Page 1Find us at www.keysight.com

W H I T E P A P E R

4 Measurements You Can Perform on the GoRTSA, Noise Figure, CAT, and OTA Portable Measurements

IntroductionMicrowave systems frequently encounter sources of interference ranging from cellular

systems and satellite ground stations, to microwave backhaul systems that

can lead to poor signal quality. This can include a dropped cell phone call, or poor

audio quality. Wireless communication systems often operate under a limited amount

of regulated radio interference due to limitations of the radio frequency spectrum.

An engineer working in the field conducts routine maintenance on and troubleshoots

deployed RF, microwave and millimeter-wave systems. On any given day, you may need

to measure a wide variety of devices or signals: cables, antennas, communications

systems, or intermittent spurious signals to ensure robust signal quality and

uninterrupted service.

To perform these functions successfully requires a basic understanding of measurements and

a portable, easy-to-use handheld instrument. This white paper will outline four common

measurements you can perform in the field: Real-Time Spectrum Analysis (RTSA), Noise

Figure, Over-The-Air Testing (OTA), and Cable and Antenna Test (CAT).

Global mobile data traffic g r ew 63% i n 2016 , according to Cisco. As demands for cellular data increases, network test is critical to ensure clear quality signals and prevent the dropped calls.

Page 2Find us at www.keysight.com

1. Real-Time Spectrum AnalysisWhat is RTSA?

Real-t ime spectrum analysis (RTSA) processes signal samples gap-free and

generates cer ta in measurements , such as sca lar, power, or magn i tude that

correspond to traditional spectrum analysis measurements.

RTSA Measurements on the GoSignal interference over wireless networks is on the rise, resulting in poor signal quality.

This has a profound impact on wireless devices and communications ranging

from car radios to mission critical appl icat ions such as publ ic safety. In a highly

dynamic signal environment, weak signals can be masked by wider or longer

duration signals. Interference may also occur during a spectrum analyzer’s dead time.

Gapless RTSA techniques reveal these transient, overlapping signal detections.

Co-channel interference detection and troubleshooting is the most challenging task

in a communications network, because interferers can be hidden 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.

This tends to be very intrusive and can disrupt normal communication services. Under

many circumstances, turning off serving transmitters is not a viable solution, depending

on the nature of the services, such as base station testing. RTSA profiles over-the-air

characteristics, being able to detect hidden interferers under the serving carrier.

Figure 1. WiFi signal captured by FieldFox with 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.

Page 3Find us at www.keysight.com

FieldFox handheld analyzers with RTSA capture quickly changing digital and pulsed

signals as narrow as 5.52 µs with 100% probability of intercept (POI) and full amplitude

accuracy. With up to 100 MHz bandwidth, FieldFox RTSA can verify 5G and other

wideband signal types. Use RTSA to verify signal integrity or identify unwanted signals

that are undetectable with traditional spectrum analyzers.

Figure 2. RTSA on the handheld analyzer can be viewed in 3 different settings: density, spectrum, and spectrogram

Figure 3. FieldFox Handheld Analzyer’s 100 MHz real-time bandwidth (RTBW) identifies a 5G NR signal.

Spectrogram: Spectrum Over Time Display

Spectrum: Trace DisplayDensity: Histogram Display

Page 4Find us at www.keysight.com

RTSA also helps with interference detection, given the widespread use and proliferation

of wireless technologies.

To gain a deeper understanding or RTSA, check out the Application Note, “Overcoming

RF & MW Interference Challenges in the Field Using Real-Time Spectrum Analysis (RTSA)”.

2. Noise FigureWhat 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 the pre-amplifier, mixer, and IF amplifier. 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.

Noise Figure Measurements on the Go

Communication system capacity is limited by internally generated noise. This noise

wil l reduce link budget, increase investment on the transmitter side or increase

antenna cost at the receiver side. One key performance indicator for a receiver is its

sensitivity, the ability to reliably discern small signals close to the noise floor. While

vector network analyzer (VNA) S-parameter and spectrum analyzer channel power

and adjacent channel power measurements focus on signal behavior, the performance

of a communication system is based on signal-to-noise ratio (SNR). To get a complete

picture of total system performance, you need an additional evaluation of internally

generated noise. Lower noise figure values typically mean better device performance.

Combining the noise figure measurements with the FieldFox two-port vector network

analyzer, spectrum analyzer, and power sensor integration will help you completely

characterize amplifiers and converters in the field.

The FieldFox handheld analyzer makes noise figure measurements easy-to-use when

making measurements in the field with, touch of a button measurements. This includes

the most common method of system noise—the “Y-factor” method—which allows

you to measure various system components including amplifiers, downconverters,

and upconverters. You can easily view the change in uncertainty with the bui l t-

in uncertainty calculator which displays vert ical bars represent ing calculated

measurement of uncertainty over the trace data in real-time. Being able to make these

measurements quickly to characterize the noise figure is important to optimize designs

in the most cost-effective manner. Decreasing receiver noise is the most cost-effective

way to optimize communication systems without reducing quality.

Page 5Find us at www.keysight.com

DUTDC Power Suppy

Required

28V On/Off DC SourceSupplied by FieldFox

N9910X-713 BNC to SMB Cable

USB Pre AmpOptional

Noise Source346 Series

Figure 4. Noise measurement with the FieldFox Handheld Analyzer.

3. Cable and Antenna Test (CAT)What is CAT?

Nearly 50 to 60% of cellular base station problems are caused by faulty cables,

connectors, and antennas.The fai lure of these components causes several

issues, including poor coverage and unnecessary handovers in cellular systems.

Cab le and an tenna measu remen ts ve r i f y and t roub leshoo t RF /M ic rowave

transmission systems and antennas. These measurements are typical ly made

along the coaxial cable, connecting a transmitter to its antenna, or between an

antenna and i ts receiver. Cable and antenna test (CAT) ident i f ies the locat ion

of poor performance in adapters and damaged antennas, as well as breaks or

bends in cable l ines.

CAT Measurements on the Go

Failure in cable system transmission lines is a common maintenance issue because

of exposure to harsh weather conditions. Sheltered cable installations can expose

components to heat, stress, and oils that could leak into the system. Cable faults can

occur at any interface between cables and connects where soldered joints and crimps

in the cable weaken and break.

Page 6Find us at www.keysight.com

Transmission lines are often very long and sometimes, the ends of a line- separate,

making end-to-end cable measurements nearly impossible. Two cable troubleshooting

techniques include:

• Distance to Fault (DTF): Reports the location of each cable fault

• Time-Domain Reflectometry (TDR): Characterizes the type of fault, such as a bend in the cable, or cut.

- A bend in the cable will appear capacitive

- A nick in the cable will appear inductive

FieldFox quickly and accurately characterizes 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 the cable l ine. You may also verify the performance of a

single antenna at the installation site with signal reflection, return loss, and voltage

standing wave ratio (VSWR). When multiple antennas are used at one site, the

antenna-to-antenna isolation may also be verif ied using FieldFox, whether the

antennas are associated with the same system or different systems.

For more information on CAT Testing, check out, “Techniques for Precise Cable and

Antenna Measurements in the Field.”

Figure 5. Points A and B show where the cable is damaged or bent in the TDR mode for cable and antenna testing.

FieldFox can perform DTF and TDR measurements simultaneously, saving time for your CAT measurement.

Page 7Find us at www.keysight.com

Figure 6. With up to 6 neighbors detectable, you can view in table, bar chart, strip chart, or spectrum.

4. Over-the-air Testing (OTA)What is OTA?Wireless networks have become increasingly complex with 4G and 5G looming on

the horizon. One major challenge is the question of what network coverage really is,

since today’s wireless networks are comprised of layers of macrocells, microcells,

and picocells. With users shifting between LTE and 5G, defining wireless coverage

can become complicated and difficult to troubleshoot. OTA measurements assess

the level of cell coverage needed to ensure continuous connectivity in various mobile

communication scenarios, including voice coverage, text messages, and data services.

OTA Measurements on the GoOver-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 or troubleshoot handover problems, such as missing neighbors.

Keysight’s FieldFox OTA appl icat ion enables OTA LTE FDD, and OTA 5GTF

demodulation to give you insights on cell coverage. This includes physical cell

ID (PCI) and control channel measures on any given frequency (often referred

to as component carrier) for all available cells. OTA measurements also help you

address the common problem of identifying missing neighbors. FieldFox OTA

provides a useful capability - it displays the strongest cell on different component

carriers. This greatly expedites the process of selecting the best frequencies, for

any given location, to optimize interfrequency handover. FieldFox can display cell

measurements in table, bar graph, and strip chart formats (see Figure 6).

Page 8Find us at www.keysight.com This information is subject to change without notice. © Keysight Technologies, 2019, Published in USA, June 6, 2019, 5992-3772EN

For more information on FieldFox, check out the following link.

For more information on 5G over-the-air measurements, check out the Application Note, “5G

Over-the-Air Performance Measurement and Evaluation Using FieldFox Handheld Analyzers.”

ConclusionKeysight designed the FieldFox to enable the variety of measurements that field

engineers commonly make in outdoor settings where it is necessary to use rugged

and portable devices. Our goal is to support your efforts to install and maintain

cellular networks, satellite ground stations, radio networks, and more. This often

requires in-field verification and adjustment of various components, such as filters,

duplexers, or antennas.

We also offer you the convenience and flexibil ity to upgrade your handheld

analyzer with user-installable license keys. No need to send the FieldFox instrument

back to Keysight for upgrades. Trial licenses are available at Keysight.com.

With the FieldFox’s 22 different measurement applications, you can work with a

single user interface that provides customizable parameters for quick measurements

that match benchtop precision. Make FieldFox your No. 1 portable field test tool for easy,

quick measurements with benchtop precision.

Learn more at: www.keysight.com

For more information on Keysight Technologies’ products, applications or services,

please contact your local Keysight office. The complete list is available at:

www.keysight.com/find/contactus