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Spectrasys LNA Noise +3 dB

Question asked by dbabitch on Apr 30, 2007
Latest reply on May 2, 2007 by dbabitch
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.