The development trend of RF measurement instruments under the condition of increasingly dense spectrum

Due to market factors, there has been a demand for test instruments to evolve as fast as wireless technology itself. For example, the ability to test low-level signals is becoming increasingly important, not only to detect interference, but also for planning wireless systems. This is because the RF spectrum is becoming increasingly crowded as mentioned above. In fact, because of the complexity of today's wireless signals, field test instruments are required to provide laboratory-grade performance. 

To ensure accurate measurements of network performance requires more than just high performance. As a field instrument, as shown in Figure 1, it must be easy to use, allowing field engineers or technicians to complete measurements with only a few keystrokes. Another key factor is size and durability. Since many workplaces are located in the field tower, the instrument must be able to withstand harsh weather and must be lightweight so that users can carry it to a long distance. It is 

not easy to find an instrument that meets the above requirements. To help simplify the selection process, this article will focus on the key factors in each requirement. 

Performance 

It is no longer a good idea to say that field instruments are inferior to bench instruments in the laboratory. Field measurements require extremely high accuracy. For example, a handheld spectrum analyzer is a common instrument used to measure low-level signals in the field. For accurate measurements, the instrument is required to display an average noise floor level of -153dBm at 1GHz so that the measured signal can be located higher above the noise floor. A few years ago, such performance was only possible on a test bench. But now almost all instruments can have such performance. 

As more 802.11 access points are installed, interference in the 2.4-5.8GHz frequency band increases. For this situation, the carrier-to-interference ratio (C/I) measurement is important because it allows access point installers to easily determine whether the interference level will cause user difficulties. This measurement can also show whether it is necessary to change to another access channel. Field testing must have a wide frequency range (preferably 9kHz-20GHz) to properly install and maintain 3G base stations. Harmonic measurements up to 13GHz and above require higher bandwidth. Wide frequency coverage is also important for spectrum monitoring. In addition to excellent dynamic range, it allows spectrum monitoring to achieve high accuracy. Figure 2 shows the advantages of a wide dynamic range. 

Field on-site spectrum monitoring instruments must also have a deep memory so that traces and scans can be stored and recalled. To effectively monitor a site, a user may need to store 13,000 traces, especially when testing intermittent interference. Instruments that allow the use of external storage devices such  as USB

flash drives make it easy to transfer large amounts of data to a computer for further analysis. Fast scanning is another important requirement for field testing today. Those that can automatically establish the fastest scans consistent with the required precision measurements will meet the needs of speed, accuracy and flexibility. If the instrument has an internal demodulator for AM, narrowband FM, wideband FM and signal sideband demodulation, it will be easier to identify interfering signals.



Figure 1: Anritsu spectrum analyzer MS2724B, frequency range 9 kHz to 20 GHz. 

Ease of use 

As the new wave of communication technology is developed, it is difficult for design engineers in standards committees to keep up with the development of various standards related to wireless technology. For field engineers and technicians, this is almost impossible. This is why it is necessary for instruments used in the field to be simple to use and have automatic measurement functions. [page]

The most useful built-in measurements should be the most versatile. Built-in measurements, including field strength, occupied bandwidth, channel power, adjacent channel power ratio, AM/FM/SSB modulation, and C/I ratio, can be made with the simple push of a button or two. 

Reducing the number of parameters that need to be set also improves accuracy and speeds up testing. The technician can fix the input attenuation to the reference level, and the RBW/VBW and span/RBW ratios can be set to the optimal values ​​required for the measurement. This further reduces the technician's burden and reduces the opportunity for error. 

Trace storage can also simplify measurements. If the instrument can store a large number of traces, they can be copied to a PC and used as a reference for future measurements or for post-analysis to detect interference ambiguity. 

Remote control tools are also very useful. It is very beneficial for an engineer to be able to control a test instrument from a desk that is miles away. The engineer can view the display and remotely control the instrument, allowing an experienced engineer to monitor multiple sites in real time in a convenient manner. Figure 2: Results show the wide dynamic range required 



to measure a -114dBm signal with a -22dBm interferer at an offset of 20KHz  . Field Applications  Certain tower-mounted locations require instruments that are very small and rugged. Over the years, field users have proven that there is a big difference between portable and handheld instruments. Many times, the instruments weigh 20-40 pounds, which is cumbersome when they must be carried to harsh mountainous areas.  Fortunately, today's field test instruments have all the measurement functions installed in a lightweight and durable chassis for easy use. The fully configured instrument weighs only 7 pounds, including the weight of the battery, and now can make measurements that previously required instruments 3-4 times heavier. This allows the instrument to be carried anywhere, including the top of a tower.  Durability is also a consideration, and today's field instruments are required to be military-grade. In addition, a large and bright LCD is required to view test results in all conditions, including bright sunlight.  Conclusion  The RF spectrum congestion caused by the deployment of 3.5G/4G networks has forced field test instruments to change accordingly. Today, field test instruments must provide laboratory-grade measurement accuracy while being easy to use, small, lightweight, and durable. Selecting the right test results based on these criteria will benefit the deployment, installation, and maintenance of wireless networks.