Signal generators are found in almost every RF/microwave test lab but, more and more, they are also needed in the field. Unfortunately, most RF/microwave signal generators are designed for fixed, rack-mount installations. That is, except for the Lab Brick compact portable signal generators from Vaunix Technology Corporation. These low-cost test signal sources provide precise, stable output signals from 50 MHz to 6 GHz and can go where the test signals are needed. They can operate from battery power in embedded applications, from remote power supplies in automatic test equipment (ATE) systems, and, with their Universal Serial Bus (USB) compatibility and graphical-user-interface (GUI) software, offer simple operation from a laptop or personal computer (PC).

The Lab Brick signal generator family (Fig. 1) currently includes five members, 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 measures 4.90 x 3.14 x 1.59 in. (124 x 80 x 40 mm) and weighs less than 1 lb. (0.45 kg), but provides all the capability of a full-sized test signal source, minus the controls and displays. Those are provided by the host USB computer, via the GUI's simple control interface (Fig. 2).

In spite of their small size and price tags, the Lab Brick signal generators deliver full-sized performance. Frequency sweeps can be set with step sizes from 0.1 to 1000 MHz. The initial accuracy of a set frequency is better than 2 ppm. Over their different frequency ranges (see table), the signal generators deliver at least +10 dBm output power at an SMA output connector. For the highest-frequency model (LSG-602), output levels can be adjusted over a 50-dB dynamic range, from -40 to +10 dBm, with 0.5-dB resolution. The other four signal generators feature even wider output control of 55 dB, from -45 to +10 dB, with the same 0.5-dB resolution. Output power settings are accurate within +1.5 dB and -0.5 dB. In addition to controlling output power, the Lab Brick GUI allows an operator to turn on and off the output power.

The Lab Brick test signal sources are based on stable, phase-locked-loop (PLL) circuits using high-performance voltage-controlled oscillators (VCOs). The single-sideband (SSB) phase noise is what one might expect from a highquality test source. For the 250-to-1500- MHz model LSG-152, for example, the phase noise is typically -95 dBc/Hz measured at 10-kHz offset from the carrier and typically -115 dBc/Hz at 100-kHz offset from the carrier. The Lab Brick signal generators exhibit excellent spectral purity, with nonharmonic spurious no worse than -70 dBc for all models, and typically -80 dBc.

The signal sources feature low output VSWR of 1.50:1 for good impedance match to a device under test (DUT) and associated analysis equipment, such as an RF/microwave spectrum analyzer. Each 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 sweptfrequency 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 frequency step size but also frequency dwell time.

Each time a Lab Brick signal generator is plugged into a host computer's USB port, it is automatically identified as a new USB device by the computer, with a green LED on the Lab Brick signal generator illuminating to show a successful connection. The Lab Brick GUI software can be opened before or after a signal generator is connected to the computer, and will display the serial and model numbers upon finding an available Lab Brick signal generator. By opening multiple instances of the GUI, it is possible to control multiple Lab Bricks from a single computer.

The GUI allows control of the generator using a computer mouse or keyboard to enter data and change settings. For example, the mouse can be used to scroll through frequency and amplitude settings with up and down keys. Adjustments can be made with standard or user-defined step sizes. The GUI also features extensive help functions and links to additional information resources.

Each Lab Brick 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. P&A: from $1399 (50-to-250-MHz model LSG-251) to $1849 (1.5-to-6.0-GHz model LSG-602). Vaunix Technology Corp., 242 Neck Road, Haverhill, MA 01833; (978) 662-7839, FAX: (978) 662-7842, E-mail: VaunixSales@vaunix. com, Web site: www.labbrick.com.