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Hi Gerard,

actually the frequency measurement through a generator and an oscilloscope is possible only if you can synchronize the oscilloscope with the generator and if you have a mixer followed by a medium frequency and a logarithmic detector at the oscilloscope input, some time ago I made a small spectrum analyzer for my old HP181, it worked fine, it had a dynamics of about 90dB and a bandwidth of 300MHZ, the mixer was a module from Microcircuits, the MF and the quartz filter were a part of an old project of QST (analyzer for penniless HAM) and the logaritmic detector was a module with an AD8307.

The circuit isn't complex to build, but is it worth it?

Today there are so many KITs and so many small spectrum analyzers at such affordable prices that I don't think you need to venture into a home construction.

Do not be fooled by a VNA (vector network analyzer), it cannot act as a spectrum analyzer except through the FFT which, as is known to all laboratory technicians, poses many problems in interpreting the displayed data, including false harmonics, aliasing and unwanted beats, it's easier to blunder than to know exactly which armines your oscillator or TX is kicking out.

The technically best solution is to invest a few dollars in a decent Spectrum Analyzer (check that it has the possibility of a VCO voltage output to drive the sweep of your generator) and with that, combined with your generator and a simple AD8307 Logaritmic Detector module , you can do all the functions you want of any VNA.

Greetings de