At 11/26/2009 09:39, you wrote: > > > > > You might need to add a several DB attenuator > > > > between > > > > the pre amp and the receiver to keep from over > > > > driving > > > > the front end. > > > > Not if you use a good receiver, or not use a preamp with > > too much gain. > > > > Bob NO6B > >What defines "too much gain" can vary wildly.
Let's take a receiver with 12 dB SINAD of 0.5 uV, about as deaf a RX as anyone here will probably use. 14 dB of theoretical, noiseless gain gets that down to 0.1 uV. Since the preamp has a finite NF, the SINAD level would be a bit higher, but not much for a low-noise preamp. 0.1 uV is about as good as you can do with a NBFM RX, as that's roughly 6 dB above kTB when T=295 K (average earth temperature). So I don't see any point in a preamp having more than 14 dB of gain, unless you're adding post-preamp lossy filtering or power splitters. Bob NO6B
