Avionics systems assist pilots in providing safe flights on commercial, industrial, and military aircraft. Failures in those systems usually leads to catastrophe, stressing the importance of proper testing of avionics systems and their components. As avionics systems become more automated and autonomous, they become more complex in their software and hardware. Suitable test equipment must keep pace with the functionality needed to “exercise” avionic systems and subsystems under real-world conditions, so that designers can fully understand the behavior of those systems, installers and maintainers know their performance levels, and pilots can count on reliable performance. Because of the complexity, a variety of test instruments and software tools are needed to test modern avionics systems to assist in development, production, and maintenance.
Modern avionics equipment suites consist of hundreds of systems and modules to help pilots fly safely to their destinations. No matter the size, whether small private planes or large commercial and military jets, aircraft depend upon avionic systems to maintain optimal routes, avoid air traffic, and steer clear of bad weather. Avionics equipment provides communications from the air to the ground, between two or more aircraft, reception of signals from orbiting satellites, and ongoing measurements of temperature, wind speeds, and other environmental parameters which can affect a flight. Two of the better-known avionics systems are distance measurement equipment (DME) and tactical air navigation (TACAN) systems. Additional systems include altimeters, weather radars, Global Positioning System (GPS) receivers, traffic collision avoidance systems (TCAS), traffic information service (TIS), and temperature measurement systems.
Sharing the Skies
Satellites provide the manmade constellations that help aircraft navigate safely through crowded skies. Satellite systems such as the aviation radio navigation service (ARNS), the global navigation satellite system (GLONASS), radio navigation satellite service (RNSS), the Galileo satellite navigation system, and the ever-popular GPS provide the signals by which satellite receivers can help aircraft (and even ground vehicles) to safely navigate. To do so, GPS and other satellite receivers must perform with the frequency accuracy and signal sensitivity required to capture and process signals from GPS satellites under a wide range of weather conditions. The test equipment for characterizing those receivers essentially takes the place of a GPS signal source (satellite transmitter) and must be capable of generating the signal frequencies of U.S. and European GPS systems, such as the U.S. L1 GPS signal frequency of 1575.42 MHz with a bandwidth of 15.345 MHz.
Test equipment capable of evaluating the performance of these systems must be capable of re-creating the signal conditions of different flight environments, with the functionality and performance that exceeds the actual operating conditions. Whether benchtop or portable, avionics test equipment should enable measurements of systems as well as transponders, such as Mode A (aircraft identification signal), Mode C (identification and altitude), Mode 4 identify friend or foe (IFF), and Mode S transponders.
Although in-field testing of avionics systems involves access to aircraft cockpit displays and system hardware, thorough avionics system testing also requires checks on software and control bus interconnections, such as ARINC and CAN data buses, and the test equipment and software capable of simulating different levels of bus traffic. It is also important to note that orbiting satellites are only part of aircraft navigation systems and parts of those systems reside in ground stations. For example, DME and TACAN system ground stations house hardware and software that must be measured and maintained and often portable test gear provides the ease of accessing remote avionics ground stations.
Testing complex modern avionics systems requires measurement solutions capable of simulating the many different operating environments. The GSG-5 and GSG-6 Series Advanced GNSS Simulators from Spectracom (www.spectracom.com), for example, can generate the signal conditions presented by any constellation of satellites, such as Galileo, GLOSNASS, and GPS satellites, from a single output connector. The compact instruments can generate as many as 64 simultaneous satellite signals at user-selected frequency bands, such as GPS L1 (1539 to 1627 MHz) and L2 (1192 to 1280 MHz) frequency bands. It operates within four frequency bands, allowing a user to generate any set of 16 channels within each frequency band. Despite the complexity of their test signals, these signal simulators are relatively easy to use. They can operate by remote control with an external computer or locally front-panel controls using built-in or downloadable software. These signal simulators also account for the different positions and orbits of satellites by creating precise test scenarios that include date, time, and satellite transmit power levels.
For multiple-function avionics system testing, the ATC-1400A Aviation Test Set from Cobham/Aeroflex (www.aeroflex.com) is a powerful rack-mountable test system well equipped for measurements on air-traffic-control (ATC) and DME systems. It can be operated from its front panel or by remote computer via a GPIB cable. With the proper accessories, it can also make measurements on TACAN systems and a wide range of transponders for a unit under test (UUT), including Mode 4 (IFF) and Mode S avionics transponders. This single-box solution contains a wideband frequency synthesizer for generation of test signals from UHF through L-band, DME operating mode with TACAN simulation for selection of pulsed signal delays and modulation, UUT pulse spacing detector with ±100 ns detection capability, range delay control, and velocity control.
When testing transponders and portability is important, the IFR / Aeroflex 6000 Avionics Ramp Test Set from Cobham (www.cobham.com) is capable of testing Mode A, C, and S avionics transponders as well as DME, TCAS, ADS-B, and TIS avionics systems in a compact housing measuring less than 8 lbs. It performs transponder measurements at both 978 and 1090 MHz and can measure transmit frequency, transmit power, and receiver sensitivity, showing results on a large 5.7-in. liquid-crystal-display (LCD) screen. The easy-to-use tester includes a detachable antenna and can evaluate a wide range of DME parameters, including interrogator transmitter frequency and peak power, pulse repetition frequency (PRF), pulse width, and pulse spacing. The hand-held instrument simulates the realistic airborne environments for verification and certification of aircraft TCAS systems. The IFR / Aeroflex 4000 navigation/communications (Nav/Comm) flightline tester performs precise measurements on HF, VHF, and UHF transmitters and can generate a variety of navigation beacon signals, all in the same compact 8-lb. instrument that can run for 8 hr or longer on a single battery charge.
When testing avionics systems and components is just part of the job, the R&S® SMBV100A vector signal generator from Rohde & Schwarz (www.rohde-schwarz.com) is a versatile vector signal generator that is well equipped to perform microwave and wireless testing from 9 kHz through 3.2 GHz (with options to 6 GHz) that can be configured with a GNSS and avionics simulator that can create many different satellite signal scenarios in real time. It includes the processing power to account for motion and velocity as well as the effects of tunnels, bridges, and other environmental factors on satellite signals.
Of course, this is just a handful of the measurement equipment that can be used for avionics system testing. Another useful measurement tool is a real-time spectrum analyzer, like the Tektronix H500, or others, available from several suppliers including Anritsu, Keysight, and Tektronix, and in portable and benchtop configurations. When scanning a frequency band of interest, the analyzer can display desired signals, such as navigation beacon signals, as well as unwanted signals, such as interference and noise.
To learn more about any of these instruments, or to rent or purchase these or other test instruments, please visit Axiom’s website at www.axiomtest.com/ to view our inventory. If you would like help selecting the right equipment for your project, contact Axiom Test Equipment’s sales department at email@example.com, or by calling an Axiom sales representative at 760-806-6600.