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Post by Sam » Tue Aug 17, 2010 6:18 pm

I reorganized my photos so all those relating to drift over time/temp are in:

I also added two more, showing drift with a bigger fan installed. This one is about 10 CFM, though to reduce the noise in one scan I ran it slower with approx. 8 CFM (a guess). Even the scan with a 2 kHz RBW filter shows much improved stability, and the 30 kHz filter phase moves within a 0.15 degree band (i.e. variation of +/-0.075 deg) after 45 minutes.

This fan is still only 40 mm square and 20 mm thick. I glued it to the case with silicone, with about 0.1" of silicone between the fan and the case, to reduce transmission of vibrations. It has a bit of a whine to it, but I can't feel any vibrations in the case.

A decent sized fan, and crude insulation of the cavity filter, seem to provide good phase and magnitude stability. I'm still using the original MO. Also I am in a room with neither direct heating nor air conditioning, so any changes in ambient temperature are slow.

Sam W.

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