Re: Add your atomic clock here
Sulaiman, Fri Nov 28 2014, 10:04AM

I bought one of those eBay Rubidium oscillators, mine was FE5680A at 10 MHz
at work I compared it with a GPS-locked 10 MHz clock beloging to one of my workmates
using X-Y Lissajous curve on a 'scope ...
frequency so close that a small phase drift in my workmate's GPS pll could be seen !
defiitely sub-0.1 Hz error = 1/10^8 error ...0.3 seconds /year, probably better.

The power consumption of the FE5680A was about 15V @ 800 mA
which is not a problem UNLESS you want to protect against power failures
(no point having a super accurate clock that looses accuracy)

I sold the FE5680A to my workmate (cheaper than I paid) for his clock experients
so I no longer own it
.. in retrospect a mistake as my MkII HF transceiver is getting closer to completion
and it would make a nice reference clock.

OTOH I have a couple of radio synchronised clocks (cheap from LIDL) that display accurate time
at GBP6 for a radio controlled clock (derived from the Frankfurt atomic time) you need a good reason to home-brew an atomic clock

If you are interrested, have a look at 'Time Nuts'

Re: Add your atomic clock here
kimbomba, Fri Nov 28 2014, 06:45PM

Video has been deleted :(

Re: Add your atomic clock here
Conundrum, Thu Jan 29 2015, 07:25PM

There are now single chip rubidium clocks apparently.



Also

Intriguingly seems to suggest that detecting changes in the flow of time with reference
to an external clock *might* be able to detect gravitational waves.


-A

Re: Add your atomic clock here
Bored Chemist, Thu Jan 29 2015, 07:52PM

I guess I'm the only person on the planet who would like to get a rubidium clock and divide the output down to 1Hz then amplify that signal and connect it to an electromagnet in the bottom of a grandfather clock with a small magnet on the pendulum.
I just like the idea of having one of these that's good to a second in a tdecade or whatever.

Re: Add your atomic clock here
Sulaiman, Thu Jan 29 2015, 08:53PM

no, you're the second ! (pun intended)

I was trying for ages to buy a pendulum clock cheaply for exactly this purpose
I even put requests on my local 'recycling' lists .. nothing.
too many people are willing to pay reasonable amounts for me to get one cheaply so I gave up.
and I have too many projects already to start building a pendulum clock from scratch.

as above, no point having a clock accurate to a second per decade if there's a power outage
so some form of ups/battery storage is required.

Conundrum; I have a double-oven XTO, the short and medium term stability is excellent but long term the frequency will drift, something to do with metallization diffusion on the crystal.

Incidentally, I read that the better old pendulum clocks were so good
that the limit of accuracy was determined by earth/moon/tide gravity changes !
also
GPS systems are corrected for relativistic effects due to motion of the satellites,
maybe comparing the GPS signals from different satellites could detect gravity waves?

Re: Add your atomic clock here
..., Thu Jan 29 2015, 10:12PM

For building a clock you are better off with a GPS module, since with an oscillator you need to deal with the synchronization to colorado (or your respective timekeeper) to keep accurate time. If you are going to just look at your cellphone and set it by eye you might as well use temperature stabilized quartz, which will be good to within a few seconds over a few years. The one tricky bit is making sure that you can get a GPS signal, but with modern gps chipsets I have had good luck even inside, as long as you are not far from a window in a multistory building. Also, keep in mind that it is much easier to get a timing lock from the GPS constellation than it is to get a position lock, since you only need a single satellite in view. Also, any GPS module will have a fairly decent oscillator onboard (necessary to be able to receive the gps signals) so even if you loose GPS lock for a few days due to poor weather or whatnot you will still be able to keep accurate time (although be careful, some modules are dumb about this and will stop outputting time data altogether upon loss of satellite link).

This cesium clock is not mine anymore, it was found in the trash at MIT; thrown away because the 'continuous operation' light (which lights while the clock is locked to the Cs reference) had burned out due to old age.

Re: Add your atomic clock here
Bored Chemist, Sat Jan 31 2015, 01:48PM

I'd also quite like on of these if there's a millionaire out there who wants to get me a late Christmas present.


The advantage to the pendulum clock with a link to a rubidium oscillator is that, if the Rb clock fails- the system still keeps pretty good time anyway.

The easy way to do it is to get a GPS module- but then you are just reading someone else's clock. You might as well just buy one of these

great clocks for time keeping- but not nearly as cool.

Re: Add your atomic clock here
klugesmith, Sun Apr 10 2016, 03:30PM

I am shopping for a consumer-grade Radio Controlled Clock, the kind almost universally marketed as "Atomic Clocks". Battery powered, LCD display, fixed location in WWVB territory.

Any hints on how to pick one with an exceptionally good antenna and receiver, for freedom of placement inside a concrete building with metal Venetian blinds on the windows? On a wood frame house, does anyone think a sheet metal roof (and exterior walls of stucco over wire mesh) will create a reception challenge?

Here's a nice NIST page about RCC's:

Are there commercial frequency references disciplined to WWVB's 60 kHz carrier and/or time codes? Or perhaps to cellular phone resources? In an urban environment, I bet those are available wirelessly in many rooms where GPS et al don't reach.

Re: Add your atomic clock here
Conundrum, Mon Apr 11 2016, 07:26PM

I am working on a way to boost the sensitivity on one of these, so far my cunning plan is to use a hand wound Litz wire pickup coil made out of clock wire.
This approach while time consuming does yield superior performance and a simple mini drill chuck can wind a couple dozen meters of wire for various projects.

Re: Add your atomic clock here
Sulaiman, Mon Apr 11 2016, 08:52PM

a common 'trick' for LW and MW radios with marginal reception is to
build a multi-turn loop antenna with its own tuning capacitor
when tuned to the same frequency as the radio,
the radio antenna acts as a parasitic load on the large loop antenna.
Should work even better at 60/77 kHz
No need to hack the innards - warranty intact.

Re: Add your atomic clock here
Conundrum, Sun Jul 03 2016, 05:16AM

Good trick, thanks for sharing.
As it happens I'm winding a coil anyway for other purposes, old inners from label printers make great formers.

Re: Add your atomic clock here
klugesmith, Tue Aug 30 2016, 06:31AM

In the springtime, in a Rite-Aid store to pick up some medicine, I happened to see and buy a radio-controlled clock for about $20, or was it $12? It's worked OK while being moved around a lot: outdoors at work for sundial project, then indoors with no WWVB reception, then home where it can turn on its radio receiver at 2 a.m. and get a time fix. The large LCD digits have a poor viewing angle, and it's easy to see faint activity in segments that are Off.

One day something was rattling around inside. Good excuse to open it up and check out the receiver and antenna. A tiny ferrite-rod loopstick antenna had broken free of its restraints, which were just a couple of dabs of hot-melt glue.




This is so cost-reduced, I stopped dreaming of tapping into a received bitstream or maybe finding a RSSI pin. The visible side of the board, with contact places for control-button pads, is literally printed -- I think there's no copper on that side of the board or in the vias.

It reliably fails to get a WWVB fix when told to search at mid-day. One of these days we'll dig out a big-loop antenna (as mentioned by Sulaiman) made for AM broadcast reception long ago. Then find a capacitor for it to resonate with at 60 kHz. Anyone know a good trick for adjusting the capacitor to match the radio station frequency of interest, if there's no noisy received audio to listen to?

The night-time radio reception seems to be undiminished since the antenna repair. This evening I captured a 15-second video showing a correction being applied. Here on You Tube:

Re: Add your atomic clock here
Conundrum, Sun Sept 11 2016, 05:05AM

Yeah, the "Atomic" clock generated a fair few sales.

I discovered a way to pick up signals from glob chips, by painting onto the back of the board silver paint and then using a thin wire + Epoxy to make a capacitative contact.
This hooked up to the gate on a sensitive JFET works very well, using 3*10M in series to mitigate static damage.