If you are listening to mostly trunked or p25 systems, the antenna that came with it should be sufficient.
Trunked or P25 systems (particularly p25) are engineered to be received within their service areas. Typical trunked systems have a max range of 30-50 miles, and the stock antenna should receive that.
Not to say that a Motorola system in a neighboring county won't come in a little better with a base antenna, but the improvement might not be as much as you would expect. Definitely not for a p25 system.
If you still want to go ahead with an exterior antenna, consider the following....
The antenna is only one part. The cable you use to go from the radio to the antenna is more important than the antenna, if it will have any significant run distance.
The antenna needs to be above all surrounding structures to significantly improve the signal. This is a roof antenna or one on a high pole.
You need to make sure you have an excellent grounding system to protect your radio.
Finally, the answers to the questions in the above post will help define what antenna to look at and how much it will help. The more remote you are, the more likely it will help.
536/436/ws1095/996p2/996xt/325p2/396xt/psr800/396t/HP-1/HP-2 & others
