I have a Rx lineup with filter/LNA/Filter/Amplif/Image-reject Mixer/Filtered IF Amp. Problem: The Spectrasys CumNF shows an noise increase of 3 dB thru the LNA. I have no problems after the LNA, the noise rises a little as expected.

The LNA NF is 1.2 dB, gain 15 dB, reverse isolation 25 dB.

The filters have 0.5 dB loss. Reasonable ripple does not affect the result.

2nd Amplif gain is 12 dB, NF = 5 dB, reverse isolation is 25 dB.

Impedances are all 50 ohms. The real hardware has the expected NF thru the LNA ~ 1.2 dB, not 3 dB.

Any ideas why the CumNF does that thru the LNA?

This version is 2007-03. An older version, no longer available to me, did not have this issue.

The LNA NF is 1.2 dB, gain 15 dB, reverse isolation 25 dB.

The filters have 0.5 dB loss. Reasonable ripple does not affect the result.

2nd Amplif gain is 12 dB, NF = 5 dB, reverse isolation is 25 dB.

Impedances are all 50 ohms. The real hardware has the expected NF thru the LNA ~ 1.2 dB, not 3 dB.

Any ideas why the CumNF does that thru the LNA?

This version is 2007-03. An older version, no longer available to me, did not have this issue.

It's really impossible to tell what's happening without the circuit in-hand. My guess would be an impedance mismatch. If you would like to email the wsx file to me we can take a look at it. If it's confidential we can delete it after we look at it.

Mark Zachmann