No way to pin that down, depends on the radio, what kind of system or frequency you're listening to and power and antenna that is being used to transmit. The only thing that you're sure of is that this will work better than the stock antenna, there are so many factors and it's very positional.
The antennas supplied with the radio (stock antenna) are designed to work using the following reasoning… it’s generally assumed the scanner will be used to receive signals specific to the area, meaning local FD’s, PD’s, etc., and the antenna supplied shouldn’t be expected to perform over that expectation. If it does, you are ahead of the game. If it doesn’t, there are aftermarket antennas out there that give better results… some are mono band antennas, some multi-band, specific to your personal needs. The aftermarket multi-band rubber duck antennas are longer but they do a better job. You can even improve over these antennas also by using a mobile gain antenna or even better, an outside antenna that’s mounted outside on your house. As for how much improvement you will see with this Remtronix, remember all things are not equal. What works for you may not work for someone else. Terrain, frequency, and other factors all enter into how well reception is. I’ve got a friend who lives closer to an agency but can’t hear them as clear as I do… he lives in a hollow and I live on a hill. He doesn’t have line of sight with the transmitting antenna but I do.
