just an fyi here. a vehicle antenna is a standard height for a reason. its 31.5 inches long. the reason for that is because its 1/4 wavelength at 1 watt. do the math and it pretty much leaves you dead center of our frequency band. a lot of companies have started going to the amplified antenna, which you see shorter antennas on vehicles, or antennas built into the rear glass somewhere. that being said, theres a bunch of circuitry inside to basically tune to the frequencies we have. theres a reason you can buy a $10 replacement mast but yet have to buy a $400 (or more) amplified antenna module. you can cut your antenna down, theres no issue with that. if you live in a city or metro area, you wont notice a difference since you are so close. but the outlying areas are where you will see a difference in reception. fm is frequency modulation. meaning if you are within range, you will get signal. am is amplitude modulation meaning the higher the am tower is, the farther you will get reception. changing the length of the antenna will affect the range of both. a 50,000 watt am channel will far outreach a 50,000 watt fm channel. if i remember right, i believe you want to cut the antenna in approx 3 inch increments until you get the desired height you want. i may need to brush up on some of the numbers, but this is what im remembering off the top of my head.
