NI responds to Agilent’s comments on VSA comparison

Furthering a debate about vector-signal-analyzer performance comparisons, a National Instruments spokesperson has responded to Agilent Technologies’ earlier comments. Agilent in turn had been responding to an NIWeek demonstration and several online videos that compare the NI PXIe-5665 and the Agilent PXA. Read my earlier post here. NI’s response follows:

“For a typical automated test use case, all measurement times include time to start the acquisition of the RF signal, time to acquire the RF signal, time to calculate the measurement, and time to transfer the measurement back to the PC. In this automated test use case, the last part (time to transfer the measurement back to the PC) is required when a customer is testing a device and needs to record the information to disk or determine if the device under test passes certain criteria. When we performed the benchmark in the video, we took the transfer time into consideration in addition to sweep and measurement times. Including the transfer time, the NI 5665 is still close to 15X faster than the Agilent PXA.

“Every instrument has a sweet spot for getting the best results on a particular test, and it wasn’t our goal to simply measure the dynamic range of each instrument. For this video, we tried to put both instruments into a typical high performance setup that a customer would use.

“For example, the Agilent PXA has a Fast ACPR mode for faster measurements; however, you cannot perform noise correction in this mode; you end up taking a hit on dynamic range for an improvement in speed. The benchmarks performed in the video account for the best possible dynamic range achievable on the setup, which includes a SAW filter with a nominal frequency of 248.6MHz. In the above mentioned setup, using Fast ACPR mode, you achieve -75 dBc ACPR in the upper channel on the Agilent PXA with a minimum of 60 ms (including transfer time to the PC using GPIB cables and no averaging). The NI PXIe-5665 does not have any such tradeoff, as we can achieve -81 dBc in 5 ms (no averaging), making us much faster than the Agilent PXA (even in its Fast ACP mode). We acknowledge that the PXA is capable of better ACPR numbers with a notch filter. The NI PXIe-5665 will also provide better results with such a filter. Moreover, in a real world situation, most engineers apply some kind of averaging to their measurements to achieve the best possible accuracy. For the demo in the video, 10 averages were used for the ACPR measurements, resulting in about 430 ms on the PXA and about 30 ms on the NI PXIe-5665.

“In the TOI measurement, both instruments were set up for 0 dB of mechanical attenuation (as opposed to the 24 dB of attenuation referenced by Agilent), and +20 dBm was the best TOI that we could get out of the Agilent PXA at the 0 dB of attenuation. As expected, the TOI improves when more attenuation is applied. The PXA does achieve + 36 dBm with 24 dB of attenuation; in fact the NI PXIe-5665 achieves better than + 36 dBm with the same 24 dB of attenuation.”