Noise Figure Measurement

[deepu.deep2112]

Dear all,

Actually for noise figure measurement of receive path I have planned to provide noise from Noise source through a 20 dB coupler in my application.For more clarification I have attached the block diagram.
I am providing noise before coupler then at coupled port power level will be degraded by 20 dB after that I have limiter where loss will be 0.8 followed by LNA with NF 1.So,I want to know whether measured noise figure will take the coupler loss in account or not? Because before LNA whatever the lossed comes that directly appears in Noise figure.

Thanks for Co-operation.

 

[johnjoe]

can you put your block diagram for clarification? If your coupler has losses, for sure it will degrade your noise figure.

 

[jiripolivka]

If you only use the coupler to inject noise to your receiver, then you must know the noise power or temperature injected.
To measure receiver NF, if you use the Y-factor method , you need two known noise temperature levels gradually introduce to receiver input. One of those levels is selected to be the ambient temperature, the other can be that coupled by the coupler.

Your noise source has it ENR, excess noise ratio. It is the ratio , often in dB, how much the noise source exceeds the ambient temperature. Many noise sources have 13...15 dB ENR. YOu can apply it directly to the receiver, or attenuated, e.g. by a coupler. Then the ENR injected to receiver input is reduced by its loss in dB.
If you intend to leave the coupler in receiver input, then you must add its insertion loss to noise figure, both in dB. Typica insertion loss of coaxial couplers is 2...4 dB.

 

[deepu.deep2112]

In my case ENR will be 20dB as coupler loss is 20 dB.so if I am right I need to select a noise source of min ENR rated as 20...is it so?

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Kindly guide me about y factor method.

 

[jiripolivka]

Please find HP/Agilent Noise Figure Primer. Google low-noise receivers and NF measurement, You need to study more and on the Forum I doubt I can teach you enough in short.

 

[deepu.deep2112]

Sure...plz teach me...I will b vry thankful to u.

 

[jiripolivka]

So go to study first. Then e-mail me to jiripol@yahoo.com if you have questions.