Vislink Strata RX, Technical Reference Manual

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Theory of Operation 9-3
Strata RX
Technical Reference Manual
9.3 RF Front End
The RF Front End is responsible for receiving the incoming RF
signal (either analog or digital) and converting it to 900 MHz for
the AGC/IF module.
The RF Front End is designed around two main modules: the
Low Noise Block Down Converter (LNB, also called the BDC),
and the Low Noise Converter (LNC). These two modules are
used separately or together to cover the various Bands.
9.3.1 Low Noise Block Down Converter (LNB)
The LNB operates by mixing a Local Oscillator (LO) signal with
the incoming RF signal, and producing a 2.0 - 2.7 GHz signal.
This 2 GHz signal is then fed to the LNC for conversion to 900
MHz.
The block diagram is shown in Figure 9-8.
Incoming Signal
The incoming signal is amplified by a Low
Noise Amplifier (LNA) and sent along to the Mixer. Depending on
the Band on which the LNB is operating, there may also be band
pass filters either before the amplifier, or after.
Local Oscillator
The Local Oscillator (LO) generates a lower
frequency using a crystal-controlled digital synthesizer. The base
frequency is set by the crystal, and the synthesizer allows the
output frequency to be varied.
This output frequency is then passed it through a multiplier to
raise its frequency to one that is exactly 2 GHz away from the
incoming signal. Depending on the Band, this frequency may be
either 2 GHz lower or 2 GHz higher than the incoming signal.
This signal is filtered to reduce spurious signals before being
applied to the Mixer.
Mixer
In the Mixer, the incoming signal is mixed with the LO
signal, resulting in two mixer outputs: the sum of the input
signals, and the difference between them. The difference signal
will be the desired 2 GHz.
Finally the 2.0 - 2.7 GHz signal is Low Pass Filtered to remove
the signal representing the sum of the two MIxer signals.
The LNB differs from the LNC in that its output is not 900 MHz,
but 2 GHz. This 2 GHz is then applied to the “AUX” input of the
2 GHz LNC, which produces 900 MHz.
Band-Switched LNB
For applications where the radio will be
able to switch between 2 GHz and some other Band, there is a
specific version of the LNB that incorporates Band Switching.
The block diagram is shown in Figure 9-7.
This version of the LNB incorporates a switch on the input that
allows bypassing the LNB entirely when the radio is operating on
the 2 GHz Band.This switch is controlled in tandem with the
switch in the 2 GHz LNC, so the LNB output is routed through
the correct signal path in the 2 GHz LNC.
9.3.2 Low Noise Converter (LNC)
The LNC operates in a similar fashion to the LNB. The LNC
mixes a Local Oscillator (LO) signal with the incoming RF signal,
and produces the 900 MHz signal.
The block diagram is shown in Figure 9-8.
Incoming Signal
The incoming signal is amplified by a Low
Noise Amplifier (LNA) and sent along to the Mixer. Depending on
the Band on which the LNC is operating, there may also be band
pass filters either before the amplifier, or after.
Local Oscillator
The Local Oscillator (LO) generates a lower
frequency using a crystal-controlled digital synthesizer. The base
frequency is set by the crystal, and the synthesizer allows the