Analyzers
pectrum analyzers are expensive pieces of equipment that should be handled with care, especially when it involves applying signals to the RF input. Some new users may not know what “care” means and how to go about ensuring the spectrum analyzer they’re using is protected from overloading and damage. The intent of this article is to describe how not to blow up your spectrum analyzer. Those new to the subject of spectrum analyzers and measurement receivers may first want to review references 1 through 3 which cover some of the basics concerning spectrum analyzers and measuring receivers in general.
It is usually the mixer that is most susceptible to damage, followed by some of the other components identified in Figure 1.
RF Input
The RF input port (usually located on the front of the spectrum analyzer) is where the signal desired to be measured goes. Before applying any signal to this port, it is prudent to first ask ourselves, “What can we do to this input? and “What can we apply here safely?”
Figure 1: RF Spectrum Analyzer Partial Front-End
It’s VERY important to carefully read and understand what it says on this label before attempting to measure any signal! The warning label will typically tell you the maximum RF signal levels that it can handle and also the maximum DC voltage levels it can handle.
Check the warning label to determine what it indicates as its maximum RF input level. A typical value is +30 dBm (1 Watt). Depending on the strength of the signal you want to measure, you may have to install an external attenuator or RF sampler (if measuring signals with high RF power) to ensure the maximum level seen by the spectrum analyzer is always maintained below its specified maximum RF input level of +30 dBm.
Figure 2: Warning Symbol found next to the RF input port
In the situation where zero DC volts is the maximum DC input level you can ensure that the signal you want to measure is AC coupled. This is accomplished by inserting a coaxial DC block in front of the RF Input port to ensure no DC voltage can “get through” to damage the mixer and other front-end components.
Summary
- MacArthur, D., “EMI Measurement Receiver Requirements (CISPR 16-1-1),” In Compliance Product Insights, September 2020.
- MacArthur, D., “Let’s Talk About Real-Time Spectrum Analyzers,” In Compliance Product Insights, September 2019.
- MacArthur, D., “What Every Electronics Engineer Needs to Know About: Measuring Receivers,” In Compliance Product Insights, September 2018.
- “#51: Basic Spectrum Analyzer Do’s and Dont’s…,” w2aew YouTube Channel, June 19, 2012.