Communications Test Advances

Modular test instruments can solve development, commissioning, and troubleshooting budget conflicts.

Based on the volume of specialized test equipment introduced in 2005, the communications industry must be thriving. Instruments addressing optical fiber, copper, and wireless components and networks cover product development, installation, commissioning, and troubleshooting activities. New or enhanced capabilities were added in both hand-held and benchtop formats.

When gathering information about these test instruments, we asked manufacturers to relate a product's intended purpose to its form factor and contrast the provision of comprehensive vs. very specific test solutions. A good starting point from which to discuss their responses is the matrix presented in Table 1. In addition to identifying hand-held tools with field test, the table shows a trend toward greater availability and use of hand-held instruments as the adoption of a particular communications technology progresses.

Table 1. Use of Hand-Held or Benchtop Instruments According to Application and Technology Adoption StageCourtesy of Sunrise Telecom

In discussing Table 1, Cyrille Morelle, director of product marketing at Sunrise Telecom, said,  In the telecommunications market, where budgets are monitored closely, most carriers delineate between applications that require portable equipment and those that can be performed in a lab setting. Typically, field installation, troubleshooting, and repair fall in the former group,• he explained,  and interoperability tests, quality control, and load testing in the latter. Of course, no liabilities in terms of quality and performance should be encountered in the lab tests. 

If you are familiar with Sunrise Telecom equipment, you might assume such a view to be natural for a modular instrumentation manufacturer. However, Mr. Morelle points out that the features, resolution, and accuracy of hand-held equipment have significantly advanced in recent years, blurring differences between benchtop and hand-held instruments in these areas.

As telecommunications technologies have become more complex and test requirements more demanding, hand-held instruments have been developed to address the need to monitor, troubleshoot, and repair in the field. These tools meet industry standards just like their benchtop counterparts. If this is the case, then what advantages does the benchtop format still have?

Part of the answer was provided by Craig Schober of Berkeley Vari-tronics Systems.  Bench measuring instruments such as signal generators, oscillators, and spectrum analyzers generally are used by engineers and scientists in laboratory environments to support the design, manufacture, and test of wireless and RF equipment. These intended applications require a high degree of analysis and accuracy. As a result, bench instruments tend to be complex in their underlying design and architecture, require considerable processing and computational power, may be too bulky for portable use, and can be expensive.

Aeroflex

 Hand-held instruments, on the other hand, are needed by technicians for deployment and maintenance of services,• he continued.  In most cases, portable instruments are not expected to provide analysis of complex waveforms or patterns, for example, but rather numerical measurements and simple information like signal strength or noise level. As a result, the underlying circuitry is far simpler, making possible lightweight, portable, and relatively inexpensive test tools. Nevertheless, since hand-held instruments are intended for field use, they must withstand harsh environments while providing long battery life. 

The latest of the company's hymenopteran-inspired products is the BeeKeeper•  Windows software application that graphically and textually scans, monitors, and logs medium access control (MAC) address information for all 802.11b WiFi networks. The BeeKeeper receiver module is an application-specific, passive, nonintrusive unit that monitors all 14 network channels.

Offering yet a third view was Hugo Draye, product manager, Datacom Group at Fluke Networks:  Hand-held instruments can and do achieve accuracy levels that are equal not only to bench instruments, but also to laboratory standards.• This strong statement may not generally be true but has been substantiated for the company's DTX Series Cable Testers.

Because of the high frequencies involved in Cat 5e, Cat 6, and 10GbE applications, the relevant standards define a higher level of accuracy to ensure that meaningful measurements are performed over the extended frequency range. For example, the ISO standards define an accuracy level IV associated with Class F links in the 1 to 600-MHz range. Greater accuracy is required because Class F has good crosstalk performance, meaning that the crosstalk signals are very small and difficult to measure.

 The DTX Series Testers meet or exceed the accuracy standards not only when tested alone, but also with the relevant adapters,• Mr. Draye explained.  Accuracy specifications and claims for the DTX Series have been independently evaluated and confirmed by Underwriters Laboratories. In addition, Fluke Networks has evaluated the performance of the DTX Series, and in many instances, the accuracy equaled that of the laboratory standard. 

The comments presented from three manufacturers of hand-held instruments have been very positive with regard to the capabilities of tools in that format. Extensive analysis features, together with considerable processing power, are the domain of benchtop instruments and generally not available in hand-held tools.

Manufacturers of benchtop instruments also have points of view on the hand-held/benchtop debate. For example, Francesco Lupinetti, CTO at Aeroflex Test Solutions, commented,  The real difference [between hand-held and benchtop instruments] resides in the particular application and the price that a customer is willing to pay to satisfy a requirement. Traditional benchtop instruments are used during integration, validation, verification, conformance, and manufacturing test. These activities generally are the most technically demanding, corresponding to a high level of accuracy and consistency.

 In contrast, hand-held instruments usually are utilized in the field for installation, commissioning, and maintenance purposes. The required levels of accuracy and consistency generally are lower for these applications than for integration, validation, verification, conformance, and manufacturing test,• he continued.  It follows that hand-held instruments often will have a reduced form factor and be less expensive than their more feature-rich benchtop counterparts. 

Interestingly, Mr. Lupinetti noted the lack of a smooth price/performance transition from less-sophisticated hand-held to feature-rich benchtop equipment. This gap is the target area for Aeroflex's highly integrated point solutions such as the PMR/TETRA Radio Test Set as well as scaleable cPCI/PXI/PXIe-based test systems.

How Many Instruments Do  You Need?
In the future, as Internet protocol (IP)-based services become ubiquitous, it will be necessary to test air and wired interfaces with the same equipment. A technician will want to ensure that the entire device is working and not just portions of it. Consequently, it is Mr. Lupinetti's view that  more functionality will be merged in single test products to cover all interfaces and features as well as test scenarios and applications. The only exception to this evolution will be for very special and simple tests such as the on/off connectivity of a DSL line where the price of the point solution will remain low and its implementation and characteristics very simple. 

This conclusion is shared by Fluke Network's Mr. Draye.  An integrated wired/wireless tool, such as the Ethernet Network Assistant Wireless, that examines traffic levels on switch links, explores paths to network servers, and discovers devices and services on the wired side of the network gives the technician a more comprehensive view of the network environment, speeding problem discovery and resolution. Using multiple tools would take more time, be more cumbersome, and not be as efficient. 

LeCroy

The practical problems of greater operational complexity and a longer learning curve balance the possible efficiency of comprehensive instruments. These drawbacks were highlighted by Francis Sideco, product marketing manager at Comarco Wireless Test Solutions:  Depending on the design of an instrument's software, greater capability brings with it greater complexity and a high learning curve. Typically, all-in-one tools cannot be designed for the specific needs of particular applications. In contrast, purpose-built tools that focus on solving a smaller set of problems can include time and work saving features specific to those problems, improving operator efficiency and productivity. 

Comarco's Seven.Five field measurement system is an example of a test product with broad capabilities but focused on only wireless phone performance. Applications include detailed analysis of cellular networks; simultaneous voice, data, and video service testing; end-to-end wireless data application validation and performance analysis; coverage and service quality testing and mapping; and advanced network protocol diagnosis.

To address the specific needs of particular applications, Sunrise Telecom's new Scalable Test Toolkit (STT) concentrates related functionality in separate modules. The Optical Network Expert (ONE) module handles synchronous optical network (SONET) and synchronous digital hierarchy (SDH) testing from 64 kb/s to 10 Gb/s, offers electrical and optical interfaces, and provides jitter measurement.

The STT Dispersion Test Module (DTM) supports network upgrade to OC-192/STM-64 or 10GbE data rates where dispersion control is critical to reducing errors. Specifically for 10GbE networks, the Ethernet Plus Module features one to 16 simultaneous tests, auto-negotiation and flow control, and packet capture and decode.

Similarly, Tektronix has targeted the particular test requirements of triple-play service deployment over universal mobile telecommunications system (UMTS) radio access networks with the NSA18 protocol analysis platform. NSA18 probes are daisy-chained to each other and connected to the controlling PC. The system collects data and leverages the capabilities of the Network and Service Analysis (NSA) for UTRAN software package. Features include automated topology discovery, detailed analysis of interactions between UMTS network components, portability of test equipment between sites, and a number of configuration options.

The company's Keith Cobler, market development manager, Network Diagnostics and Management, commented,  Efforts to merge more functionality into a single test instrument are apparent in the Network Service Analyzer. The NSA18 provides scalability to meet low-cost as well as technically demanding network measurement applications.

 However, by focusing on the test and measurement end user, it has become apparent that, in some cases, separate, not merged, instruments may be preferred. For example, for 3G network troubleshooting and maintenance,• he continued,  there are RF technicians and network technicians. Their test equipment needs are fundamentally different. 

Product Innovations
Whether hand-held or benchtop, communications test instruments can be categorized as application-specific or general-purpose and within each grouping as passive, active, or intrusive. For example, Anritsu has introduced the MS2026A VNA Master , a hand-held vector network analyzer (VNA) that performs corrected one- and two-port measurements from 2 MHz to 6 GHz. This is a general-purpose tool intended for field use but with sufficient accuracy and dynamic range to address manufacturing test applications.

Similarly, the company's hand-held MS2721A Spectrum Master• Spectrum Analyzer, capable of measurements to 7.1 GHz and featuring independent settings for resolution and video bandwidths, matches many benchtop analyzer specifications.

Fluke Networks

In contrast, the Willtek Communications Model 9102 Hand-Held Spectrum Analyzer includes capabilities specifically focused on antenna system testing. When used with the 9131 EMF Measurement Option, the analyzer measures radiation from base stations and radio broadcast stations. Test results are provided in report format via the associated 9100 Data Exchange Software option.

LeCroy's UWBTracer is an example of an application-specific, passive tool. Wireless USB (WUSB) is defined in the USB-IF standards, and one implementation uses the WiMedia• Alliance's Ultra Wideband (UWB) common radio platform. The UWBTracer acquires and analyzes over-the-air UWB traffic. The companion UWBTrainer is a traffic-generation system, which falls into the application-specific, active test set classification.

Another application-specific, passive tool, but targeting digital subscriber line (DSL) applications, is the DSL Xpert• from TraceSpan• Communications. This device nonintrusively records and analyzes the communications between the digital subscriber line access multiplexer (DSLAM) and customer premises equipment (CPE), providing not only relevant measurements but also warnings of asymmetric digital subscriber line (ADSL) stand-ard incompatibility. Because the DSL Xpert does not emulate either the DSLAM or CPE and is not based on a proprietary ADSL chip set, it is an independent, unbiased system that can be updated as the ADSL standard is amended.

Agilent Technologies

EXFO launched a number of optical physical layer products and Ethernet/SONET test modules in 2005, indicative of the company's expansion into network analysis. When optical physical layer features and GbE, 10GbE, or SONET network-specific analysis capabilities are combined, a more comprehensive test solution results. The FTB-400 Universal Test Platform is an example of an architectural approach that supports portable and integrated test solutions.

Depending on your application needs, an FTB-400-based test system can be assembled from any of EXFO's FTB modules, including optical time domain reflectometers (OTDRs), optical loss test sets (OLTSs), polarization mode dispersion (PMD) and chromatic dispersion (CD) analyzers, optical spectrum analyzers, multiwavelength meters, SONET/SDH analyzers, and Ethernet testers. The custom integrated solution complies with GR-196-CORE drop-test standards, and the tough shell and rubber bumpers ensure that the FTB-400 and its modules survive splashes, knocks, and temperature extremes. FTB-400 instruments are application-specific and can be both active and passive.

As IP becomes more pervasive, and with it voice over IP (VoIP), guaranteeing audio quality equivalent to that of the plain old telephone system (POTS) is important. Microtronix Systems provides VoIP manufacturers with an IP phone audio performance test solution. Unique to the test approach is direct digital communications with the phone, avoiding any analog conversion. Highly repeatable and accurate measurements result from using this application-specific and active test product.

Finally, there is a class of benchtop instruments intended for research and development applications unlikely to spawn hand-held counterparts. A good example is the Agilent Technologies Model 83496A Clock Recovery Module. This plug-in module for the company's 86100C Wide-Bandwidth Oscilloscope provides a continuously variable clock rate from 50 Mb/s to 13.5 Gb/s while maintaining less than 300-fs rms jitter.

In addition, the company introduced the Model N4010A Wireless Connectivity Test Set with Bluetooth• functionality. The instrument can act as a Bluetooth master, perform inquiry, and establish a paged connection in the test mode or the normal mode. An integral sequencer runs tests using standard or user-specific settings. This test set is an example of an integrated product that provides a complete solution to test problems within a particular technology.

Conclusion
Many comparisons of hand-held vs. benchtop instruments have been presented, most provided by manufacturers of one or the other format. JDSU produces both hand-held and benchtop optical power meters, a position perhaps more favorable to an unbiased opinion. According to Jim Nerschook, the company's vice president,  The OLP-55 Hand-Held Optical Power Meter is small, lightweight, splash-proof, and inexpensive. The key parameters are limited to three or four fixed wavelengths, a -60- to +10-dBm dynamic range, and adequate accuracy.

 In contrast, the benchtop MAP meter offers calibration over the entire 800- to 1,700-nm wavelength range and very high accuracy. Additional specifications for the type of detector, polarization dispersion loss, noise level, linearity, and return loss are provided,• he explained.  Fast measurement speed ensures high manufacturing throughput, and the benchtop format is a better fit for rack-mounted test applications. Typically, if there is a need to measure a particular parameter, price is a secondary consideration. 

Hand-held tools must be used where portability and cost are paramount and benchtop instruments where detailed analysis and a high level of data processing are involved. Creating a more comprehensive solution within a single tool is helpful but may be restricted in its application unless based on a modular architecture. You need the proper tool for the job.