FROM EDN EUROPE: Signal analyser peers deeper into spectral data

Tektronix has extended the performance of its real-time signal analyser with the RSA3408A, which can view (up to) a 36-MHz-wide bandwidth in the dc to 8-GHz range (Picture). It samples, captures and digitizes the complete sample bandwidth continuously, performs FFTs on the data, and presents data in a variety of formats including spectrograms. Compared to its predecessor, it has twice the sample bandwidth due to a faster ADC; 4 dB more dynamic range; but an increased resolution of 2000×.

This figure is achieved because the previous instrument collected 1024 samples, per-formed an FFT, and repeated the exercise. FFT results were stored, but not the samples. The 3408A has much more memory; it stores the samples for post-processing and is equipped with complex triggering so that pre- and post-trigger display can be obtained with spectral data. It also has much more processing power; the post-processing can be set to perform overlapped FFTs, with a user-selectable degree of overlap. Previously, the instrument performed an FFT on samples 1 - 1024 of sample set 1; then repeated the process on sample set 2, and so on. Now, at maximum resolution, it will perform an FFT on samples 1 - 1024 of sample set 1; then it will begin at sample 2 of sample set 1 and use the 1024 samples through to sample 1 of set 2; and so on, "walking through" the successive sample sets. The point of this exercise is that it reveals data that is latent in the sample sets, but is not revealed by simple successive FFTs. In a demonstration using a frequency-hopping signal, with a power ramp, the trigger can be set at the point where the power ramps up. Using pre-trigger and a spectrogram display, the display shows the frequency of the signal track in from its previous hop channel, settle to the target channel, and (by use of color to represent power) ramp up in power. It is the extraction of the latent data that underlies the claim of 2000× resolution gain. The instrument can be equipped with signal masks for all commonly used digital radio standards and modulation types, and can be used for EMI, RFID, chirped radar and spectral monitoring tasks.

Tektronix, +44 1344 392000, www.tektronix.com.