Below is a two part project for an RF Spectrum Analyzer from QST Magazine. Even if you don't build the project there's some great information in here regarding RF filters, mixers, oscillators and more.
Spectrum Analyzer (Part One)
A mong the many measurement tools sought by the amateur experimenter, the most desired but generally considered the least accessible—is the radio-frequency spectrum analyzer or SA. This need not be simple and easily duplicated, this homebuilt analyzer is capable of useful measurements in the 50 kHz to 70 MHz region. The design can be extended easily into the VHF and UHF region with methods outlined later. The instrument is configured to be self-calibrating, or capable of calibration with simple home-built test gear.
Spectrum Analyzer (Part Two)
One use for a spectrum analyzer is amplifier evaluation. We can illustrate this with a small amplifier from the test-equipment drawer—an old module that has been pressed
into service for a variety of experiments. This circuit, shown in Figure 11, is used for illustration only and is not presented as an optimum design. It’s a project that grew from available parts and may be familiar to some readers. The circuit uses four identical 2N5179 amplifier stages. A combination of emitter degeneration and parallel feedback provides the negative feedback needed to stabilize gain and impedance. (Ideally, construction and measurement of a single stage should precede construction of the complete amplifier.)
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