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Noise Figure measurement of the Receiver (Read 4882 times)
wccheng
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Noise Figure measurement of the Receiver
May 24th, 2004, 12:29am
 
Dear all,

      I have a simple receiver which is included LNA, downconversion mixer and the VCO.
      Do I need to add the low pass filter at the IF output for the noise figure measurement?
      How could I measure it in order to get the correct noise figure result?

Best Regards,

wccheng ???
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Itay
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Re: Noise Figure measurement of the Receiver
Reply #1 - Dec 24th, 2004, 12:18pm
 
Hello,

Sure, you have to add it to the total noise figure. The noise figure of a passive element like filter or attenuator is equal to its loss (only with absolute value). You can measure it with VNA (Vector Network Analyzer) and add it to your measurement. You can calculate the total NF result by using Frii's formula:

NFtot=NF1+NF2-1(G1)+NF3-1/(G1*G2) etc..

Good luck,
Itay
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pancho_hideboo
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Re: Noise Figure measurement of the Receiver
Reply #2 - Jan 25th, 2005, 2:23am
 
Whether you have to put LPF after mixer or not, it depends on IF spectrum purity.

If IF output have much undesired spectrum than desired IF spectrum(e.g. local leak which have generally large power leak), an input of NF meter will be over loaded, then you can't measure NF correctly.
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milkdragon
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Re: Noise Figure measurement of the Receiver
Reply #3 - Sep 1st, 2005, 5:26pm
 
You can use the Y-parameter measurement.  Simply apply a noise source at the input, turn the noise source on and off to see the difference of the noise floor from the spectrum analyzer, record also the ENR of your noise source, then you can get the NF

LPF is not a must, but your receiver chain has to have high gain, or otherwise it would introduce error
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