What do you mean by overload? How come there is too much garbage as
long as my NF is low?

I actually need 143dB gain. What kind of problem I will have if I just
use 6 stages of amplifiers, like 1stage(20dB, NF2.4dB) 2nd stage(30dB,
NF3db), 3rd stage(43dB, NF 6.2dB), 4th stage(43dB NF6.2dB). It seems my
NFtotal is pretty low. What's my problem?

Thanks.

Dale Parfitt wrote:
wrote in message
ups.com...
I am wondering what's the bad effect of cascading a lot of low noise
amplifiers? It seems that if I devide 90dB into 4 LNAs I will have much
less noise figure. Can I use 5 LNAs in series? Any disadvantage about
this way? Thanks.

If your 1st LNA has the lowest noise figure and sufficient gain, it will set
the noise floor.
You can work the cascaded amplifier equations and see what you will need.
90dB seems like a LOT of front end gain- unless this is very narrow band, I
would be very concerned about overload resulting in all kinds of in band
garbage.

Dale W4OP