The New VNA Masters At A Glance

Portable instrumentation used to imply a digital multimeter (DMM) or some other fairly simple measurement tool. But the latest family of VNA Master portable VNAs redefine the amount of measurement capability possiible from a handheld package. Ideal for cable and antenna measurements in the field, the VNA Master instruments include models MS2026B with a frequency range of 5 kHz to 6 GHz and model MS2028B, with coverage of 5 kHz to 20 GHz. And, although portable units, these are not instruments to be taken lightly, with dynamic range extending to 65 dB through 20 GHz and measurement accuracy buttressed by a powerful 12-term error-correction algorithm. Capable of running for more than 2 hours on battery power, these analyzers can bring laboratory-like measurement accuracy and precision to any site, whether indoors or outdoors.

Both instruments are true two-port vector analyzers with integral low-noise test sources that can be automatically switched to provide measurements of all four scattering (S) parameters with a single connection to a device under test (DUT). Those integral sources feature frequency accuracy of 1.5 ppm, and enable measurement resolution of 1 kHz through 20 GHz. The built-in sources provide as much as +3 dBm test port power to 3 GHz and - 3 dBm test port power through 20 GHz.

In addition to the simplicity of evaluating a DUT's forward and reverse transmission characteristics, the new VNA Masters bring a new level of speed to portable vector network measurements with the switchedsource architecture, typically providing switching speed of 525 μs/point when operating from 5 kHz to 6 GHz and 750 μs/point when operating through 20 GHz. For measurements that require large numbers of data points, such as antenna measurements, this type of speed provides near instanteous updates of any adjustments made to a DUT, even when those measurements are being made in the field. It is this rapid tuning speed, and the fast on-screen update rates of the Vector Masters' full-color TFT display screens, that enable practical filter tuning with the portable VNAs. One of the more common measurements performed in the field at communications installations is to determine the loss of long runs of coaxial cable or even to find faults in those cables. The VNA Master portable VNAs can perform these measurements on coaxial cables as well as on waveguide (using waveguide adapters). With access to one end of a long cable run, the VNA Masters can determine the loss of the cable by making a one-port reflection measurement. This is done as a single-connection, "round-trip" measurement, sending test signals from the instrument port, through the cable, to a short connected to the other end of the cable, and then measuring the levels of the reflected signals returned to the VNA Master's test port. Because the test signals are covering a total distance that is twice the length of the cable being tested, the measured results are automatically divided by two within the analyzer to provide valid information on the actual loss of the cable. Of course, the accuracy of these measurements relies on adequate test port power from the VNA Master, in order to overcome the total losses of the cable, especially for long runs. The cable connectors and any adapters used should also provide good impedance matches (low VSWR) ot prevent reflections that can degrade the measurement accuracy. The VNA Masters work with a 12-term shortopen- line-thru (SOLT) calibration to achieve high directivity for such measurements, typically 42 dB to 5 GHz, beter than 36 dB to 15 GHz, and better than 32 dB through 20 GHz.

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