High-frequency instrument manufacturers have adopted numerous modular formats based on fitting modules into a mainframe-type chassis, such as AXIe, PXI, and VXI modules, but one modular format has taken off quite nicely even without the aid of “link-to-tradition” mainframe chassis: USB modules. These modules may be as simple as a small package with an input and output and USB port. They operate as stand-alone modules, without need of a plug-in chassis—many without need even of a power supply (in addition to the USB supply).

Companies such as Vaunix Technology Corp. have aggressively developed numerous measurement functions in compact modular form, all of which can be connected to a computer’s USB port and controlled by software on the computer. Vaunix has created modules for such functions as phase shifting and digital attenuation over broad operating bandwidths. The firm’s “Lab Brick” USB-powered test equipment includes numerous models of signal generators in the LMS Series (Fig. 2).

2. The LMS Series of Lab Brick signal generators includes models reaching as high as 4000 MHz. (Photo courtesy of Vaunix Technology Corp.)

The LMS Series of Lab Brick signal generators from Vaunix includes models for use from 70 to 450 MHz, 250 to 1500 MHz, 600 to 3200 MHz, and 1000 to 4000 MHz. The miniature signal generators allow users to select from an internal or external 10-MHz frequency reference oscillator; they can run on just USB power, with no additional battery required. These signal generators do not skimp on performance because of their small size, and can provide as much as +13 dBm output power to 4000 MHz. They tune frequency with 100-Hz frequency resolution and can switch frequencies and output levels with 100-μs switching speed. The signal generators offer phase-continuous linear-frequency sweeping capability, and military testers will be pleased to find that pulse modulation is available as an option.

A company long associated with rack-mount and mainframe instrumentation, Agilent Technologies, has shown that it can do quite well in the modular instrument arena as well. The firm supports a variety of different test module formats, including AXIe, PXI, VXI, and even USB modules. Agilent also offers “LXI: Going Beyond GPIB, PXI, and VXI,” a free-of-charge, 10-page application note (No. 1465-20). The document offers a comparison of various modular measurement formats, with a healthy push for LXI as a format to be considered.

Late last year, the firm introduced its model M9703A eight-channel digitizer based on the AXIe module format (Fig. 3). With its wide-bandwidth, real-time digital-downconversion (DDC) functionality, the digitizer module (and its phase-coherent acquisition channels) is ideal for making measurements in high-channel-count applications, such as in radar, direction-finding (DF), and satellite beam-forming systems.

3. The model M9703A eight-channel digitizer is based on the AXIe module format and operates from DC to 2 GHz. (Photo courtesy of Agilent Technologies.)

The M9703A eight-channel digitizer operates across a frequency range of DC to 2 GHz with a sampling rate of 1.6 GSamples/s. It includes tuning and zooming capabilities to precisely set center frequency and bandwidth, as well as real-time decimation capabilities for tight control of dynamic range. The digitizer module is compatible with the firm’s 89600 Vector Signal Analysis software for advanced measurements, such as signal analysis and demodulation, under software/automated control.

4. This five-slot AXIe chassis holds five M9703A AXIe 12-b digitizers to form a 40-channel acquisition system. (Photo courtesy of Agilent Technologies.)

This AXIe digitizer module, when combined with one of the company’s two-slot or five-slot AXIe chassis, allows users to scale the number of parallel acquisition channels without the use of switches, reaching as many as 40 signal-analysis channels in only 4U of rack-mount space with five AXIe M9703A digitizers (Fig. 4). Such a measurement system allows simultaneous acquisition of data on a large number of channels under dynamic conditions, reducing test and calibration time.