At 11/26/2009 07:31, you wrote:
> > "Mike Dietrich" <m.dietr...@...> wrote: > > The main way of thinking is that you want to put the > > pre-amp after the band pass filter. > > The reason for this is that if it is before the b/p > > filter, it amps anything it sees, noise and unwanted > > stuff alike. If its behind the b/p filter, it only > > amps the signals that are left and need it. > >It's a good way of thinking... but many of us in the >commercial radio world are thinking more along the lines >of what happens to the preamplifier and the receiver >during large input signal events. How does the preamp >and the receiver perform during signal over-loads and >how to best prevent those over-loads from causing >grief. Sounds like the best answer to the above is Mike's comment above yours. I personally find very few situations where I'd want to put a preamp ahead of a pass cavity filter. I guess that has to do with the quality of the radios I use (GEs). MVPs & Mastr IIs don't need pass filtering unless they have the UHS preamp installed. If the preamp goes ahead of the pass filtering, it's vulnerable to overload from out-of-band signals as well as lightning damage. If the preamp has integral filtering (helical resonators), it may not be as prone to the above, but it won't have the low noise that a good coaxial cavity filter/PHEMT preamp combo can achieve. > > 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
