Don't really know why but a couple of sites I programmed in get this annoying loud feedback like an electronic jackhammer or something and I have to lock them out. One is a certain frequency on the Cheyenne Mtn site and another is the San Carlos Correctional Facility(right on the same campus when my job is). Maybe they are secure and that's why the scanner isn't picking them up, doesn't really bother me but seems odd when many other frequencies on those same sites are readable. I was even able to get the Pueblo PD okay. Am using the 800Mhz antenna and it seems to be working as good as any for this system and picking up really good.