As a rule I’m against pre-amps with most general radio dealer type budget off the shelf scanners – most scanners/receivers in that price range don’t have the front-end sensitivity/selectivity or resistance to 2nd & 3rd order inter-modulation required to handle the variation in rf signal level & quality we are faced with in modern day rf environments.
From what you have said, and ignoring the coax & antenna side of things – which other members have quite correctly pointed out can be improved on. It wouldn’t suprize me if you realized a significant improvement in received & demodulated signal if you added a good quality VHF/UHF inline/coax type pre-amp – and by significant I mean a good 10dB + across the VHF/UHF range of freqs.
…… and as far as preamps go there isn’t much around that beats the real world performance improvements that the products from Angle Linear offer (Angle Linear Home Page
) – new, or off eBay.
A quick note on antennas: your 25Mhz-1300Mhz omni is a big big compromise. My guess is that it isn’t offering you any decent Gain (+) across much more than say about 150Mhz – 200Mhz of its overall bandwidth - at best! In other words, for the rest of it’s coverage it’s going to be reducing the received signal level – and the further you are from town (or the signal source) the greater that compromise & reduction in signal level presented to the receiver fron-end is going to be.
By all means keep it, but take a look at the antenna I posted up on this thread (Co-phasing LPDA questions
– reply #21): It’s a Yagi type antenna – with an average of around 6.5dB gain from around 250Mhz – 1200Mhz bandwidth. It also has another nice characteristic: it’s pretty good at blocking out any signals that don’t fall within its’ forward facing 20degree odd wide beam-width, meaning it will also block out a ton of noise that would otherwise interfere with whatever you are trying to listen to. 20degree coverage from 7miles out of town should cover all if not just about all the town signal source area you listen to(?).
You come across them on eBay often – but they are also well within the average DIY’ers scope to construct. Loads & loads of plans and theory about Yagi type antennas on the internet.
As a rule preamps should be connected inline at the antenna end of the coax – not the scanner/receiver end of the coax.