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ctech4285
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Thermal noise?

Thu Oct 21, 2010 7:44 pm

i did some wiking specifically: http://en.wikipedia.org/wiki/Johnson%E2 ... uist_noise
the thermal noise floor for 20mhz wide channel with 50ohms is -101dbm, and that happen to be very close to what the R52nh card reports most of the time.
-174dbm is there thermal part at 300kelvin
if one where to cool down the receiver amplifier to lets say 30kelvin one would push the noise floor to -111dbm a 10 fold improvement on you link budged. for sure not practical unless you looking for something to substituted 50dbi antenna.

but anywho my question is do you have to cool the antenna down too or just the pre amplifier in the radio card?
 
SurferTim
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Re: Thermal noise?

Thu Oct 21, 2010 9:48 pm

30 kelvin = -243.15C. Are you kidding? Any idea what the refrigeration unit to get that kind of temperature would cost?

ADD: Now for the good news: According to the two scientists who discovered the background noise from the "Big Bang", only the receiver needs cooling. Not the antenna :D
 
ctech4285
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Re: Thermal noise?

Fri Oct 22, 2010 12:45 am

yeah as i said this is not that practical to save the 200$ to buy a bigger antenna..it's probably the electricity usage for a couple of days....
but man if you get down to 1k you have a 300 fold increase in sensitivity
i suppose you could stack up 20 or so peltier elements and burn 50kw to do it....
but if you get close too the theoretical limit you would need 300 times more energy then the amount you transfer....so the size of the refrigeration unit would not be that bad if you just keep the power consumption down and use something thats a little more efficient then Peltier elements...but then again i don't think anything practical exist for cooling lower 220k or so
i am wondering if someone has played with this yet...
 
Beccara
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Re: Thermal noise?

Fri Oct 22, 2010 12:57 am

1K are you sure your talking in the right degrees here? You'd need LN2 full time to maintain 1 Kelvin. Anyway at some point the electronics will fail and/or you'll have condensation problems. Maybe just try fan cooling to try and keep the temp's at room temp
 
netrat
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Re: Thermal noise?

Wed Oct 27, 2010 4:51 pm

1K are you sure your talking in the right degrees here? You'd need LN2 full time to maintain 1 Kelvin. Anyway at some point the electronics will fail and/or you'll have condensation problems. Maybe just try fan cooling to try and keep the temp's at room temp
LN2 boils at 77K, liquid helium is 4K. You'd need some exotic cooling to get down 1 Kelvin, I'd take a wild guess and say hundreds of thousands if not millions of dollars to get that cold.

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