For long range radars, you require a low frequency to stop the signal being attenuated before you can receive it. For short range radars, attenuation is not a problem so you can use a higher frequency to give you better target discrimination properties.

The below table shows the exam facts you need to know.

Radar TypeFrequencyRange
En-Route Surveillance600-1200 MHz200-300 nm
Terminal Surveillance1200-3000 MHz60-80 nm
Airfield Surveillance1200-3000 MHz20-30 nm
Airfield Surface Movement15-17 GHzUp to 5 nm
Airfield Surface Movement Indicator15-17 GHzUp to 5 nm
Ground Movement15-17 GHzUp to 5 nm
Surface Movement15-17 GHzUp to 5 nm
Precision Approach9-10 GHzUp to 9nm
Airborne Weather9.735 MHzUp to 150 nm

Note that ASMR, ASMI, GMR and SMRSMR —1) Humidity: Saturation Mixing Ratio2) Radar: Surface Movement Radar are all the same thing under different names: an airfield surface movement radar for tracking aircraft that are taxiing around an aerodrome.

When trying to remember the ranges, it helps if you think about what the radar is trying to achieve:

  • Enroute tracks aircraft in airways
  • Terminal tracks aircraft in the terminal manoeuvring area
  • Airfield radars track aircraft within the ATZ
  • Surface movement radar tracks aircraft on the airfield.

This will give you a clue as to how far they need to be able to see.

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