User's Manual

Receiver Circuits
18 Return signals from the antenna are fed through the rotating joint to the transceiver,
which routes the received signal via the duplexer to an internal low noise RF receiver,
digital receiver and signal processor.
19 Sensitivity Time Control (STC) is applied to the low noise RF receiver to increase the
dynamic range of the receiver. The noise figure of the receiver is £4 dB, measured at the
output of the analogue to digital converter. The low noise receiver contains the capability to
adjust the mean noise level prior to analogue to digital conversion.
20 The output from the low noise RF receiver is converted to a third intermediate frequency
in three stages. The bandwidth of the first intermediate frequency is 1220 MHz ±20 MHz.
The bandwidth of the second intermediate frequency is 580 MHz ±20 MHz. The bandwidth of
the third intermediate frequency is 60 MHz ±12 MHz.
21 The intermediate frequency is applied to an analogue-to-digital converter which outputs
14 bit two’s complement digitised samples to the digital receiver. The centre frequency
of the digitised samples is 20 MHz ±80 Hz and the instantaneous bandwidth is £20 MHz.
22 The digital receiver translates the signals to the baseband frequency and provides
In-phase and Quadrature (I and Q) outputs to the digital signal processor. The in-phase
and quadrature phase outputs of the digital receiver are both rounded to 18 bits, and the format of
the output is two's complement.
23 The digital signal processor uses digital pulse compression before applying the signals to
the limiting and compensation function. Motion compensation removes the effect of own
ship motion from the received signal vector. The limiting and motion compensation function has
a Doppler output channel and a Logarithmic output channel.
24 The Doppler channel is currently not implemented.
25 The input to the Logarithmic channel is used for video processing. The video processing
function aligns the amplitude data into a contiguous range ordered data stream, aligns the
single bit detection video into a contiguous range ordered data stream and aligns the logarithmic
amplitude data into a contiguous range ordered data stream.
26 The video is converted to analogue video for output to conventional display systems, e.g.
Nucleus 3, Manta and MantaDigital. In the future digital video will also be output from
the LAN link.
27 Due to the characteristics of RACON systems, the processing applied to targets and
objects within the digital signal processor is not suitable for the detection of a RACON.
To solve this, a specific RACON processing channel is included. This enables RACON signals
to be processed and integrated into the surface picture processed video output.
KH1264
Chap ter 3
Page 3.8 Is sue 2