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
Measures Impedance
Ratio
Impedance
Transformer
SWR Meter
1. Forward, adjust Sensitivity to “SET” (Transmitting)
2. Reverse, read SWR (Transmitting)
Antenna Tuner Action
Note that “SWR Meter”, when used with Antenna Tuner,
Doesn’t actually measure SWR on feedline
Measures Impedance Ratio
Between Zload and design Z = 50 Ohms
“SWR =1:1” means Zload = 50 Ohms
Transmitter
is Happy, because
it can deliver power
to antenna system!
Low SWR
Here
“Impedance
Transformer”
High SWR
on feedline is still
present and is
usually OK
Dummy Load
Use to prevent
Radiation when
Testing Transmitter
(instead of using
Antenna)