Raytheon Pathfinder 1200 Instruction Manual page 67

6.1 BLOCK DIAGRAM DESCRIPTION
6.1.1 General
The overall system block diagram can be considered as being comprised of two main
sections. One for the scanner unit circuit diagram; the other for the display unit circuit
diagram. The following description of the block diagram explains the individual circuits
described in Chapter 6.2 and 6.3.
The motor-encoder and SHM pulse generator are used to synchronize; the bearing
of the radar display, display timing and transmit-triggering. Setting the operate switch to
"STBY" position activates the power supply which in tum provides operating voltages
to all circuits of the radar. After about 90 seconds, setting the operate switch to "ON"
position allows transmitter triggering and the radar becomes operational.
6.1.2 Scanner Unit
The scanner unit includes the scanner drive mechanism together with the transmitter
and receiver. These three sections are housed within a 25" radome.
1) Radiator
The radiator is a horizontally polarized, resonant, center-fed slotted wave guide
array. The radiator is driven at 27 rpm by a motor-encoder via a reduction mechanism.
2) Motor-encoder
The scanner motor is a dc motor which incorporates a reduction mechanism and
encoder. The input voltage of the motor is 12 V de. The concoder generates a bearing
sync pluse every 0.176 degree or 2048 pulses for each complete rotation or the
scanner.
3) SHM Pulse Generator
The SHM pulse generator consists of a reed switch and permanent magnet which
is mounted on the main reduction gear. The SHM pulse resets the bearing counter in
the display unit to zero.
4) Modulator
A line-type pulser is used in the modulator. The charging method used is de
charging. A silicon controlled rectifier (SCR) is used as the high power switch of the
pulser.
The pulse selection relay (K20 1) is controlled by the RANGE switching on the
control panel of the display unit. This will provide short pulses when the 0.25, 0.5,
I or 2 nm range switches are selected and long pulses on the 4, 8 or 12 nm ranges.
The pulse repetition frequency (PRF) rate is 920 Hz.
5) Magnetron Transmitter
A voltage of the required pulse width is fed to the magnetron which generates
high energy oscillations in the region of 9445 MHz for the duration of the input pulse.
The operating point of magnetron is at a voltage of -3.6KV and a current of 3A.
6-2