Kongsberg Simrad RA83, Руководство по обслуживанию

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93842105-00
2.1.6 Receiver
The receiver comprises an FEM and an IF amplifier.
(1) FEM (6/12kW)
The FEM, H101 mainly consists of RF amplifier, a balanced mixer, and an FET oscillator circuit.
Reflected echo signals received by the antenna are fed to the FEM through the duplexer and
converted into IF signals of 60 MHz.
The local oscillator generates at 9470 MHz and it can be adjusted by the tuning control voltage of 12
V +/- 5 V provided from U6 to U9 on IF AMP Board and U14 on Modulator Board.
(2) IF amplifier (6/12kW)
The log IF amplifier consists of low noise linear pre-amplifier, band-pass filter, logarithmic amplifier,
and tuning circuit. The pre-amplifier is the transistor Q6 with gain of about 20 dB to maintain the low
noise.
The band-pass filter consisting of L1 and C54 controls the receiver bandwidth. The receiver
bandwidth is designed to be able to change in accordance with the transmission pulse width so as
not to degrade both the short and long range performance, with oppose each other, while the
transmission pulse width is changed.
(Generally, emphasis is laid on high resolution in the short range and high sensitivity in the long
range.)
The bandwidth change is carried out by varying a Q-factor of the tuning circuit, L1 and C54. The
bandwidth is controlled by U10-P01 signal. The U10-P01 signal fed to the line of R50. When it is off,
the diode, CR2 is turned off. This rises the Q of the tuning circuit, and the IF bandwidth becomes
narrow. Conversely, it widens when the signal is on. The IF bandwidth is 3 MHz in the narrow band
and 15 MHz in the wide bandwidth. The relationship between the transmission pulse width and IF
bandwidth is shown in Table-2.1A.
The logarithmic amplifier consists of 4 pieces of the custom-made IC, AA209ASP, U2 to U4.
Another custom-made IC AA235BFP, U8 includes AFC (Automatic Frequency Control) circuit. The
ATS signal is an initial tuning switch for the auto tuning system. The M-TUNE and M.T signal are for
manual tuning system. The M.T is duty-controlled pulse signal for analog tuning system controlled
from the Processor unit.
The video signal is fed to the level adjust circuit and trigger mixing circuit on the Modulator PCB, Q1
to Q6. The video signal is mixed with the trigger and fed to the Processor unit.
Table-2.1A Transmission Pulse width and IF bandwidth Relationship
Transmission Pulse IF bandwidth
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0.08 uS, 0.25 uS wide
0.5 uS, and 1.0 uS narrow
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(1) FEM (25kW)
The FEM, FM101 mainly consists of an RF amplifier, a balanced mixer, and an FET oscillator circuit.
Reflected echo signals received by the antenna are fed to the FEM through the duplexer and
converted into IF signals of 60 MHz.
The local oscillator generates at 9470 MHz and it can be adjusted by the tuning control voltage of 12
V +/- 5 V provided from U6 to U9 on IF AMP Board and U14 on Modulator Board.
(2) IF amplifier (25kW)
The log IF amplifier consists of a low noise linear pre-amplifier, a band-pass filter, a logarithmic
amplifier, and a tuning circuit. The pre-amplifier is the transistor Q6 with gain of about 20 dB to
maintain the low noise.
The band-pass filter consisting of L1 and C54 controls the receiver bandwidth. The receiver
bandwidth is designed to be able to change in accordance with the transmission pulse width so as
not to degrade both the short and long range performance, with oppose each other, while the
transmission pulse width is changed.
(Generally, emphasis is laid on high resolution in the short range and high sensitivity in the long
range.)