the impact of LNA in presence of a jammer

[novice_user]

Jammer and LNA

Hello guys,
I read multiple papers below (attached files) but still couldnt understand the impact of LNA in presence of a jammer? Impact of increasing/decreasing the gain state of LNA in presence of jammer how affects sensitivity?

Help is really appreciated..have been struggling with this topic for a while ...

Thanks

 

[biff44]

Re: Jammer and LNA

In the world of communications receivers, you need a certain signal-to-noise ratio at the front end for it to work. If you have a bad signal-to-noise ratio, you can get bit errors, garbled speach, of often no communications at all. Some receiver systems have "coding gain" so that you can stand a poorer signal-to-noise ratio due to mathematical processin trickery.

One way to screw up your signal to noise ratio is to let signals that are "out of band" to fold into your receive band. Lets say you have a receiver working at 2.43 ghz, and there is a wireless lan 6 inches away running at 2.41 GHz, and another one running at 2.42 GHz. The receiver you are trying to use sees those jamming signals. If the LNA front end has a poor intercept point, and nothing else attenuates those jammer frequencies, the 2.41 GHz mixes with the 2nd harmonic of 2.42 GHz in the LNA, to jam your desired channel at 2.43 GHz. i.e. 2.42X2 -2.41=2.43