Portable frequency standard SYN-Rb
with automatic compensation of ageing effects of the built-in rubidium
The portable frequency standard SYN-Rb
was designed at the Institute of Electronics and Telecommunications,
Poznan University of Technology. It is equipped with the rubidium
oscillator and generates several synchronous in frequency and in phase
reference signals with a very high accuracy of frequency. The frequency
of output signals may be synchronized to an external source coming
from e.g. a telecommunication network or an external GPS receiver.
The output signals are TTL signals with output current limited to
30mA. The source has seven basic outputs: 4x2048kHz, 1MHz, 5MHz, 10MHz.
Four 2048kHz signals can be transmitted directly to reference inputs
(B inputs) of four measuring channels of the SP-3000 or SP-2000 measuring
system as reference signals replacing the signals of much more expensive
caesium standard. With such application of the SYN-Rb source, the
signals synchronizing SYN-Rb should be removed (hold-over state of
the rubidium oscillator). To compensate frequency changes of the rubidium
oscillator caused by aging effects, its frequency should be periodically
tuned to external standard or to 1pps impulses from an external GPS
receiver. Relative frequency error 1×10-11 is maintained by the source
through at least 2 days after the synchronization signal was removed.
During this time the source may be transported and used as a source
of reference signal in the measuring of parameters of synchronization
network. Additionally, the SYN-Rb source may be equipped with cards
realising user functions, e.g. changing the shape or the frequency
of the input signal into the shape or frequency required by the user.
When SYN-Rb is permanently synchronized to GPS signal, it may serve
as a cheap Primary Reference Clock (PRC) with long-term frequency
error less than 8 10-13 (level Stratum 1). If, additionally, a synchronization
signal from a telecommunication network, e.g. from T4 SDH output,
is added to SYN-Rb, an extraordinarily cheap SSU (SASE) clock will
be obtained, with basic synchronization path from a telecommunication
network and with a backup line from an external GPS receiver.
Apart from the possibility of automatic compensation of frequency
changes caused by aging processes occurring in the rubidium oscillator
by means of different input signals, another positive feature of the
SYN-Rb source, comparing to many similar devices, is a built-in accumulator,
ensuring power supply maintenance during transportation. During long-lasting
transportation of SYN-Rb (i.e. longer than 1 hour), the SYN-Rb may
be powered from a car lighter socket, by means of a converter =12V/~230V.
The power supply maintenance allows to avoid the frequency retrace
error of rubidium oscillator and to work with the source already a
few minutes after reaching the test place.