My recommendation on improving your radio's signal strength is to upgrade your antenna system in this order.
1. Improve your feed line. Using your favorite coax loss calculator, here's one if you don't already have a favorite (
Coax Calculator), and find what coax will give you the lowest loss at the highest frequency you use. Compare it to what you currently use to see if you should upgrade to eliminate loss or decide what to replace your old/worn coax with. Use good quality connectors, eliminate unnecessary adapters (it's OK to have one type of connector on one end and another type on the other end if that's what's needed to do the job!), seal things up to prevent water damage.
2. Replace the antenna with one that has higher gain or is made specifically to cover the band(s) you use. A wide-band antenna will give you a large frequency range, but little distance. A band specific high-gain antenna will give you long distance but a fairly narrow frequency range. Assume that the gain is listed in dBi unless they specifically say dBd when comparing antennas. Add 2.15 dB to those that state they're in dBd to make your comparisons using a common reference point.
Be aware that they antenna makers often mislead you on what band(s) their antennas cover. If they say the antenna will transmit on 144 - 148 MHz and 420 - 450 MHz but will also work on 30 - 1,200 MHz. Read that to say it will work well on 144 - 148 MHz and 420 - 450 MHz, work rather well on frequencies near those (say 135 - 160 and 400 - 500), and work very poorly on the rest. They only say it will "work", not that it will "work
well".
3. Analyze your signal levels where you listen and around the band to find those that may swamp your receiver, add noise, desense, and other issues. Add filters, move antenna, redirect feed line, etc. to correct identified problems if possible. Issues may be strong FM, TV, Paging, NOAA Weather Radio, Cell Phone, or other powerful transmitters nearby. It could also be a leaky Cable-TV cable spewing the signal out covering up your desired signals. Think of it this way, it's easy to hear someone talking softly in a quiet library and may be impossible to hear someone talking loudly in a noisy bar. You want your signals to be like that library, not competing for your scanner's detector's attention like that noisy bar.
4. Add some amplification to your signal. This should be your last resort. It can work, but it often can make things worse unless you're very careful and add filters or other devices to prevent overdriving, desense, and other issues that will cause amplification to not do what most folks think it should.
