(Sighs, looks down at mug full of decaf)

Looks like I picked a bad week to give up caffeine

Yeah it's totally obvious my idea won't work, now that you've explained it. All right, with the goal still in mind of improving my system performance, let me ask another question:

Existing tuner has NF of 7dB. Goal is to reduce this dramatically, by 5 or even 6dB. What is the minimum gain a preamp would need to accomplish this? (Assume preamp NF of roughly 1dB.)

Apply

Friis' Equation:

F_total = F1 + (F2-1)/G1 + (F3-1)/(G1*G2) + ...

In your case, you only have a two-stage system, so this simplifies to:

F_total = F1 + (F2-1)/G1

Converting to linear ratio, 1 dB NF is equal to a noise factor of 1.26 and 7 dB is equal to a noise factor of 5.01. Your target NF is 7-5 = 2 dB which works out to a noise factor of 1.58.

We can then substitute:

1.58 = 1.26 + (5.01-1)/G1

Solving for G1 yields a linear gain of 12.5, or approximately

**11 dB** for an LNA with a noise figure of 1 dB.

Designing an LNA with this kind of performance should be achievable. However, your P1dB will be pretty bad unless you bias your transistor with a *lot* of current. For a good introductory reference on RF design, I recommend "RF Circuit Design" by Chris Bowick.