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Old 27th Oct 2022, 10:03 pm   #192
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: 6-gang FM stereo tuner heads

A crystal oscillator ought to be a few of orders of magnitude better than that, so you're probably using the crystal oscillator to measure the sum of the phase noise of the local oscillators in your analyser.

You also have to take into account that the -3dB bandwidth of your IF resolution is not quite the same as the equivalent rectangular noise bandwidth. Also there's a subtle one in that many analysers perform logging before averaging and this distorts the pdf of the noise.

If your analyser has a "Noise Marker" function and it's been thoroughly done, it should account for these things for you.

One way of measuring phase noise down to lower levels is to do a mix-down with a known clean signal source, and measure the result with an audio spectrum analyser... they often have reduced phase noise pro rata to the lower frequency LOs they depend on.

A good low phase noise measurement is quite an achievement. There are some good phase noise testers, but the prices are frightening.

David
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