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A Field Engineer’s Survival Guide: Five Everyday RF Measurements

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by Sarah Gross, Product Marketing Engineer, Keysight Technologies

Introduction

As a field engineer, you never know exactly what problem you will face on any given day at a job site. Some days, you have the equipment you need to solve the issue, and other days, you don’t. Whether the network needs installation, maintenance, or troubleshooting, it’s best to be prepared for the unexpected.

A handheld analyzer can serve as your multitool in the field. They can help you analyze cables and antennas, scan for interference, measure 5G KPIs, and more, but they are only as good as the person who uses them. This article serves as a survival guide for field engineers testing RF equipment in the field. Get to know these five measurements well and you’ll be prepared for whatever the field throws at you:

  • Real-time Spectrum Analysis (RTSA)
  • Noise Figure Measurements
  • Cable and Antenna Tests (CAT)
  • Over-The-Air (OTA) testing
  • Electromagnetic Field (EMF) Exposure Evaluation

Real-Time Spectrum Analysis (RTSA)

What is RTSA? RTSA processes signal samples without gaps and generates measurements, such as scalar, power, or magnitude, that correspond to traditional spectrum analysis measurements as shown in Figure 1.

Figure 1: A Wi-Fi signal captured by Keysight’s FieldFox handheld analyzer using 10 MHz bandwidth on the left and 100 MHz bandwidth on the right. With 100 MHz bandwidth, you can visualize the whole band in one display.

Signal interference over wireless networks is on the rise, resulting in poor signal quality that leads to dropped calls or choppy audio. It has a profound impact on wireless devices and communications, ranging from car radios to mission-critical applications such as public safety.

Traditional spectrum analysis techniques contain dead time wherein the analyzer processes the data for display. Intermittent interference signals may occur during such dead time. Additionally, in a highly dynamic signal environment, wider or longer duration signals mask weak signals and cause interference. Gapless RTSA, on the other hand, detects and reveals these transient, overlapping signals so that you can visualize the interferer.

Co-channel interference detection and troubleshooting are the most challenging tasks to do in a communications network because interferers can hide under the serving frequency. Typically, a user has to turn off the carrier transmitter to find any other signals that appear in the same frequency channel before eliminating or reducing their impact. Turning off the carrier signal tends to be intrusive and can disrupt normal communication services. Besides, under many circumstances, turning off serving transmitters is not a viable solution, depending on the nature of the services, such as base station testing. Fortunately, RTSA profiles over-the-air characteristics, detecting hidden interferers under the serving carrier.

Noise Figure Measurements

What is noise figure? Noise figure measures the degradation of the signal-to-noise ratio as a signal passes through an active or passive device.

Noise figure uniquely characterizes entire systems, in addition to their components, including preamplifiers, mixers, and intermediate frequency amplifiers. By controlling the noise figure and gain of the components, the designer controls the noise figure of the overall system. Once you identify or know the noise figure, you can easily estimate system sensitivity from the system’s bandwidth.

One key performance indicator for a receiver is its sensitivity — the ability to reliably discern small signals close to the noise floor. A communication system’s performance relies on its signal-to-noise ratio. Lower noise figure values typically mean better device performance.

Figure 2: A screenshot of a noise figure measurement including uncertainty calculations

Internally-generated noise, however, can hinder a device’s performance. Internally-generated noise reduces the link budget, increases investment by the transmitter, and increases the antenna cost at the receiver. To obtain a complete picture of system performance, you need an additional evaluation of internally-generated noise. Decreasing receiver noise is the most cost-effective way to optimize communication systems without reducing quality.

The ability to perform noise figure measurements, in addition to network analysis, spectrum analysis, and power sensor capabilities, enables you to completely characterize amplifiers and converters in the field. Handheld analyzers typically make noise figure measurements using the “Y-factor” method. This technique allows you to measure system components such as amplifiers, downconverters, and upconverters. You can easily view the change in uncertainty in real time with the built-in uncertainty calculator that displays vertical bars over the trace data as portrayed in Figure 2. Being able to make these measurements quickly to characterize noise figure is important to optimize designs in the most cost-effective manner.

Cable and Antenna Test (CAT)

What is CAT? Cable and antenna measurements verify and troubleshoot RF/microwave/mmWave transmission systems and antennas. These measurements occur along the coaxial cable that connects a transmitter to its antenna, or between an antenna and its receiver. CAT identifies the location of poor performance in adapters and damaged antennas, as well as breaks or bends in cable lines.

Faulty cables, connectors, and antennas cause many cellular base station problems. The failure of these components in cellular systems causes several issues, including poor coverage and unnecessary handovers. Component failure frequently is the result of harsh weather conditions that cause damage to exposed cable system transmission lines. Sheltered cable installations are also subject to heat, stress, and oils that leak into the system. Additionally, cable faults commonly occur at interfaces between cables and connects where soldered joints and crimps in the cable weaken and break.

When a fault does occur, transmission lines are often too long to make end-to-end cable measurements. Here are two cable troubleshooting techniques to try when end-to-end measurement is impossible and a kink or cut forms in a line:

Distance to Fault (DTF) reports the location of each cable fault, shown in Figure 3.

Figure 3: The yellow trace shows a DTF measurement of a cable with an open end, and the blue trace, stored to memory, shows the same cable terminated in a 50 Ω load

Time-Domain Reflectometry (TDR) characterizes the type of fault, such as a bend in the cable, or cut. A bend in the cable appears capacitive (the trace reflects downwards) while a cut in the cable appears inductive (the trace reflects upwards).

Sophisticated handheld analyzers quickly and accurately characterize an entire cable transmission system, as well as the individual components in the system. With DTF and TDR measurement capabilities available at the touch of a button, you can quickly pinpoint the location and type of damage in a cable line. You may also verify the performance of a single antenna at the installation site with signal reflection, return loss, and voltage standing wave ratio functions. When there are multiple antennas at one site, handheld analyzers also verify the antenna-to-antenna isolation, whether the antennas are associated with the same system or different systems.

Over-the-Air (OTA) Testing

What is OTA? OTA measurements assess the level of cell coverage needed to ensure continuous connectivity in various mobile communication scenarios, including voice, text messages, and data services.

Wireless networks continue to grow increasingly complex, especially with pioneering technologies such as 5G. Because today’s wireless networks consist of layers of macrocells, microcells, and picocells, network coverage is a significant challenge. With users shifting between LTE and 5G, operators face difficulties in defining and troubleshooting wireless coverage.

Over-the-air antenna testing in the field is the best way to verify that each cell has sufficient neighbors for successful handovers. With OTA measurements, you can scan an area to determine how many cells are available, identify which cells are good neighbors, and troubleshoot handover problems, such as missing neighbors.

OTA applications enable LTE and 5G New Radio (5G NR) demodulation to give you insights on cell coverage. This information includes physical cell ID and control channel (often referred to as component carrier) metrics on any given frequency for all available cells. OTA measurements also help you address the common problem of identifying missing neighbors. 

Figure 4: 5G NR OTA scan results from Keysight’s FieldFox handheld analyzer showing a table with demodulated information and a bar chart with cell signal strength

Some analyzers provide a useful capability — they display the strongest cell on different component carriers, shown in Figure 4. This capability expedites the process of selecting the best frequencies for any given location to optimize inter-frequency handover. 

Electromagnetic Field (EMF) Exposure Evaluation

What is EMF exposure evaluation? Operators must verify EMF exposure levels for compliance and often use EMF-specific measurements and a triaxial antenna to do so in the field.

Electromagnetic radiation is the energy emitted from electromagnetic waves propagating through space. This energy occurs at varying frequencies that range from direct current (DC) circuits (0 Hz) to radioactive gamma rays (30 EHz). Radio frequencies (RF) fall between ~3 kHz to 300 GHz and can be further divided into frequency bands depicted in Figure 5. Microwave bands cover the RF ranges between ~3 to 30 GHz while millimeterWave (mmWave) bands range from ~30 to 300 GHz.

Figure 5: A visualization of the electromagnetic spectrum and the corresponding technology frequencies Image from the International Telecommunication Union (ITU)

In terms of wireless communication and as technology has developed over time, the RF spectrum has become more crowded. Currently, many commercial technologies function in the low band, radio frequencies. As consumers add more and more “smart devices” to their lives, the push to explore higher frequencies grows larger.

The characteristics of 5G signals require more base station antennas than LTE — especially in densely populated areas. In addition to an increasing number of antennas, 5G mmWave signals have different EMF properties than previous standards. Because of this, operators have to verify EMF exposure levels in the field for compliance. In order to adhere to set limits and maintain a safe environment for the public and workers, companies implementing 5G must verify their EMF levels during deployment.

Exposure limits for EMF radiation differ by country. Many countries base their regulations on findings from organizations such as the International Commission on Non-Ionizing Radiation Protection (ICNIRP), the Institute of Electrical and Electronics Engineers (IEEE), and the U.S. Federal Communications Commission (FCC).

Conclusion

Installing and maintaining cellular networks, satellite ground stations, radio networks, and other communications systems often requires in-field verification and adjustment of components, such as filters, duplexers, or antennas. As OTA systems become more complex and evolve over time, field engineers have to carry a handheld instrument that performs all the tests needed to keep a network up and running — and they have to know how to use it. By understanding the basics of the measurements and technologies discussed in this article, field engineers are better equipped to handle the challenges that RF networks present.

About the Author

Sarah Gross

Sarah Gross is a Product Marketing Engineer for Keysight’s FieldFox handheld analyzers. She holds a Bachelor’s degree in Mechanical Engineering and is currently pursuing her MBA. With experience in both the medical device and IT industries, Sarah uses her technical background to connect customers with the state-of-the-art test and measurement technology that Keysight provides. When not developing impactful marketing plans and collateral or studying for school, you can find her enjoying the mountains of Colorado.

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