Re: Question: how to reduce NF in a Receiver?

Sorry, but I think that with a front end high gain LNA you have no reason to add a second amplifier.

The noise figure of an RF chain (receiver in ur case)is given by

F=F1 + (F2-1)/G1 +(F3-1)/G1G2 +............+(FN-1)/(G1G2....GN-1)

suppose u have an Rf chain like

Filter------>amplifier------>attenuator

L=3dB G=20dB L=2dB
NF=4dB

Here G1=1/2(-3dB) F1=2(3dB) G2=100(20dB) F2=2.5(4dB)
G3=1/1.58(-2dB) F3=2dB

so F=2+3+.012=5.012(7dB)

so if u want to reduce overall noise figure of ur Rx use low loss first component and also use high gain LNA the rest of component will not affect the NF much.

Hoping this will help u.

Checking a 1st LNA bias point(amplifier tail curent),
and impedance eq Gamma-OPT.

Hi,

If you didn't take care of the NF in the LNA stage itself and even before it then, there is not much you can do after the LNA cause NF is additive. If you produce a poor NF, you will not be able to fix that.

Enjoy,
RF_Router

using optimum gamma of the transistor datasheet if it is uncinditionally stable or near it as much as possible if it is conditionally stable and use optimum dimension for stub and transmission line at input and output

RF_Router is right. First stage is the most important stage. After that there is nothing you can do. LNA must be stable also in your range of frequencies. In contrast as it helps NF is that oscillator must be very unstable.

After all these considerations, what is your NF achieved?

T Zul