RF test on the go

The Willtek Communications Model 9101 portable spectrum analyzer eliminates the need to carry a bulky instrument to the field when you need to make RF spectral measurements up to 4.0 GHz. The 9101 lets you measure signals in cell phones, personal communications services (PCS) products, Bluetooth devices, and wireless LANs, and you won't need a child's wagon to transport the 2.5-kg, 355x190x85-mm instrument to your test site. And if you stick close to home, you'll find it fits comfortably on your lab bench.

Perhaps for these reasons, Test & Measurement World readers have voted the Willtek 9101 the 2004 Test Product of the Year. They chose it from among the 12 winners of the annual Best in Test Awards that we announced in our December 2003/January 2004 issue. (For the complete story about the Best in Test Awards, see www.tmworld.com/bit.)

The Willtek Model 9101 portable spectrum analyzer.             Product manager Ludger Boeggering (left) and project leader Georg Klein led the development of the Willtek 9101 handheld spectrum analyzer.

Engineers primarily use the Model 9101 to make spectral amplitude measurements on signals from wireless devices, but the applications go further. Ken Hall, EMC engineer at Hewlett-Packard (Roseville, CA), voted for the 9101 because he sees applications for it in attenuation measurements at open-area test sites. Standards have pushed EMC measurements above 1 GHz, and Hall needs measurements at frequencies up to 2.4 GHz. He likes the 9101's small size and weight, but he also likes its programmability. Hall says that the programming commands mimic those of larger, heavier instruments, which makes it easier to automate the instrument with existing software.

Designing an instrument with such a wide frequency range and small size was no easy task. Capacitive effects on components can cause their performance to degrade at high frequencies. To find suitable components, project leader Georg Klein organized a joint project with a university—Germany's Ruhr-Universitaet Bochum. Willtek uses components as small as 1 mm in size. Klein notes that "Placing these components on the PCB required the latest production technology."

To meet the size requirements, Klein and his team of engineers developed digital video filters and digital resolution-bandwidth filters. Digital filters offer advantages in size and stability over analog filters. Klein says, "We avoided errors caused by temperature drifts and mechanical impacts with digital filters. We also avoided long-term instability problems."

The engineers, though, didn't want to use a digital signal processor (DSP) to run the filter algorithms because DSP calculations slow the instrument's performance. Instead of using a DSP, Klein's team used a field programmable gate array (FPGA) that runs the algorithms faster, yet still allows for upgrades.

Boeggering says, "We see several markets and user groups for the 9101. There are the traditional markets in engineering and service . . . But there are other types of users and applications as well, such as interference measurements in biomedical environments and wireless toll collect stations, as well as WiFi (WLAN) installations. These applications require spectrum analysis in a highly portable instrument with a large, easy-to-read screen such as the 9101."