Lowering the noise figure in a rf preamp

Reduce temperature is the obvious one. Liquid nitrogen (or better).

Select a different uhf preamp.

Actually LN2 is a bit too cool (though I think I get your point) :-). In gamma particle detectors - made of a large Ge crystal cooled down to liqud nitrogen - the preamp FET is cooled to something higher, about -90 C (rather than the whole -190 C), they seem to work best there...

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Dave (from the UK) wrote:

Reducing the temperature depends on the type of semiconductor. A doped silicon one, aka bipolar may stop working when the usually thermally excited conduction electrons do not populate the fermi surfaces anymore. A FET is a completely different story. There the conduction is done by a field sensitive channel. FETs can work down to LHE.

Rene

Didi wrote:

Fets are different from bipoar indeed. Perhaps they can work down to LHe. For some reason, though, the detector manufacturers opt for about -90 C - all I know is this is common practice based on extensive experimentation over the last few decades. Invent a major noise reduction technique in this field based on your knowledge and get it sold, I may be among those interested.

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Rene Tschaggelar wrote:

It appears that dry ice (frozen CO2) sublimates at -109.3°F or -78.5°C; I've seen it used in an acetone bath to get not quite as cold as LN2. Then again, depending on your mounting arrangement, you might not need any liquid at all - just drop some chunks into a copper chamber...

Cheers! Rich

Raise the antenna gain. And its height.

Shorten the cable between antenna and amplifier.

Improving the noise figure of a UHF preamp will do little or no good if the signal is not there in the first place.

Measure your input S/N on a VFR or something similar.

Doesn't seem to work much with tv satellite receivers. Lowering the temperature apparently trashes the gain for no net benefit.