How to Optimize Spectrum Analyzers/Signal Analyzers - 5 Tips for Optimizing Transmitter Testing

Optimizing spectrum analyzer transmitter testing is easier than you think. We will introduce 5 tips that can help you improve efficiency and obtain clearer spectrum measurement results. You will learn how to use some simple methods to speed up the measurement speed of spectrum analyzers, reduce measurement errors, and improve the reliability of measurement results.

Learn how to perform tests more efficiently by:

1. Calibrate the test system

2. Optimizing resolution bandwidth can improve test speed or accuracy

3. Improve sensitivity when measuring low-level signals

4. Minimize analyzer distortion products

5. Use measurement application software to speed up measurement, improve measurement accuracy and reliability

Tip 1: Calibrate the test system

Correcting the Test System Before the device under test (DUT) signal enters the signal analyzer, cables, adapters, and probes can alter the signal, causing your measurements to be inaccurate. But there is a way to fix this. You can restore signal accuracy by applying corrections in the Keysight X-Series signal analyzer.

To apply corrections, you need to measure the signal delivery network using a known signal source to stimulate it. The signal delivery network refers to everything you use to connect the DUT to the signal analyzer, including cables and connectors. Making these measurements with a known signal source reveals how the signal delivery network affects your measurements when you connect the DUT.

Enter correction factors measured from the signal transmission network to offset these errors introduced into the signal analyzer. You can enter correction factors directly in the user interface using SCPI commands or load them from a file.

The X-Series supports eight different correction arrays and eight complex correction arrays that can be turned on and off as needed. The figure to the right shows the frequency response of the signal delivery network before and after correction.

Before correction

After correction

Use the signal analyzer's built-in correction capabilities to eliminate the effects of cables, adapters, and noise.

Tip 2: Optimizing the resolution bandwidth can improve the test speed or accuracy of the spectrum analyzer

Resolution bandwidth (RBW) has a significant impact whether you are making fast or detailed measurements.

If you are only going to do a few quick random checks, such as verifying the quality of a few devices in a production line, you may be inclined to set a wider resolution bandwidth. The resolution bandwidth determines the span of the swept measurement spectrum. With a wider resolution bandwidth, you can achieve fast sweeps and faster testing, but the detail and accuracy of the measurement will be affected.

If you plan to make detailed and accurate measurements, such as EMC (electromagnetic compatibility) testing or looking for spurs, then you need to set a narrower RBW. The narrower the RBW, the more detail you capture, which means you can catch spurs that are very close.

Narrow RBWs also reduce the displayed average noise level (DANL), resulting in an improved signal-to-noise ratio. Note, however, that the downside is that it requires longer sweep times. For example, a measurement with a 10 kHz RBW on a 200 MHz span might take 2.4 seconds, while a measurement with a 3 kHz RBW on the same span might take nearly 27 seconds. The sweep time has increased by a factor of 10. You should choose the RBW that best suits your measurement needs and test priorities.

Tip 3: Improving Sensitivity When Measuring Low-Level Signals

Do you have a headache finding low level signals? These signals like to hide in the margins of noise and high power signals. Three simple tips can help:

1. Minimize input attenuation

2. Reduce the resolution bandwidth

3. Adding a preamplifier to the test system

By minimizing input attenuation and adding a preamplifier, you can get the signal level far above the analyzer's noise. A narrow resolution bandwidth reduces measurement noise and narrows the edges of large signals, allowing you to resolve very close signals. Applying these techniques improves the signal-to-noise ratio, allowing different signals to stand out clearly, allowing you to find low-level spurs.

Tip 4: Minimize spectrum analyzer distortion products

Spectrum analyzers/signal analyzers are often used to characterize the distortion of amplifiers or mixers. When characterizing a device, you need to find a small signal in the presence of a large signal. You already know that adjusting RBW and attenuation can help you find the signal you are looking for. However, there is more to consider when it comes to distortion.

Every spectrum analyzer/signal analyzer has distortion, and you have to figure out if it is coming from the analyzer or the DUT. The analyzer's distortion changes with the amount of power going into the mixer. When you reduce attenuation to reduce noise, the input signal power going into the analyzer goes up, causing the analyzer's distortion products to increase. You should carefully adjust the attenuator and RBW settings to find a balance between lowering the noise floor and increasing distortion.

Advanced Tip: You can also use dual traces to determine if distortion generated in the analyzer is affecting the measurement. For a detailed description of this process, refer to the "Identifying Internal Distortion Products" section in the Signal Analysis Measurement Basics Application Note .

Tip 5: Use measurement application software to speed up measurements and improve spectrum analyzer measurement accuracy and reliability

The increasing complexity of wireless systems and transmitted signals can make manually configuring transmitter measurements difficult and time-consuming. Fortunately, measurement applications make it easy to set up both complex and traditional measurements on your signal analyzer.

These applications can automatically configure the test, setup, cursor and reporting tools to quickly complete the measurement setup. Measurement applications are divided into two main categories: general purpose and standards-specific.

General purpose applications focus on traditional analysis tasks such as measuring channel power, occupied bandwidth, spurious emissions, harmonics, and phase noise. These applications are very helpful in the development and manufacture of RF/microwave transceivers and their related components. The X-Series analyzers come standard with general purpose measurement applications.

Test applications that support specific industry standards can speed up the design and troubleshooting process. Wireless software packages for different standards (including LTE, GSM, W-CDMA and Bluetooth®) can automatically configure and run RF conformance tests to evaluate and troubleshoot your design. Whether you are engaged in manufacturing, teaching or designing, measurement applications are a good helper for you to simplify and standardize your test system.

Summarize

Spectrum analyzers/signal analyzers can quickly reveal measurements that are better than you think. Keep these simple measurement tips in mind and apply them wisely, and you’ll see your test results improve dramatically and your test time decrease dramatically.