Meinberg TCR170PEX - Manual (Page 16)

16
Master oscillator
As standard, TCR170PEX is equipped with a TCXO (Temperature Compensated
Xtal Oscillator) optionally an OCXO LQ/MQ/HQ (Oven Controlled Xtal Oscillator)
as master oscillator. The internal timing of the module, basis for the software clock,
the pulses and the generated time code, is derived from this oscillator. If the reciver
is synchronized by an incomming time code, the oscillator is adjusted to its nominal
frequency. The current correction factor is stored in a non volatile memory (EE-
PROM) of the system. Therefore a high accuracy in holdover mode of +/- 1 * 10E-8 is
achieved, if the receiver was synchronous for at least one hour.
The 10 MHz standard frequency is available at a contact strip with TTL level into
50
Ω.
Functionality of the generator
The time code generator of TCR170PEX is based on a DDS (Direct Digital Synthe-
sis) frequency generator, which derives the sine carrier of the modulated code from
the reference clock of the master oscillator. The modulation of carrier amplitude
(modulated codes) or pulse duration (unmodulated, DC level shift codes) is synchro-
nized to the pulse per second (PPS) of the system based on the software clock.
The generated time code is independant from the settings for the
received code. It is possible to generated a different format and
offset from UTC therefore.
Outputs
TCR170PEX provides modulated and unmodulated (DC level shift) outputs. As an
option, an optical output can be equipped instead of the modulated output. It is
available as ST-connector for GI 50/125µm or GI 62,5/125µm gradient fiber.
Modulated output
The amplitude-modulated sine carrier is available a BNC-coaxial-plug connector in
the bracket. The carrier for IRIG-B and AFNOR signals is 1 kHz. The signal amplitu-
de is 3V
pp
(MARK) and 1V
pp
(SPACE) into 50
Ω. The encoding is made by the
number of MARK-amplitudes during ten carrier waves. The following agreements
are valid:
binary ‘0’ : 2 MARK-amplitudes, 8 SPACE-amplitudes
binary ‘1’ : 5 MARK-amplitudes, 5 SPACE-amplitudes
position-identifier : 8 MARK-amplitudes, 2 SPACE-amplitudes