When trying out antennas, amplifiers and external filters you should look at the noise level for analog channels and D_ERROR for digital systems and totally ignore the RSSI and signal strenght bars as those could be looking at a 10Mhz wide frequency span and not only the monitored frequency. Also when using amplifiers it will increase the signal strenght but it is the noise level that you want to be as low as possible or you are only adding more noise to your reception. If you are using the full 15dB amplification you probably are overloading the scanner, or very close to it. I have different scanner brands and no scanner can take more than a 6dB gain, at the scanners antenna port and using no external filters, without loosing sensitivity. The best way to set gain level are to use a
variable 20dB attenuator after the amplifier and adjust it for best signal quality, the lowest noise or d-error value.
I would think that a noise level of 1000 would the max where noise becomes annoying. Remember that when someone talks or there are other sounds in the transmission it will increase the noise level. The noise number will only indicate a more or less steady vaule when there's a carrier without anyone talking. That could make it difficult to see any changes you make to your setup and it's probably best to use your ears with analog signals and the d-error value for digital as the digital stream are modulated at a constant level.
/Ubbe