It is possible to use the impedance matching concepts to construct vertical antennas substantially shorter than the 1⁄4 wavelength at which the antenna is resonant. By adding an inductance in series with the antenna, a so-called loading coil, the capacitive reactance of this antenna can be cancelled leaving a pure resistance which can then be matched to the transmission line. Sometimes the resulting resonant frequency of such a system (antenna plus matching network) is described using the construct of electrical length and the use of a shorter antenna at a lower frequency than its resonant frequency is termed electrical lengthening.
For use with more than one channel changes are made to increase what property? What could be coupled with an antenna to form pure resistance? What element would this pure resistance be coupled with? What phrase describes the process of purposely using a lower standing antenna at a less than peak frequency?