Rohde & Schwarz 1138.4000, Руководство по обслуживанию

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Radio Unit R&S CRTU-RU Instrument Design and Function Description
1140.0050.82 3.11 E-4
tuning range. All LOs are synchronized by the MMCX connector
110.8MHz at the bottom of the module with the reference frequency
from the REFERENCE BOARD.
Besides, an MMCX connector at the top of the RXTX BOARD1/2 is
designed as input with the second transmitter IF (RESIF2TX) which is
activated via software switches.
Receiver functions
On the receiver side (RX), the RF signal is fed in at the SMA connector
RFRX1 (bottom of module) of the RXTX BOARD1/2 which is provided
by the RF FRONTEND.
On the RXTX BOARD1/2, this signal is taken via a switchable
attenuator with fine stepping and large attenuation range in order to
match the level according to the level applied.
Subsequently, this signal is converted to an IF frequency of 10.7 MHz
by means of triple signal conversion (IF1, IF2, IF3) and several filter
and amplifier stages and provided at the MMCX connector IF3RX1 (top
of module) for the DIGITAL BOARD.
This procedure is necessary to achieve a high image-frequency
rejection and a high dynamic range with a simultaneously high
intermodulation suppression.
For the receiver side, an extra LO1RX (local oscillator) is provided with
a large tuning range and a very fine frequency resolution used for
setting the receive frequency, an LO2 fixed-frequency oscillator shared
with the transmitter and an extra LO3RX with a very small tuning
range.
All LOs are synchronized by the MMCX connector 110.8 MHz at the
bottom of the module with the reference frequency from the
REFERENCE BOARD.
A further MMCX connector RESIF3RX (top of module) provides a
buffered RX IF signal which is taken to the rear of the CRTU Radio
Unit via a coax cable. This signal output can be activated via a
software switch.
Besides, an MMCX connector at the top of the RXTX BOARD1/2 is
designed as output with the second receiver IF (RESIF2RX) which can
be activated via software switches.
Correction processor
The RXTX BOARD1/2 contains an extra correction processor with
large flash PROM.
It controls all the static and dynamic settings on the RXTX BOARD1/2
and, as a special feature, also the attenuator pads and amplifiers of the
RX and TX attenuator on the RF FRONTEND.
Besides, the correction processor permits to read out the individual
module error data from the EEPROMS of the respective modules in a
so-called correction procedure (automatic module data adjustment)
and calculate the deviations for all possible signal paths. These
deviations are stored as correction values in the flash PROM. The
correction processor then sets the desired level settings, corrected by
the correction values, in the flash PROM so that frequency, linearity
and temperature responses of the modules are compensated for.
This ensures the excellent level accuracy of the CRTU Radio Unit
which is essential for most measurements.