Test & Measurement
Fraternal twins on a control mission
Even in the age of satellite navigation, terrestrial flight navigation systems (ILS, VOR, marker beacons) are still indispensable. It is therefore all the more important that these systems function properly. This requires regular testing and verification. Two new analysers – one for ground use and one for in-flight testing – can handle all of the required measurements. Klaus Theißen, product management, Spectrum Analysis, Rohde & Schwarz tells us more
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egular checking and maintenance of terrestrial navigation systems based on ground inspection as well as flight inspection are key requirements stipulated in ICAO Doc 8071 and ICAO Annex 10. Here, the results of ground and air measurements must be comparable in order to prove the stability and integrity of the systems as well as the measurement procedures. According to ICAO rules and regulations, the level of agreement also determines how frequently the measurements are to be repeated. The R&S EVSF1000 VHF/UHF Nav/Flight analyser (Fig. 1) and the R&S EVSG1000 VHF/UHF Airnav/Com analyser ensure the required level of comparability with their identical signal processing hardware and software. Despite their compact design, these specialised instruments deliver measurement accuracy as good as the best laboratory equipment. Compared with their predecessor, the R&S EVS300, they offer better handling (e.g. convenient spectrum preview) as well as improved performance (e.g. much higher sensitivity).
A specialist for ground measurements Although terrestrial flight navigation transmitter systems have integrated monitoring functions, regular inspection and maintenance of these systems using independent measuring instruments is essential. Static analyses as well as dynamic measurements (e.g. runway measurements) are among the tasks that must be performed by officials in charge of maintaining the systems, i.e. airport operators, their subcontracted flight inspection organisations or government agencies. The battery-powered R&S EVSG1000 was developed precisely for such applications. The analyser’s 6.5" colour display is easy to read even in direct sunlight and provides a complete overview of all settings and results. The spectrum preview in particular is very useful for measurements in the field because it displays both the IF spectrum of the measurement signal and the filter bandwidths that are used, so incorrect measurements are virtually impossible. The instrument’s functionality is rounded out by numerous features such as integrated
Figure 2a & b: When performing ground inspections on localisers, certain antenna heights are recommended that are best obtained using a suitably equipped test vehicle. To perform dynamic runway measurements, such a vehicle is needed anyway. For glide slope measurements, the antenna must be positioned even higher
recording of all measured values (R&S EVSG-K21) including GPS position data (R&S EVSG-K20) and external triggering capabilities (PPS, wheel sensor, etc.).
Runway measurements – a challenge for CAT III systems For ILS CAT III systems, analysis of the localiser along a runway is one of the most critical ground measurements, requiring a temporary shutdown of the runway to air traffic. To minimise the interruption while still obtaining reliable results, the R&S
Figure 3: The course deviation from the centre line is obtained from the difference in depth of
modulation (DDM) for the 90 Hz and 150 Hz signals at the receiving location
EVSG1000 offers high measurement speed (100 measurements/s with R&S EVSG-K22) and fast data storage (R&SEVSG-K21). This allows trouble-free drive tests at speeds over 60 km/h without undersampling of high-frequency scallops caused by reflections. The R&S EVSG-K1 option enables the R&S EVSG1000 to perform simultaneous and independent measurements of the level and phase relationships between the course and clearance signals of a dual-frequency (2F) ILS system.
Figure 1: Measurement flights with drones (here, the R&S EVSF1000 is installed) are used in ground inspections to reach hard-to-access places (photo: Skyguide
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Time is money – also with measurement flights Due to their cost, it is important to minimise the number and duration of the required measurement flights. Of course,
times (e.g. using RTK GPS or DGPS). Powered by the drone’s on-board voltage, the R&S EVSF1000 delivers extremely stable measurement results in this application. The ILS glide path is typically analysed in this manner. Using a drone, this measurement can be performed in the far field. Due to the greater distance from the transmit antennas, the results are significantly more reproducible than with mast measurements on the runway (mast measurements are performed at the threshold). The mast is not high enough for measuring the glide path signal further ahead of the touchdown point – a problem that is eliminated by using a drone.
www.rohde-schwarz.com Components in Electronics October 2018 35
to achieve this, a high-performance measuring instrument is needed. Equipped with two signal processing channels, the R&S EVSF1000 is able to simultaneously perform two independent measurements on any desired frequencies, e.g. measuring the localiser and glide slope signals during the landing approach or simultaneously checking two CVOR/DVOR stations. Steep- edged preselector filters prevent the formation of intermodulation products near powerful FM transmitters so that the measurement is not corrupted. During flights on the edge of the coverage area, the low-noise frontend ensures stable results even when faced with signals well below the specified measurement range. If a GPS receiver with PPS synchronisation is connected, each measured value can be correlated to the associated GPS time and position.
Mast too short? Terrain too rough?
Due to its size and weight, the R&S EVSF1000 is ideal for use on board drones (Fig. 1). Drone flights are obviously no replacement for aircraft-based measurement flights, but they complement ground inspections at locations that are inaccessible with vehicles or masts. Of course, the current position of the drone must be known with high precision at all
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