This test covers fundamental concepts of Secondary Surveillance Radar (SSR) and Distance Measuring Equipment (DME). Select the best answer for each question.
1. What is the primary purpose of Secondary Surveillance Radar (SSR) compared to Primary Radar?
2. What frequency band does DME primarily operate in?
3. In SSR systems, what is the purpose of Mode S?
4. How does DME calculate the distance between an aircraft and a ground station?
5. What is the typical interrogation frequency for SSR systems?
6. What is the primary limitation of DME regarding distance measurement?
7. In SSR terminology, what does "squawk" refer to?
8. How are DME channels typically paired with VOR stations?
9. What is the main advantage of SSR over primary radar?
10. What is the typical accuracy of DME distance measurements?
1. Correct Answer: b) To obtain additional information from aircraft through transponder responses
SSR differs from primary radar by actively interrogating aircraft transponders, which respond with information such as identity, altitude, and other data, rather than simply detecting reflected signals.
2. Correct Answer: b) 960-1215 MHz (L-band)
DME operates in the L-band frequency range of 960-1215 MHz, which provides a good balance between range resolution and resistance to atmospheric attenuation.
3. Correct Answer: b) To enable selective addressing of individual aircraft
Mode S (Select) is an enhanced SSR mode that allows ground stations to selectively interrogate specific aircraft using unique 24-bit addresses, reducing frequency congestion and enabling data link capabilities.
4. Correct Answer: b) By measuring the time delay between interrogation and reply
DME calculates distance by measuring the round-trip time of radio signals between the aircraft interrogator and ground transponder, then converting this time to distance using the speed of light.
5. Correct Answer: a) 1030 MHz
SSR ground stations transmit interrogations at 1030 MHz, while aircraft transponders reply at 1090 MHz to avoid interference between interrogation and response signals.
6. Correct Answer: a) It measures slant range, not ground distance
DME measures the straight-line (slant) distance between the aircraft and ground station, which differs from the ground distance, especially when the aircraft is at high altitude near the station.
7. Correct Answer: b) The transponder code set by the pilot
"Squawk" refers to the four-digit transponder code (from 0000 to 7777 in octal) that pilots set as instructed by air traffic control to identify their aircraft on radar displays.
8. Correct Answer: a) Each VOR frequency has a corresponding DME channel
DME channels are paired with specific VOR frequencies, allowing pilots to automatically tune to the correct DME channel when selecting a VOR frequency for navigation.
9. Correct Answer: c) It provides identification and additional data from aircraft
The key advantage of SSR is its ability to obtain specific information from aircraft, including identity, altitude, and other data, which primary radar cannot provide without cooperative targets.
10. Correct Answer: a) ± 0.1 nautical miles
Modern DME systems typically have an accuracy of about ±0.1 nautical miles or better, making them highly reliable for navigation purposes.