ANTENNA SIZE

An antenna, present at both the transmitting and the receiving end of a wireless link, must have a height that is a specific fraction of the wavelength of the signal it is meant to carry -- specifically, a quarter-wavelength, $h=\dfrac{\lambda}{4}$, where the wavelength itself is $\lambda=\dfrac{c}{\nu}$, with $c$ the speed of light and $\nu$ the frequency of the signal being transmitted. This single formula is what ties a signal's frequency directly to a very concrete, physically-buildable engineering quantity: the antenna's height. Because wavelength is inversely proportional to frequency, a low-frequency signal needs an impractically tall antenna, while a high-frequency signal needs only a modest one -- and this is precisely the practical reason, developed with a worked comparison in the following note, that raw low-frequency baseband signals are not transmitted directly over long distances, but are instead modulated onto a …