MEASUREMENTS

Antenna Measurements

Feedline and Load

SWR Standing Wave Ratio Z load = Z o (Feedline characteristic impedance) ? If Z load = Z line, SWR = 1, else SWR > 1 SWR > 1:1 Due to Reflections from load, and Constructive and Destructive interference “Standing Waves”

Acceptable “SWR”? 1:1 is perfect match 2:1 is fairly good, but transmitter may start to reduce power output 4:1 is poor, may stress parts, some power lost as HEAT in feedline, and transmitter will reduce power output

Antenna Tuner and SWR Meter Impedance Transformer Measures Impedance Ratio

SWR Meter 1.Forward, adjust Sensitivity to “SET” (Transmitting) 2.Reverse, read SWR (Transmitting)

Antenna Tuner Action “Impedance Transformer” Measures Impedance Ratio Between Z load and design Z = 50 Ohms “SWR =1:1” means Z load = 50 Ohms Note that “SWR Meter”, when used with Antenna Tuner, Doesn’t actually measure SWR on feedline High SWR on feedline is still present and is usually OK Low SWR Here Transmitter is Happy, because it can deliver power to antenna system!

Dummy Load Use to prevent Radiation when Testing Transmitter (instead of using Antenna)