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40MHz network analyzer from OMICRON uses USB-equipped PC

Posted: 21 Jul 2005 ?? ?Print Version ?Bookmark and Share

Keywords:benchtop? bode 100? omicron electronics?

PC-hosted instrumentation fascinates me, as it often unleashes the horsepower of sophisticated lab gear right on my benchtop. Even though that's old hat these days, I'm always intrigued by a new package and eager to put it through its paces.

Paper tiger?

Unfortunately, pricing hasn't been established yet for this product (watch this space for updates on that). Worse, the firm's US offices say it's still "under development," while the European arm is rolling it out as a ready-to-go package. Is this a paper tiger?

When it finally debuts for real, the Bode 100 from OMICRON electronics promises to operate even with a modest 500MHz Pentium box. Your PC will also need at least 256MB of RAM, a CD-ROM drive, and a USB v1.1 or 2.0 interface.

The software is intended for Windows 2000 or Windows XP. Although the press release (on the left) seems to be written by someone who isn't well versed in the King's English, the Bode 100's machine-readable user manual is well written, and illustrated with color screen images.

A multi-function package

In essence, the Bode 100 comprises a multi-function hardware and software package that lets you measure the gain and phase of passive and active circuits, as well as systems. Your PC is connected to the Bode 100 hardware using USB. For its part, the hardware is equipped with BNC coaxial cable connectors for both low phase-error input channels, and for its signal generator's output. Inputs can be either low impedance (50 ohms) or high-Z (1 megohm).

You can use Bode 100 for applications such as the analysis of closed-loop control systems, video designs, or even RF circuits up to a modest 40MHz in frequency.

Although this isn't a piece of VHF/UHF RF test gear, the Bode 100 can measure impedance and admittance, as well as reflection coefficients, for many RF stages in the high-frequency portion of the spectrum. As such, it should find applicability in the design of IF (intermediate frequency) strips and other blocks, even in some RF systems with front-ends operating above 40MHz, and perhaps into the microwave regime.

A DDS source

In use, an internal bridge lets you make accurate measurements by connecting your DUT (device under test) to the Bode 100's DDS (direct digital synthesis) source. The unit can also make single-frequency and swept measurements.

Speaking of the system's data converter-equipped microcontroller-based DDS, it lets you adjust both the level and the frequency of the needed excitation that's applied to the DUT. In use, two receivers then process the DUT's response. Finally, a built-in DC converter generates all the requisite voltages for powering the circuitry. Check out the block diagram.

This mix of graphical software and compact hardware will let you do things such as measure the complex gain of amplifiers and filters, and watch what happens if you change their termination impedance. You can readily measure reflection coefficients and determine return losses. You should find that handy when measuring the impedance of many circuits, even very high-Q circuits such as quartz crystals.

Plots and charts

Once measured, the systems Windows software will generate a Smith chart for you, and create Bode plots of control circuits that let you see things such as group delay. The software even shows you how to connect your DUTs, drawing interconnection diagrams on-screen.

The software's user interface will also instruct you how to quickly calibrate to compensate for things such as phase shift in your cabling. If you need higher accuracy in the system's impedance/reflection mode, for example, you can readily compensate for the setup.

Without calibration the reference plane of the impedance measurement is at the hardware's BNC connector. If your DUT is connected with a cable, impedance isn't measured at the DUT input but at the input of the cable. Doing a calibration can let you make the measurement at the DUT itself.

Small frequency spans

In operation as a vector network analyzer, the Bode 100 combines a gain phase meter and an impedance meter, displaying measured values as a function of frequency. Due to its high resolution DDS, even extremely small frequency spans are possible, which is just the ticket for analyzing high-Q devices. In use, the system's frequency sweep can be linear or logarithmic to produce Bode plots in the whole frequency range.

Results can also be displayed as magnitude or phase, and you can show real and imaginary parts of impedance, as well as group delay, and more. Polar plots for gain and impedance measurements can also be generated. The vector network analyzer will operate from 10Hz to 40MHz, delivering 10mV RMS to 1V RMS into 50-ohm loads.

Last, but not least, the Bode 100 includes a sinewave generator that can sweep from 10Hz up to 40MHz. you can use it to help measure intermodulation distortion, or to generate amplitude modulation. It can generate an amplitude sweep from 10mV to 1V RMS. Two independent sinewaves can also be superimposed.

Once derived, measurement results can be used on your PC platform for additional analysis and post-processing, or they can be popped into other PC-hosted programs for documentation and communications.

- Alex Mendelsohn


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