WWVB - Atomic Clocks

[W1RKW]

I just bought a weather station that has an "atomic" clock. It receives WWVB for it's synchro signal which is, I believe, on a carrier of 60kHz according to the NIST website.  I'd be curious to know the propogation characteristics of a freq. that low.  Anyone have any knowledge they can share?

[flintstone mop]

The coverage is phenomenal!!! I love that technology. Great idea...You never have to worry about setting clocks.
Fred

[WA1GFZ]

Many standards use WWVB. I've seen times then the level drops but usually pretty usable. I would thinK GPS more accurate for launching ICBMs out of Colchester.
BTW my DVD gets updated off the cable and is always on the money.

[W1RKW]

The reason I ask about the propogation charateristics at 60kHz, is the clock didn't sychronize for several hours and after reading the instructions, they stated that the signal is best received during the evening hours. It didn't sychronize until about 1400 DST, 2 or so hours later.  So that got me to thinking about propogation at that frequency.  I know nothing about signal down that low.  I know there are Lowfers who mess around with this stuff but I never gave it much thought about propogation characteristics.  At this point, it's mysterious.

Frank, when you come over remind me to show you the new missle silo I've been working on. I stopped work on the 813 rig to work on the silo since the weather has been good. Actually, the 813 rig is disguise to be the missle lauch control system. I've borrowed the technology from EB.

[AF9J]

Hi Bob,

There is some nightime skywave that low in freq.,  but most VLF skywave propagation is a form of ionospheric ducting, where the upper part of the boundary is the D-layer, and the lower part of the boundary is the earth.  One of the reasons you may not have heard WWVB until night, is because the D-layer was too ionized by the sun to prevent absorption from removing the signal to your path.   When the sun went down, the D-layer lost enough ionization for the signal in the duct propogate, and not get absorbed by the D-layer.  Hmmm, you know, I should really hook up that VLF receiveng converter I picked up for $20 at the hamfest a few weeks ago.

73,
Ellen - AF9J

[W2PFY]

I just bought a weather station that has an "atomic" clock.

Just curious, what is the half life of that Atomic Clock? Do you need any special
shields to protect yourself and family from Gama rays or whatever radiation it creates? I thought about getting one but with all the talk about cell phones causing brain cancer, I am somewhat careful as to what I will introduce into my home.

[Bill, KD0HG]

Hi Bob,

There is some nightime skywave that low in freq.,  but most VLF skywave propagation is a form of ionospheric ducting, where the upper part of the boundary is the D-layer, and the lower part of the boundary is the earth.  One of the reasons you may not have heard WWVB until night, is because the D-layer was too ionized by the sun to prevent absorption from removing the signal to your path.   When the sun went down, the D-layer lost enough ionization for the signal in the duct propogate, and not get absorbed by the D-layer.  Hmmm, you know, I should really hook up that VLF receiveng converter I picked up for $20 at the hamfest a few weeks ago.

73,
Ellen - AF9J

Yup, the 60-100 miles between the ionosphere and earth's surface act as a waveguide at those 5,000 meter frequencies. Almost worldwide propagation with very little loss. Summer QRN can adversely affect the sigs as can the usual sources of RFI.

They put some sort of smokin' signal into here from 40 miles away on the R-389.

Then there was WWVL on 20 KHz, which signed off in the early 1970s, IIRC.

More info:
http://tf.nist.gov/timefreq/stations/wwvb.htm

[KB2WIG]

Yes, its been here before...............

http://www.lownoiserecords.com/wwv_the_tick.html

[WA1GFZ]

Many of these systems use a FLL with very fine steps to eliminate phase noise. It may take a long time to lock up. I worked on one once that took a good day to lock on and was very accurate after than. Most systems use an active loop antenna.
Bob you running conventional or did you score a physics package. fc

[W1VD]

WWVB is solid copy 24/7 here in CT (using directional 137 and 500 kHz receive antennas) even during the high static summer season. Suspect the 'atomic' clocks have more of a problem with power line garbage (switching power supplies, light dimmers, etc.) than gathering enough WWVB signal. You might try moving the clock  and see if it syncs up quicker.

Some interesting information on WWVB:

http://tf.nist.gov/general/pdf/1406.pdf

Toward the bottom there are graphs of expected signal levels at selected locations throughout the year. Field strength measurements at this location fit in nicely on the curves.

 

[K3ZS]

I worked on a prototype clock in the 70's that synched and decoded WWVB.    At that time the signal was weaker than it is now and had to use an outdoor antenna.    The signal was always better at night (in PA).   The actual time is sent over a the whole minute.    So to initially set the time automatically the receiver has to copy a whole minute perfectly.    Once the time is set it can maintain synch from the 60Khz carrier and correct the minute on the minute mark.

[k4kyv]

So to initially set the time automatically the receiver has to copy a whole minute perfectly.   

Like the old FCC code tests. 

[W1RKW]

Frank, I'm not sure what I have and plus I'm not sure what your asking but if I hazard a guess I'm running conventional.  At this time the clock signal strength meter on the weather station is showing full strength is also showing locked.  Occasionally, it goes into a search mode. Which I suspect is due to signal fade. When I got home from work today (around 2pm) I reset the clock and it went into a search mode.  Unlike yesterday it sychronized and locked fairly quickly, maybe 5 minutes compared to yesterday but it did a few searches aftwards. Right now at 400PM it's showing locked and full strength.

I find these low signals mysterious and fascincating at the same time.

got into a discussion with someone at work today about Lowfing.  He was telling me a few years ago he was messing around with low signals and would connect his sound card to his ground and would monitor signals using an FFT program.  Apparently there's stuff way down low in the audio frequency range, ie. military stuff.  Deciphering it is one thing but at least hearing it (or in this case seeing it) proves that it's there.

[WA1GFZ]

Put an antenna on your sound card and run a spectrum monitor program. Heck you could even run Flex software. My Racal works pretty well down to about 15 KHz.

[AF9J]

I just bought a weather station that has an "atomic" clock.

Just curious, what is the half life of that Atomic Clock? Do you need any special
shields to protect yourself and family from Gama rays or whatever radiation it creates? I thought about getting one but with all the talk about cell phones causing brain cancer, I am somewhat careful as to what I will introduce into my home.

They use Cesium 133 as the isotope for the WWV and WWVB clocks.  

http://www.4physics.com/phy_demo/at_clock/at_clock.htm

The half-life is like 3 million years. So it's a realtively stable (albeit low level radioactive element).

73,
Ellen - AF9J

[kb3ouk]

My grandad has a weather station with one of those clocks in it. And if I'm right , the actual atomic clock is in Fort Collins, Colorado. The "atomic" clock we have are actually receivers the receive the  signal from WWVB. If I listen closely on 60khz. I can actually copy the signal, but it is VERY weak.
Shelby KB3OUK

[Mike/W8BAC]

Spot On Shelby!

No need to worry about Cesium 133 or anything else. The clock is in safe hands out west and the radio signal is what sets your clock. Good catch.

I use the GPS constellation for frequency and time standards here when a nats pattudy is needed.

I remember the HeathKit "Worlds Most Accurate Clock". It synchronized to WWV (or VB) I think. Anybody here owned one? Whats the story?

Mike

[Ian VK3KRI]

I just bought a weather station that has an "atomic" clock.

Just curious, what is the half life of that Atomic Clock? Do you need any special
shields to protect yourself and family from Gama rays or whatever radiation it creates? I thought about getting one but with all the talk about cell phones causing brain cancer, I am somewhat careful as to what I will introduce into my home.

A real 'atomic' clock is not radioactive at all. (well more than anything else floating around). It makes use of a beam of particles from an emitter using a specific isotope of caesium.  The particles interact with a microwave field of a very specific frequency( 9.192631770Ghz)  in a certain way. Basically a feedback loop tunes the frequency for maximum smoke at the collector and a divider divides down to some useful frequency. 

The frequency is exactly  9.192631770Ghz because the 'atomic' second  is defined as 'the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.' 

I'd be more worried about the RF from the towers on the building I work on than the 1/2 dozen 'atomic' clocks that were on the next floor until a year ago. Or then again maybe the synchrotron in the building next door. 
                                                                                                            Ian VK3KRI