While resolving RF interference problems in complex RF environments can be a tricky task, gapless recording offers a viable solution to the measurement challenges presented by the typical signal analyzer. The technique solves the problem of not knowing when or where an interference event will occur, or how long it will last, by enabling continuous acquisition of data over long durations. Because there is no gap in the data recorded, the signal-of-interest, such as an intermittent RF event, is easily captured.
Figure 2: In this block diagram, the signal analyzer in Figure 1 has been modified for gapless recording Click on image to enlarge
An example of a signal analyzer modified for gapless recording is illustrated in Figure 2. It is the same signal analyzer shown in Figure 1. However, it now includes a high-speed data link or bus that allows the engineer to move data from memory as it is acquired. By bypassing processing and display updates, and writing acquired data directly to final storage using a circular Random-Access Memory (RAM) buffer, it’s possible to create high-bandwidth recordings with no gaps in the data. With a circular RAM buffer, the engineer can simultaneously write to and read from it. When recording at wide bandwidths for long durations, a Redundant Array of Independent Disks (RAID) storage system is required.
One such wideband gapless recording solution is Agilent Technologies’ dual-channel M9392A PXI Vector Signal Analyzer, which can provide two independently tunable channels—each able to record data at 100-MHz bandwidth over many hours (Figure 3).
Click on image to enlarge
Figure 3: Agilent’s gapless recording system comes in predefined packages that rely on the wide bandwidth and fast throughput benefits of PCIe, and are used with either a regular PC hard disk drive or external mass storage. The system shown here offers 32 TB of storage.
While wideband recording in an RF environment has proven itself useful as a characterization tool for long duration RF interference studies, powerful search tools can reduce the burden of searching long recordings for culprit signals. The Agilent 89600 Vector Signal Analyzer software, for example, can be used with the M9392A to provide key insight into the characteristics of the interferer and its effects on the victim signal in select data obtained during gapless recording. Using such software simplifies and reduces the time to find target signals-of-interest and also speeds up the process of analyzing and fixing problems.
It may also be helpful if the gapless recording solution sports key functionality like time-stamping so that recorded data can be mapped to an absolute time, triggering and pre-triggering. Pre-triggered data provides engineers access to signal data leading up to a specific trigger event.
Another key capability is dual-channel recording. In a single-channel recording system it can be difficult to trigger on only the desired signal. As a result, more data is usually recorded than is actually required to ensure the interference event is captured. This additional data takes time and resources to process. A dual-channel recording system like the M9392A reduces the likelihood of false triggering and provides an innate ability to record just the data that’s needed. Signals can be acquired and triggered on one channel, while being recorded on the other. By enabling more efficient discovery of the signals in the RF environment, such discretionary triggering saves a great deal of time and also helps the engineer more effectively solve interference problems.