Two narrow signals can only be separated, if the resolution bandwidth is smaller than the distance between these two signals. Resolution bandwidth affects is the ability to separate or resolve closely spaced signals. The result is the same, and many RF engineers do think of resolution bandwidth as a moving window or filter that crosses a span. The window also doesn’t move, the spectrum is slid past the window instead. Anyhow the resolution bandwidth filter or window isn’t square but has a Gaussian or similar shape. One way to help understanding resolution bandwidth is to think of it as a window that moves across the span, measuring the level as it goes. The trace showing power versus frequency is drawn from left to right, usually repeatedly. Most spectrum analyzers use heterodyne based analyzers to measure spectrum by sweeping across a span. Most often the center frequency of the signal of interest is known, and by using span it’s easier to zoom in and zoom out by just increasing or decreasing the span.įor basic spectrum measurements, resolution bandwidth is, by far, the most important setting.
The range 840 MHz to 860 MHz is the same as a center of 850 MHz and a span of 20 MHz.
The names are self-explanatory: center is the frequency in the middle of the display, and span is the width of the display. These values could be entered into a spectrum analyzer as start and stop frequencies, but center and span are used more commonly. These settings are used when making almost any kind of spectrum measurements.Ĭenter and span define the frequency range to be measured by setting the stop and start frequencies.Īs an example, to measure power between 840 MHz and 860 MHz. There are four essential parameters needed to operate a spectrum analyzer. Other measurements like occupied bandwidth or adjacent channel leakage ratio, would be difficult or impossible to manually measure. These measurements could be done manually but automating them increases efficiency and accuracy. Most spectrum analyzers automate certain power versus frequency type measurements, like AM modulation depth or third order intercept. This is also the most fundamental measurement on a spectrum analyzer: a plot of power versus frequency. Spectrum analyzers are frequency-domain instruments, showing power versus frequency. The following is an introduction to basic spectrum analyzer operation. Understanding basic spectrum analyzer operationĪuthor: Paul Denisowski, Test & measurement expert R&S®Essentials | Spectrum analyzers fundamentals
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