Kongsberg Simrad RA83, Service Manual

Page: 13 / 210

93842105-00
2 - 3
2.1.1 Antenna
The antenna is a slotted array antenna, which radiates a horizontally polarized electromagnetic
wave. The outline of antenna is shown in EXPLODED VIEW. The end of rotary coupler is connected
to the transmitter and receiver through a circulator. The antenna pattern in the vertical plane is wide
enough (approximately 22/25 degrees) to ensure target detection even if the own ship rolls and
pitches.
2.1.2 HM (Heading Marker) pulse generator
A magnet fixed on main gear produces a HM pulse by closing the contact of reed-switch, S1/S101.
When magnet just arrives at the front of the reed-switch, the pulse is sent to Processor unit through
AC235AFP, U10 (6/12kW) or U14 (25kW) together with azimuth pulse. On the 6/12/25kW, the
azimuth pulse is generated 216 pulses/rotation with photo-interrupter under the motor and
converted to 2048 pulses/rotation with PLL circuit.
2.1.3 Antenna drive motor
The antenna drive motor, M101 is a DC-motor.
For 6/12kW:
A DC-motor drives the antenna controlled by U18 and Q28 to Q30.
For 25kW:
A DC-motor drives the antenna controlled by U18 and Q40 to Q42.
2.1.4 Duplexer
The duplexer consists of a circulator and a diode limiter. The circulator passes the output power
from the magnetron, V1/V101, to the antenna with very low loss, and prevents passing the power to
the receiver side. The diode limiter short circuits during transmitting and protects the FEM (Front
End Module) from damage.
2.1.5 Transmitter
The transmitter comprises a modulator and a magnetron. The modulator is a switching-type,
solid-state modulator that uses the switching action of a FET. The modulator generates a
high-voltage, negative going pulse to drive the magnetron in accordance with the trigger pulse.
(1) Modulator (6/12kW)
The FET (2SK1450), Q19, Q21, Q22 (and Q23, Q201, Q202 for RB718A) generates a high-voltage
pulse across the primary winding of the pulse transformer, T101, and this pulse voltage is stepped
up to supply the higher voltage (4.5kV/5.8kV) power to the magnetron, V101. The pulse width is
controlled by the AC235AFP, U10. The rectifier, CR101, CR102 and a resistor R101 are used to
absorb the counter electromotive force that is developed when the magnetron is turned off.
(2) Magnetron
(6/12kW)
The magnetron, V101 oscillates at 9410 MHz (+/- 30 MHz) and peak power is approximately 6 kW
(RB717A/AP) or 12kW(RB718A/AP). The negative-going pulse is applied to the cathode.
(3) Modulator
(25kW)
A high voltage added to the primary of the pulse transformer is stepped up and stabilized by L13, U1,
Q24 and CR2. The FET (2SK1450), Q14-Q17, Q20-Q23, Q25-Q28, Q30-Q33 generates a
high-voltage pulse across the primary winding of the pulse transformer, T101, and this pulse voltage
is stepped up to supply the higher voltage (8kV) power to the magnetron, V101. The pulse width is
controlled by the AC235AFP, U14. The rectifier, CR101, CR102 and a resister R101 are used to
absorb the counter electromotive force that is developed when the magnetron is turned off.
(4) Magnetron
(25kW)
The magnetron, V101 oscillates at 9410 MHz(+/- 30 MHz) and peak power is approximately 25 kW.
The negative-going pulse is applied to the cathode.