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3rd January 2004, 04:07 #1
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noise figure
I ask a question,
if nf of amplifier is 2 dB,24 db gain uder 50oHm system.
if the input impedence is∞, how much if the nf?

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3rd January 2004, 04:35 #2
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Re: noise figure
You will have to look at the data sheet for the transistor. It will have graphs of noise figure vs source impedance. It will be larger at the extremes of source impedance. (zero, infinite)

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5th January 2004, 05:12 #3
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Re: noise figure
Hi,
If the LNA is designed for 50 ohms normally the best noise figure will be achieved close to 50ohms but not exactly. The difference will be around 0.51.0dB in gain and around 0.25dB in NF.
At any other impedance the NF and gain performance will be very much worse.
BRM

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5th January 2004, 07:53 #4
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Re: noise figure
The NF and gain are all recieved under a certain input & output impedance. If you change its impedance without modifying your circuit, the gain and NF will be deteriorated greatly.
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