Ask Dr. SETI ®
Dear Dr. SETI:
The Doctor Responds:
OK, so that is indeed a slight improvement. But now the problem becomes the rest of the system -- antenna noise temperature might be another 50K or so, mostly dominated by sidelobes. And sky temperature (which varies with where you're pointing) may add, say, another 10K or so. So unless you dry-ice the Earth, your system noise goes down only from 110K to maybe 94K, a 0.7 dB improvement in sensitivity (which translates to a 8% increase in range). Well, every light year counts, so don't let me discourage you from trying dry ice! (Liquid Nitrogen would be even better, with something like 77K evaporation temperature at standard pressure. In the prior example, this would lower LNA noise to 13K, system noise to 73K, and improve our range by about 23%!)
Here is a spreadsheet to help you with such computations.
Other cooling options also come to mind. Some of our members have successfully employed solid state Peltier Effect cooling devices to lower the ambient temperature of their preamplifiers. Like cryogenic cooling, these devices can do nothing to reduce antenna noise temperature, sky temperature, or Earth-temperature sidelobe pickup.
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this page last updated 28 December 2002
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