Spectrum Analyzers Field User Guide

1 Spectrum Analyzers Field User Guide utilizing Anritsu's Handheld Spectrum Master , Site Master , Cell Master , and BTS Master . RF Measurements A Users' Spectrum analyzer Block Diagram Description RF Measurements Using Markers Why use a Spectrum analyzer ? Why use a Spectrum analyzer ? Instrument Setup Spectrum analyzer Setup (Part 1) > DC Block Attenuator PreAmp First IF RBW Filter Envelope VBW Filter Spectrum analyzer Setup (Part 2) Marker Measurements Mixer The first mixer level is critical for proper performance. If an Over-the-Air (OTA) signal is Trace Limits & overdriving the first mixer, false signals, or spurs, may Detector Units appear. The noise floor may also rise and hide signals Modes Measurements of interest.

2 This can happen even if the OTA signal is outside of the current span. Spectrum Analyzers display an overload message if overload occurs. The first response is often to raise the Swept reference level, either directly or by manually Sweep increasing the attenuation of the step attenuator. Local Generator Oscillator An alternative is to use an external band pass filter to limit OTA signals to the band of interest. While filters do a great job of attenuating unwanted signals, you must have the right Block Diagram Description Block Diagram Description (continued) filter that passes the signal you Spectrum analyzer users need to understand major The detector samples the IF signal and converts it to are measuring with minimal loss.

3 A Spectrum analyzer lets you see signal analyzer functional blocks. While most of the choices digital samples. The Anritsu has a selection of filters for this purpose. Markers make it easy to verify amplitude &. problems. If you can't see it, you can't fix described here are made automatically, manual selections input to the detector frequency points on the Spectrum ; the marker it. are possible and can be helpful. normally is many Coupled mode is the default more samples than An external filter can table lets you see up to 6 markers and delta The DC block prevents DC voltage from entering the operating mode for Spectrum reject high-level signals Why use a Spectrum analyzer ? can be displayed on Analyzers . In this mode, that limit low-level values at a glance.

4 Instrument, and allows measuring lines with DC power. measurements. Spectrum Analyzers display RF signals from base the screen. attenuation, RBW, and VBW. The step attenuator helps to prevent overdriving the first Instrument setup is faster when using Markers. The stations and other emission sources. They find rouge The detector groups values adjust automatically, set by the user's choice of marker functions Peak Search and Marker Freq to signals, measure carriers and distortion, and verify mixer; excessive level at the first mixer causes distortion reference level and span. In coupled mode, both span samples, creating one Center can be very helpful, as they will find and center base stations. Unlike a power meter, they validate visible on the display.

5 Spectrum Analyzers normally enable and reference level affect the noise floor. group for each the strongest signal. carrier frequency and identify desired and undesired the step attenuator when the reference level is over display point. It then Manual mode allows attenuation, RBW, VBW and to signals. -20 dBm or so. The step attenuator raises the noise floor Unique marker measurement capabilities include fixed The detector chooses how to display chooses one number be set directly from the instrument's front panel. when enabled, but allows measuring higher signal levels. and tracking delta measurements ( Delta or is Spectrum analyzer Setup signals when the RBW is less than a related to each Manual mode allows making finer tradeoffs in noise You can think of this as matching the dynamic range of the display point.)

6 Shorthand for difference). group for display. level, distortion, trace variation, and sweep speed. RF signals have a frequency, bandwidth, and power. analyzer to the input signal level. Peak displays the largest sample of each group. Fixed markers are useful for delta measurement when To best view an RF signal, three things need to be A preamplifier is often the first block in a Spectrum Manual attenuation capability is helpful when the signal is intermittent. In this case, the reference set. This is the default detector and is useful when checking for distortion. A quick check to see if a signal analyzer . Use it for weak looking at CW signals, as well as an intermittent marker can be fixed, or frozen, at a specific amplitude, signals, lower than about is spurious is to change the step attenuator 10 dB.

7 If even if the signal goes away. A tracking marker follows Adjust the center frequency to center the desired or bursty signal. -50 dBm. When on, it the signal doesn't change, all is well; it is a real signal. changes in trace amplitude. signal. Entering a known carrier frequency is a RMS calculates the average power of the reduces the noise floor by If it changes by 10 dB or more, it is an internally common way to do this. Other common methods use grouped samples and displays that. This is useful about 10-15 dB. Turn it off if generated intermodulation product. Sometimes the Marker delta measurements can either use marker 1 as the knob or arrow buttons, a channel number, or the when measuring noise or noise-like signals.

8 Many the RF signals are higher distortion can simply be ignored; in other cases the reference, allowing six delta measurements, or use Marker to Center function. cellular signals are noise-like. than -40 dBm or so. increase the attenuation until the distortion level each of the six markers to have their own delta marker. Adjust the span so that the desired signal covers Negative displays the smallest sample of each doesn't change. This will allow up to 6 delta measurements and 12 total about half of the screen. group. This is useful when looking for dropouts of markers on one screen. This is a good way to measure The preamplifier reduces the The first mixer is the first a signal, mostly in zero span. Manual RBW capability is helpful when a lower noise Adjust the reference level to bring the top of the noise level, allowing lower-level down-conversion stage, the floor, even at the expense of a slower sweep speed, is and document signals.

9 Signals to be seen in the yellow Sample picks just one of the input samples signal near the top of the screen. trace, where they couldn't be stage that changes the RF Quasi Peak (not shown) is useful and EMC desirable, or faster sweep speed is needed, at the seen without the preamp in the frequency to an intermediate (Electromagnetic Compatibility) measurements. expense of higher noise floor and poorer frequency Quick Conversion: dBm to Watts This is a flexible process. Often, it is best to start out green trace. frequency (IF). The step This is a special detector type that emulates the resolution. Every 10 times change in RBW means a 10. with a close center frequency, an approximate attenuator and preamplifier allow adjusting the input signal response of the human ear to impulses.

10 DB change in the noise floor. reference level, and narrow the span (span down) in Rule of doubles: Every 3 dB change in power to match what the first mixer needs to see. stages, re-centering the signal as you go. Otherwise, Sweep speed is normally set automatically. It can be Some Spectrum Analyzers will have a lower noise floor, doubles or halves the power. the signal may move off the side of the screen as you IF section contains further mixers and creates more IF helpful to set lower sweep speeds manually when at any given RBW, than others. The noise figure The Times Ten rule: Notice how the 10's digit in span down. frequencies. working with intermittent signals. In this case, the Max- specification determines this, or you can estimate the dBm row corresponds to the number of zeros Resolution Bandwidth (RBW) sets the level of signal detail Hold trace setting is also helpful.