Your Antenna Determines What You Can Hear
Scanner performance is a chain. Your receiver sets the floor, but your antenna sets the ceiling. A $700 Uniden SDS100 with a rubber duck on the kitchen counter delivers worse reception than a $150 scanner with a properly installed Tram 1411 at 30 feet. Upgrading the antenna is almost always the highest-leverage improvement you can make.
Base-station antennas break into three families: wideband discones cover 25–1300 MHz with unity gain, dual-band verticals give higher gain on ham bands at the cost of narrower coverage, and directional antennas (Yagis, log-periodics) trade omnidirectional reception for high gain in one direction. For the majority of scanner hobbyists, a discone is the correct answer.
But antenna selection is only part of the equation. Mounting height often matters more than antenna choice. Coax cable quality can throw away half of what the antenna collects. Lightning protection is non-optional for anything mounted outdoors. The guides in this hub cover each of these pieces in detail.