# Antenna length for a frequency modulated signal.

I thank you in advance for your assistance.

AlexHalford

I am given to understand that the length of an antenna is proportional to the wavelength of the signal that is fed to it (a quarter wavelength, for example). In the case of a signal modulated by amplitude, the frequency (and therefore wavelength) of the carrier wave remains unchanged. However, in the case of a signal modulated by frequency, the signal fed to the antenna will vary in frequency (and, therefore, wavelength). My query is this : how would one go about calculating the length of an antenna for a frequency modulated signal? Its frequency is not constant, so to construct an antenna of say, a quarter of the wavelength, would be impossible.

I thank you in advance for your assistance.

AlexHalford

I thank you in advance for your assistance.

AlexHalford

active| newest | oldestThis will give you the proper electrical length for a 1/4 wave antenna usable for FM.

If you want a ground plane antenna use 2808 / frequency for the vertical length and 2948 / frequency for the length of the radials. 1/4 wave antenna formulas. ARRL Lab can be contacted @ 1-860-594-0214

International 1-860-594-0355

depthis a tiny fraction of the actual broadcast frequency - think about it, channels are only separated by 50kilohertz, so the mod depth must be less than THAT, and the broadcast frequency minimum is 88megaHertz.Maths: 50 E 3/88E6 = 0.05%

Steve

On a receiver it is even less important to have a perfect antenna.

L