Frank Gentges fgentges at
Sun Dec 5 21:53:45 CST 2004


In the microwave range, we are seeing low noise amplifiers for satellite 
antennas readily available with noise temperatures below 100 degrees 
kelvin.  These amplifiers use gallium arsinide transistors and run at 
ambient termperature.  I have wondered what these devices would do at 
lower frequencies for low noise.

This all suggests hams could build amplifiers with noise temperatures 
less than the termperature of the amplifier and its devices.  Cooling 
normal devices too far may cause them to cease operation rather than 
lower the noise level. Perhaps a compensated bias arrangement could 
overcome at least some of this problem.

All that said, cooling might be an alternative approach that would get a 
ham into low noise designs.  In other words, "never say never".


Hal Feinstein wrote:

> I know that radio astronomers often supercool some of their receiving 
> equipment to lower the
> noise  and thereby improve its sensitivity.  As a thought  experiment, 
> would it be practical for a ham
> to supercool parts of  the receiving chain of a system that was built 
> to receive a very weak signal?
> I'm thinking that the equipment, for example a low noise converter, 
> could be placed into some kind of protective jacket and emersed in 
> some supercool O2 or CO2 (dry ice).  First, does it make sense from a 
> radio engineering/physics point fo view?   Second, is their a 
> practical way to do this without elabroate equipment.   Third, anyone 
> in the amateur community tried this?
> --hal  wb3kdu
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