MEASUREMENTS

Antenna Measurements

Feedline and Load

SWR• Standing Wave Ratio

• Zload = Zo (Feedline characteristic impedance) ?

• If Zload = Zline , 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 RatioBetween Zload and design Z = 50 Ohms“SWR =1:1” means Zload = 50 Ohms

Note that “SWR Meter”, when used with Antenna Tuner,Doesn’t actually measure SWR on feedline

High SWRon feedline is stillpresent and is usually OK

Low SWRHere

Transmitteris Happy, because it can deliver powerto antenna system!

Dummy Load

Use to prevent Radiation whenTesting Transmitter(instead of using Antenna)