Jim Brown wrote: > Sensitivities in the order of .35 uV for 12 dB SINAD are common and they > can be improved with a preamp, but if you are already using a receiver > with .15 or so sensitivity, you will not be able to see any improvement > by adding a preamp. In fact, it is quite possible to decrease the > sensitivity due to overload in the preamp.
This is a very good, succinct sentence that "says it all". Nicely done, Jim. > Do a test on the repeater receiver to see what it's sensitivity is at > present and compare to the figures given above to see if a preamp can > add any useful sensitivity to the system. Agreed here too. As my elmers taught me... "If you didn't measure the system before you made the change, how do you know if you made it better or worse?" To get maximum performance out of any system, is a process that includes full performance measurements BEFORE adding or changing anything. If you KNOW your usable receiver sensitivity going in, including site noise with the antenna connected, and perhaps some other basic things like the noise-figure of your chosen receiver... You can then choose appropriate pre-amplification and filtering to match the circumstances that match your particular radio, antenna, duplexer... or what I call "overall system" configuration. What kind of VHF receiver is it? What's the factory spec for 12 dB SINAD? Is it already performing to that level? That's first... then pre-amps. One logical step at a time... is the easiest way to find "maximum" receiver performance. Nate WY0X
