Table of contents

1. A brief history of Time Code Receivers
2. What is time ?
3. Time from a fountain of cold atoms
4. Background of Time code reception
5. Schematic animation of Time code reception



A brief history of Time Code Receivers  

Beginning of the 20th century it was realized that radio waves were the best medium to distribute time information.

Between 1910 to1916 vessel communication station called Norddeich Radio, located in Germany, provided the first, but not for public use time code transmission.

From 1917 on the German public broadcast station called NAUEN distributed 2 times a day time code information for public use on long wave

During the years a global network of Time Code Station was built.
Additional to the terrestrial based station also a network of satellites was brought to the orbit for international exchange of time information.

Beside the satellite based time transmitters, long wave is still a very important means of distribution of the signal.
The behavior of long wave frequency allows simply distribution to large areas.
The waves are able to penetrate buildings and can also be received in certain distance under ground. The receiver and its antenna can be build small and economically.

The satellite based network is not suitable for consumer products, because of the behavior of the high frequency this signal is not able to be received inside buildings or anywhere is being obstructed from sky. The signal is damped from each part between antenna and satellite. Even rain and fog are able to damp the signal.

Since 1986, application of the time code receiver has been a big success for all types of consumer products.

The first time code receiver was developed from TEMIC in cooperation with Junghans.
All the earlies, more or less discrete solutions, were super-heterodyne receiver with bulky crystal filters and a lot of transistors mainly located in a transistor-array. These solutions where always main powered and current consumption was no criteria.
The new developed concept used a straightforward principle. This offered the possibility of lower power consumption (250µA) as well as a supply range down to 1 Volt.
A new solution under the technical leadership of Junghans
Together with the FFMU, the Research institute of the Research Community for Micro mechanic and Watch Techniques at Stuttgart was developed.
The topic of this device was a amplitude-frequency-converter. Also the sensitivity was increased. This chip was controlled by a micro controller. But this solution was not very successful, because the software for the micro controller was more extensive than only for decoding and time keeping.
The company Ruhla in the former GDR starts to develop time code controlled applications
An indepentent software and hardware solution for RC watches was developed by the "Ruhla" company. A super-HET solution was used as receiver.
A new IC under contract which Junghans was developed from Temic
The packed version of this IC was free for the open market. With this design the power consumption was drastically reduced (by factor 10) to 25 µA. It was still the concept of straightforward receiver what was used. A reduction of external components was going along with this new design.
HKW starts after reunion of Germany a development of an own time code receiver
Based on the know-how as a former developer for the Ruhla company, HKW specialized on the development of RF watch and clock technique.
First receiver from HKW in Super heterodyne technique
This receiver was a solution with two antenna inputs, which could be switched by a micro-controller in order to achieve a omni-directional reception.
A special low cost version, not free for the open market was developed together with Junghans and Temic.
The IC had an internal selection and does not need any addition crystal. As a PLL principle, the 32kHz crystal at the micro was used. This design was not too successful, because in difficult receiving areas the receiver with an own crystal filter was the better choice.
HKW introduced the first straightforward receiver with two input possibilities for different antenna selections
This improved gerneration of the HKW receiver needs less components.
HKW introduced the second-generation receiver to the market
This receiver was an extended version for the use 1,5 V and 3 V Applications
A new development, independent from Junghans, was started from TEMIC.
The intention of this, still existing, design was to be free for the open market without restrictions and furthermore to combine all the experience together to have a reliable and sensitive as well as current saving solution.
The current consumption of this chip is about 15 µA and the sensitivity was again slightly increased by better stability. A new principle of decoding was introduced by using an A/D converter in order to gain more information out of the received signal.
HKW offered the 3rd generation of time code receivers
This 3rd generation was again optimized in sensitivity and current consumption
C-MAX decided to take over the distribution for time code receivers from HKW
C-MAX, a leading manufacturer and distributor of various RF-devices, takes over sales and marketing activities for HKW receivers with big success in Asia .
Temic (now named Atmel) and HKW decided together to do a new design
It was the intention of both companies, Atmel and HKW, to combine their know how to provide to the market the most professional and state of the art solution. The new part replaces all the designs with similar function with exception of the automotive part existing at Atmel's portfolio. The new design was improved in sensitivity and needs less external components. Designing with this part is more easy than ever before.
Release of the new IC development UE6005 to the market
Start of the IC production
C-MAX start the development of a revolutionary new IC design

With the intention to create an optimised receiver IC with extended features and to meet customer needs more explicit, C-MAX starts the development of a new generation of receiver IC's

Introduction of the new receiver IC CME8000 to the market
Start of the IC production
What is time  

Based on international conventions, the second is defined as 9 192 631 770 times of the time, a Caesium Nuclide (133Cs) needs to change from one to the other energetic level. This time is much more precise known than for instance the time period of a mechanical resonator. The change of the energetic levels can be forced and the Caesium-atom emits a frequency of 9 192 631 770 Hz.

Time from a fountain of cold atoms  

Since 1967, the second has been defined via the resonance frequency between selected energy levels of the atom caesium 133, a non-radioactive element. The definition followed development and common understanding of atomic physics and quantum mechanics and demonstration of the first caesium atomic clock with a thermal atomic beam in 1955. This unassuming device is a caesium frequency standard, sometimes referred to as an atomic clock.

In many respects the atomic fountain clock is just the logical further development of the atomic clocks with a thermal atomic beam, which have been in operation long time. As early as in the fifties, Jerrold Zacharias of the Massachusetts Institute of Technology tried to prolong the time of flight in relation to that achievable with a thermal atomic beam. To reach this aim, he tried to set up the first caesium fountain in which the slow atoms from a vertical thermal source were to turn back under the effect of the gravitational force. He wanted to prove that their state had changed after they had flown through the same resonator field while rising and falling down again. Zacharias was not successful: By collisions in the area of the atomic beam source the number of sufficiently slow atoms in his thermal beam, which was small anyhow, was reduced to such an extent that no signal could be detected. The atoms were too "hot"; their relative velocities too high.

The situation is altogether different today: By laser cooling cold caesium atoms are collected in a cloud . The relative velocities of these atoms lying in the range of one to a few cm/s. NIST-F1, the time and frequency standard for US, is a caesium fountain atomic clock developed at the NIST laboratories in Boulder, Colorado.
First, a gas of caesium atoms is introduced into the clock's vacuum chamber. Six infrared laser beams then are directed at right angles to each other at the centre of the chamber. The lasers gently push the caesium atoms together into a ball. In the process of creating this ball, the lasers slow down the movement of the atoms. Laser cooling drops the temperature of the atoms to a few millionths of a degree above absolute zero, and reduces their thermal velocity to a few centimetres per second
Two vertical lasers are used to gently toss the ball upward (the "fountain" action), and then all of the lasers are turned off. This little push is just enough to loft the ball about a meter high through a microwave-filled cavity. Under the influence of gravity, the ball then falls back down through the microwave cavity. A scenario which reminds one of a fountain.
In a similar way as in a conventional atomic clock the energy state of the atoms is manipulated and checked. At the beginning the atoms are prepared in a single energy state; during the up- and down-movement they fly, however, through the same microwave field. The laser cooled atoms pass twice through a microwave cavity, once on the way up and once on the way down. The result is an observation time of about one second, which is limited only by the force of gravity pulling the atoms to the ground.

During the trip, the atomic states of the atoms might or might not be altered as they interact with the microwave signal. When their trip is finished, another laser is pointed at the atoms. Those atoms whose atomic state were altered by the microwave signal emit light (a state known as fluorescence). The photons, or the tiny packets of light that they emit, are measured by a detector.
This process is repeated many times while the microwave signal in the cavity is tuned to different frequencies. Eventually, a microwave frequency is found that alters the states of most of the caesium atoms and maximise their fluorescence. This frequency is the natural resonance frequency of the caesium atom (9 192 631 770 Hz), or the frequency used to define the second.
As you might guess, the longer observation times make it easier to tune the microwave frequency. The improved tuning of the microwave frequency leads to a better realisation and control of the resonance frequency of caesium. And of course, the improved frequency control leads to what is one of the world's most accurate clocks.
The signal from the atomic clock is fed to a unit called a Time Code Generator. This produces the time code which is distributed by each station.
The signal must now be amplified by powerful radio transmitters and distributed via radiowaves. Radiowaves travel at the speed of light (~300 000 km per second).
This is the way we can participate at this accurate clock (description according information's from NIST and PTT)

Background of Time code reception  

Time code transmitters are different from such for Audio or TV broadcasting. They provide information of the present time (based on an atomic time normal - see above) the day, the month and the year and the relevant Daylight saving time. The information is transmitted via a long wave transmitter in the frequency range of 40 to 80 kHz. This frequency range is the best solution to construct receivers with low power consumption. The transmitters are amplitude modulated. The information is a bit stream with pulses in different length. Every second a pulse is transmitted. All the information is transferred in one minute time frame

All time laboratories around the world are using this frequency as the time-base.

Schematic animation Time code reception