two automatic clocks, and they only seem to pick up the signal at
> night, sometimes.

I'm up here in Edmonton (53N 113W), and my OSI clock picks up the signal
at all appointed check times (day and night). Antenna placement and
orientation is CRITICAL to reliable reception (no nearby fluorescent
lights or light dimmers)

> 3  -  Decode WWV broadcast.  These are at several shortwave frequencies.
> I know 10MHz is one of them, and I think there are also broadcasts at
> 2.5MHz, 5MHz, and 15MHz, but I'm not sure.  These may be more difficult to

& 20Mhz
www.boulder.nist.gov/timefreq/stations/wwv.html
10,000 W on 5, 10, and 15 MHz; and 2500 W on 2.5 and 20 MHz

> decode, but the coverage should be wider.  I'm not totally sure they even
> have encoded data on them.

They do.
"The modulation level is 50 percent for the steady tones,
50 percent for the BCD time code, ..."

>
> 4  -  Canada also broadcasts a time standard.  The radio station is called
> CHU if I remember right.  I don't know whether it contains coded
> information that a micro can use.

It does. See opening paragraph

Robert

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2002\12\17@135448 by Tony Pan

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Thank you everyone for the information. I now have an idea what comprise a
radio clock receiver.

I may at first attempt to design the whole circuit without using a
commercial receiver IC.

Basically I need to design a radio receiver circuit that is tuned to 60KHz
signals. I also need a ferrite antenna.

Can you point me to some online resources about designing a radio receiver
circuit? Also where to look for a ferrite antenna?

Thanks,
Tony

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2002\12\17@135450 by Tony Pan

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> However the world has moved to using GPS to globally
> distribute accurate time. It is just FARRRRR more reliable.

Is it cheaper?

Thanks,
Tony


{Original Message removed}

2002\12\17@141320 by Dave Tweed

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Olin Lathrop <TakeThisOuTolin_piclistEraseMEspamspam_OUTEMBEDINC.COM> wrote:
> Tony Pan <RemoveMEweidong.panspamTakeThisOuTVERIZON.NET> wrote:
> > I really need to design a product that knows the official U.S. time,
> aside
> > from other features. Can someone tell me what is required for the
> hardware
> > and software to acquire the official time? And what kind of connections
> are
> > required?

Olin, you need an email client that doesn't try to re-wrap your quotes;
it's *really inconvenient* for those of us who want to reply to you...
Also, you should include an attribution line like the one I inserted
above.

> If the gizmo already has an internet connection, then the contacting a
> NNTP server requires no additional hardware.

I think you mean NTP or SNTP; NNTP is for Usenet news.

However, beware of releasing a horde of products that all pound on one
preconfigured (S)NTP server; you'll get its owner upset.

> 2 - Decode the WWVL long wave broadcasts.

It's WWVB, on 60 kHz. There are similar services in other regions.

> 3 - Decode WWV broadcast. These are at several shortwave frequencies.
> I know 10MHz is one of them, and I think there are also broadcasts at
> 2.5MHz, 5MHz, and 15MHz, but I'm not sure. These may be more difficult to
> decode, but the coverage should be wider.  I'm not totally sure they even
> have encoded data on them.

Yes, they do. It's the same data as on WWVB, encoded on a 100 Hz audio
subcarrier. You can hear it below the tones, clicks and voice announcements
if you have a shortwave receiver with decent bass response. I don't think
they broadcast on 2.5 MHz any more; just 5, 10 and 15 MHz.

> 4 - Canada also broadcasts a time standard.  The radio station is called
> CHU if I remember right.  I don't know whether it contains coded
> information that a micro can use.

Yes, it does -- a Bell-103 compatible (300 baud) modem signal in seconds
:31 through :39 of each minute. CHU broadcasts on 3.330, 7.335 and 14.670
MHz. I wrote a 2-part Circuit Cellar article on decoding this signal in a
DSP. Unfortunately, it isn't available online, but you can follow this link
if you want to look it up: http://www.dtweed.com/circuitcellar/xtweedda.htm

==========

So, to summarize, you can go with wired or wireless. Wired options include
a modem or LAN connection, or direct connection (e.g., RS-232) to another
device that knows what time it is. Wireless options include longwave,
shortwave, GPS, and certain TV channels (e.g., PBS stations, although
accuracy on these can be pretty spotty). I think you can also get the time
of day in the RDS subcarrier on certain FM broadcast stations.

You need to think about which of these fit in well with the other functions
and requirements of the product.

-- Dave Tweed

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2002\12\17@141529 by M. Adam Davis

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There are essentially three methods to obtain the US atomic clock time:

User input (unreliable)
Wired
Wireless

We'll assume that user input is not appropiate for your needs (which we
don't know since you didn't tell us the required accuracy and frequency
of update).

Wired options are:
Phone to atomic clock (requires modem, accurate to the delay of the
phone network)
Phone to internet, get time from atomic clock (requires modem, internet
connection, accurate to the delay of the internet, but can be
compensated for significantly)
Ethernet to internet, get time as above(requires ethernet internet
connection, broadband internet account of sharing of dialup from PC on
premise, accurate to delay of internet, but can again be compensated for)

Wireless options are:
WWVB (Requires low power radio receiver and simple decoding.  Accurate
to several milliseconds, depending on decoding hardware.  Could be
accurate to microseconds with better radio and decoding hardware)
GPS/GLOSNASS(sp?) (requires Global position radio (american, russian,
mix), and clear view of sky.  Accurate to milliseconds depending on
radio, and can be accurate to microseconds and better)

The lowest cost option is likely to be the WWVB signal.  It's trivially
simple to receive (though gets more complex if you want to receive it
*well*), and can be decoded by the microcontroller fairly easily.  The
signal can be received through buildings depending on the antenna and radio.

-Adam


Tony Pan wrote:

{Quote hidden}

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2002\12\17@141731 by hard Prosser

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In our part of the world (NZ & Australia I think) there is a system using a
"zach (?) pager" that receives time signals on the paging network to
control clocks, sprinklers etc. You may be able to use this (they claim
accuracy is traceable to atomic standards).
I've been meaning to try & identify the signals & see if I can use it but
so far haven't had time.
The systems sends out two signals per hour - the first is a "time mark" and
the second contains the actual time that the "time mark" was actually sent.
This gets around the delay between sending a paging signal to the network &
its actual transmission.

May be of interest but I expect that GPS may be a better way to go

Richard P





Hi,

I really need to design a product that knows the official U.S. time, aside
from other features. Can someone tell me what is required for the hardware
and software to acquire the official time? And what kind of connections are
required?

Thanks a lot!

Tony

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2002\12\17@142145 by Jim

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> I don't think they broadcast on 2.5 MHz any more;
> just 5, 10 and 15 MHz.

According to their site they are using 2.5 MHz - and I recall
receiving them at 2.5 MHz in the last few months as well (at night -
presently I can only detect a bit of heterodyne at 2.5 MHz with the
BFO on).

Also, add 20 MHz as an 'active' freq to that list too (presently
receivable here in N. Tejas).

RF Jim

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2002\12\17@143226 by Robert Rolf

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Tony Pan wrote:
>
> Thank you everyone for the information. I now have an idea what comprise a
> radio clock receiver.
>
> I may at first attempt to design the whole circuit without using a
> commercial receiver IC.
>
> Basically I need to design a radio receiver circuit that is tuned to 60KHz
> signals. I also need a ferrite antenna.

It's probably cheaper for you to buy Radio Shaft 'Radio Clocks' and strip
out what you need. The OSI units (rebranded) have the RF section in
the antenna and already provide raw data out. There are a couple of
web sites with articles on how to use them, complete with PIC code.

> Can you point me to some online resources about designing a radio receiver
> circuit? Also where to look for a ferrite antenna?

Yeah, it's called a 'search engine'. You can filter the results just
as well as I can.

> > However the world has moved to using GPS to globally
> > distribute accurate time. It is just FARRRRR more reliable.
>
> Is it cheaper?

What's your time worth? What accuracy do you need? A GPS disciplined
VCXO is a LOT cheaper than a Rubidium clock.
How reliable does your 'time set' have to be? Can you freewheel
with a RTC chip for hours or days or months? These factors all
affect how cheap your solution can become.

If I were doing it I'd probably use a temperature compensated xtal osc
and live with the few seconds a month of drift it would have.
The time could be reset whenever the data was retrieved, and
the firmware could learn what compensation was needed to stay
'on time'. It all depends on what accuracy and resolution you need.


R

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2002\12\17@144027 by Spehro Pefhany

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At 11:54 AM 12/17/02 -0500, you wrote:

>I really need to design a product that knows the official U.S. time, aside
>from other features. Can someone tell me what is required for the hardware
>and software to acquire the official time? And what kind of connections are
>required?

The NIST site has a nifty little application that sets your computer
clock to their clock. Not sure if they offer the source code for it. I have
it run then terminate every time my computer boots to keep the time within
less than a second of the official time (it takes into account that I am
in the Eastern time zone).

Of course once you start considering Daylight Saving Time and time zones,
there's no "Official U.S. Time"- it can even vary by county if you're in
a rogue state like Indiana. Or change compared to neighboring towns
a couple times a year if you're near the Arizona-California border.
At least the hour transitions are all at the same time, unlike Canada
which has the Newfies to contend with (30 minutes out of synch).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffSTOPspamspamspam_OUTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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2002\12\17@160036 by Jim

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> In our part of the world (NZ & Australia I think) there is a system
> using a "zach (?) pager" that receives time signals on the paging
> network

Pagemart, now WebLinkWireless, employed a "ReFLEX 25" network
that was HIGHLY dependent on GPS for synchronization throughout
the system -

both in time - for the transmitted data packets (all packets were
              time stamped as to WHEN to be delivered since the
              transmit sites operated in a 'simulcast' fashion)

and in phase - the radio 'sites'/towers in an area of the system
              transmitted in a 'simulcast' fashion the same
              'messages' or what are more correctly known as
              "R25 data frames" thereby requiring phase lock
              to a common standard.

So, knowing the protocol a ReFLEX 25 system (anyway!) could be
used for synchronization/time keeping.

RF Jim



{Original Message removed}

2002\12\17@161250 by Jim

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Tony, I'm digging into this a little 'cause I've got
interest for a project using WWVB/US Time clock.

I came across the following sites in doing a little
search for a ferrite rod antenna:

http://psn.quake.net/wwvbsdr.html

http://users.argonet.co.uk/users/tudor/interface/rugby.htm

http://lakeweb.com/rf/wwvb/

http://psn.quake.net/wwvbmail.txt


Ferrite rod stock w/engineering info:

http://www.bytemark.com/products/rod1.htm


PIC Based WWVB Decoder
http://www.geocities.com/hagtronics/wwvb.html
http://www.geocities.com/hagtronics/vlf.html


RF Jim



{Original Message removed}

2002\12\17@172528 by Sean H. Breheny

face picon face
Hi Jim,

Your explanation makes sense and perhaps I am wrong, but I think that skip
is significant at the edges of the coverage area. If you look at the plots
of signal strength vs. location on WWVB's site you will see some ridges
(parallel regions of high strength with regions of low strength between
them) that look awfully characteristic of skip near the edges of the
coverage area. In addition, the area changes shape and size significantly
throughout the day. Have a look at
http://www.boulder.nist.gov/timefreq/stations/wwvbcoverage.htm

Sean

At 12:28 PM 12/17/2002 -0600, you wrote:

{Quote hidden}

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2002\12\17@181933 by Olin Lathrop

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> Wireless options are:
> WWVB (Requires low power radio receiver and simple decoding.  Accurate
> to several milliseconds, depending on decoding hardware.  Could be
> accurate to microseconds with better radio and decoding hardware)

If you are going to claim those kinds of accuracies, you have to
compensate for distance from the trasmitter.  Here in Massachusetts I get
the WWVB signal about 11mS late.  Fortunately that's good enough to know
whether I'm late for dinner.


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(978) 742-9014, http://www.embedinc.com

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2002\12\17@182644 by M. Adam Davis

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It is cheaper if you account for the fact that with a very high end
receiver you can obtain extremely accurate time, as though you had a low
end atomic clock yourself.

The phone network relies on these, and I imagine they are less expensive
than some previous methods used.

The signal varies less with weather than wwvb, and the GPS can auto
calculate the more exact time since it knows where the receiver is
located relative to each of the 4 or more atomic clocks that are
transmitting to it, and the speed of the transmission.

-Adam

Tony Pan wrote:

{Quote hidden}

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2002\12\17@183527 by William Chops Westfield

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   > However the world has moved to using GPS to globally
   > distribute accurate time. It is just FARRRRR more reliable.

   Is it cheaper?

"TECHNICALLY CHEAPER?" - No way.  GPS requires a specialized reciever, DSP,
a space-satellite launch capability, a bunch of satellites in orbit, and so
on.  State-of-the-art stuff, for some definition.

Actually cheaper?  Perhaps soon, anyway.  You want GPS to accomplish a lot
of things, and accurate time comes along for free.  GPS is a consumer item
and receivers are mass produced.  Less successful vendors have their
inventories appear on surplus markets.  I was a bit shocked when someone
added code to cisco routers to interface to GPS receivers JUST so that the
router could be an accurate time source for NTP ("Network Time Protocol.")

NTP might be something to look into too.  Assuming an internet connection,
you can get synchronized time to within well less than typical network
delays, using "magic."  You can also consider dialing 1-800-POPCORN or
equivilent, periodically, via cellphone technology...

BillW

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2002\12\17@190038 by Tony Pan

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Thank you everyone.

Right now I want to know if a commercial WWVB receiver IC provides a
significantly better quality than a regular radio receiver circuit does. The
manufacturer that we design for will make tens of thousands boards.
Therefore every penny counts. If a regular radio receiver circuit is cheaper
and has comparable quality we will design from scratch without using a
receiver IC. Does anyone know?

Thanks,
Tony


{Original Message removed}

2002\12\17@190502 by Jim

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> but I think that skip is significant at the edges of the
> coverage area.

THIS is the area that the old-timers call the 'fading-wall',
where ground wave and sky-wave meet and alternately interfere
(cancel) or reinforce each other. This has also got to be
a factor in experiences by some people some distance away
from Colorado (note: those charts ALSO show a fairly strong
level of field stength where the 'red' ends!).

If you look at those 'prop' charts - ALMOST the entire
continental US is covered during the day (again, to some
arbitrary level) - with considerable extension over water
at night (along with a small portion into the NE). But again,
NOTE the signal level at which those charts are plotted at
too (life, and signal strengh, does NOT simply end when the
'red' runs out!).

Compare the coverage for any AM broadcast station - or
even longwave station (200-400 KHz) and the usable coverage
area comes nowhere as close as the propagation for 60 KHz
does (during the day esp.) and that's because of the
**excellant** ground-wave propagation that 60 HKz enjoys.

Ground wave is *the* name of the game at 60 KHz - otherwise
you would have *no* usable signal strength roughly 5% beyond
line-of-sight ... this is also the reason why a 5,000 watt AM
radio station 150 miles away is easily receivable on a 2" long
ferrite loopstick YET a 100,000 watt FM station is not - ground
wave is the answer ...

RF Jim

{Original Message removed}

2002\12\17@191928 by Jim

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> "TECHNICALLY CHEAPER?" - No way.

Hmmm ... a number of Cellular/PCS infrastructure manufactureres
include the use GPS at a cell site - as an accurate reference
source. This as evidenced by the *two* little white radomed GPS
antennas at these cll sites sites ...

> GPS requires a specialized reciever, DSP,

... no more complicated than, say, an uplink receiver
at any given Cellular/PCS cell site ...

> a space-satellite launch capability, a bunch of satellites in orbit, and
so
> on.  State-of-the-art stuff, for some definition.

FORTUNATELY, erverythign is taken care of by somebody else
on what's called the "Space Segment" part of GPS ...

> Actually cheaper?  Perhaps soon, anyway.  You want GPS to accomplish a lot
> of things, and accurate time comes along for free.

It's been well within the grasp of a number of 'users' as
was demonstrated above!

> GPS is a consumer item and receivers are mass produced.

Bzzzt!  Beep! Beep! Beep! Beep! Beep! Error!!!

'Consumer item'? Care to explain in light of the
fact that GPS was a born out a military development
project AND many levels of GPS service/accuracy are
available depending on the equipment chosen?


RF Jim

{Original Message removed}

2002\12\17@192537 by Andy Kunz

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>Bzzzt!  Beep! Beep! Beep! Beep! Beep! Error!!!

You forgot "Danger Will Robinson."

;)

Andy

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2002\12\17@194038 by Robert.Rolf

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Tony Pan wrote:
> Right now I want to know if a commercial WWVB receiver IC provides a
> significantly better quality than a regular radio receiver circuit does. The

Define 'regular'? There are specialized chips made specifically to receive
60 kHz signals. See Phillips & Temic's site.
60 kHz is basically 'audio' for most op-amps.

> manufacturer that we design for will make tens of thousands boards.

Now we have an important piece of information we were missing. 10k runs
allow for a significant 'up front' engineering cost.

But does the unit have to work outside the USA? In mountainous valley's
where the WWVB signal doesn't reliably reach? What does your product do when
it cannot get 'good' time? What happens when the government turns off WWVB
for cost savings (because GPS is "better"? Remember Loran?).

> Therefore every penny counts. If a regular radio receiver circuit is cheaper

Not necessarily. Penny pinching can hurt you in the long run if it makes
the product less reliable or narrows your reachable market.

> and has comparable quality we will design from scratch without using a
> receiver IC. Does anyone know?

How much engineering time do you want to spend reinventing the wheel?
What sort of product life are you expecting? IOW, will the RF chip still be
available in a decade? (Anyone want to buy some 1702 EPROMs <G>?)
Only you know the answer to those questions.

Robert

> {Original Message removed}

2002\12\17@201448 by William Chops Westfield

face picon face
   > GPS is a consumer item and receivers are mass produced.

   Bzzzt!  Beep! Beep! Beep! Beep! Beep! Error!!!

   'Consumer item'? Care to explain in light of the
   fact that GPS was a born out a military development
   project AND many levels of GPS service/accuracy are
   available depending on the equipment chosen?

Sure.  Manufacturers of GPS receivers count on making and selling millions
or tens of millions of units.  Units are sold at consumer electronics
outlets at prices intended to make one consider throwing away the two-year
old version and buying a new one because it's smaller, cuter, and has more
"consumer" features.  Units are incorporated into other consumer items, like
cars and recreational vehicles.  They're assembled overseas.  More dollars
are spent on advertising than on mil-spec support documents.  It's a
consumer item.

OK.  Maybe I should have said "a GPS receiver is a consumer item" rather
than implying "the GPS system is consumer-targetted technology."  Does that
make you happier?  Origin of technology really doesn't matter much, though,
or next we'll have to talk about how the Internet is a Military
nuclear-strike survivable CCC network...

BillW

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2002\12\17@210456 by Lee Mairs

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>Here in Massachusetts I get the WWVB signal about 11mS late.  Fortunately
that's good enough to know
> whether I'm late for dinner.

Hmmmnn.  You never met my ex-wife...

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2002\12\17@215128 by Jim

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> make you happier?  Origin of technology really doesn't matter
> much, though, or next we'll have to talk about how the Internet

Much better.

Just don't fall into that trap of complacency and lump ALL
GPS NAVSTAR into one small consumer-oriented, limited
feature-set basket.

THAT would make my day.

Forget your roots and you forget your heritage and the
rememberance of the trials and tribulations (and the
original intent) of what the purpose of the journey was
in the first place (accurate, high-dynamic position and
velocity information. THE REST is up to you ...).

RF Jim

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2002\12\18@005116 by Chris Hunter

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----- Original Message -----
From: "Robert Rolf" <RemoveMERobert.RolfspamspamBeGoneUALBERTA.CA>
To: <spamBeGonePICLIST@spam@spamspam_OUTMITVMA.MIT.EDU>
Sent: Tuesday, December 17, 2002 6:45 PM
Subject: Re: [PIC]: How to obtain the official US time clock?

> Germany also has a standard time broadcast as does Japan.

....and so does the U.K - 60 kHz from Rugby, referenced to the NPL caesium
clock.  Excellent signal throughout most of Europe.

Chris

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2002\12\18@011207 by Brooke Clarke

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Hello Tony:

There are a number of ways to know what time it is.
The simplest is to set a time piece like a watch and look at it to know the
time.

It's not clear in your post what you really need.  I'm now working on a very
accurate oscillator that's also low in cost so that once set it would know the
time.

If you need to set a clock then you're talking about time transfer.  There are a
number of ways of doing that:

WWV HF radio
Many HF radio stations all over the Earth transmit the time, in the U.S. WWV in
colorado does this on a number of frequencies like 2.5, 5 10, 15 and 20 MHz.
These short wave broadcasts have both a human voice announcement and a digital
signal that can be read my a machine.  This signal fads in and out depending on
the time of day and the time of year as well as the distance from the receiver
to Fort Collins, Colorado.  accuracy can be in the millisecond range if you know
the distance between the transmitter and the receiver.  If the distance is not
known then you need to add that uncertainty which might amount to 11
milliseconds.  Might be replaced by GPS?

WWVB LF radio
In addition there is the WWVB LF transmission at 60 kHz.  A few years ago the
transmitter power was increased so that this signal now covers all 48 states.
Shortly there will be a 60 kHz transmitter on Hawaii.  The chips mentioned on
the PIC list were designed for watches and clocks in low power applications and
have very high impedances so care is needed when interfacing to them.  Again if
the Tx to Rx distance is not known the same error as above is involved.  If the
distance is known then the accuracy is much better. Not likely to be replaced by
GPS because it sends DST info not on GPS.

GPS 1.5 GHz microwave radio
A GPS receiver knows both it's location and the time.  It is the most accurate
time transfer method that is in the public domain.  It does not have any bits
for Daylight Savings Time (WWV and WWVB do have these bits).  GPS does provide
world wide coverage which WWV and WWVB do not.

WWVS 400 Mhz GEOS Satellite
This is an old system that either is or soon will be shut down.

Stable frequency sources (but no time broadcast):

LORAN-C 100 kHz LF radio
The Loran-C system does not broadcast any time information, but can be used to
maintain a clock with very high accuracy.  Started as a coastal navigation
system, there are now Loran-C chains in the U.S. interior so that most of the
U.S. is covered by Loran-C.  Not likely to be replaced by GPS because used as
backup system for aircraft WAAS.

Television Color burst & Start of line (both off the air and cable)
These singnals can be used as rough frequency standards.

Brooke Clarke, N6GCE
http://www.precisionclock.com

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2002\12\18@081521 by Olin Lathrop

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> Television Color burst & Start of line (both off the air and cable)
> These singnals can be used as rough frequency standards.

Actually the color subcarrier is quite a good frequency standard by most
measures.  It is certainly far better than a quartz crystal.  Major
networks derive their color subcarrier from atomic clocks.  It used to be
that these color subcarrier frequencies were regularly compared to the
official time standard and the results published.  This provided the legal
traceability back to the atomic standards to a high accuracy.  This is
probably still going on, but I don't know.  Search the net if you want
details.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2002\12\18@105355 by Tony Pan

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Thanks. Sorry I wasn't providing enough information because at the beginning
I wasn't sure what information is relevant.

For our product, accuracy is not crucial. The users only need to know "if
they are late for dinner". The unit will display the clock and run features
based on the time of day. But if the clock fails, it still can run other
primary features but just would not be so smart. The user can manually set
the clock if he wants to. So, the clock feature is not crucial either but
it's a selling point of the product therefore it should work. But if it
doesn't it's not the end of the world.

Cost is the most important. If we can save some money in production by not
using the receiver ICs we are willing to "re-invent the wheel", providing a
"regular" circuit can do a decent job. By "regular" I mean the standard
radio receiver circuit that one can find in a text book.

I think my question is: does anyone know if the "regular" radio receiver
circuit does a decent job of receiving the WWVB signal (in most places of
North America)?

Tony



{Original Message removed}

2002\12\18@141222 by Jim

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> I think my question is: does anyone know if the "regular" radio receiver
> circuit does a decent job of receiving the WWVB signal (in most places of
> North America)?

You might try the manufacturers 'technical help' desk or retailers
of current product that is out there - like Radio Shack and others -
to get a feel from them what their experience is (if they'll
talk!).

Along those lines - Grove Radio http://www.grove-ent.com/ (or other
small mail-order outfits) might be able to better answer those
questions than anybody (if they sell anything along those lines
like this http://www.grove-ent.com/CLK01.html).

Other factors dictate reception of these receivers, I think. Here
in the Dallas, Tejas area a freind of mine has a wrist watch that
uses WWVB (60 KHz) and he finds that it sets itself just fine!

As to your question - "[does] the "regular" radio receiver
circuit [do] a decent job of receiving the WWVB signal?" - can
you meet all the design goals that some of these special IC's
offer - such as operation from 1.5V batteries, low power
consumption, etc, - without spending a lot of your engineering
hours/time designing, modelling and testing your design?


RF Jim


{Original Message removed}

2002\12\18@152325 by Peter L. Peres

picon face
On Tue, 17 Dec 2002, Tony Pan wrote:

*>Thank you everyone for the information. I now have an idea what comprise a
*>radio clock receiver.
*>
*>I may at first attempt to design the whole circuit without using a
*>commercial receiver IC.
*>
*>Basically I need to design a radio receiver circuit that is tuned to 60KHz
*>signals. I also need a ferrite antenna.
*>
*>Can you point me to some online resources about designing a radio receiver
*>circuit? Also where to look for a ferrite antenna?

Oh dear.

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