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10 Technical Appendix
10.2 Antenna and Receiver Information
There are 2 types of radio signals commonly used for timing applications: satellite signals from Global Nav-
igation Satellite Systems (GNSS) , and long wave signals from specific time code transmitters operated by
some countries.
Most GNSS signals can be received world-wide, while long wave signals can only be received up to a certain
distance around the transmitting station. Also, GNSS receivers can usually track the signals from several
satellites at the same time, so the signal propagation delay can be determined and compensated automatically,
while long wave receivers usually receive only the signal from a single station. Last but not least the available
bandwidths and signal propagation characteristics are another reason why GNSS reception usually yields a
higher degree of time accuracy than long wave reception.
10.2.1 Reference Time Sources
10.2.1.1 Meinberg GPS Receiver
The satellite radio clock was developed with the aim of providing users with a highly accurate time and fre-
quency reference. High accuracy and the possibility of worldwide use, 24 hours a day, are the main features
of this system, which receives its time information from the satellites of the Global Positioning System. The
Global Positioning System (GPS) is a satellite-based system for radio-positioning, navigation, and time-transfer.
This system has been installed by the United States Department of Defense (Defense Department) and provides
two levels of accuracy: the Standard Positioning Services (SPS) and the Precise Positioning Services (PPS).
The structure of the sent data of the PLC has been released and the reception has been made available
for general use, while the time and navigation data of the even more accurate PPS are transmitted encrypted
and therefore only accessible to certain users (mostly military). The principle of location and time determination
with the aid of a GPS receiver is based on the most possible accurate measurement of the signal propagation
time from the individual satellites to the receiver.
The GPS satellites orbit the earth on six orbital tracks in 20,000 km of altitude once in about 12 hours.
This ensures that at any time at least four satellites are in sight at any point on the earth. Four satellites must
be received at the same time so that the receiver can determine its spatial position (x, y, z) and the deviation
of its clock from the GPS system time.
Control stations on earth measure the orbits of the satellites and record the deviations of the atomic clocks
carried on board from the GPS system time. The determined data are sent to the satellites and sent to earth
as navigation data by the satellites. The highly precise track data of the satellites, called ephemerides, are
needed so that the receiver can calculate the exact position of the satellites in space at any time. A set of
track data with reduced accuracy is called almanac. With the aid of the almanacs, the receiver calculates at
approximately known position and time, which of the satellites are visible from its location. Each of the satel-
lites transmits its own ephemerides as well as the almanacs of all existing satellites. The GPS clock operates
with the "Standard Positioning Service". The data stream of the satellites are decoded and evaluated by the
microprocessor of the system, like that the GPS system time is reproduced with a deviation of less than 100 nsec.
Different running times of the signals from the satellites to the receiver are automatically compensated by
determining the receiver position. By tracking the main oscillator, a frequency accuracy of 1e-12 is achieved,
depending on the oscillator type. At the same time, the age-related drift is compensated. The current correction
value of the oscillator is stored in a non-volatile memory of the system.
microSync Date: 22nd June 2020 47