By Jonathan Imberi
The amateur bands are sometimes talked about in wavelengths. A wavelength simply relates to the operating frequency. The Greek letter Lambda () is used as an abbreviation for wavelength. The U.S. customary system of measurements is commonly used, especially if you are going to measure a length with a ruler or tape measure. The following equation can be used to find the wavelength in feet for a specific frequency, in megahertz (MHz) :
where f is the frequency in megahertz.
If you wanted to know the wavelength for 146.580 megahertz, you would divide 984 / 146.580 and the answer would be approximately 6.7 feet :
984 / 146.580 = 6.7130577 feet *
Now if you wanted to know the wavelength for 440.120 megahertz, you would divide 984 / 440.120 and the answer would be approximately 2.2 feet :
984 / 440.120 = 2.2357538 feet *
These two equations show the simple relationship between operating frequency and wavelength. The wavelength is longer at lower frequencies, and shorter at higher frequencies.
*Please note that these equations DO NOT give the length of a wire to use for an antenna. These formulas calculate the wavelength of the RF signal in space. The RF signal will actually travel slower through an antenna wire. This, combined with several other factors, will require an antenna wire to be shorter than the actual wavelength in space.
An antenna always has a design frequency or amateur band that it covers. Most of the popular antennas are less than one long. One of the most common antennas is the 1/2- dipole antenna. Antennas are simply tuned circuits. A simple antenna such as a 1/2- dipole or a 1/4- vertical has a resonant frequency. These antennas do their best at their resonant frequency, just as do all tuned circuits.
The capacitor value or inductor value is varied in a tuned circuit to change the resonant frequency. This can be done by simply changing the antenna's length, which then affects its capacitance and inductance, thus changing its resonant frequency.