July 21, 2013

FCC Technician Exam Question Of The Day (T9B01)

Q) Why is it important to have a low SWR in an antenna system that uses coaxial cable feedline?

A) To allow the efficient transfer of power and reduce losses


NJ2X Notes:
A perfect standing wave ratio (SWR) is 1:1.  Higher SWR is the result of an antenna and feedline that do not have matching impedances.  Any SWR greater than 1:1 indicates some of the transmitted energy is being reflected back toward the transmitter.  This reflected energy results in RF energy being radiated from the feedline as heat (an efficiency loss).  In some cases, the reflected energy can even cause damage to the transmitter.