#### Ngu Kek Siang

##### Newbie level 3

Calculate noise figure:

.ac dec 50 400MEG 3g

.NOISE v(vout) vin 1

Calculate S11 and S22:

.net v(vout) vin rin=50 rout=50

.print s11(db) s11(m) s11(p)

.print s22(db) s22(m) s22(p)

However, I get negative NF after calculate from the following:

**** resistor squared noise voltages (sq v/hz)

element 0:r3

rs 9.1186f

1/f 0.

total 9.1186f

rx 5.2622k

...

**** total output noise voltage = 433.9253f sq v/hz

NF = 10log(9.1186f/433.9253f) = -16.77dB

and get 0 value for S11 and S22:

freq s11 s11 s11

db mag phase

400.00000x 0. 1.0000 180.0000

418.85142x 0. 1.0000 180.0000

...

2.41024g 0. 1.0000 180.0000

freq s22 s22 s22

db mag phase

400.00000x 0. 1.0000 180.0000

...

2.41024g 0. 1.0000 180.0000

Can I know did I do wrongly? Or why these values appear?

Thank you.