LEARNING CURVE

Every year, CQ dedicates its October issue to emergency communications (EmComm) and all the hams who volunteer their time to aid their communities in need. Aiding our communities with communications, especially during emergencies, is a primary reason for the existence of the Amateur Radio Service. Preparing ourselves and our stations for the rigors of EmComm and community service is an ongoing process, one that depends on our individual EmComm awareness and personal involvement. As ham radio operators, we primarily communicate from the comfort of our shacks (radio rooms) at our homes or from our mobile installations. But what if we need to set up for a few days (or longer) from a remote location? As you may recall from studying for your license, a simple length of wire can serve as an antenna on several ham radio bands. Sounds good in theory, but just how do we accomplish such a trick?

Antenna Resonance

To be honest, there’s no trick; rather, it’s <> as: “When the antenna input impedance is entirely real, i.e. Zin = R + j*0.” In other words, at a single radio frequency, the antenna’s capacitance and inductive reactance cancel out leaving only resistance. Please note the importance of the word, “single.” Theoretically, every antenna has only one resonant frequency, which is determined by the length of the radiating element (aluminum tube or wire). That doesn’t mean that as we move away from the resonant frequency that the antenna will cease to work. The antenna will still radiate, but if we move too far from its resonant frequency, SWR (standing wave ratio) will increase and less power will be transferred to the antenna. Power that isn’t radiated turns into heat.