Howtosignalprocessing
1. The wire should be at least 10 feet long for it to have any considerable impact on the range of your radio. Anything less will not work as effectively as you need it to.
How long should an FM wire antenna be?
The overall length for the antenna should be about 150 cms, i.e. each leg should be 75 cms. This length should make the resonant frequency fall slightly in the lower half of the FM broadcast band, but often the more popular stations may be found in this region.
How long can a FM antenna BE?
For example, the common quarter-wave whip antennas used on FM radios in the USA are approximately 75 cm (2.5 feet) long, which is roughly one-quarter the length of radio waves in the FM radio band, which are 2.78 to 3.41 m (9 to 11 feet) long.
Is a longer FM antenna better?
Luckily, antennas work almost (longer antennae do work better, but still) as good if you make them some reasonable fraction of the wavelength you want to get—in the case of most car radio antennae, that's about a quarter the wavelength.
