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The price of an analyzer is, in part, derived from its cost. If the analyzer is designed using low-cost components, its price will look attractive. However, its performance can be limited. For instance, a single-loop local oscillator design may be cost effective, but it may introduce enough phase noise distortion to render the measurements useless. Likewise, a low-cost microprocessor used in place of a digital signal processor (DSP) for performing demodulation may cause the spectrum analyzer to execute at a very slow pace.

Another issue is sweeping architectures. Many traditional analyzer manufacturers still use a sweeping architecture. While this is good for microwave and millimeter-wave spectrum analysis, many newer RF analyzer suppliers forgo this traditional swept system and create a similar measurement using signal-processing techniques.

Measurement speed is another factor. Consider how the measurement data is processed. Some instruments use multiple processors to get a fast result, while others leave the main processor for general instrument housekeeping and use an FPGA or ASIC to execute the measurement. Also, there are some that just have a single microprocessor do all the work. While the latter may be the most cost effective for a manufacturer, it could be unacceptably slow with more complex modulation schemes.

One of the largest contributors to instrument price is the frequency range. Many analyzers have frequency breaks around 2.5 GHz, 6 GHz, 13 GHz, and 26 GHz. High-performance instrumentation can often go up to 50 GHz. If working on cellular products or products that operate in the ISM band, such as 802.11b/g wireless LAN devices, often the most cost-effective analyzer is one with an upper frequency range of less than 3 GHz.

Figure 1. Typical parameters of a basic signal.

Figure 1 shows a typical signal spectrum. There are two signals: a carrier wave (CW), and a smaller interfering signal. The carrier wave has a few key characteristics including amplitude, frequency, phase noise, and broadband noise. The amplitude is the spectral energy emitted by the device at a specific frequency. The phase noise, represented by the skirt of the signal, indicates how stable or spectrally pure the signal is. The local oscillator in the product usually contributes to the phase noise of the signal. To the left is an unwanted or spurious signal, which may be due to a large transmitter close by or be generated by some other part of the system, such as a microprocessor clock.

The better the amplitude measurement, the more reliable or certain the result will be. When looking for analyzers, don’t settle for worse than 0.6 dB or less than 3 GHz measurements

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