Real-Time Analyzer Captures Elusive RF Signals

Oct. 13, 2006
These broadband signal analyzers combine capture bandwidths to 110 MHz with simultaneous SFDR of 73 dB to display even microsecond-duration events.

Spectrum-analyzer designers are faced with increasingly complex signals in modern radar and communications systems. As a result, today's spectrum analyzer is becoming more like an oscilloscope than the traditional swept-tuned instrument of years past. The latest Real-Time Spectrum Analyzers from Tektronix ( Beaverton, OR), the 9-kHz to 6.2-GHz model RSA6106A and 9-kHz-to-14-GHz model RSA6114A offer advanced triggering capabilities with the power of capturing instantaneous bandwidths as wide as 110 MHz while simultaneously achieving a spurious-free dynamic range of 73 dB.

The RSA6100A Series of Real-Time Spectrum Analyzers are visually striking instruments (Fig. 1), with a 10.4-in. XGA touch screen display. But it is what they capture and how they show it that makes the analyzers so powerful. Armed with patented DPXTM waveform image processor technology, the analyzers can produce live RF spectrum displays some 1000 times faster than a conventional swept-tuned spectrum analyzer. The DPX technology, which employs a parallel-processing architecture to continuously convert time-domain information into the frequency domain, processes more than 48,000 spectrum measurements per second, compared to about 50 per second for conventional spectrum analyzers.

This fast capture and processing speed provides 100-percent probability of intercept for signals as brief as 24 µs, ensuring the capture and display of signal instabilities and transients. DPX technology provides a means of displaying both frequent and infrequent events, computing Discrete Fourier Transform (DFT) at frame rates above which can be detected by the human eye and converting them into a full motion display. DPX distills a massive amount of information in a way that the human eye can see. Events can be color coded by rate of occurrence into a bit-mapped display for ease of analysis (Fig. 2). The RSA6100A analyzers rely on the Windows XP operating system, allowing an almost unlimited number of time-correlated, analysis windows.

In terms of performance, the analyzers can be ordered with a standard bandwidth of 40 MHz, courtesy of a 100-MSamples/s, 14-b digitizer, or with Option 110 and a 110-MHz bandwidth by means of a 300 MSamples/s, 12-b digitizer. Measurement spans can be set from 100 Hz to 14 GHz, depending on the model. Measurement real-time bandwidths can be set from 100 Hz to 110 MHz, depending upon options, with minimum acquisition length of 2 samples. The analyzers provide deep capture memory for capturing all events within the measurement bandwidth, for as long as 1.7 s at 110 MHz, 81.9 s at 1 MHz, and 1.45 hours at 10 kHz (with Deep Memory Option 02).

Although they possess triggering and display capabilities similar to a modern scope, these analyzers also boast outstanding RF performance, with 0.1-Hz center frequency setting resolution and resolution bandwidths from 1 Hz to 5 MHz. The typical single-sideband (SSB) phase noise is -96 dBc/Hz offset 1 kHz from a 6-GHz carrier, -107 dBc/Hz offset 10 kHz from the same carrier, -132 dBc/Hz offset 1 MHz from the same carrier, and -142 dBc/Hz offset 10 MHz from the same carrier. The second harmonic is typically -80 dBc, while the third-order intercept is typically +17 dBm at 2.130 GHz with typical third-order intermodulation distortion of -80 dBc.

On the amplitude side, the analyzers-boast typical displayed average noise level (DANL) of better than -145 dBm/Hz through 6.2 GHz ( -137 dBm/Hz through 14 GHz for the model RSA6114A) without the optional (Option 01) preamplifier and typically -170 dBm/Hz with the preamplifier on. The typical adjacent-channel leakage ratio (ACLR) performance is -70 dB uncorrected, dropping to -79 dB when noise corrected for a 3GPP downlink test signal. The analyzers can make measurements to a maximum input level of +30 dBm, resulting in a measurement range on the order of 175 dB! To aid in large-signal measurements, the analyzers are equipped with input attenuation of 0 to 75 dB, adjustable in 5-dB steps.

To simplify complex measurements, the RSA6100A Series analyzers provide a host of automatic measurements. The programmed power and frequency measurements include channel power, adjacent-channel power, multicarrier adjacent-channel power ratio (ACPR) and ACLR. General-purpose measurements include frequency error, phase error, EVM, origin offset, gain imbalance, quadrature error, rho, and constellation. For those who need automatic pulsed measurement capability, the Advanced Measurement Suite (Option 20) includes rise time, fall time, pulse width, pulse peak power, and pulse average power. Additional measurements feature power versus time, phase versus time, peak-to-average (crest factor), duty cycle, and pulse droop.

The Frequency Mask Trigger (FMT, Option 02) allows an operator to trigger on the occurrence of a unique pattern of events in the spectrum. It can be used to generate spectrograms showing both frequency and amplitude changes over time. The wide dynamic range of the FMT function, which works across the full 110-MHz measurement bandwidth, allows triggering on weak signals while ignoring known strong signals. The FMT feature is particularly well suited for capturing short-duration or time-varying signals, and ideal for applications such as surveillance and radar.

The growing complexity of modern communications and radar signals demands more powerful spectrum analysis, and the RSA6100A Series of Real-Time Spectrum Analyzers has been developed to meet those needs. These instruments are well suited for the growing-list of advanced waveform applications, including wideband software-defined radios (SDRs), surveillance systems, systems employing frequency hopping, systems with burst signals, and networks with adaptive modulation.

Tektronix, Inc.,
14200 SW Karl Braun Dr., P.O. Box 500,
Beaverton, OR 97077; (800) 835-9433,

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