BOOK_CONTENT
From The Radioman's Manual of RF Devices, Principles and Practices

3.2 The Swept-Tuned Spectrum Analyzer

The swept-tuned spectrum analyzer is commonly used by RF communication technicians, engineers, and amateurs. This type analyzer is a superheterodyne receiver with special circuits and characteristics (see Figure 3 1). Though this block diagram indicates a single conversion analyzer, typically, a spectrum analyzer would employ triple conversion.


Figure 3 1: A simplified block diagram of a spectrum analyzer. Modern spectrum analyzers are much more complex.

The RF attenuator and the IF amplifier gain are connected. For a given reference level, if the RF attenuation is increased by 10dB the gain of the IF amplifier is increased by 10dB to maintain the reference level. The RF attenuator is used to keep high signal levels from overloading the mixer, thus reducing the level of distortion products at the output of the mixer.

The low-pass filter, located between the RF attenuator and the mixer, removes the image frequencies, thus minimizing undesired responses in the spectrum analyzer. The mixer is where the input signal is beat against the local oscillator (LO) signal to produce the difference or IF frequency. The resolution bandwidth filter (RBW) is centered at the intermediate frequency and can be set for different bandwidths, depending upon the spacing of the signals to be resolved. After the signal is detected, it is passed through a narrow-band video filter to clean up the display.

The LO is a very important part of the spectrum analyzer. The frequency stability and phase noise of the LO becomes a limiting factor in...

Copyright Noble Publishing Corporation 2004 under license agreement with Books24x7

Products & Services
Spectrum Analyzers and Signal Analyzers
Spectrum analyzers and signal analyzers display raw, unprocessed signal information such as voltage, power, period, wave shape, sidebands, and frequency. They can provide the user with a clear and precise window into the frequency spectrum.
RF Mixers
RF mixers convert RF power at one frequency into power at another frequency to make signal processing easier and more efficient.
RF Frequency Converters
RF frequency converters are integrated component assemblies required for converting microwave signals to lower (or intermediate) or higher frequency range for further processing.  
Comb Generators
Comb generators create harmonic frequencies from which one frequency can be selected with a narrow filter and filtered out.
RF Phase Detectors and Comparators
RF phase detectors and comparators are circuits or instruments that provide a DC output voltage proportional to the difference in phase between two RF signals.

Topics of Interest

3.3 Features and Characteristics To cover all of the features and characteristics of a spectrum analyzer would require much more space than this chapter would allow. However, the most important...

The traditional method for implementing a spectrum analyzer is the swept heterodyne block diagram. Similar to a radio receiver, the spectrum analyzer is automatically tuned (swept) over the band of...

BARE-BONES SPECTRUM ANALYZER While an ac voltmeter can provide an indication of the field strength to which a probe is exposed, it does not provide any indication of the spectral contents of an...

What is a Spectrum Analyzer? A measuring instrument that displays an electrical signal according to its frequency. When the signal and local oscillator are added at the mixer input, the suitable input...

This application note is intended to explain the fundamentals of swept-tuned, superheterodyne spectrum analyzers and discuss the latest advances in spectrum analyzer capabilities. At the most basic...