Radio Navigation Theory Flashcards
What are the main two types of radar?
Primary Surveillance Radar (PSR)
Secondary Surveillance radar (SSR)
What is the radar screen called?
Plan Position Indicator (PPI)
What is a Primary Surveillance radar (PSR)?
What are the disadvantages of PSR?
While a big advantage of primary radar is that no special equipment is required in an aeroplane, it does have some operational disadvantages, including:
- Clutter from precipitation and high ground
- Uneven returns from different aircraft
- Blind spots
The radio energy in the reflected signal received at the radar dish may be quite small, depending on the strength of the original dish may be quite small, depending on the strength of the original transmission, how good a reflector the target is, its distance from the radar antenna, and so on. A radar that us sensitive enough to pick up weak returns from targets may also pick up returns from terrain and precipitation, leading to ground clutter and weather clutter on the screen. During periods of heavy rain, primary radar may be significantly degraded.
What device can PSR use to reduce excessive clutter?
Some radars incorporate an electronic sifting device known as a moving target indicator (MTI) that only allows signals from moving targets to be sown on the screen, in an attempt to eliminate clutter from stationary objects.
What is a Secondary Surveillance Radar (SSR)?
Secondary surveillance radar removes most of the limitations of primary radar simply by adding energy to the return pulse from the aeroplane, using a device carried on board the aeroplane known as a transponder.
What is mode S Secondary Surveillance Radar?
Mode S is a Secondary Surveillance Radar system which interrogates aircraft by means of a unique 24-bit aircraft address, allowing for a higher number of maximum targets in busy airspace. Mode S SSR is being implemented in two stages:
1. Mode S Elementary Surveillance (ELS)
2. Mode S Enhanced Surveillance (EHS)
What is Mode S Elementary Surveillance?
Aircraft with Mode S ELS equipment will be able to report as follows:
- Aircraft identity
- Altitude within 25ft intervals
- Transponder capability report
- Flight status (airborne / on the ground)
- SI code capability
What is Mode S Enhanced Surveillance?
Aircraft with Mode S EHS equipment builds advanced features on the Mode S Elementary Surveillance functionality features, Advanced aircraft reporting features include:
- Selected altitude entered into Flight Management Systems.
- Roll and track angle information
- Groundspeed
- Magnetic heading
- Indicated airspeed (IAS) and Mach-number
- Vertical rate
What is ADS-B?
Aircraft can broadcast information, derived from onboard GPS receivers via the ADS-B surveillance system. Unlike normal SSR operation, the data is broadcast and does not require interrogation from ground stations. ADS-B is enabled by the interfacing of suitably equipped GPS receivers and Mode S SSR transponders.
What is VOR?
The VOR is a very high frequency radio navigation aid that is extensively used in instrument flying. Its full name is the very high frequency omni-directional radio range, commonly abbreviated to the VHF omni range, VOR, or omni.
Each VOR ground station transmits on a specific VHF frequency between 108.00 and 117.95 megahertz (MHz).
What is DME?
Distance-measuring equipment (DME) can provide you with extremely useful information: the distance of your aircraft from a DME ground station. DME uses radar principles to measure this distance, which is the slant distance rather than the horizontal distance (or range). For most practical purposes, the DME distance can be considered as range, expect when the aeroplane is within a few miles of the DME ground station.
What is the NDB and ADF?
The non-directional beacon (NDM) is the simplest form of radio navigation aid used by aircraft. It is a ground-based transmitter that transmits radio energy in all directions, hence its name - the non-directional beacon.
The automatic direction finder (ADF), fitted in the aeroplane has a needle that indicates the direction from which the signals of the selected NDB ground station are being received. This is extremely useful information for pilots flying in instrument conditions and/or at night. In days past, the combined ADS/NDB system was referred to as the radio compass.
What is VDF?
Some aerodromes are equipped with radio aerials that can sense the direction of VHF-COM signals received from an aeroplane. This information is presented to the air traffic controller as a radial line on a cathode ray tube similar to a radar screen or, with the most modern VDF equipment, as a very accurate digital readout of bearing.
The controller can then give the pilot the bearing of the aircraft relative to the aerodrome. This is known as very high frequency direction finding, and is often abbreviated to VDF or VHF D/F.
Information available from VDF:
QDM - Magnetic bearing to the station
QDR - Magnetic bearing from the station
QTE - True bearing from the station
