Diamond Discone with 50' of RG-6 into the pre amp, Short jumper into the scanner i lose my Chattanooga trunked system, If i come right from the antenna into the radio i get Chattanogga back.
I tried 2 Pre Amps, A 11db and a 15 db with the same results....
Do some antennas work better w/o a pre-amp?
A pre-amp will make no difference to how an antenna performs - but it can make a ton of difference to how the receiver performs.
In short a pre-amp will:
- raise a signal level that is to low to a level that your scanner/receiver can work with it (i.e. demodulate)
- raise a signal so much it saturates the receiver front end - and then you'll hear nothing or just noise.
Interestingly research shows that in something like 65% - 85% of cases where folk think they need a pre-amp, the 2nd point above turns out to be the result. What is actualy needed is a filter.
Remember antennas receive everything - not only the desired signal. They present your receiver front-end with a whole bunch of frequencies and it is up to the receiver front-end mixers to tune into and isolate the frequency you want to demodulate and listen to, and block out the rest. If the signal you are tuning into does not have a sufficient strength in relation to signals around it, or harmonics of the tuned frequency are above a certain level (thats your Signal to Noise Ratio), so that it is unable to stand-out from all the other signals, then the front-end is not going to be able to extract it from everything else and will land up mixing the whole lot together: end result - no demodulation, just silence or noise.
Solution: filter - not pre-amp.
Problem with filters: good filters can cost quite a bit of money - in some cases as much as an average scanner! - which discourages folk from buying them. But properly chosen and setup they will turn the cheapest far east scanner/receiver into a world class performer.
