HP 5962-9217E free download

File name 5962-9217E.pdf

Agilent PN 89400-12 Understanding Time and Frequency Domain Interactions in the Agilent 89400 Series Vector Signal Analyzers Product Note A key strength of the Agilent Techno- logies 89400 Series vector signal analyzers (VSAs) is their ability to move easily between time and fre- quency domain measurements. This flexibility is ideal for analyzing signals that change with time, whether they are modulated, burst, pulsed, or transient. However, when using both domains simultaneously, one quickly finds Figure 1. Description of FFT terms that measurement parameters in one domain interact with those in the other. Changing resolution bandwidth T = time record length (sec) while RBW is the analyzer's 3 dB affects the length of the time display, Nt = number of time samples measurement bandwidth, usually which may or may not be affected by t = sampling interval spanning more than one frequency the frequency span selected, and so point. forth. Each block of Nt samples yields a block of N frequency points (i.e. a The proportionality constant in equa- Some of these interactions reflect spectrum) where: tion (1) is simply the ratio of span to unchanging physical law, while oth- sampling frequency, and is equal to ers are the result of algorithms or F = spectrum width, or span (Hz) 1/2.56 for baseband spans and 1/1.28 operating modes built into the ana- N = number of frequency points for zoom. lyzer's firmware for operating con- f = frequency point spacing venience. Although they can all be Equation (2) may also be written as: described mathematically, the graphi- The frequency domain data is tied cal approach developed here will per- to the time domain data by two fun- RBW = ws/T haps give the user a more intuitive damental relationships that are the feel for the analyzer's operation. foundation for much of the discussion where ws is the window shape factor. to follow. These are: The value for ws is dependent on Fundamental concepts window type, as follows: Agilent 89400 Series VSAs operate F 1/t (1) by capturing a waveform in the time RBW l/T (2) Window Type ws domain and using it to calculate a spectrum (frequency domain) display. Note that resolution bandwidth Flat Top