Block Diagram of Marine RADAR-
1. Power Source: AC
2. Delay Line: Stores the energy received from the power source.
3. Trigger Unit: Sends spike waves signals to the modulator and the display processor.
4. Modulator: is a device that switches the magnetron on and off as required. Each spike-wave from the trigger causes the modulator to release one powerful DC pulse (square wave of 10,000 to 15,000 volts) from the delay line to the magnetron.
5. Magnetron: is a high power RF oscillator capable of being switched on and off, for a short duration (equal to PL) at the desired PRF, by the pulses from the Modulator. The output of the magnetron consists of RF pulses of electromagnetic energy that are sent to the scanner through a hollow, metal tube called a Wave Guide.
6. Scanner: sends the pulses out and receives the echoes, one direction at a time.
Since it rotates at a constant speed, the entire area around it gets scanned regularly.
7. TR Cell is the abbreviated name for transmitting/receive switch.
It blocks the receiver branch of the waveguide during transmission so that the transmitted pulse does not directly enter the receiver and damage it.
Soon after the transmission is over, the TR cell allows the echoes that are received to pass into the receiver.
8. Local Oscillator oscillates at a constant low power RF about 30 to 60 MHz above or below the magnetron frequency, the difference is called the intermediate frequency (IF).
9. Mixer mixes the echoes with the local oscillations and makes available, to the IF amplifier, the echoes reduced from RF to IF.
10. IF AMPLIFIER amplifies the IF signals several million times and passes them on to the video amplifier.
11. VIDEO AMPLIFIER controls the amplification of signal voltages fed to the display processor unit.
12. DISPLAY PROCESSOR UNIT is the brain of the RADAR set. It creates a rotating trace, makes available all other functions and controls needed to operate the RADAR, display symbols & words inside & outside the circular part of the screen.
13. DISPLAY UNIT consists of a rectangular screen within which a circular part provides a visual display of all targets in the vicinity. Because it gives a bird's eye view or plays, the circular area within the screen is called the Plan Position Indicator (PPI). All controls needed to operate the RADAR set are provided on this unit.