I built my own HF converter and incorporated an active, tunable RF pre-selector. I included switched gain, attenuation and bypass. The bypass mode was for use as an HF spectrum analyzer.
I made sure the LO in the converter was very clean before driving the mixer stage.
The noise figure of the pre-selector was less than 1 dB.
I ended up selling the whole setup to a friend and have been contemplating ordering another dongle and building another pre-selector.
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