Direction by measuring antenna azimuth, range by signal travel during time, no altitude.
Refer to figure.. primary surveillance radar psr primary surveillance radar psr operates by emitting radio wave pulses from a rotating antenna. when these pulses encounter an aircraft or object, some of the energy is reflected back to the antenna. the psr uses a polar coordinate system to provide information on the detected targets. it calculates the range, which is the slant distance from the antenna to the target, and the bearing, which is determined by the antenna's azimuth.range. the range is determined by comparing the time it takes for the pulse to be emitted and received, utilizing the speed of light as the propagation speed. it's important to note that the range provided is not the horizontal distance, but the slant distance from the antenna to the target.bearing. bearing measurement in radar systems utilizes the searchlight principle, where radio pulses are focused into narrow beams. this can be achieved by reducing the wavelength or electronically enlarging the antenna in advanced systems. the narrow beam is then rotated at a consistent speed. by analyzing the direction of the received echo, the bearing of the object can be determined based on the azimuth of the antenna at the time of receiving the echo. this directional information is measured from a fixed reference point or datumprimary surveillance radar psr calculates bearing antenna's azimuth and range signal travel time of a target providing a two dimensional position. altitude is not provided.
Question 222-2 : A functional mode s transponder interrogated in mode a. what is provided to the atc screen apart from the aircraft position bearing and range ?
Transponder code only.
The aircraft is interrogated from the ground station by a predetermined series of pulses on the carrier frequency of 1030 mhz its transponder then transmits a coded reply on a carrier frequency of 1090 mhz. the modes of operation are mode a an interrogation to identify an aircraft.. mode c an interrogation to obtain an automatic height read out of an aircraft referenced to 1013 hpa.. mode s a development of the basic ssr fully compatible with the conventional mode a and c units, providing air to ground, ground to air, air to air data link and height read out in increments of 25 ft.mode s selective addressing. enables data exchange using communications protocols. mode s data link can serve as an alternative or supplementary method for various atc services that are traditionally carried out using vhf voice communications. this utilization of data link technology enhances the safety and reliability of the atc system by minimizing errors associated with voice based communication. numerous types of messages and services within atc can benefit from data link backup, like flight identification altitude clearance confirmation take off clearance confirmation new communication frequency for sector hand off pilot acknowledgement of atc clearance transmission to the ground of aircraft flight parameters minimum safe altitude warninga mode s transponder is fully compatible with conventional mode a and c ground units. this means that if a mode s transponder is interrogated in mode a, the transponder responds as if it was set in mode a, providing aircraft identification transponder code to the atc radar screen.
Question 222-3 : In a satellite assisted navigation system gnss/gps , a fix is obtained by ?
Measuring the time taken for a minimum number of satellites' transmissions, in known positions, to reach the aircraft's receiver.
Question 222-4 : What is the minimum number of satellites required by a gps in order to obtain a three dimensional fix ?
4.
.to carry out three dimensional 3d operation 4 satellites..to carry out two dimensional 2d operation 3 satellites.
Question 222-5 : Gps satellites transmit on two l band frequencies with different types of signals..which of these are generally available for use by civil aviation ?
L1 coarse acquisition c/a with selected availability s/a.
Question 222-6 : Which of the following coordinate systems is used by the navstar/gps receiver to calculate position latitude, longitude and altitude ?
Wgs 84.
Question 222-7 : Which of the following lists all the parameters that can be determined by a gps receiver tracking signals from 4 different satellites ?
Latitude, longitude, altitude and time.
Question 222-8 : In a satellite assisted navigation system gnss/gps a position line is obtained by ?
Timing the period that is taken for a satellite's transmission to reach the aircraft's receiver.
.the gps receiver computes the time taken for the signal to travel from the satellite to the receiver.
Question 222-9 : In which frequency band do satellite assisted navigation systems gnss/gps provide position information that is available to civil aircraft ?
Uhf.
.each satellite broadcasts ranging signals on two uhf frequencies, l1 1575.42 mhz and l2 1227.6 mhz...vor operating frequencies vhf.localiser vhf.marker beacon vhf..dme operating frequencies uhf.glide slope uhf.gnss/gps uhf.l1 and l2 frequencies used by navstar/gps uhf..ils localiser and glide slope vhf and uhf bands...microwave landing system mls shf.airborne weather radars shf.locator lf/mf
Question 222-10 : What is the minimum number of satellites required for the navstar/gps to carry out two dimensional operation ?
3.
.to carry out three dimensional 3d operation 4 satellites..to carry out two dimensional 2d operation 3 satellites.
Question 222-11 : Ignoring pulse length, the maximum pulse repetition frequency prf that can be used by a primary radar facility to detect targets unambiguously to a range of 200 nm is. pps = pulses per second ?
Question 222-12 : Which of the following lists are all errors that affect the accuracy and reliability of the satellite assisted navigation system gnss/gps ?
Question 222-13 : In order to carry out an independent three dimensional fix, receiver autonomous integrity monitoring raim and failure detection and exclusion of any faulty satellite, signal reception is required from a minimum number of how many satellites ?
6.
.raim receiver autonomous integrity monitoring is a technique whereby a receiver processor determines the integrity of the navigation signals. raim is achieved by consistency check among pseudo range measurements..the basic raim requires 5 satellites but a 6th is necessary for isolating a faulty satellite from the navigation solution.
Question 222-14 : Signal reception is required from a minimum number of satellites that have adequate elevation and suitable geometry in order for a satellite assisted navigation system gps to carry out independent three dimensional operation without the receiver autonomous integrity monitoring raim function..the ?
4.
Question 222-15 : The distance between a navstar/gps satellite and receiver is ?
Determined by the time taken for the signal to arrive from the satellite multiplied by the speed of light.
.the pseudorange is the pseudo distance between a satellite and a gps receiver..to determine its position, a gps receiver will determine the ranges to at least four satellites as well as their positions at time of transmitting. knowing the satellites' orbital parameters, these positions can be calculated for any point in time. the pseudoranges of each satellite are obtained by multiplying the speed of light by the time the signal has taken from the satellite to the receiver. as there are accuracy errors in the time measured, the term pseudo ranges is used rather than ranges for such distances.
Question 222-16 : The reason why the measured distance between a navstar/gps satellite navigation system satellite and a receiver is called a pseudo range is because the ?
Calculated range includes receiver clock error.
.satellites use an atomic clock actually 4 , for high precision, and continuously transmit their positions, plus a code number in a set code, at exactly the same time. the set code appears to be random, but isn't, which is why it is known as pseudo random noise code. it is the means by which a receiver recognises signals from a particular satellite...since the transmission time is known, the distance the signal has travelled can be calculated from its arrival time. the receiver matches each satellite's code with an identical copy in its database. by comparing any shift with its internal clock, it can calculate a pseudo range, which is similar to comparing a broadcast copy of a song against one already playing on a cd player if they both started at the same time, the received one would be slightly behind from the time delay. if several songs are received at the same time from multiple sources, the gps receiver can correct for errors in its own clock and determine actual travel times...the principle used is that, if three perfect measurements can locate a point in space, four imperfect ones can eliminate clock offsets, or cancel out some timing errors..an error is therefore deliberately introduced, and algebra is used to compute where all possible points could intersect. the result given is your position. because it is calculated, the word pseudo is used,and the measured distance between a satellite and a receiver is called a pseudo range because the calculated range includes receiver clock error.
Question 222-17 : What type of satellite navigation system navstar/gps receiver is most suitable for use on board an aircraft ?
Multichannel.
.most gps receivers in use today are multi channel type meaning that they can track one satellite per channel. a typical receiver will have 12 channels allowing it to track up to 12 satellites simultaneously..the receiver uses the latest almanac data to determine which satellites are visible at its location.
Question 222-18 : The receiver aerial for a navstar/gps system should be mounted ?
On the upper side of the fuselage in the vicinity of the centre of gravity.
Question 222-19 : In the navstar/gps satellite navigation system, re use of selective availability would give the option to artificially degrade the accuracy by ?
Dithering the satellite clock.
.the c/a code coarse acquisition, clear access, or civil access is modulated on the l1 carrier only. the p code precise or protected is modulated on both carriers..there are two limitations for civilian users, namely selected availability and anti spoofing, briefly referred to as sa and as, respectively. both deteriorate the achievable accuracy for civilian users significantly..selective availability sa , the denial of full accuracy, is accomplished by 'manipulating' navigation message orbit data epsilon and/or the satellite clock frequency dither. so far, only the satellite clock frequency has been manipulated. with this dithering process the gps satellite clocks are artificially degraded by adding a signal with an unknown frequency and amplitude to the know clock behavior. this is done to degrade the performance of gps for the 'normal' users. both, the frequency and amplitude of the added signal, change rapidly over time. the amplitude of this 'clock dithering' is of the order of 0.3 microseconds which corresponds to roughly 100 meters and the frequency is of the order of only a few minutes..this sa clock dithering limits the accuracy of real time position estimates to 25 meters rms.
Question 222-20 : In the event of the re use of selective availability, how does this affect, if at all, the navigation accuracy of the navstar/gps satellite navigation system ?
It degrades position accuracy by manipulating satellite signals.
.gps selective availability sa is a currently disabled, since may 2000 function of the navstar / gps system which permits the us department of defence to downgrade the l1 signal available to unauthorised civilian users by adding intentional, time varying errors to gps signals..these errors of up to 100 meters 328 ft to the l1 signals were intended to deny the use of civilian gps receivers for precision weapon guidance, although typical sa errors were 10 meters 32 ft horizontally and 30 meters 98 ft vertically.
Question 222-21 : In the navstar/gps satellite navigation system, receiver clock error ?
Is corrected by using signals from four satellites.
One of the most significant error sources is the gps receiver's clock. because of the very large value of the speed of light, c, the estimated distances from the gps receiver to the satellites, the pseudoranges, are very sensitive to errors in the gps receiver clock for example an error of one microsecond 0.000 001 second corresponds to an error of 300 metres 980 ft. this suggests that an extremely accurate and expensive clock is required for the gps receiver to work. since manufacturers prefer to build inexpensive gps receivers for mass markets, the solution for this dilemma is based on the way sphere surfaces intersect in the gps problem...it is likely that the surfaces of the three spheres intersect, since the circle of intersection of the first two spheres is normally quite large, and thus the third sphere surface is likely to intersect this large circle. it is very unlikely that the surface of the sphere corresponding to the fourth satellite will intersect either of the two points of intersection of the first three, since any clock error could cause it to miss intersecting a point. however, the distance from the valid estimate of gps receiver position to the surface of the sphere corresponding to the fourth satellite can be used to compute a clock correction.
Question 222-22 : The influence of the ionosphere on the accuracy of the satellite navigation system navstar/gps is ?
Minimised by the receiver using a model of the atmosphere and comparing signals transmitted by the satellites.
Question 222-23 : What are the effects, if any, of shadowing by parts of the aircraft e.g. wing on the reception of signals from navstar/gps satellites ?
It may prevent the reception of signals.
.gps satellites transmit a low powered radio signal that travels by line of sight. this means it will pass through clouds, glass or plastic but will not go through most solid objects such as a wing. it will no longer be able to provide the user with a current location, until it can resume a link to at least three satellites and then update its position.
Question 222-24 : Which of the following geometric satellite constellations provides the most accurate navstar/gps position fix ?
3 satellites with a low elevation above the horizon and an azimuth of 120° from each other together with a fourth directly overhead.
. 2605
Question 222-25 : In relation to the navstar/gps satellite navigation system, what is involved in the differential technique d gps ?
Fixed ground stations compute position errors and transmit correction data to a suitable receiver on the aircraft.
Question 222-26 : Which of the following statements about the accuracy that can be obtained with the differential technique d gps of the satellite navigation system navstar/gps is correct ?
The nearer a receiver is situated to a d gps ground station, the more accurate the position fix.
Question 222-27 : How does a receiver of the navstar/gps satellite navigation system determine the elevation and azimuth data of a satellite relative to the location of the antenna ?
It calculates it by using almanac data transmitted by the satellites.
Question 222-28 : In relation to the navstar/gps satellite navigation system, search the sky is a ?
Procedure that starts after switching on a receiver if there is no stored satellite data available.
Question 222-29 : Which of the following, if any, is a prerequisite if a receiver of a navstar/gps satellite navigation system is to be used in combination with a multi sensor system ?
The prescribed ifr equipment must be installed and operational.
Question 222-30 : Which of the following is the datum for altitude information when conducting flights under ifr conditions on airways using the navstar/gps satellite navigation system ?
Barometric altitude.
.icao doc 8168, part ii, section 3, chapter 1.all fmcs and some stand alone basic gnss receivers provide altitude information..however, the pilot must still comply with the published minimum altitudes using the barometric altimeter. where the fmc provides vertical information, flight director guidance cues, or coupled autopilot operation, the pilot should follow the appropriate information or cues along with any necessary cross checks with the barometric altimetry.
Question 222-31 : Which of the following statements about the visibility of navstar/gps satellites is correct ?
It varies, depending on the time and observer's location.
Question 222-32 : How many operational satellites are required for full operational capability foc of the satellite navigation system navstar/gps ?
24.
Question 222-33 : Which of the following satellite navigation systems has full operational capability foc and is approved for specified flights under ifr conditions in europe ?
Navstar/gps.
.there are two main global navigation satellite systems gnss currently in existence with a third which is planned to be fully operational by 2012. they are.. usa navstar gps navigation system with timing and ranging global positioning system.. russian glonass global navigation satelitte system.. european galileo...currently, only navstar/gps satellite navigation system is approved for specified flights under ifr conditions in europe.
Question 222-34 : Gps system satellites transmit their signals on two carrier waves 1575 mhz and 1227 mhz and supply two possible codes accessible according to user civil or military..commercial aviation uses ?
Only the 1575 mhz carrier wave and one code.
.each satellite broadcasts ranging signals on two uhf frequencies. l1 1575.42 mhz.l2 1227.6 mhz..there are currently two modes of operation, sps standard positioning service for civilian users , and pps precise positioning service for authorised users... sps is a positioning and timing service provided only on frequency l1..sps was originally designed to provide civil users with a less accurate positioning capability than pps..pps uses both frequencies l1 and l2.
Question 222-35 : Which statement about dilution of precision dop is correct ?
The value of dop depends upon the geometry and number of satellites in view.
.the position dilution of precision pdop is the geometric effect resulting from satellites being too close together. satellites that appear farther apart in the sky provide a more accurate position solution than ones close together. in the latter case, the position accuracy is degraded in a similar fashion to when position lines from ground based navaids navigational aids are less than 45°. since the ephemeris of each satellite is known by the gps global positioning system receiver, it is possible to calculate which combination of gps satellites provides the best geometry at a given time. this is translated into a figure called the position dilution of precision pdop. since the satellites move across the sky relative to the user, the pdop is always changing. a low pdop is better. a pdop of 4 to 6 is considered good. position solutions calculated when the pdop is from 6 to 10 should be used cautiously because they may have significant error. a pdop that is above 10 indicates unacceptable error...the icao international civil aviation organization states that a pdop of less than 6 is required for en route navigation, with a pdop of 3 or less required for nonprecision approaches i.e., not ils types.
Question 222-36 : The different segments of the satellite navigation system navstar/gps are the ?
Control, space and user.
. main tasks of the control segment are. managing sps performance. navigation data upload. monitoring satellites..the space segment consists of a notional constellation of 24 operational satellites...the user segment is the gps receiver side.
Question 222-37 : One of the tasks of the control segment of the satellite navigation system navstar/gps is to ?
Monitor the status of the satellites.
. main tasks of the control segment are. managing sps performance. navigation data upload. monitoring satellites..the space segment consists of a notional constellation of 24 operational satellites...the user segment is the gps receiver side.
Question 222-38 : The main task of the user segment receiver of the satellite navigation system navstar/gps is to calculate receiver position by ?
Selecting appropriate satellites automatically, to track the signals and to measure the time taken by signals from the satellites to reach the receiver.
. user segment.gps supplies three dimensional position fixes and speed data, plus a precise time reference. the gps receiver used in aviation is a multi channel type and is able to determine the distance to a satellite, by determining the difference between the time of transmission by satellite and the time of reception.
Question 222-39 : One of the tasks of the space segment of the satellite navigation system navstar/gps is to ?
Transmit signals which can be used, by suitable receivers, to determine time, position and velocity.
.the space segment consists of a notional constellation of 24 operational satellites..they are orbiting the earth in orbits inclined 55° to the plane of the equator in a nearly circular orbit of the earth at an altitude of 20 200 km 10 900 nm..each satellite broadcasts ranging signals on two uhf frequencies l1 and l2 providing for suitable receivers, signals to determine time, position and velocity.
Question 222-40 : In civil aviation, the height value computed by the receiver of the satellite navigation system navstar/gps is the ?
Height above the wgs 84 ellipsoid.
.the geodetic reference datum used is wgs 84...in the civil aviation field, altitudes and flight levels are.defined in terms of atmospheric pressure. points on the ground are defined by their planimetric coordinates and by their orthometric height or altitude, which use as their reference the geoid corresponding to mean sea level...the heights derived from gnss systems use the wgs 84 ellipsoid as their reference and are thus different from the values of the orthometric height at the same point...the height difference between the ellipsoid gnss height reference and the geoid orthometric height reference is called the undulation of the geoid. this value thus defines the distance of the geoid above positive undulation of the geoid or below negative undulation of the geoid the reference ellipsoid..this gives us the relationship..undulation of the geoid = ellipsoidal height orthometric height altitude..the aeronautical information service publishes the values of the undulation of the geoid for each ifr aerodrome..this value, conventionally designated gund, is expressed in feet. it will be shown on the charts as and when they are amended.
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