Results
#1. A primary radar has a pulse repetition frequency of 275 pps. The time interval between the leading edges of successive pulses is:
Time interval between between leading edges = PRI
PRI= 1/prf
PRF = 275 pps
PRI = 1/275 =0.00364 second = 3.64 milliseconds
#2. A primary radar system has a pulse repetition frequency of 450 pps. Ignoring pulse width and flyback at the CRT, the maximum range of the radar would be:
The formula for Rmax is
C / (2 x PRF).
C stands for the speed of light= 300,000,000 m/s
With a PRF of 450 pulses/s,
the Rmax is = 300,000,000 / 900 = 333333 m which is equal to 333km.
Thus the radar can sample up to 333km during each pulse.
333km = 180 nm
#3. When flying a Precision Approach Radar in the UK, vertical displacement is based upon:
ATC will assume that an aircraft is using QFE on final approach when carrying out a radar approach and any heights passed by the radar controller will be related to the QFE datum. It should be noted that the Obstacle Clearance Height is always given with reference to the aerodrome or threshold elevation.
now not being used
#4. The frequency band and rate of scan of Airfield Surface Movement radars are:
Aerodrome Surface Movement Radars or Indicators (ASMR or ASMI) operate at very short wavelengths of about 3.8cm (SHF).
The beams are narrow with high rotation rates (60 RPM).
On occasions it is possible even to identify aircraft types from the return
More higher frequencies of EHF are rarely used because of scattering and absorption of the signal by moisture and particles in the atmosphere which make them impractical.
#5. When carrying out a precision radar approach, talkdown normally ceases at _______ nm from touchdown:
When the pilot has been handed over to the PAR controller and established radio contact, he will be told not to acknowledge any further instructions and to check that his landing gear is down and locked. Thereafter the controller maintains a continuous flow of instructions to the pilot e.g. “You are 3½nm, slightly above the glideslope, increase your rate of descent; turn left 3°, heading 272”. Ranges are usually given every mile until 4nm to go; thereafter at every ½nm. From 2nm ranges are given every ¼nm. The talkdown terminates at ½ nm, or less.
#6. A ground based radar with a scanner rotation of 60rpm, a beam width in the order of .5° and a PRF of 10000pps would be:
The formula for Rmax is
C / (2 x PRF).
C stands for the speed of light= 300,000,000 m/s
With a PRF of 10000 pulses/s,
the Rmax is = 300,000,000 / 20000 = 15000 m which is equal to 15 km.
Thus the radar can sample up to 15km during each pulse.
15km = 8 nm= Range
Aerodrome Surface Movement Radars or Indicators (ASMR or ASMI) operate at very short wavelengths of about 3.8cm (SHF).
The beams are narrow with high rotation rates (60 RPM).
#7. The SHF band has been selected for Airfield Surface Movement Indicator (ASMI) radars in preference to the EHF band because:
Aerodrome Surface Movement Radars or Indicators (ASMR or ASMI) operate at very short wavelengths of about 3.8cm (SHF).
The beams are narrow with high rotation rates (60 RPM).
On occasions it is possible even to identify aircraft types from the return
More higher frequencies of EHF are rarely used because of scattering and absorption of the signal by moisture and particles in the atmosphere which make them impractical.