7
Standard frequencies
The 5 MHz and 10 MHz standard frequencies are derived directly from the master
oscillator of the preconnected GPS-clock. This oscillator is phase locked to the precise
PPS-signal (pulse per second generated from GPS-receiver), thus the standard frequen-
cies are locked to the PPS also. After passing an additional filter and an amplifier circuit,
the standard frequencies can be optionally fed to BNC-connectors.
Telecom signals
These signals can be devided into two groups:
the clock outputs and the ‘framed’ outputs, that are provided by a framer and line
interface device on the board LIU. All clock signals needed for generation of the
‘telecom outputs’ are phase locked to a 4.096 MHz reference clock, which is generated
by a frequency synthesizer on the preconnected GPS-clock. This synthesizer is phase
locked to the PPS-signal and frequency locked to the master oscillator of the clock.
The module LIU is able to generate signals for the American T1- or the European E1-
system. The mode of operation depends on the position of a DIP-switch or the state of a
control input in the following way:
DIP-switch 1 „ON“ or control input „low“:
E1-mode
DIP-switch 1 „OFF“ or control input „high“:
T1-mode
The clock outputs are standard frequencies of either 1544 kHz (T1) or 2048 kHz (E1).
Four unbalanced and four balenced outputs according to ITU-T G703-13 (CCITT
recommendation ‘Physical/electrical characteristics of hierarchical digital interfaces) are
available via BNC- and BNC-Twinax-connectors.
The ‘framed’ outputs are consisting of data signals known from digital telephony,
which are distributed by using a special frame structure. As a synchronization unit, LIU
only generates a ‘framed all ones’ signal (data byte 0xFF hex) with a transmission speed
of either 1.544 Mbps (T1) or 2.048 Mbps (E1). Four outputs according to ANSI T.403
(T1-mode) or ITU-T G703-9 (E1-mode) are available either unbalanced via BNC
connectors or balanced via BNC-Twinax connectors. Two different line codes used for
error correction are known for the transmission of framed signals. The board LIU
generates B8ZS- (in T1-mode) or HDB3-coded (in E1-mode) output signals by
standard. The generated coding depends on the position of the DIP-switch no. 4 in the
following way:
DIP-switch 4 „OFF“:
HDB3- (E1) or B8ZS-coding (T1)
DIP-switch 4 „ON“:
AMI-coding
