4
TV Test Transmitter ¸SFM
NICAM modulator
The modulator generates a standard
QPSK signal with the correct IF
(33.05 MHz/32.348 MHz) for standards I
and B/G. A NICAM signal at the correct
RF is available for standard L/L’. In this
case, the VSB characteristic is identical to
that of standard B/G, i.e. the IF of the
NICAM carrier for standard L/L’ is also
33.05 MHz.
Since pulse filtering and the modulator
are digital, a signal is obtained with the I
and Q signals in quadrature without any
phase error.
The NICAM modulator has inputs for an
external data stream and a clock signal.
When the external NICAM data stream
fails, the test transmitter automatically
switches over to a pseudo-random bit
sequence (PRBS). Modulation can be
switched off (continuous wave). A
defined bit error rate can be set for the
NICAM data stream.
The internal generator delivers a stan-
dard NICAM data stream which com-
prises a frame-alignment word, select-
able control and additional data bits plus
the digitally coded audio signals. The
required signal coding can also be
selected. The appropriate intercarrier is
available at a separate output.
RF upconverter
The RF upconverter has an internal and an
external IF input; the external one can be
tuned to any IF vision carrier frequency
between 32 MHz and 46 MHz. Thus almost
any IF signal can be converted to the RF. At
the RF it is possible to select the upper or
lower sideband.
By virtue of this selection capability, all
L/L’ channels can be generated to stan-
dard. With the lower sideband selected,
TV standards at any IF are possible (e.g.
standard M, Japan, 58.75 MHz).
An RF output impedance of 50
Ω
or 75
Ω
(optional) can be selected.
Special configurations for intermodula-
tion and linearity measurements in the
form of programs may be called up. Level
combinations for vision, sound 1 and 2
and sideband as specified in the stan-
dards are set with the modulation
switched off. Linearity measurements are
performed by automatic vision-carrier
level switching every two seconds.
If parameters for the vision, NICAM and
sound modulators are set to non-stan-
dard values, the display outputs a warn-
ing. However, compliance with the
appropriate standard can be restored
with a single keystroke.
Remote control
The ¸SFM is equipped with an IEC/
IEEE interface to SCPI and also has an
RS-232-C interface for the remote control
of all functions.
Settings can be loaded from or to an
external memory card via a PCMCIA con-
nector. Software updates can be carried
out via the memory-card interface and
the serial interface.
A powerful processor system controls all
¸SFM modules via the serial SERBUS
developed by Rohde&Schwarz. The
SERBUS allows modules to be plugged
into any slot.
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