RF-signal-analysis instruments: now faster and smarter
By Dan Strassberg, Contributing Technical Editor -- EDN, September 5, 2006
The growing complexity of wireless-communication standards is motivating users of RF signal-analysis instruments to demand units that can make more complex measurements than do existing products. Moreover, the economics of such businesses as mobile phones, whose manufacturers annually produce hundreds of millions of units, necessitate drastic reductions in test times, not only in production, but also in product development. This situation has motivated Agilent and Tektronix to introduce new RF signal-analysis products. Even if only by accident, the companies invited comparisons by making their announcements on the same day.
At first, though, it might appear that, despite the similarities, comparisons between these products could be unfair because the base prices of Agilent’s LXI Class C-compliant N9020A MXA signal analyzers are considerably lower than those of Tektronix’s RSA6100A real-time spectrum analyzers. MXA prices start at $25,900 for a unit that covers 20 Hz to 3.6 GHz. Prices for the widest-bandwidth member of the series, which covers 20 Hz to 26.5 GHz, start at $42,900. The company will also continue to offer its higher performance, higher priced PSA spectrum-analyzer line. Meanwhile, RSA6100A prices start at $69,900 for a unit that covers 9 kHz to 6.2 GHz.
Prices enter the same ballpark, however, if you carefully pick units that offer similar frequency ranges and if you equip the selected Agilent product with options that enable it to make many of the measurements that are the Tek products’ forte. Also, each product family boasts a dynamic range of approximately 73 dB, and each includes a member whose frequency range extends to approximately 14 GHz. Tek’s RSA6114A covers 9 kHz to 14 GHz. Agilent’s N9020A-513 covers 20 Hz to 13.6 GHz. The Tek unit, whose standard measurement bandwidth is 40 MHz (and, optionally, 80 or 110 MHz), carries a base price of $75,900. You can purchase the Agilent unit with an analysis bandwidth of 25 MHz. So equipped and with a hardware connection and signal-analyzer software, the Agilent unit carries a price of $62,420. Additional options can easily increase this price beyond $70,000.
Both analyzer families use heterodyne downconversion to bring the signals of interest to a relatively low frequency and then use high-speed, high-resolution ADCs to convert the signals to the digital domain in which DSP-based techniques enable rapid analysis. Moreover, the instruments can store and recall the digitized data, allowing postprocessing, which can reveal phenomena that you may want to examine further.
The character of the Agilent instruments depends on the analysis software you load into them. They can become vector-signal analyzers, spectrum analyzers, or both. Although Tek does not offer such options, it offers some capabilities that the company calls revolutionary. Potential customers will almost certainly agree.
The most dramatic new feature is Tek’s first-time incorporation into RF signal-analysis instruments of its proprietary DPX (digital-phosphor) technology, which was originally developed for use in real-time-sampling digital oscilloscopes. With this technology, you can display rapidly changing broadband spectra as what amount to real-time videos. At the end of each video, a color-keyed image remains on the screen to show the percentage of time the signal occupied each portion of the displayed frequency band. The instruments do not, however, display waterfall diagrams—the traditional presentation of time-varying spectra—although Tek insists that the units display the same information in a more easily understood form. The live spectrum displays are possible not only because of the DPX technology, but also because of the units’ DSP-based capability to perform 48,000 spectral analyses/sec. According to Tek, that number is almost 1000 times the analysis speed of the fastest competing instrument.
Another feature of the RSA6100 series is an improved version of FMT (frequency-mask trigger), which Tektronix first offered in earlier real-time spectrum analyzers. FMT lets you trigger measurements based on the occurrence of unique patterns of events in the spectrum. Coupled with the instruments’ high dynamic range, FMT allows triggering on weak signals and ignores known strong ones. The company says that legacy swept-frequency spectrum- and vector-signal analyzers lack similar capabilities.
Returning to Agilent, the company also announced a family of RF signal generators at the same time as it announced the MXA signal analyzers. The MXG family comprises three analog-signal generators—the N5181A MXG series—and two vector-signal generators that make up the N5182A MXG series. Each of the five generators, which are companion products to the MXA family, covers a frequency range that begins at 250 kHz. The analog series includes units whose frequency coverage extends to 1, 3, and 6 GHz at base prices ranging from $6200 to $15,000. Within the vector series are two units whose coverage extends to 3 and 6 GHz and whose base prices are $16,000 and $25,000. Among the family features are simplified self-maintenance, and what Agilent terms the industry’s fastest switching speeds and best ACPR (adjacent-channel power ratio).
