EEVblog Electronics Community Forum
Electronics => RF, Microwave, Ham Radio => Topic started by: CopperCone on September 17, 2017, 11:52:32 am
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What is considered state of the art for a 'experimental' laboratory receiver?
I figure that radio astronomy might have the best equipment, but they also have big dishes, so I am not sure what field to look at.
If compared to a spectrum analyzer, -? dBm.. I guess like -220dBm?
are there cryogenic equivalents to things like squids?
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Without cooling, I've done LNAs at 2GHz with 0.3dB noise figure. Thermal noise floor in a 1Hz bandwidth in 50ohms is -174dBm. That can be reduced by cooling. Noise = kTBR with T in Kelvin, so you need to get to -120 degrees C to half the noise floor, ie a 3dB improvement.
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what kind of LNA is that?
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what kind of LNA is that?
An expensive one I bet. ;)
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me too. Is it a wideband amplifier you put into a spectrum analyzer with spectrum limited?
Are there special coaxial cables? Does a regular good coaxial cable (like rf141) work at -100C? How about liquid nitrogen temps?
I would be interested in getting an amplifier setup that uses liquid nitrogen (i have a dewar)... liquid helium is off the budget right now though.
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I think in Dave's video to the Canberra DSN comm center they mentioned that they could get a usable signal at -160 to -165dB or so using cryo cooled LNAs directly on the back of the antenna. I'd imagine that in a lab environment you could do better, maybe a couple orders of magnitude, but I think it's a real tall order to get to even -200dBm without a ton of software averaging noise reduction or something.... even then, that's quite a ways below the stuff I've heard of.
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Once you have a good LNA with very low noise floor then, as KDJS was saying, Noise = kTB. If you want to lower the noise floor, you are going to need a good filter. Do you know the bandwidth you require to cover?
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I was looking for more a 'near theoretical measurements' graph as a go to. I don't have a specific signal in mind.
A case study if you will.