Let's clear one thing up, a "CATV amp" can be a line amplifier (LA) or distribution amplifier (DA) and in both cases has greater than 50dB gain, far in excess of a scanner's front end signal handling ability. Consider the fact that they amplify VOLTS, not microvolts, if nothing else the internally generated noise cannot be buried in signal as it is in true CATV applications. Because they amplify "DC to light" like any wide band amp overload and intermod from both in band and out of band signals is a common problem unless you live out in nowhere land with no transmitters around for miles.
Gee, I wish Rat Shack and others wouldn't mislead you with inappropriate terms, you can't buy a CATV amp over the counter being that ordinarily they're only sold to cable TV companies by specialized wholesale distributors. Don't nit pick now, I had a special order CATV diplexer made up by a manufacturer in Canada so they DO sell one unit lots to individuals but you have to know where and how to order them. The word was "ordinarily", people have misread me before.
Last but not least, if you want the REALLY GOOD stuff you MUST do your own research and know what you're looking for. Like I said in so many words, you won't find it at Rat Shack, Grove or any other distributor catering to the casual hobbyist.