Description of the radar set, tactical-technical characteristics
Figure 1: Antenna AQF of Type 243Q in conjunktion with Type 941 air warning radar
|frequency:||157 … 187 MHz
|pulse repetition time (PRT):|
|pulse repetition frequency (PRF):||50 or 100 Hz|
|pulsewidth (τ):||10 µs|
|peak power:||1 kW|
|hits per scan:|
Type 243 is operating in A-Band Mark Ⅲ interrogator being used to identify aircraft as hostile or friendly. The antenna type AQF is non-directional, i.e. range only is given. This interrogator was used on small ships in conjunction with air warning radars.
The transponder is called IFF Mark Ⅲ if fitted in aircraft and Type 253 if fitted in ships. In the U.S. Navy they are known as ABK and BK respectively. They are all identical.
The IFF sweeps its waveband every 2½ seconds and under normal conditions will, therefore, send back a response every 2½ seconds provided the beam of type 243 or 242 is pointing towards it. This response may take the form of a narrow pulse (6 … 10 µs), a wide pulse (17 … 28 µs), of a very wide pulse (80 µs), and it is normally displayed in a downwards direction on the A-scope of the parent radar set where it can be easily related to the location echo, as shown in Figure 2. The IFF response appears at a slightly greater range (about 200 yards for a strong response and up to 500 yards for a weak response.)