Question about receiver budget

I simulated a simple receiver using ADS budget,which has a amp,mixer and another amp.I find the noise figure is always 3dB more than that of non-image noise.But I read the "pratical rf system design".in page 69,it says,if the gain of first amp is low such as 5 dB,the difference between the noise and non-image noise is 1dB.
what's wrong?

what is the noise figure is it SSB , or DSB
it sure will affect the total noise figure of the system

Khouly

hi,

what do you mean with non-image noise? is your receiver zero-if or heterodyne? the contribution of the image noise to the noise figure depends on your receiver topology: homodyne or heterodyne for example...

it should be 3 dB difference between DSB and SSB.But in "pratical rf system design",it is not!

3dB degradation is the worst case due to the thermal noise at the image frequency.

I would recommend the book ?RF Design Guide ? Peter Vizmuller? (pag 16)

https://www.edaboard.com/viewtopic.php?t=35713