Kongsberg Simrad RA83, Service Manual

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93842105-00
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The bandwidth change is carried out by varying a Q-factor of the tuning circuit, L1 and C54. The
bandwidth is controlled by U14-P01 signal. The U14-P01 signal fed to the line of R50. When it is
switched 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 bandwidth and 15 MHz in the wide bandwidth. The relationship between the transmission
pulse width and IF bandwidth is shown in Table-2.1B.
The logarithmic amplifier consists of custom-made IC, AA209ASP, U2 to U4. Another custom-made
IC AA231BFP, U8 includes AFC (Automatic Frequency Control) circuit. The ATS signal is 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 level adjust circuit and trigger mixing circuit on Modulator Board Q43, Q44
and Q48 to Q51. The video signal is mixed with the trigger and fed to the Processor unit.
Table-2.1B Transmission Pulse width and IF bandwidth Relationship
Transmission Pulse width IF bandwidth
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0.08
us, 0.3 us wide
0.6 us, and 1.2 us narrow
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2.1.7 Performance Monitor
KPM-20 performance monitor
The KPM-20 performance monitor (call PM on and after) is an unit on the side of the scanner
unit to monitor the radar performance both transmitter and receiver function. The operation
overview is as follows;
(1) Monitoring transmit performance:
The PM monitor the transmitter performance with receive the signal transmit from the radar
antenna with the KPM-20 antenna. The PM detect, amplify, and output the radar transmit signal
with microwave receiver circuit in KPM-20. The timing of the transmit performance monitoring is
just the end of the generation of the transmit trigger.
(2) Monitoring receiver performance:
The PM monitor the receiver performance with receive the microwave signal transmit with the
KPM-20 antenna through the radar antenna. The PM transmit the microwave signal with delayed
timing of 240 micro-seconds from the radar transmitting, approximately 20NM in range. The
signal will be appeared on the IF signal received with the radar antenna together with typical
reflecting echo signal.
(3) Evaluation of the transmitter/receiver performance:
The transmit and received signals are processed with PM circuit (E41-5000) as peak level
detection, sample, and hold. Then, the signal is converted to digital data with A/D converter on
the modulator PCB and send to the display or processor unit. Evaluations are carried out with the
control software in the display or processor unit.
Control PCB(E41-5000)
The PCB(E41-5000) has the KPM-20 transmit/receiver timing control, signal peak detection,
sample, and signal hold circuit on the board. The Fig.2.43 is the block diagram for E41-5000
PCB.
(1) Power supply for -5V
The switched capacitor power supply IC(LT1045CP) U2 and U6 convert the voltage from 12V to
-5V. The U2 is for the E41-5000 and U6 for the KPM-20. The output current rating is 100mA for
each. The output voltage can be adjusted by R8 and R16 respectively.
(2) Receiver timing generator
The 1 us width PM TRG signal is generated delayed with 240 us from transmit trigger(TRG2).
The U4, U5, and U7 generate timing pulses for receiver system. The 15 us control signal fed to
the analogue switch U9 for peak detection circuit is generated by the circuit.
The 50 us width sampling signal gate is generated based from PM-GATE of KPM-20.
(3) Peak detector and sample & Hold