C9

Question 1

ATC Interrogator:
Frequency
Spacing

Answer 1

1025-1150Mhz, 126 Frequencies, 1Mhz spacing

Question 2

Signal from DME ground station is routed to preselector and mixed with local oscillator frequency to produce _________.

Answer 2

63Mhz IF signal

Question 3

Identification of Main Lobe from ATC

Answer 3

Main Lobe (P1) must be 9db higher than Side Lobe Suppression pulse (P2). P2 radiated 2µs after P1

Question 4

ATC reply signals

Answer 4

F1 C1 A1 C2 A2 C4 A4 B1 D1 B2 D2 B4 D4 F2

Question 5

ATC Interrogation Signal Modes and numbers

Answer 5

Mode A (Non-Military Identification): 8µs between P1 and P3, 2µs between P1 and P2, Pulse width of 0.8µs
Mode B (Civil Identification): 17µs between P1 and P3, everything else same
Mode C (Altitude Reporting): 21µs between P1 and P3, everything else same
Mode D (Waste of space): 25µs between P1 and P3, everything else same

Question 6

ATC Pulse Pairs:
Interval
Duration
Repetition rate (for interrogation)
Repetition rate (for track mode)

Answer 6

Pulse pairs 12-36µs apart, each lasting for 3.5µs, repetition rate between 5 to 30 pairs per second (track mode) and 90 pp/s (interrogation)