10 Secondary Surveillance Radar (SSR) Flashcards
What is the Principle of Operation of a Secondary Surveillance Radar (SSR)?
- Radar continuously transmits an interrogation signal
- AC are constantly listening for this signal
- When an AC receives an interrogation signal it responds accordingly
What frequencies do the Interrogation and Response signals for an SSR work at?
- Interrogation signal: 1030 MHz
- Response signal: 1090 MHz
- In the UHF band
What advantages does SSR have over standard Primary Radar?
- Since the response is sent back via a different frequency only real responses are received (echoes and reflections can be ignored)
- Greater range for much less transmission power
- Attaches AC data tag, including Actual Speed, Altitude and Ident
- Can give ATC instant notification of an emergency, unlawful interference or radio failure
How many different codes can be issued on an SSR at any one time?
- 4096
- 4 digit code, numbers 0-7
Regarding an SSR, describe Mode A
- A setting on the AC transponder
- When it receives an interrogation from a SSR, it transmits the AC transponder code
- Uses pulses 1, 2 and 3
Regarding an SSR, describe Mode C
- A setting on the AC transponder
- When it receives an interrogation from a SSR, it transmits the AC transponder ID and AC pressure altitude
- Pressure altitude based on 1013.25 hpa MSL
- Uses pulses 1, 2 and 3
Regarding an SSR, describe Mode S
- A setting on the AC transponder
- When it receives an interrogation from a SSR, it transmits Actual data (ID, Spd, Alt) and Selective data (Spd, Alt, Hdg, Altimeter setting)
- Uses pulses 1, 2, 3 and 4
For an SSR, what is the purpose of pulse 2?
- Pulse 2 is used to suppress the side lobe created by the rotation of the SSR
- If the strength of pulse 2 is greater than the strength of pulse 1 and 3 then the AC knows it is side lobe and so suppresses it
For and SSR in mode S, describe a short response and a long response
- Short response returns only mode S data and is used to interrogate specific information ATC needs
- Long response returns data for mode A, C and S. So returns all information
Describe the two interrogation methods used by an SSR Mode S
- All Call: returns all Actual data regarding the AC (i.e. What is it actually doing now)
- Selective Call: returns specific data regarding what has been selected in the AC
For an SSR, what are the two Mode S surveillance types?
- Elementary Surveillance (ELS)
- Enhanced Surveillance (EHS)
For and SSR, what are the different transponder codes?
- 7700: Mayday
- 7600: Radio Failure
- 7500: Hijacking
- 2000: Entry to airspace from an area where SSR is not used
Describe the ‘Fruiting’ error associated with SSR
- 2 or more ground stations in close proximity and one sends an interrogation signal to an AC
- The AC responds to the interrogation and the response is picked up by the other ground stations
- These unwanted replies appear as interference
- Other stations remove AC from their systems via a process called ‘de-fruiting’
Describe the ‘Garbling’ error associated with SSR
- If 2 AC are within 1.7nm of each other and in line
- An interrogation signal from the ground station is received by both
- Responses from each AC interfere with each other and can block each other’s signal
- Can lead to a fake target being displayed on the ground station
All AC are given a unique code (like an address), what type of code is this described as?
Hexadecimal Code
