In what ways is using USB-based modules over traditional bench instrumentation beneficial when performing fundamental RF measurements?

Leonard Pelletier, Applications Support, Freescale

Freescale’s RF product group activities include demonstrations of its RF power devices' performance capabilities at various trade shows and events. Setting up these offsite demonstrations requires a significant quantity of test equipment and power supplies in order to support a re-creation of standard operating conditions for its high-power, amplifier line-up assemblies. At times, the overall mass of the test equipment can outweigh the items being tested, and it becomes slightly unclear as to which item is actually being demonstrated, the RF devices, or the RF test equipment.

Making travel demonstrations easier is the universal serial bus (port) (USB)-based RF test equipment. While the overall maximum test capability of these USB-based equipment sets is slightly less sensitive, slower, and has a less dynamic range than their full-sized, large-boxed lab bench cousins, in most cases, the test capability provided is more than adequate for demonstrating the RF performance capability — with no degradation in test functionality. With these, canned software programs that accompany these USB test systems, can port the collected data into other data collection software tools. This allows users to combine the data from the USB-based testers with additional data that was collected using more conventional general purpose interface bus controlled test equipment sets, and then post process the data to show real time, overall system performance.

There are two limitations to the USB-based test equipment. One is the relatively low limited DC current capability, presently limited to 900 mA @ 5 VdV, with the latest USB 3.0 standard. Typically, this is enough current to power most sensor heads and monitoring ports without the use of an external power supply. The other limitation is the expected lifespan of a standard male USB connection, which is limited to an average lifespan of about 1,500 insertions and extractions. That may seem like a large number, but there have been several occurrences of a USB port connector wearing out and becoming intermittent or damaged due to excessive or improper insertion.

After a thorough investigation of the pros and cons, we are convinced the benefits afforded are significant — thereby relegating the older and heavier lab bench varieties as a thing of the past.

Scott Blanchard, President, Vaunix

USB-based modules are providing the streamlined functions, cost, size, power, and simplified programmability test engineers are looking for. Even the most fundamental RF measurements are becoming complicated. Building a test stand with traditional instrumentation becomes expensive, and quite often you have overkill in one place, in order to make up for a deficiency somewhere else. Vaunix offers various programmable USB signal generators for as low as $1,400. USB equipment is not only cost efficient, but the current draw is far lower. This eliminates the need for forced cooling in, and is the key to making an ATE stand portable.

As complexity increases, engineers want a simple and cost effective method for programming their test instruments. Vaunix offers a wide variety of easy-to-use drivers, along with sample programs that are easy for test engineers with even the most basic software background to use.

In our fast-paced environment, where time-to-market is key to securing market share, quick shipping is essential. USB suppliers, like us, recognize that to compete we have to deliver in days not weeks.
As our industry continues to evolve, the cost advantages of USB will be recognized in reduced capital expenditures, and in the reduced time for programming, reduced energy costs, and reduced time-to-market.

Ben Maxson, Applications Engineer, Copper Mountain Technologies

USB based instruments are gaining popularity because they are much more flexible and accommodating to the applications in the RF and Microwave space. USB is obviously a ubiquitous technology, and that point of connection really eases data transfer of test results in any system. Engineers have often struggled with getting results from their VNAs or other machines after testing, because older instrumentation can be incompatible with the technology commonly used in labs today. With USB driving data transfer, an engineer’s workflow can be sped up and interruptions for data transfer can be reduced.

On top of that, USB based instruments are typically more portable and smaller, because the test system is streamlined. They can be transferred between locations and connected to different PCs without losing their essential test function.

Copper Mountain Technologies vector network analyzers, for example, save all their data on an external PC, completely separate from the measurement hardware of the VNA. The Vector Reflectometer family is particularly unique in the test and measurement world, for example, because its extremely compact measurement module uses a USB connection as a single point of connection for power and data transfer. There is definitely a trend toward USB based instruments in T&M for their ubiquity, ease of use, and the flexibility they offer when incorporating an instrument into an existing lab or field setting.

This article appeared in the September/October print issue.