Software Developed for Mobile WiMAX Testing

National Instruments introduced the NI Measurement Suite for Mobile WiMAX (IEEE 802.16e-2005), a software suite that engineers can use with modular RF instrumentation for automated testing of Mobile WiMAX devices. With this software suite, engineers can perform Mobile WiMAX component and device testing faster than with traditional instruments, and with better accuracy and greater flexibility.

Based on PXI Express instrumentation powered by multicore technology, the suite can perform error vector magnitude (EVM), power and spectral measurements three to five times faster than traditional instruments. PXI WiMAX test systems from National Instruments also provide a low-cost, R&D-grade instrumentation alternative to traditional instruments. With a typical residual EVM accuracy of -46 dB at 3.5 GHz (-10 dBm), this test system can perform significantly more accurate measurements than alternative production test-grade instruments. Additionally, the suite provides engineers enhanced flexibility with the same equipment used for testing Mobile WiMAX devices to test hardware that complies with other standards such as Fixed WiMAX, wireless local area network (WLAN), GPS, and GSM/EDGE/WCDMA cellular standards.

The Measurement Suite for Mobile WiMAX supports channel bandwidths from 1.25 to 28 MHz and fast Fourier transform (FFT) sizes 128, 256, 1024 and 2048, as well as all Mobile WiMAX modulation types with both convolution coding and turbo convolution coding. The Measurement Suite for Mobile WiMAX also can generate or analyze signals with up to eight zones and 16 bursts. Combined with the NI PXIe-5663E RF vector signal analyzer and NI PXIe-5673 RF vector signal generator, the measurement suite also provides continuous frequency coverage from 85 MHz to 6.6 GHz.

By including the NI Signal Analysis Toolkit for Mobile WiMAX and the NI Signal Generation Toolkit for Mobile WiMAX, the suite offers programming APIs and virtual instrument panels for signal generation and analysis in programming environments including the NI Lab VIEW graphical system design platform. In addition to a LabVIEW API, the toolkits install with an equivalent C-style API for engineers using C, C++, .NET, or similar programming language.

The Measurement Suite for Mobile WiMAX supports multiple PXI hardware configurations to meet different application needs. A standard NI test bundle for Mobile WiMAX includes anNI PXIe-5663 6.6 GHz vector signal alayzer, NI PXI e-5673 6.6 GHz vector signal generator, NI PXIe-1075 18-slot high-bandwidth chassis and a NI PXIe-8108 dual-core controller to provide high-performance flexibility to a variety of automated test systems.

www.ni.com

Lab Brick Generates Signals for Portable Testers

The Lab Brick® family of USB-compatible signal generators cover frequencies from 50 MHz to 6 GHz in a fraction of the cost and size of traditional test signal sources.

Signal generators are essential to most test systems, but they are typically too large and expensive for portable measurement applications. In cases where portability is important, the Lab Brick® family of signal generators from Vaunix Technology Corporation includes five low-cost, compact models covering a total range of 50 MHz to 6 GHz with high output levels and excellent spectral purity. They can be powered and controlled by means of a Universal Serial Bus (USB) equipped personal computer (PC) or laptop computer, or operate under battery power or with a remote power supply for embedded or automated applications.

The five members of the Lab Brick® signal generator family are models LSG-251 (50 to 250 MHz), LSG-152 (250 to 1500 MHz), LSG-222 (500 to 2200 MHz), LSG-402 (1000 to 4000 MHz), and LSG-602 (1500 to 6000 MHz). Each Lab Brick® signal generator (Fig. 1) measures 4.90 x 3.14 x 1.59 in. (124 x 80 x 40 mm) and weigh less than 1 lb. (0.45 kg). It can be connected to a host computer by means of a standard USB cable and controlled by means of Graphical User Interface (GUI) software run on the host computer. The simple GUI features large display windows to quickly view and adjust the signal generator’s frequency and amplitude.

The Lab Brick® signal generators each deliver at least +10 dBm output power across their full operating-frequency ranges. Signals are available at an SMA connector, and output levels can be adjusted via the GUI software over a control range of 50 dB (-40 to +10 dBm) for the 6-GHz model LSG-602 and 55 dB (-45 to +10 dBm) for the other four models. Output-level settings are accurate within +1.5 dB and -0.5 dB. In addition to controlling output levels, the GUI allows an operator to complete shut off the signal generator’s output power. Frequency can be set with 100-kHz resolution, with initial accuracy (before aging) of better than ±2 PPM.

In spite of being low-cost, portable units, these high-performance signal generators boast low phase noise and excellent spectral purity. For the 250-to-1500-MHz model LSG-152, for example, the single-sideband (SSB) phase noise is typically -95 dBc/Hz offset 10 kHz from the carrier and -115 dBc/Hz offset 100 kHz for the carrier (Fig. 2). For the 50-to-250-MHz model LSG-251, the phase noise is typically -105 dBc/Hz offset 10 kHz from the carrier and -125 dBc/Hz offset 100 kHz from the carrier. For the 1000-to-4000-MHz model LSG-402, the phase noise is typically -85 and -105 dBc/Hz, respectively, at 10- and 100-kHz offsets, while for the 1500-to-6000-MHz model LSG-602, the phase noise is typically -75 and -95 dBc/Hz, respectively, at 10- and 100-kHz offset frequencies. For all models, harmonics are typically -10 dBc while spurious content is typically -80 dBc.

The Lab Brick® signal generators include a green LED status indicator to show connection to a USB host computer. When the host computer recognizes a Lab Brick® signal generator, it loads the GUI software and displays that signal generator’s serial number and model number. The GUI software can track and control several connected Lab Brick® signal generators, simplifying multiple-signal test setups. In addition, each Lab Brick® signal generator can store settings in internal memory, allowing it to power up in a specific instrument state. This same capability also allows a Lab Brick signal generator to be used in an embedded or remote instrument application without USB control required to achieve a given instrument state. In non-USB applications, the Lab Brick® signal generators can operate with battery power or remote power supply. For automatic-test-equipment (ATE) applications, a programming guide is available for each Lab Brick® signal generator. In addition, they are programmable by means of LabView software drivers from National Instruments (www.ni.com).

A Lab Brick® signal generator provides several operating modes, including continuous-wave (CW) and swept-frequency operation. In CW mode, the sources deliver a fixed-frequency, sinusoidal output signal. In the swept-frequency mode, the generators can perform a single sweep or continuous sweeps across a user-defined frequency band in user-defined frequency steps. A user can define not only the frequency step size but the frequency dwell time.

The RoHS-compliant signal generators are supplied in rugged aluminum housings complete with mounting holes. Lab Brick® signal generators comply with international requirements for electromagnetic-compatibility (EMC) emissions and immunity for Class A ISM devices to ensure that they don’t interfere with other ISM-band equipment. Each Lab Brick® signal generator is shipped with a 6-ft.-long USB cable and a USB flash memory drive containing the GUI software and a software file copy of the user manual. Lab Brick® signal generators can be used with any PC or laptop computer with USB 2.0 port (or powered USB hub) and running the Windows 2000, XP, or Vista operating system.

www.vaunix.com

Internet Meters Set to Release Aug. 2010

The integrated measurement of advertising across both TV and internet viewing might happen sooner than we thought. Nielsen now expects to have a portion of its people meter households covered with “Internet meters” prior to the 2010-2011 broadcast season.

Once that happens, count on internet viewing on Hulu.com and the network’s websites having the same national advertising load as the telecasts for at least 3 days after airtime, so it will count in the C+3 commercial ratings that the networks sell to advertisers.

Urged by clients to move faster, Nielsen responded Tuesday with a plan to accelerate the rollout of the Internet meter to its national people meter sample. The plans call for Nielsen to complete the roll out by Aug. 31, 2010, instead of some time in 2011.

The initiative, now called TVandPC will create the industry’s first single source measure of viewing to both TV and online. Once the rollout is complete, Nielsen will be able to report online video viewing from 7,500 national-people-meter homes, representing about 20,000 people and 12,000 computers.

Handheld ADSL 2+ Tester Provides Increased Performance

Toronto, Canada – GAO Instruments offers its compact, handheld and easy-to-use test instrument – ADSL 2+ Tester, which is used to test ADSL, ADSL2, ADSL 2+ and RE-ADSL2 lines. This multi-functional tester quickly determines whether the line tested complies with appropriate standards and clearly displays test results through its high resolution, backlit LCD, and indicates alarms and the connectivity of WAN or LAN.

This ADSL 2+ tester, model A0300010, conducts ADSL2+ line parameter testing, TX and RX data packet accounting, PING testing and ISP login simulation. The tester writes VPI, VCI, user name and password automatically according to embedded configuration parameters and also allows the input of configuration and margin values via Test Manager Pro software. It supports a maximum measurement distance of 6.5km and is able to store over one hundred test results; test results can be downloaded to a PC for further analysis, printing, and output. Configurations and margins can also be saved and downloaded through its software interface.

GAO Instruments also offers a series of ADSL testers for customers to choose from.

Broadband Across America from JDSU

MILPITAS, CA – JDSU launched “Broadband@Work Across America,” a campaign to help raise
awareness and educate rural service providers on the technical issues and
challenges that could impact their ability to successfully deploy broadband
services in towns across the country.

The campaign is inspired by the 2009 American Recovery and Reinvestment Act,
which provides $7.2 billion to accelerate broadband service deployment to
rural and under-served regions in the nation. The first deadline for broadband
stimulus grant applications was recently completed on August 20, 2009, and two
more will be scheduled until all funding is awarded on September 30, 2010.

Broadband@Work Across America leverages JDSU’s decades of expertise in
broadband network test and management solutions as well as optical components
and equipment, to help rural telecommunications providers use stimulus funds
to deploy broadband services through fiber-to-the-home (FTTH), digital
subscriber line (DSL), wireless, and hybrid fiber-coaxial (HFC) systems, among
others.

JDSU’s Broadband@Work Across America campaign will be featured at OSP Expo
2009 in Minneapolis, September 2-3, booth #508. JDSU will be exhibiting its
leading broadband test and measurement solutions and displaying the new
campaign theme, literature, special offers, giveaways and other supporting
materials.

“With proper testing, rural telecommunications providers can avoid facing
technical issues in their broadband deployments that cost time and money,”
said Dave Holly, president of JDSU’s Communications Test and Measurement
business segment. “JDSU’s Broadband@Work Across America campaign offers
information, training and solutions to help providers deploy broadband
services as quickly as possible.”

Source Measure Unit from Agilent Technologies, Inc.

SANTA CLARA, CA – Agilent Technologies Inc. introduced a three-channel source
measure unit (SMU) that can simultaneously provide power and perform
measurements in applications such as parametric testing of diodes, LEDs, CMOS
integrated circuits and other semiconductor devices. The U2723A USB modular
SMU`s compact size saves benchtop space, and its improved throughput saves time.
It is the latest addition to Agilent`s family of paperback-sized USB modular
instruments.

The compact U2723A, which supplies voltage (± 20 V) and current (120 mA) on all
three channels, can operate in four-quadrant mode and also provides accurate
current measurements down to nanoamp levels. With 15 ms rise time, the SMU
improves throughput, especially during mass testing of semiconductor devices. It
also simplifies automated testing with up to two embedded test scripts per
channel.

The Agilent U2723A can be used as a standalone instrument or as a module plugged
into the compact U2781A USB modular-products chassis. For standalone use, the
U2723A can be connected to a PC via USB, and testing can be performed with the
bundled Agilent Measurement Manager (AMM) software. To simplify integration into
new or existing test systems, AMM includes a code-conversion capability that
translates commands into forms compatible with popular programming languages
such as C#, C++, Agilent VEE and Microsoft® Visual Basic.

Automated Gearbox Testing builds in Consistency

Ann Arbor, MI – The U.S. military has demanding requirements for the hardware it needs. Take, for instance, a set of gearboxes built by Excel Gear Inc., Roscoe, Ill, (excelgear.com) for missile launchers on the U.S. Navy’s new DDG1000 series of ships. The gearboxes are drive elements for the servo systems that rotate and elevate the missile launcher. For good servo performance the boxes must meet the Navy’s requirements for stiffness, efficiency, and low backlash.

A prototype was tested using a time consuming manual method. Although satisfactory, the method required careful checking to prevent data entry errors. Requirements for the test system called for high accuracy, elimination of measurement errors, and elimination of data entry errors. The company’s experience automating the test procedures provides a useful design lesson.

After successfully completing the prototypes, Excel Gear president N.K. Chinnusamy, decided the production run needed improved assembly procedures and to automate the test methods. Preload on the bearings was identified as an important factor – too little preload allowed excessive backlash while too much decreases efficiency and generates heat. A measurement accurate enough to size an optimum preload spacer is difficult because before the spacer is in place, the bearing can tip from side to side.

The company manufactured a set of fixtures to prevent bearing tipping and improve the repeatability of the preloads. The fixtures also improved the efficiency of the first production boxes and reduced their backlash from what had been attained in the prototype boxes.

Types of tests

The units called for several tests. For example:

Temperature tests during run-in: The primary sources of heat in the gearbox are seal friction, bearing friction, and oil churning. The heat generated by oil churning distributes throughout the box and dissipates through the case. Seal and bearing friction are concentrated and, if excessive, will cause failure. Temperatures are checked near the bearings on the high-speed shaft, where measurements on the prototype boxes showed the highest temperatures. These areas were also near the seals. Although it isn’t possible to separate the heat generated by the bearings and seals, the seals seem to generate the most heat.

Temperatures were recorded for two hours with the box running at maximum speed. After cooling, the test was repeated with the box running in the opposite direction. In the test, temperatures rose rapidly at first and then at a decreasing rate. While the temperatures do not reach equilibrium, in operation the boxes will not run continuously for two hours, and they will reach top speed only intermittently.

Gear-train stiffness: This characteristic, measured with the output shaft locked, was the ratio of the input-shaft motion to the torque applied, in Nm/rad. Torque was applied using a hydraulic actuator with two opposed cylinders driving two racks against a pinion. The racks are held in the pinion by a bushing. This results in friction force opposite to the direction of motion. Because the friction in the hydraulic actuator would cause measurement inaccuracies, the torque is measured between the actuator and the input shaft using a Dataflex 42/1000 torque transducer. This sensor has a capacity of 1,000 Nm in either direction. Torque is determined by measuring the twist in the transducer shaft using rotary encoders in a differential circuit. An encoder rotor is mounted at each end of the shaft. Because the encoder read heads are mounted to the stationary part of the transducer, there are no slip rings. The A-quad-B output from the transducer is converted to a voltage by an encoder electronic box. The voltage output range is 0 to 10V with a no load value of 5V, and the calibration constant is 0.200 Nm/mV.

Rotary motion was measured using a 2,000 line rotary encoder (resolution of 0.018° ). Because the input shaft extends through the box, the encoder is mounted on the opposite end of the shaft from the hydraulic actuator. When the box is in operation, a brake is mounted on this end of the shaft.

The A-quad-B output from the encoder is converted to a voltage by the programmable encoder-control box. The range and number of volts per degree can be set depending on the amount of rotation to be measured. The output has a range of 0 to10V. For this test, the output was 8.100° per V and the no-rotation voltage was 5V.

Gear train backlash: Some backlash is necessary to provide running clearance for the gears. Too little backlash results in overheating and premature failure, and too much degrades servo performance. Backlash is determined from the data collected for gear train stiffness.

Breakaway torque: For these boxes, it was low and measured manually using a snap-torque wrench. Although automated tests are usually preferred, a few are so simple that the programming required is not justified. This test, for instance, was the only one not automated.

Gearbox power losses over the full range of speeds: Input torque was measured with the gearbox running at a set of speeds both clockwise and counterclockwise. The torque is a nearly linear function of speed with a small component of stiction. This is preferred in a servo system because it contributes to servo loop damping. Because the torque is nearly a linear function of speed, the power-loss curve is nearly parabolic.

Test equipment

Accompanying images show the test equipment and The test hardware table lists a few of its details. The software used, DASYlab, is a graphical programming language. It is programmed by placing block diagrams representing data collection operations on a screen and connecting them with “wires” to control data flow. In the system used here, processed data is written to disk in a tab-separated format suitable for further analysis using Microsoft Excel.

Programming the data collection: The DASYlab block diagram provides an example programming screen. Each block represents an operation on the data such as collecting, scaling, saving to disk, and displaying. This programming method is faster than writing code. For example, the voltage output from the torque transducer, encoder, and thermocouples was connected to the electronic interface box. This box has a built in reference junction for the thermocouples. The device also has digital and analog outputs but these were not used. The interface box scans its inputs and converts from analog to digital values. These are passed to the computer through a USB connection at about 1Hz. This is relatively slow for data acquisition, but more than adequate for these quasistatic tests.

In the DASYlab program, the first box is an input box that “talks” to the hardware and places the input values on its outputs in digital form. Typically this is a special module that works only with particular hardware. Most other boxes do not depend on the type of hardware in the system. The other boxes used are numerical displays, graphical displays, and output boxes to record the data on disk. These boxes have corresponding components on a display screen. This screen can be a virtual instrument, that is, it can look like instruments such as voltmeters, oscilloscopes, and chart recorders. For this test the program converts the inputs to engineering units and displays the values several ways. Digital displays show the current numerical values of inputs.

Another display, an XY-plot, shows rotation on the Y-axis and torque on the X-axis. This feedback gives a preview of results. It can save much time because if something is wrong, such as a broken wire or failed thermocouple, it quickly becomes apparent. The test can be stopped, the problem corrected, and the test resumed. A problem that goes undetected until the data is analyzed wastes the entire test period.

A disadvantage of DASYlab is that this program had to be written with the computer attached to the interface hardware. It would be a great advantage to write the program sitting in front of a desktop computer rather than working in the test area using a laptop.

Details of the analysis

Backlash and Compliance: One advantage of automated data collection is the larger amount of accurate information than can be manually collected in a reasonable period. The additional data gives a better picture of the equipment characteristics than would otherwise be possible. In Backlash and compliance, the red line simulates points collected when the torque was varied from zero to maximum, to minimum, and back to zero three times. (The data shown are not actual values but they are an accurate representation of the type of data collected.) The data showed good consistency and repeatability, which produces confidence in the results. For instance, the blue line shows the curve fitted to the backlash and compliance data. The length of the vertical line at zero-load is reported as backlash. The slope of the lines fitted to the observations is the stiffness. This is a conservative method for determining such values. The normal manual four-point test would have given both lower backlash and compliance numbers. The four-point test uses two torques that are just a little higher than breakaway torque in each direction and two torques that are a quarter to one half of the full load torque.

Converting from manual to automated testing: The first use of an automated system involves debugging because the test system, as well as the tested device, may have problems. An advantage to starting this system was that previous manually collected results were available for reference. Problems with the test system are seen quickly. For the first test, some manual measuring devices were used in parallel with the new test equipment. This either verified the results or showed problems. For example, an incorrect scaling factor was quickly detected and corrected. This illustrates one principle of successful testing: Check the calibration of the test equipment before running the tests.