Post on 13-Jan-2016
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)