Is mixer a passive device when calculating noise figure?

[jason_class]

noise figure

Hi All

I would like to know should we consider mixer as a passive device when calculating Noise figure as for the example in the attachment where we see there is gain for the mixer.
Kindly enligthen
Thank you

rgds
jason

 

[flatulent]

Re: noise figure

Use the classical cascade calculation algebra and use the noise figure and gain as numbers (not dB). This formula works for all passive and active stages. Passive stages have the noise F as the loss value. A 3 dB resistive attenuator has a gain of -3 dB and a noise figure of 3 dB. Diode ring mixers usually have a noise figure that is 2 dB worse than the loss. -6 dB gain and 8 dB NF are usual values.

 

[biff44]

Re: noise figure

That is true, but only if you have a filter or restricted bandwidth gain somewhere in the system that removes the unwanted image noise. Without that filter, things are 3 dB worse.

 

[Rafouille]

Re: noise figure

Hi biff44,

your remarks is only true for mixer, or not?
Thanks

 

[jason_class]

Re: noise figure

Thank you All.
Let me retry the calculation. I will write back sooner

cheers


Jason

 

[jason_class]

Re: noise figure

Thank you Flatulent and all who helped me here. I pass my subject and I am so happy.
I want to thank you all for the kind and generous heart to help
Thank you

Jason