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N9918B 26.5GHz “FieldFox” Microwave Analyser Keysight’s FieldFox range of handheld microwave analysers have impressive capabilities. These have recently been expanded even further; in particular, adding the 100MHz real-time bandwidth necessary to work with the new 5G mobile technology. W e reviewed Keysight Technologies’ N9917A Network/Spectrum Analyser in our June 2017 issue (siliconchip.com.au/Article/10686). We found it to be a comprehensive piece of test gear, providing many features useful to those working in RF fields. Depending on the options installed, its main functions include: • Spectrum analyser • Real-Time Spectrum Analyser (RTSA) • Vector Network Analyser (VNA) • Vector voltmeter • Time Domain Reflectometry (TDR) • Extended Range Transmission Analysis • Interference analysis • Cable and Antenna Analyser (CAT) Our previous article gave an overview of what these functions are and how they can be used. As we noted in that article, we do not have the experience or test equipment to do justice to such a specialised and advanced piece of equipment. If we had kept that one, it would probably be the most advanced piece of test gear in our laboratory. The same comments apply to the newer Analyser we are reviewing here, but even more so. The N9917A is touted as a handheld unit, but it weighs 3kg, so you probably won’t want to be holding it all day (unless you particularly want a forearm workout!). It is clearly quite rugged though; that’s important for a tool that could be used frequently ‘in the field’ and exposed to very trying conditions. A side strap makes it easy to carry and hold, and there is a folding stand to allow it to sit on a flat surface at a comfortable working angle. It has an internal, removable rechargeable battery for portable operation. The large LCD screen is supplemented by a comprehensive backlit keypad with large keys, meaning that the device is easy to use, even with gloves on. Three sides of the unit are decked out with various ports. The top sports the two main RF ports, an input for a GPS antenna and the external reference or trigger input. The right-side features an assortment of computer interfaces, including LAN, USB (device and host) and an SD card Review by Tim Blythman 80 Silicon Chip Australia’s electronics magazine siliconchip.com.au socket. These ports are protected by separate gasketed doors. The left side has connections for DC power to run the unit and charge the battery (provided by an external supply similar to a laptop PSU), bias power out and a headphone jack. There is also a speaker. The audio output can be used when working with AM and FM broadcasts, to listen to the demodulated audio. The space below these ports along the left-hand side leaves the perfect area to grasp the unit with the help of the side strap. New features The N9917A was – and remains – a very capable and well laid out piece of test gear, and would be well at home in the hands of even the most experienced RF engineer. Being from the same FieldFox range, it is no surprise that the N9918B looks similar to the N9917A that we reviewed previously. In fact, apart from the part number designation above the LCD screen, outwardly, the unit is otherwise identical. But there are differences. Table 1 shows the main difference in characteristics between the two units. As noted, the Maximum Real-time Bandwidth is now 100MHz up from 10MHz, but this is not the only change. Many of the other RF performance parameters, such as dynamic range, sweep speed and attenuator range have been improved. So, while the outward appearance is much the same, we would not be surprised if the hardware RF internals are quite different. Like the N9917A, many of the features are optional. That includes the ‘headline’ 100MHz real-time bandwidth (there is also a 40MHz bandwidth option; the default is still 10MHz). The only standard feature is the Cable and Antenna Analyser. Most options do not have to be selected at purchase time, but are simply enabled through a licence key (although you’ll probably get a better deal if you spec all the options you need initially). You can see a complete list of the software-enabled options in Table 2, overleaf. There is also a detailed configuration guide which shows what options are available and what their respective software and hardware requirements are. You can view this online at siliconchip.com.au/link/ab1v 5G support One of the fields where the N9918B will become very useful is in the design, testing, implementation and maintenance of 5G mobile networks. It appears the critical feature here is being able to do real-time analysis of signals with 100MHz of bandwidth. While the existing 5G networks in Australia are running at a modest 3.5GHz, Telstra is trialling operation at millimetre-wave frequencies around 26GHz; perfectly within N9917A N9918B Maximum Frequency 18GHz 26.5GHz CAT/VNA Start Frequency 30kHz 30kHz SA Start Frequency 5kHz 5kHz VNA System Dynamic Range 100dB > 114dB Best Speed at 1001 Point, 1 Sweep 432µs/pt 171µs/pt Output Power -1dBm 8dBm Trace Noise 0.004dB 0.001dB Number of Built-In Ports two two Instrument Type      Combination Analyser    Combination Analyser Cable and Antenna Analyser Yes - Standard Yes - Standard Spectrum Analyser Yes - Optional Yes - Optional Vector Network Analyser Yes - Optional Yes - Optional Standard Attenuator Range 30dB 40dB Standard Attenuator Step 5dB 5dB DANL <at>1GHz -155dBm -163dBm Maximum Analysis Bandwidth 10MHz 100MHz Phase Noise <at>1GHz (1MHz offset) -113dBc/Hz -124dBc/Hz Phase Noise <at>1GHz (30kHz offset) -111dBc/Hz -117dBc/Hz Phase Noise <at>1GHz (10kHz offset) -108dBc/Hz -115dBc/Hz Spur Free Dynamic Range > 105dB > 104dB TOI <at>1GHz (3rd Order Intercept) +15dBm +11dBm Applications Available Yes Yes Maximum Real-Time Bandwidth 10MHz 100MHz Bandwidth Options 10MHz (standard) 10MHz, 40, 100MHz Table 1: comparison between the (older) N1997A and the new N1998B Keysight Analysers. the capabilities of the N9918B. With the possibility of 5G using even higher frequencies, an external down-converter can be used to work with frequencies as high as 110GHz (!). One of the suggested options for the N9918B is a Phased Array Antenna which is designed to simulate the antennas used in 5G equipment. Thus, the N9918B is well-suited to being used in characterising and verifying the operation of 5G millimetre-wave networks. Support for the Phased Array Antenna requires several dependent options to be installed too. It appears that Telstra is in fact using Keysight equipment in their 5G trials. The photo overleaf shows a 5G work crew using a unit which looks suspiciously like the N9918B! One of the other software options that is available is a GPS receiver, which requires a separate GPS antenna. This option can also be used to increase the frequency accuracy of the N9918B. The apparent use for this is to be able to map 5G and other network coverage, including timestamps as well as location data. There is also an LTE (4G) addon, so existing networks can also be similarly analysed. Other features Apart from the 5G feature noted above, all the options The right side of the unit with the three locking doors open. The LAN and USB device ports can used for remote control and offloading captured data. The SD card and USB device ports provide an alternative means for copying data from the analyser to a PC. siliconchip.com.au Australia’s electronics magazine June 2020  81 N9918B-010 N9918B-030 N9918B-208 N9918B-209 N9918B-210 N9918B-211 N9918B-212 N9918B-215 N9918B-233 N9918B-235 N9918B-236 N9918B-238 N9918B-302 N9918B-307 Vector Network Analyser Time Domain Remote Control Capability USB Power Sensor Measurements Versus Frequency Extended Range Transmission Analysis (ERTA) Vector Network Analyser Transmission/Reflection Vector Network Analyser Full 2-port S-parameters Mixed-Mode S-Parameters TDR Cable Measurements Spectrum Analyser Pre-amplifier Interference Analyser and Spectrogram Spectrum Analyser Time Gating External USB Power Sensor Support GPS receiver Table 2 - the extensive N9918B options list that are available on the N9918B are also available on the N9917A. So for the most part, it’s the RF specifications that set it apart; the 5G support would simply not be possible without the improved bandwidth. It’s also worth noting that the 100MHz bandwidth is not mandatory. While not available as a post-purchase upgrade, there are variants which support either 10MHz, 40MHz or 100MHz bandwidth. N9918B-308 N9918B-309 N9918B-310 N9918B-312 N9918B-330 N9918B-350 N9918B-351 N9918B-355 N9918B-356 N9918B-370 N9918B-377 N9918B-360 N9918B-378 N9918B-352 N9918B-358 Vector Voltmeter DC Bias Variable Voltage Source Built-in Power Meter Channel Scanner Pulse Measurements Real-time Spectrum Analyser (RTSA) I/Q Analyser (IQA) Analog Demodulation Noise Figure (NF) Over-the-Air (OTA) LTE FDD Over-the-Air (OTA) 5GTF Phased Array Antenna Control Over-the-Air (OTA) 5G NR Indoor and Outdoor Mapping EMF Measurements At the top of the analyser, the input/ output N-connectors and SMA sockets for GPS antenna and reference input all have water-proof caps. Conclusion Other uses noted for the higher parts of the spectrum include satellite and radar technologies; not fields that many engineers even have access to, and unfortunately, not something that we can easily test. But we found in our earlier tests at lower frequencies that the FieldFox Analyser is a very capable unit that ‘does what it says on the tin’. We have no reason to suspect that this latest version is any different. This unit, with the 100MHz bandwidth option, is clearly pitched as a tool for engineers working on 5G mobile phone networks; indeed, this feature is one of the first mentioned in the Technical Overview document. If that describes you, then we think you will quickly realise what you could do with such a device. You can read more in Keysight’s technical overview at siliconchip.com.au/link/ab1w or read through the complete SC product page at siliconchip.com.au/link/ab1x Keysight has very clearly pitched the N9918B as an essential tool for working on the new 5G networks, and it appears that Telstra engineers are using it for precisely that purpose. 82 Silicon Chip Australia’s electronics magazine siliconchip.com.au