MRC DRS4000, Руководство пользователя и техническое руководство

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Theory of Operation 6-3 DRS4000 Receiver User and Technical Manual
Each BDC operates by mixing a Local Oscillator (LO) signal
together with the incoming RF signal and producing a UHF
output signal in the range of 110 to 860 MHz. The incoming
signal is filtered and then amplified by a Low Noise Amplifier
(LNA) and is sent along to the mixer. See
Figure 6-2 for a
functional block diagram of the block downconverter circuitry.
The LO generates either a lower or a higher frequency
(depending upon the BDC’s operating band) using a Phase Lock
Loop (PLL) synthesizer. The 2 GHz BDCs use a low-side local
oscillator (its frequency is on the low side of the RF band) while
the 7 GHz BDCs use a high-side local oscillator. The
synthesizer’s frequency is fixed and programmed via the on-
board micro-controller. This LO frequency is then amplified and
filtered to reduce spurious signals before being applied to the
mixer.
In the mixer, the incoming RF signal is mixed with the LO signal
resulting in a signal equal to the difference between the two
signals. This signal is then amplified and low-pass filtered to
remove the signal representing the sum of the two signals.
Regulated DC power (+8.5/+18.5 VDC) for the BDCs is supplied
via the BDC connectors on the same UHF cable that carries
output from the BDCs.
6.1.2 RF Switching Module
The RF switching module, which is controlled by the processor
module, provides a 4x4 switching matrix and allows selective
switching of antenna input ports to the four-channel input tuner
module. This allows users to customize their antenna input
selections.
The 4x4 RF switching module uses BCD controls for the
selection lines that are driven from the processor module.
Figure 6-2: Block Diagram of Downconverter
6.1.3 Four-Channel Input Tuner Module
The four-channel input tuner module is based on solid state
technology for commercial applications support using a common
tuner module.
The tuner module translates the UHF frequency of the tuners
(110 to 860 MHz) to IF frequencies of either 70 MHz or 36.2
MHz. The tuner produces 70 MHz core (for LMS-T) or 36.2 MHz
(for DVB-T), which is digitally down-sampled into the Maximal
Ratio Combining (MaxRC) cores within the COFDM diversity
module.
Automatic gain control (AGC) is integrated in to the tuner module
providing approximately 65 dB of dynamic range.
6.1.4 COFDM Diversity Module
The COFDM Diversity Module contains the Coded Orthogonal
Frequency Division Multiplexing (COFDM) demodulation and
diversity reception circuitry.
The IF signal is processed by the main demodulator integrated
circuits (ICs). The COFDM demodulator automatically detects
RF Input
Band
Filter
Low-noise
amplifier Mixer Amplifier
Low pass
filter
Local
oscillator
Amplifier Low pass
filter