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ttrf
Joined: 11 Jan 2003
Posts: 15
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 03 Jan 2004 4:07 noise figure |
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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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flatulent
Joined: 19 Jul 2002
Posts: 4926
Helped: 328
Location: Middle Earth
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03 Jan 2004 4:35 Re: noise figure |
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| 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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03 Jan 2004 4:35 Ads |
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brmadhukar
Joined: 21 Jun 2002
Posts: 844
Helped: 29
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05 Jan 2004 5:12 Re: noise figure |
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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 0.5-1.0dB 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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panpan
Joined: 03 Dec 2003
Posts: 5
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05 Jan 2004 7:53 Re: noise figure |
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| 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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