Spectrum analysers: No longer mere standalone devices

A spectrum analyser is the most elementary and essential part of test equipment for someone designing or repairing electronic equipment that uses radio frequency signals. This is the most common frequency domain test and measurement (T&M) instrument used for checking the frequency and power levels of signals. Spectrum analysers usually display raw, unprocessed signal information such as voltage, power, period, wave shape, sidebands and frequency. They help in providing a clear, precise reading of the frequency spectrum.

By Richa Chakravarty

Thursday, January 12. 2012: A spectrum analyser has some similarities to an oscilloscope because it provides a graphical display. However, rather than giving a display of amplitude and time, like an oscilloscope does, a spectrum analyser gives a display of frequency against the amplitude (typically power). Essentially, a spectrum analyser scans a band of frequencies set by the user, and notes the signal levels, displaying them on a screen. In this way, it is possible to obtain a plot of the signals appearing in any band of frequencies. The most common spectrum analyser measurements are modulation, distortion and noise.

Types of spectrum analysers available

There are two types of spectrum analysers available in the market, namely, handheld and benchtop. Though both instruments serve the same purpose, they are used differently. Benchtop models are superior in features and specifications, and are more costly than handheld models. Therefore, during the initial design phase, benchtop models

are mainly used. Handheld models are normally used during deployment or the final stages, mainly in the field.

“Both types of spectrum analysers have their pros and cons. Low frequency benchtop spectrum analysers are in demand in educational institutes, engineering colleges, repair centres, in the R&D space and among organisations working in the low frequency area. Handheld spectrum analysers are truly useful for field applications where portability is important, apart from other features. Mobile wireless network installation, maintenance and optimisation require these handheld analysers. They are used for spectrum monitoring, analysis, and interference testing,” informs Madhukar Tripathi, manager, telecom sector, Anritsu Pte Ltd India.

Benchtop models are used mainly in labs and design centres, while handheld models, due to their inherent portability, are used for field testing. Explains Sadaf Arif Siddiqui, technical marketing specialist, Agilent Technologies India Pvt Ltd, “A typical example is the wireless communication segment. During the initial stages of chipset or transmitter/receiver development, benchtop models are preferred. Once the product is developed and ready to be installed (at a base station, for instance), technicians normally use handheld models to check power levels or interfering signals.”

Innovative features and technological developments

Spectrum analysers are being upgraded to meet today’s network testing demands. Traditional spectrum analysers used to show only basic measurements and

involved a lot of manual work as the user had to put up markers on the signal to check different parameters such as frequency, power levels, etc. Also, these were not so user friendly and they had various limitations with respect to performance and specifications. Shares Sadaf Arif Siddiqui, “Due to rich software algorithms and superior technical designs, these analysers are aptly called signal analysers in the true sense. These instruments not only come with superior hardware specifications but also automatic measurements and ease of use. Just by pressing a button on the front panel, the user can immediately and automatically tune the signal and check the characteristics.” Other new features are PC compatibility, an in-built Windows platform, I/O ports (USB, LAN, GPIB, etc), optional tracking generator, etc, all of which makes this instrument easy to use.

“A number of power calculations in different units with comparisons, modulation analysis and various types of connectivity to other systems are the added features incorporated in these devices. While on one hand, handheld analysers are gaining popularity on the basis of their ease of use, light weight and being battery operated, benchtop spectrum analysers come with various additional features such as a tracking generator,” shares JK Baldua, technical director, Scientech Technologies Pvt Ltd.

The growing use in the field of communications has led to an increase in the demand for LTE testing, so the LTE option is now being added to spectrum analysers. The same spectrum analyser can now have GDSM GPRS, WCDMA and LTE measurement capability in a single box. Also, with the increasing bandwidth requirements, the products being introduced cater to a wide spectrum measurement requirements in a real time scenario.

As designers work with digital RF technology, they require real time spectrum analysers with a combination of a dynamic range and image rejection at very wide bandwidths. Innovative features like digital picture exchange (DPX) are being introduced in spectrum analysers, which are proving indispensable to designers in their discovery of previously unseen signal anomalies.

The new spectrum analysers also support applications in spectrum management, particularly in intelligence, regulatory monitoring and defence applications. “The latest of the spectrum analysers has signal discovery and triggering advantages. It dramatically reduces time-to-insight for high frequency applications because users can trigger on low level signals that are obscured or completely missed by traditional analysers,” shares Sai Venkat Kumar, Pacific marketing, Tektronix India Pvt Ltd.

Added to these innovative features, today the devices come with an upgradeable CPU, memory, disk drives and I/O ports, all of which extend the instruments’ longevity. While earlier, a lot of time was spent on aligning the signal and checking the centre frequency, span and resolution bandwidth, now, with the help of the auto tune button, users need not worry about all these settings. This simple button can automatically arrange the alignment available on a signal analyser. Another innovative feature, the global positioning system (GPS), is also being incorporated in the spectrum analyser. This option enables a customer to put the time and location stamp on measurements.

“Today, spectrum analysers are available in the 160 MHz analysis bandwidth with a very low displayed average noise level (DANL). Other features available are demodulation and analysis of almost all telecom and TV signals, apart from accurate noise figure and phase noise measurements. Also, features like the

vector network analyser (VNA) are now available in handheld models. This analyser helps in measuring both amplitude and phase properties,” shares NV Valsalan, director, T&M, broadcast and business development (A&D), Rohde & Schwarz India Pvt Ltd.

What players offer

Selecting an ideal instrument for business can be complex and time consuming as every project and user is unique. Keeping this in mind, T&M players today offer a wide selection of analysers and applications that fit within a variety of budgets. Under the handheld product category, Anritsu offers the 43GHz spectrum analyser with a master software tool (MST), which is a powerful PC based post-software tool used for reporting instruments. It comes with a script master which is an automated tool that allows the user to follow operator specific tests in the same manner, in order to avoid any error in measurement. Anritsu’s products are used in the design, manufacture and maintenance of wired or wireless solutions, RF and microwave solutions, and optical solutions, among other data communications applications.

“The E-series analysers offer the best accuracy and have a mapping facility that is very useful in interference hunting applications. Along with this, indoor maps can be uploaded into the spectrum analyser and used for building coverage applications. E-series spectrum analysers are also suitable for all wireless technologies—a single instrument can cover GSM, GPRS, W CDMA, LTE, and WiMAX technologies, thus saving on capital expenditure,” shares Madhukar Tripathi.

In the same handheld category, Agilent offers the N9344C spectrum analyser that automates routine tasks and helps in saving time, while ensuring consistent results. Some of its field ready features include a rugged and fanless design, which provides a clear view both during day and night. The performance provided by this handheld instrument is almost similar to benchtop devices. Also, using the innovative task planner, it reduces test set-up times by 95 per cent. But the latest offered by Agilent is the X-series, which is an evolutionary approach to signal analysis that spans instrumentation, measurements and software. It gives users the flexibility to satisfy business and technical requirements across multiple products and programs. The PXA signal analyser is the highest performer of the X-series and is the evolutionary replacement for current performance signal analysers. It provides frequency coverage up to 50 GHz, and ensures present and future flexibility through optional measurement capabilities and hardware expandability.

LeCroy offers a spectrum analyser-cum-oscilloscope as an additional feature, mainly for electrical signals that are captured by these instruments. With this capability, very low frequency signals can be displayed, which otherwise would not be possible on spectrum analysers; or if it could, the option would be very expensive. They come in two variants—as a math fast fourier transform (FFT) option, where a user has to manipulate the sampling rate and record the length to capture signals of interest, and the other as a spectrum analyser option that provides the user with easy RF controls. Informs Prabhanjana Rao, regional sales manager, India SE Asia and ANZ, LeCroy, “The biggest advantage with oscilloscope based FFT/SA is that both the time domain and frequency domain can be viewed simultaneously with electrical and timing measurements. This offers processed data, which means the signals are captured and then the math function like FFT is applied to transfer from the time domain information to frequency domain information.”

Today, the ever evolving technology has opened various doors for designers and engineers to achieve new levels of technology. The complexity of debugging

issues in modern wireless systems, combined with the lack of equipment designed for the task, has opened markets for products like mixed domain oscilloscopes (MDOs) with built-in

spectrum analyser capabilities. MDOs help engineers to simultaneously visualise multiple points in a design, looking at the analogue, digital and RF aspects of the system’s operations, which enables faster tracking of design issues. These oscilloscopes also help engineers to rapidly solve complicated design issues and gain a better understanding of the real world performance of the system at a high level. Explains Sai Venkat Kumar, “More than 60 per cent of oscilloscope users also use a spectrum analyser to troubleshoot with embedded system designs that have integrated wireless functionality. This requires them to work in both the time and frequency domain. The MDSO4000 mixed domain oscilloscope series of Tektronix is the first oscilloscope ever to integrate the functionality of a spectrum analyser to provide a unique tool that will save days or even weeks of debugging time, allowing designers to work on both domains.”

Moving towards high end devices, Rohde & Schwarz has launched its new models—FSV and FSW. With excellent RF characteristics, FSV is an ideal instrument for both development and

production, featuring the smallest level measurement uncertainty in its class. It provides innovative measurement functions with an all new hardware design to enable great performance, reliability and ease of service. FSW is one of the most advanced analysers with high bandwidth and low phase noise. With the clearest user interface, this device exceeds all current standards in signal and spectrum analysis, according to the company.

Apart from inhouse manufacturing, Scientech Technologies offers different models of analysers from various popular brands. Informs JK Baldua, “The handheld series from Micronics, Japan (its principal), provides all major features of benchtop analysers.” Also, the company offers 3GHz Rigole and Caddo 1GHz/500MHz spectrum analysers that come with or without tracking generator.

Similarly, the robust hardware design of the PXA offered by Agilent delivers outstanding sensitivity and a wide dynamic range. Through external harmonic mixers, the PXA can measure signals of up to 325 GHz and beyond. Its advanced performance, flexibility, capability and expandability enables it to address demanding applications in aerospace, defence, commercial communications and more. In addition, it includes extensive remote language compatibility features that make it easier to replace existing high performance spectrum analysers. “Some of the technological innovations happening in this domain are capable of new levels of signal detail with outstanding RF performance, increased test throughput, with the ability to protect system investments and refresh legacy systems with a highly compatible replacement. The ability to measure small signals in the presence of very large signals is unparalleled and enables users to develop the most advanced radar, surveillance and wireless communications systems,” adds Sadaf Arif Siddiqui.

KEY PLAYERS

Look before you buy

Depending on the basic specifications, built-in features and various specifications like the frequency range, dynamic range, options, configuration and category (whether indigenous or imported), the cost of these analysers can range from a few thousands to lakhs of rupees. Thus, buyers should look for better specs, high performance, service, after sales and technology support when buying spectrum analysers, apart from just the budget.

“Before buying a spectrum analyser, customers should freeze on their measurement needs rather than copying the specifications from the datasheet of a company. They should define their requirements and ask for offers from many vendors in order to meet their requirements. In general, the most important RF parameters that define the quality of a spectrum analyser are the noise figure of the instrument, the third order intercept point, the 1DB compression point, RBW, features signal analysis functionality, power consumption, and RF attenuator switching steps. It is important not to get carried away by marketing gimmicks based on software correction of test results without having a good look at the RF characteristics of the instrument,” suggests Valsalan.

Some other buying tips are:

• Features and specifications: Depending on the total investment budget, buyers must look for bandwidth requirements, dynamic range, resolution bandwidth and connectivity options
• Brand of the instrument: It is equally important for buyers to procure the equipment from a brand that is known for its quality, cost effectiveness and experience in its relevant field
• Local support (technical, service, calibration and repair): This is one of the most vital pieces of information for the buyer to look for. Opt for a brand that offers local support and after sales service.
• Ease-of-use: As per your requirement, opt for a device that not only serves your purpose but is equally comfortable to use and is hassle free
• Code compatible with legacy instruments: While migrating from obsolete instrumentation to new equipment, buyers should look into the compatibility factor as well. The emulation of obsolete instrumentation must include not only code compatibility but also behavioural compatibility. A buyer should be aware of this, especially when legacy models are replaced: new models are not necessarily compatible with the old ones
• Support for different applications: Along with easy handling, make sure that the device is able to support or can be connected to other devices as well; for example, it should have PC compatibility apart from USB, LAN and GPIB ports

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